WO2008070048A2

WO2008070048A2 - Active surfaces, including microfluidics, displays, sensors, light interaction and control

Info

Publication number: WO2008070048A2
Application number: PCT/US2007/024788
Authority: WO
Inventors: David Andrew Edwards; Howard A. Stone; Jonathan Jacques Kamler; Robert Renauld Mcgrath; Sandra Lia Di Capua; Elizabeth Helen Knopf
Original assignee: President And Fellows Of Harvard College
Priority date: 2006-12-04
Filing date: 2007-12-04
Publication date: 2008-06-12
Also published as: WO2008070048A3

Abstract

The present invention generally relates to surfaces having microf luidics, displays, windows, sensors, light interaction, control, etc. One aspect of the invention is directed to a display (10) containing microf luidics (14). Another aspect of the invention is directed to systems and methods for controlling the absorbance and/or transparency of a substrate. The invention, in still another aspect, is directed to the emission of light. In yet another aspect, the invention is directed to a substrate having a controllable substantially transparent region. The invention, in still another aspect, includes the production of text and/or an image on a surface. Other aspects of the invention include surfaces able to produce energy, surfaces able to sense external stimuli, self -cleaning surfaces, and/or surfaces able to control the environment surrounding the surface. Another aspect of the invention includes embodiments having surfaces able to transfer and/or transform energy. Yet other aspects of the invention include arrays of such surfaces, kits involving such surfaces, methods for making and/or using such surfaces, methods of promoting such surfaces, or the like.

Description

ACTIVE SURFACES, INCLUDING MICROFLUIDICS, DISPLAYS, SENSORS. LIGHT INTERACTION AND CONTROL

RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application Serial

No. 60/872,806, filed December 4, 2006, entitled "Active Surfaces, Including Microfluidics, Displays, Sensors, Light Interaction and Control," by Edwards, et al., incorporated herein by reference.

FIELD OF INVENTION The present invention generally relates to surfaces having microfluidics, displays, windows, sensors, light interaction, control, and the like.

BACKGROUND

In current architectural and engineering designs, there is interest in creating "smart" surfaces that interact dynamically with their surroundings and respond to people's needs, preferences, and/or aesthetic sensibilities.

SUMMARY OF THE INVENTION

The present invention generally relates to surfaces having microfluidics, displays, windows, sensors, light interaction, control, etc. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.

One aspect of the invention is directed to an article, for example, a display device. In one set of embodiments, the article comprises one or a plurality of fluidic elements. In one embodiment, one or more elements independently comprises a fluidic chamber sized so as to be visible to the naked eye and/or to an observer at a distance of at least about 10 cm, at least about 1 m, at least about 3 m, etc., a channel such as a microfluidic channel in fluidic communication with the chamber, and a device for controlling entry of fluid from the channel into the fluidic chamber. In some cases, the channel is sized such that, when the chamber is filled with a fluid having a color, the channel is not observable to the naked eye and/or to an observer at a distance of at least about 10 cm, at least about 1 m, at least about 3 m, etc. In another embodiment, one or more elements independently comprises a fluidic chamber having a smallest dimension of at least about 10 micrometers, and a microfiuidic channel, in fluidic communication with the chamber, having a largest cross- sectional dimension no larger than about 10 micrometers. In some cases, the elements also may each comprise a device for controlling entry of fluid from the microfiuidic channel into the fluidic chamber. In certain instances, the elements are present at a density of at least about 5,000 elements/inch².

In still another embodiment, one or more elements may independently comprise a first fluidic chamber, a first channel such as a microfiuidic channel in fluidic communication with the first chamber, a second fluidic chamber, a second channel such as a microfiuidic channel in fluidic communication with the second chamber, a third fluidic chamber, and a third channel such as a microfiuidic channel in fluidic communication with the second chamber. In certain instances, the first chamber, the second chamber, and the third chamber are not spatially distinguishable to the naked eye and/or to an observer at a distance of at least about 1 m, at least about 3 m, etc.

In one embodiment, one or more elements may independently comprise a fluidic chamber for containing a fluid selected to interact with light in a predetermined manner, at least one access channel in fluidic communication with the chamber for introducing fluid into or removing fluid from the chamber, and a device for controlling entry of fluid from access channels into fluidic chambers. In some cases, the fluidic elements, or a subset thereof, are together controllable as a series of visual pixels for display of an image resulting from interaction of light with a combination of the fluidic elements, and/or the fluidic elements, or a subset thereof, are together controllable to affect passage of light through and/or reflection of light from a combination of the fluidic elements. The article, according to another set of embodiments, includes a fluidic chamber sized so as to be visible to the naked eye and/or to an observer at a distance of at least about 1 m, at least about 3 m, etc.; a first channel such as a microfiuidic channel, in fluidic communication with the chamber, containing a first fluid having a first color; a second channel such as a microfiuidic channel, in fluidic communication with the chamber, containing a second fluid having a second color distinguishable from the first color; and a third channel such as a microfiuidic channel, in fluidic communication with the chamber, containing a third fluid having a third color distinguishable from the first and second colors.

In yet another set of embodiments, the article includes a display device containing a plurality of pixels, where some or all of the pixels are controllable using a device able to alter a non-electrical property of a fluid contained within the pixel. The article, in still another set of embodiments, includes a display device containing a plurality of pixels, where each pixel is defined, at least in part, by at least one channel such as a microfluidic channel. The article, in yet another set of embodiments, includes a display device containing a plurality of pixels defined by fluid within channels, where at least some of the channels have an aspect ratio of at least about 10:1.

Another aspect of the invention is a method. In one set of embodiments, the method includes acts of providing a display device containing a plurality of pixels, and controllably altering the color of a pixel by chemically reacting a fluid contained within the pixel to produce a color change. The method, according to another set of embodiments, includes acts of providing a display device containing a plurality of pixels, and controllably altering the color of a pixel by introducing a colored fluid into the pixel. Still another set of embodiments are directed to a method including acts of providing a plurality of channels (such as microfluidic channels) that are substantially parallel, and adding a plurality of droplets to one or more channels to create text and/or an image. The method, according to yet another set of embodiments, includes acts of providing a substrate containing a channel such as a microfluidic channel, and controlling fluid with the channel to produce non-predetermined text and/or a non-predetermined image. In one set of embodiments, the method includes an act of flowing fluid in a channel, where the fluid is used to display text and/or an image that is presented orthogonally to the flow of fluid in the channel.

Yet another aspect of the invention is directed to an article. For example, in one set of embodiments, the article comprises a substantially transparent substrate containing a channel such as a microfluidic channel, and a fluid, contained within the channel, that substantially alters the total absorbance of the substrate, relative to the substrate in the absence of the fluid. According to another set of embodiments, the article includes a substrate substantially transparent to light having a first wavelength and not substantially - A -

transparent to light having a second wavelength, where the first wavelength and second wavelength are not predetermined.

Still another aspect of the invention is directed to a method. In one set of embodiments, the method includes an act of altering the total absorbance of a substrate comprising a channel such as a microfiuidic channel containing a fluid by altering a property of the fluid, and/or by causing movement of fluid within the channel. In another set of embodiments, the method includes acts of providing a substrate having a total absorbance to infrared light and/or ultraviolet light, and controllably altering the total absorbance of the substrate to infrared light and/or ultraviolet to a second, non- predetermined value. The method, in still another set of embodiments, includes acts of selecting a wavelength range, and altering fluid within a substrate such that the substrate is substantially transparent, or is not transparent, to the selected wavelength range.

An aspect of the invention is directed to an article, for instance, having a substantially transparent region. For instance, the article, in one set of embodiments, includes, a substrate, a region of which is substantially transparent, and a device able to alter the shape and/or position of the region of the substrate which is substantially transparent. In another set of embodiments, the article includes a substrate able to create a non-predetermined colored shadow.

Another aspect of the invention is directed to a method. For example, in one set of embodiments, the method includes acts of providing a substrate having a substantially transparent region and a region that is not substantially transparent, and controllably altering the shape and/or position of the transparent region of the substrate. In another set of embodiments, the method includes acts of providing a substrate having a region that is not transparent, directing light through the substrate to produce a shadow, and controllably altering the shape and/or position of the shadow.

The method includes, in one set of embodiments, an act of displaying a plurality of non-predetermined images on a plurality of substrates, at least some of which comprise channels such as microfluidic channels and/or are substantially transparent, such that the plurality of substrates collectively displays a global image. In another set of embodiments, the method includes an act of providing a surface able to display a plurality of non-predetermined images, wherein the surface is the surface of a vehicle, a building, a fabric, furniture, or the like. In accordance with still another set of embodiments, the method includes an act of displaying a non- predetermined perforated image on a substrate.

Still another aspect of the invention is directed to articles having an integral external surface. In one set of embodiments, the article includes a vehicle having an integral external surface comprising a channel such as a microfiuidic channel. In another set of embodiments, the article includes a building having an integral external surface comprising a channel such as a microfiuidic channel. The article, in still another set of embodiments, includes a vehicle having an integral external surface able to display non- predetermined text and/or a non-predetermined image. In yet another set of embodiments, the article includes a building having an integral external surface able to display non-predetermined text and/or a non-predetermined image. According to one set of embodiments, the article includes a substrate controllable to produce a non- predetermined perforated image.

One aspect of the invention is directed to methods, such as methods for sensing and/or altering an environment. In one set of embodiments, for instance, the method , includes acts of providing a substrate comprising a plurality of channels such as microfiuidic channels, and altering a property of the environment by altering a fluid within the channel. The substrate may comprise a surface having a surface area of at least about 1 ft², in some cases. The method, in accordance with another set of embodiments, includes an act of substantially altering the temperature of a substrate comprising a channel such as a microfiuidic channel by altering the concentration of a light-absorbing species contained within the channel. In yet another set of embodiments, the method includes an act of substantially altering temperature of a substrate comprising a channel such as a microfiuidic channel by causing a chemical reaction to occur in the channel. The method includes, in still another set of embodiments, an act of cleaning a surface of a substrate, the substrate comprising a channel such as a microfiuidic channel, by directing a cleaning fluid into the channel. In accordance with yet another set of embodiments, the method includes acts of passing a fluid through a substrate comprising a channel such as a microfiuidic channel, and determining an external stimulus applied to the substrate by determining a property of the fluid. Another aspect of the invention includes an article. The article includes a self- cleaning surface comprising a channel such as a microfluidic channel, according to a first set of embodiments. The article, in another set of embodiments, includes a substrate comprising a plurality of channels such as microfluidic channels, at least a portion of which are in fluidic contact with the environment surrounding the substrate. In some cases, the substrate comprises a surface having a surface area of at least about 1 ft².

The invention, in yet another aspect, is a method. The method includes, in one set of embodiments, acts of providing a substrate comprising a channel such as a microfluidic channel, directing a nonconducting fluid into the channel, and altering the conductivity of the fluid in the channel such that a closed electrical circuit within the substrate is formed. The method, in another set of embodiments, includes acts of providing a substrate comprising a channel such as a microfluidic channel, directing a nonconducting fluid into the channel, and replacing at least a portion of the nonconducting fluid with a conductive fluid such that a closed electrical circuit within the substrate is formed. In still another set of embodiments, the method includes an act of producing a non-predetermined electrical circuit in a substrate comprising a channel such as a microfluidic channel by directing a conducting fluid into the channel.

In one set of embodiments, the method includes acts of providing a substrate comprising a channel such as a microfluidic channel containing a fluid, causing the fluid to absorb energy in a first location within the substrate, moving the fluid from a first location to a second location within the substrate, and controllably releasing the energy from the fluid in the second location.

Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and/or inconsistent disclosure with respect to each other, then the document having the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:

Figs. IA- ID illustrates a display device having substantially parallel fluidic channels, according to one embodiment of the invention; Figs. 2A-2F illustrates a display device having fluidic elements, according to another embodiment of the invention;

Figs. 3A-3I illustrates a display device having looped, intersecting, and/or overlapping fluidic channels according to yet another embodiment of the invention;

Figs. 4A-4E illustrates a display device controllable by polarization, according to still another embodiment of the invention;

Figs. 5A-5B illustrate various channel geometries and flow mechanisms, in yet another embodiment of the invention;

Figs. 6A-6C illustrates energy exchange, in one embodiment of the invention; and Fig. 7 illustrates an example of a building using a substrate of the invention.

DETAILED DESCRIPTION

The present invention generally relates to surfaces having microfluidics, displays, windows, sensors, light interaction, control, etc. One aspect of the invention is directed to a display containing microfluidics. Another aspect of the invention is directed to systems and methods for controlling the absorbance and/or transparency of a substrate, for example, to visible, infrared, and/or ultraviolet light. The invention, in still another aspect, is directed to the emission of light. In yet another aspect, the invention is directed to a substrate having a controllable substantially transparent region. The invention, in still another aspect, includes the production of text and/or an image on a surface, for example, the surface of a vehicle or a building. Other aspects of the invention include surfaces able to produce energy (e.g., via solar power), surfaces able to sense external stimuli, self-cleaning surfaces, and/or surfaces able to control the environment surrounding the surface. Another aspect of the invention includes embodiments having surfaces able to transfer and/or transform energy. Yet other aspects of the invention include arrays of such surfaces, kits involving such surfaces, methods for making and/or using such surfaces, methods of promoting such surfaces, or the like. Various aspects of the present invention are directed to substrates comprising channels such as microfluidic channels. The channels may be present at any location, and/or at any depth, within the substrate. As a specific non-limiting example, the channels may be near the surface of the substrate. In some embodiments, the channels may be positioned within the substrate so as to provide a suitable amount of insulation, e.g., to convective heat transfer from a fluid within the channel.

By controlling fluid within the microfluidic channels, various properties of the surface can be controlled, for example, optical properties such as color, absorption, transparency, polarization, etc., or other physical properties, as discussed below. In some cases, the substrates may have relatively large surface areas, for example, at least about 0.01 m², at least about 0.03 m², at least about 0.1 m² (about 1 ft²), at least about 0.3 m , at least about 1 m , at least about 3 m , or at least about 10 m . Some or all of the substrate may contain microfluidic channels. For example, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the substrate may contain microfluidic channels, by area or by volume. It should be understood that, in any of the description herein, the substrate may include one or a plurality of channels. For example, in some embodiments, a substrate may include two (or more) sets of channels (i.e., not in fluidic communication), for example intertwined, adjacent, or on parallel surfaces (for example, on an inner surface and an outer surface of the substrate, in the bulk and towards the surface of the substrate, etc.).

As used herein, a "channel" is a conduit associated with a substrate that is able to transport one or more fluids specifically from one location to another. Materials (e.g., fluids, particles, etc.) may flow through the channels, continuously, randomly, intermittently, etc. The channel may be a closed channel, or a channel that is open, for example, open to the external environment surrounding the substrate. The channel can include characteristics that facilitate control over fluid transport, e.g., structural characteristics (e.g., straight channels, curved channels, zigzagging channels, branched channels, etc.), physical/chemical characteristics (e.g., hydrophobicity vs. hydrophilicity) and/or other characteristics, e.g., to exert a force (e.g., a containing force) on a fluid when within the channel. The channels may be present in any suitable configuration. For example, there may be one or multiple channels present. In some cases, the channels may be present as parallel vertical channels, overlapping arrays of channels, channels forming one or more closed loops, open loops (e.g., corkscrew-shaped), branched channels (e.g., a channel that splits into smaller channels, and in some cases, progressively smaller channels), or the like. The fluid within the channel may partially or completely fill the channel. In some cases the fluid may be held or confined within the channel or a portion of the channel in some fashion, for example, using surface tension (i.e., such that the fluid is held within the channel within a meniscus, such as a concave or convex meniscus).

The channel may have any suitable cross-sectional shape that allows for fluid transport, for example, a square channel, a circular channel, a rounded channel, a rectangular channel (e.g., having any aspect ratio), a triangular channel, an irregular channel, etc. The channel may be of any size. For example, the channel may have a cross-sectional dimension, or a largest dimension perpendicular to a direction of fluid flow, within the channel of less than about 100 millimeters in some cases, less than about 30 millimeters in other cases, less than about 10 millimeters in other cases, less than about 3 millimeters in other cases, less than about 1 millimeter in other cases, less than about 500 micrometers in other cases, less than about 400 micrometers in other cases, less than about 300 micrometers in other cases, less than about 200 micrometers in other cases, less than about 100 micrometers in other cases, or less than about 50 or 25 micrometers in still other cases. In some embodiments, the dimensions of the channel may be chosen such that fluid is able to freely flow through the channel. The dimensions of the channel may also be chosen in certain cases, for example, to allow a certain volumetric or linear flowrate of fluid within the channel. The channel may have an aspect ratio (length to average cross-sectional dimension) of greater than about 2:1, greater than about 3:1, greater than about 4:1, greater than about 5:1, greater than about 10:1, greater than about 30:1, greater than about 50:1, greater than about 75:1, greater than about 100:1, greater than about 150:1, greater than about 300:1, greater than about 500:1, greater than about 750:1, or greater than about 1000:1 or more in some cases. In another set of embodiments, the channel may have a cross-sectional dimension such that the channel is not observable to the naked eye and/or to an observer at a distance of at least about 1 m, at least about 3 m, etc. For example, as discussed below, the substrate may be used in a display device that can be observed from a distance. In some cases, a channel of the substrate is a microfluidic channel. As used herein, a "microfluidic channel" is a channel comprising at least one fluidic element having a sub-millimeter cross section, i.e., having a cross-sectional dimension that is less than about 1 mm. For example, the microfluidic channel may have a cross-sectional dimension that is less than about 500 micrometers, less than about 300 micrometers, less than about 100 micrometers, less than about 30 micrometers, less than about 10 micrometers, less than about 3 micrometers, or less than about 1 micrometer or smaller. In some cases, a microfluidic channel can have a cross-sectional dimension such that the microfluidic channel is not observable to the naked eye. However, in other cases, a microfluidic channel may have a cross-sectional dimension such that the microfluidic channel is observable to the naked eye. In the descriptions that follow, it should be understood that reference to a "microfluidic channel" is by way of example only, and other channels may also be used as well, for example, a channel having a cross-sectional dimension of less than about 100 mm.

The substrate containing the channel may be any suitable substrate able to define a microfluidic channel. For example, the substrate may be a solid or flexible material such as glass, wood, a metal such as steel, a plastic or a polymer, or a fabric. Thus, the substrate may be, for example, a window (e.g., of a wall or a building), a surface of a vehicle, a surface of a building, a surface of furniture, clothes, etc. The substrate may be transparent or at least substantially transparent, translucent, or opaque. The substrate may also be porous, in some embodiments. A porous surface may be useful, for example, to allow for controlled evaporation, e.g., from the channel. Porous substrates, and uses for such substrates, are discussed in more detail below.

As a non-limiting example, in one embodiment, the substrate is a window, e.g., a window of a wall, a vehicle, a building, etc. The window may be transparent, partially transparent, or translucent in some cases. The window may be, e.g., single-paned or having more than one pane (e.g., with an interior space that may comprise air, at least a partial vacuum, an isolative amount of argon or CO₂, etc.), and have any suitable dimensions. For example, the window may have an overall thickness of between about 10 mm and about 3 cm. The window may be formed of any suitable material, e.g., glass or plastic. The window may have any size, for example, a height and/or a width each independently of between about 1 m and about 3 m, and/or shape (e.g., square, round, triangular, polygonal, irregular, flat, rounded, non-planar, etc.). In some cases, the window may be used as a display device or a device having a controllable substantially transparent region; in other cases, the window may be a self-cleaning window, a window able to control and/or alter the environment surrounding the window, a window in which the total absorbancy can be controlled, etc., as described in detail herein. Those of ordinary skill in the art will know of systems and methods for producing a substrate comprising a microfluidic channel. For example, in one embodiment, the substrate may be fabricated from polymeric and/or flexible and/or elastomeric materials, and can be conveniently formed of a hardenable fluid, facilitating fabrication via molding (e.g. replica molding, injection molding, cast molding, etc.). The hardenable fluid can be essentially any fluid that can be induced to solidify, or that spontaneously solidifies, into a solid capable of containing and/or transporting fluids contemplated for use in and with the fluidic network. In one embodiment, the hardenable fluid comprises a polymeric liquid or a liquid polymeric precursor (i.e. a "prepolymer"). Suitable polymeric liquids can include, for example, thermoplastic polymers, thermoset polymers, or mixture of such polymers heated above their melting point. As another example, a suitable polymeric liquid may include a solution of one or more polymers in a suitable solvent, where the solution forms a solid polymeric material upon removal of the solvent, for example, by evaporation. Such polymeric materials, which can be solidified from, for example, a melted state or by solvent evaporation, are well known to those of ordinary skill in the art. A variety of polymeric materials, many of which are elastomeric, are suitable, and are also suitable for forming molds or mold masters, for embodiments where one or both of the mold masters is composed of an elastomeric material. A non-limiting list of examples of such polymers includes polymers of the general classes of silicone polymers, epoxy polymers, and acrylate polymers. Epoxy polymers are characterized by the presence of a three-membered cyclic ether group commonly referred to as an epoxy group, 1 ,2-epoxide, or oxirane. For example, diglycidyl ethers of bisphenol A can be used, in addition to compounds based on aromatic amine, triazine, and cycloaliphatic backbones. Another example includes the well-known Novolac polymers. Non-limiting examples of silicone elastomers suitable for use according to the invention include those formed from precursors including the chlorosilanes such as methylchlorosilanes, ethylchlorosilanes, phenylchlorosilanes, etc. Silicone polymers are preferred in one set of embodiments, for example, the silicone elastomer polydimethylsiloxane. Non-limiting examples of PDMS polymers include those sold under the trademark Sylgard by Dow Chemical Co., Midland, MI, and particularly Sylgard 182, Sylgard 184, and Sylgard 186. Silicone polymers including PDMS have several beneficial properties simplifying fabrication of the microfluidic structures of the invention. For instance, such materials are inexpensive, readily available, and can be solidified from a prepolymeric liquid via curing with heat. For example, PDMSs are typically curable by exposure of the prepolymeric liquid to temperatures of about, for example, about 65 °C to about 75 °C for exposure times of, for example, about an hour. Also, silicone polymers, such as PDMS, can be elastomeric and thus may be useful for forming very small features with relatively high aspect ratios, necessary in certain embodiments of the invention. Flexible (e.g., elastomeric) molds or masters can be advantageous in this regard.

The channel may contain one or more fluids. As used herein, the term "fluid" generally refers to a substance that tends to flow and to conform to the outline of its container. Typically, fluids are materials that are unable to withstand a static shear stress, and when a shear stress is applied, the fluid experiences a continuing and permanent distortion. The fluid may have any suitable viscosity that permits at least some flow of the fluid. Non-limiting examples of fluids include liquids and gases, but may also include free-flowing solid particles, viscoelastic fluids, and the like. In one embodiment, the fluid is not a gas.

Any suitable technique may be used to move fluid within the channels. For example, electrokinetic forces, magnetohydrodynamic forces, capillary forces, hydrostatic pressures, thermal gradients, density differences, electrocapillary effects, chemical reactions (e.g., via fluid expansion) or forced pressures may be used to move the fluid. In some cases, for instance, the movement of bubbles within the fluid may be used to move the fluid. The fluid may be moved passively (e.g., by ambient heat) and/or actively (e.g. by valves, pumps, etc.). As an example, a fluid within a channel may be heated, which may alter its density (e.g., causing the fluid to expand or become more buoyant), which may be used to move the fluid within the channel. Those of ordinary skill in the art will know of these and other devices and methods suitable for causing a fluid to move in a channel such as a microfluidic channel. In some cases, electronics or a computer may be used to move or control fluid within the channels.

In some embodiments of the invention, the fluid may contain one or more species, which may be dissolved or suspended therein. For example, a fluid may contain surfactants, solutes, particles, salts, ions, buffers, preservatives, solubilizers, stabilizers, dyes, fluorescent species, gases (e.g., as bubbles, or dissolved within the fluid), or the like. In some cases, the species may be selected to alter a physical property of the fluid, for example, an optical property (e.g., color, absorbance of light, transparency, polarization, refraction, reflection, emitted radiation, control of incident radiation, etc.), an electrical property (e.g., conductivity, resistivity, electrical change, etc.), a magnetic property (e.g., if a species is magnetic), and/or a physical property (e.g., viscosity, density, temperature, etc.). Non-limiting examples include photochromic particles, beads with various optical or electromagnetic properties, soluble dyes, moisture- absorbing salts, conducting polymers, magnets, etc. Additional examples are discussed in detail below. Additional non-limiting examples include color-bearing or light- emitting components such as dyes, colored fluids, colored beads, fluorescent dyes, fluorescent gases, molecules that fluoresce when combined, fluorescent biological organisms, or the like. The fluid may be of any suitable color, depending on the fluid and/or species within the fluid. For instance, the fluid may be clear, opaque, or fluorescent in some cases, and may be of any color, for example, white, black, gray, red, orange, yellow, green, blue, purple, etc. In some cases, fluids of different colors may be used. For example, in some cases, three fluids may be used that are red, green, and blue; cyan, magenta, and yellow; red, yellow, and blue; etc.

One aspect of the invention is generally directed to display devices having microfluidics. Depending on the size of the display device, the display may be observable from a distance of at least about 10 millimeters, at least about 1 centimeter, at least about 1 meter, at least about 10 meters, at least about 1 kilometer, etc. In certain embodiments, the display comprises a plurality of fluidic elements, which may be arranged in an array. A fluidic element may have one or more fluids therein, which can be manipulated through the use of micro fluidic channels and/or other micro fluidic devices. The array may be regularly or irregularly arranged (e.g., as in a rectangular array), and the fluidic elements may be present in any suitable density, for example, at least about 1 element/cm², at least about 10 elements/cm², at least about 50 element/cm², at least about 100 elements/cm , at least about 500 elements/cm , at least about 750 elements/cm (at least about 5,000 elements/in ), at least about 1,000 elements/cm , at least about 3,000 elements/cm², at least about 10,000 elements/cm², at least about 30,000 elements/cm², or at least about 100,000 elements/cm². Typically, the fluidic elements are individually identifiable and visible under proper lighting conditions by an observer having normal vision, without the use of any devices such as magnifying glasses or microscopes, and may define a pixel of a display device. Thus, an array of such fluidic elements, when viewed together, may represent a text and/or an image (which may be still or moving in some cases, i.e., a video), which may be arbitrarily chosen, e.g., the text or image may be non-predetermined. Accordingly, certain embodiments of the invention are directed to a display device containing a plurality of pixels, such that the color of the pixel may be controlled by introducing and/or removing a colored fluid, for example via one or more microfluidic channels. In some cases, the fluidic element may be able to emit light. In one embodiment, the fluidic elements are backlit with a light source. In some cases, a fluidic element may include one or more fluidic chambers. The fluidic chamber may be of any suitable size, for example, having a smallest dimension of at least about 10 micrometers, at least about 30 micrometers, at least about 50 micrometers, at least about 75 micrometers, at least about 100 micrometers, at least about 500 micrometers, at least about 1 mm, at least about 5 mm, at least about 1 cm, etc. The fluidic chamber may also be of any suitable shape, for example, square, round, triangular, hexagonal, polygonal, etc. In one embodiment, the fluidic chamber is a fluidic channel, such as a microfluidic channel, e.g., the microfluidic channel has a size or dimension that is visible to the naked eye. In certain instances, the fluidic chamber has a size or dimension so as to be visible to the naked eye. In some embodiments, the fluidic chambers forming the fluidic element are not each spatially distinguishable to the naked eye. In certain embodiments, the fluidic element may contain 2, 3, 4, or more such fluidic chambers. For example, a first chamber may be used to display red, a second chamber may be used to display green, and a third chamber may be used to display blue, such that the fluidic element, when viewed by an observer, appears to be colored (i.e., due to an appropriate combination of red, green, and blue).

One or more microfluidic channels may be in fluidic communication with the fluidic chamber, e.g., a fluid in a microfluidic channel can be made to flow into the fluidic chamber, or vice versa. Fluids within the microfluidic channel may be added to the fluidic chamber and/or removed from the fluidic chamber by any suitable method. Examples of devices for controlling the entry of fluid from the microfluidic channel into the fluidic chamber include, but are not limited to, valves, pumps, or devices able to produce forces or conditions such as electrokinetic forces, magnetohydrodynamic forces, capillary forces, hydrostatic pressures, thermal gradients, density differences, electrocapillary effects, chemical reactions, or forced pressures, e.g., as previously described.

The microfluidic channel may be of any size, for example, as discussed above. In some instances, the microfluidic channel has a cross-sectional dimension such that the microfluidic channel is not observable to the naked eye. In one embodiment, the microfluidic channel sized such that the microfluidic channel is not observable to the naked eye when the fluidic chamber is filled with a fluid having a color. It should be noted that colored fluids can sometimes create optical "illusions" or "tricks," where an observer is not able to observe the microfluidic channel due to the presence of a colored fluid in the fluidic chamber, when the observer would otherwise be able to observe the microfluidic channel in the absence of a fluid in the fluidic chamber.

In one set of embodiments, a fluidic element may be defined by a fluidic chamber having a plurality of microfluidic channels in fluidic communication with the chamber, for instance, a first channel containing a first fluid having a first color (e.g., red), a second fluid having a second color (e.g., green), and a third fluid having a third color (e.g., blue). Typically, the colors will be distinguishable from each other. Color can be created in the fluidic chamber, which may represent a pixel of a display device, by adding appropriate amounts of fluid (including no fluid) from the various microfluidic channels. Similarly, upon removal of the fluid from the fluidic chamber (e.g., by replacing the fluid with a colorless fluid), the color of the fluidic chamber would be removed. Accordingly, by adding and/or removing appropriate fluids, the color of the fluidic chamber can be controlled as desired.

In another set of embodiments, a fluidic element may be defined by more than one fluidic chamber, for example, first, second, and third fluidic chambers. The fluidic chambers forming the fluidic element may not each be spatially distinguishable to the naked eye. Each chamber may be in fluidic communication with a microfluidic channel containing a fluid, which may be colored. For instance, the first fluidic chamber may be in fluidic communication with a first fluid having a first color (e.g., red), the second fluidic chamber may be in fluidic communication with a second fluid having a second color (e.g., green), and the third fluidic chamber may be in fluidic communication with a third fluid having a third color (e.g., blue). With respect to each fluidic chamber, color can be created in the fluidic chamber by adding appropriate amounts of fluid from the microfluidic channel. Accordingly, by controlling the colors of each of the fluidic chambers in the fluidic element, the color of the fluidic element (which may define a pixel of a display device) may be controlled as desired.

In yet another set of embodiments, the color of the fluidic element may be controlled by a chemical reaction or a non-electrical property of a fluid. As a non- limiting example, a pH-sensitive dye may be used, where the pH-sensitive dye appears as a first color at a first pH, and as a second color at a second pH. By controlling the pH of the fluidic element (e.g., upon addition of suitable amounts of acid and/or base, e.g., via a microfluidic channel), the color of the fluidic element may be controlled. Other suitable dyes include temperature-sensitive dyes, moisture-sensitive dyes, voltage- sensitive dyes, pressure-sensitive dyes, or the like.

It should be noted that any substrate may be used as a display device, including any of the substrates described herein. For example, the substrate may be glass, wood, a metal such as steel, a plastic or a polymer, a fabric, etc., for instance, as in a surface of a vehicle, a surface of a building, a surface of furniture, clothes, a window, etc. The substrate, in another set of embodiments, may be a stand-alone substrate that can be used as such, attached to an object (e.g., to a wall, a vehicle, a buliding, etc.), and used as a display device (e.g., a sign, an advertisement, etc.). Thus, any substrate able to define a microfluidic channel may be used as a display device, and the substrate used as a display device may be an integral part of the article and/or separate from the article. As a specific example, a vehicle, such as a car, a truck, or a bus, may comprise a metal or plastic surface comprising a display device as described above, where the surface is an integral part of the vehicle itself and/or is separately formed as a separate display device, then attached to the vehicle. Such a display device may be used to display non- predetermined text and/or a non-predetermined image, and can be used, for instance, to rely information, for advertising or promotion, for instructing, for educating, for displaying logos, for displaying map or travel information, to display a still image, to display a movie or other video (which may be interactive in some cases), or the like.

In still another set of embodiments, a display device has a plurality of channels, such as microfluidic channels, which may be substantially parallel. The channels may have any suitable dimensions. In a direction that is longitudinal to the channel, pixels may be defined by droplets within the channel, e.g., colored fluidic droplets. For instance, in one embodiment, colored fluidic droplets may be added to the microfluidic channels to create an observable pattern, for example, text and/or an image, an abstract artistic pattern, etc. The droplets may be added to one or multiple channels simultaneously.

In one set of embodiments, the pixels may be relatively large, for example, if the display device is used for outdoor advertising. For example, the pixel may have a smallest dimension (e.g., length or width, from the observer's point of view) of at least about 1 mm, at least about 3 mm, at least about 1 cm, at least about 3 cm, at least about 10 cm, at least about 30 cm, at least about 100 cm, at least about 300 cm, at least about 1 m, etc.

Another aspect of the invention is generally directed to systems and methods for controlling the absorbance and/or transparency of a substrate to light, for example, to visible, infrared, and/or ultraviolet light. Other wavelengths of light may also be applicable in some cases, besides visible, infrared, and ultraviolet light. As used herein, the term "light" generally refers to electromagnetic radiation, having any suitable wavelength (or equivalently, frequency). For instance, in some embodiments, the light may include wavelengths in the optical or visual range (for example, having a wavelength of between about 400 nm and about 700 nm), infrared wavelengths (for example, having a wavelength of between about 300 micrometers and 700 nm), ultraviolet wavelengths (for example, having a wavelength of between about 400 nm and about 10 nm), or the like. The light may have a single wavelength, or include a plurality of different wavelengths. For instance, in some cases, the light may have a range of wavelengths between about 350 nm and about 1,000 nm, between about 300 micrometers and about 500 nm, between about 500 nm and about 1 nm, between about 400 nm and about 700 nm, between about 600 nm and about 1 ,000 nm, between about 500 nm and about 50 nm, etc. In other cases, the light may be monochromatic or substantially monochromatic (i.e., having a single wavelength or a narrow wavelength distribution). The monochromatic beam of light may have a narrow distribution of wavelengths. For example, at least about 90%, at least about 95%, at least about 97%, or at least about 99% of the wavelengths comprising the light may be within 5 nm or 3 nm of the average wavelength of the light. In certain cases, the light may be polarized (e.g., linearly or circularly).

In some embodiments of the invention, the total absorbance of a substrate containing a fluid (e.g., within a channel) may be substantially altered by altering the fluid. For example, a property of the fluid may be altered (e.g., density, pH, etc.), the fluid may be moved within the channel, the fluid may be replaced with another fluid, a substance may be added to the fluid, or the like. As used herein, the "total absorbance" of a substrate is the absorbance of the entire substrate to light (e.g., visible light), irrespective of the components or structure of the substrate, i.e., the total absorbance of the substrate is the average absorbance of all portions of the substrate. In some embodiments, the total absorbance can be determined by measuring light intensities, e.g., at particular wavelengths. The total absorbance, in certain instances, may be increased or decreased by at least about 10%, at least about 20%, at least about 30%, at least about 50%, at least about 75%, at least about 100%, at least about 200%, at least about 300%, at least about 500%, etc.

In some cases, the absorbance of the substrate at a specific wavelength (or range of wavelengths) may be altered as desired, and in some cases, the absorbance may be controllably altered to non-predetermined values or characteristics, e.g., between a first absorbance level or spectrum and a second absorbance level or spectrum. For example, the fluid may be selected such that the substrate is transparent or substantially transparent to visible light, infrared radiation, and/or ultraviolet light, or the substrate is opaque to visible light, infrared radiation, and/or ultraviolet light. A substantially transparent substrate allows light to be transmitted through the substrate without significant scattering. The substantially transparent substrate may be able to transmit electromagnetic radiation in some cases such that a majority of the radiation incident on the substrate passes through the substrate unaltered, and in some embodiments, at least about 50%, in other embodiments at least about 75%, in other embodiments at least about 80%, in still other embodiments at least about 90%, in still other embodiments at least about 95%, in still other embodiments at least about 97%, and in still other embodiments at least about 99% of the incident radiation is able to pass through the substrate unaltered. The amount of absorbance and/or transparency may be set to any desired level, depending on choice of the fluid and/or species contained within the fluid, and in some cases, the absorbance and/or transparency (and/or total absorbance and/or transparency) of the substrate, with respect to different wavelengths of light, may be set to any desired level. As a non-limiting example, a substrate may have a total absorbance of 80% with respect to a first wavelength of light (e.g., visible light, or light of a specific color) and 30% to a second wavelength of light (e.g., ultraviolet or infrared, a specific color, etc.). In some cases, the desired level may be one that is not pre-determined in advance, but can be arbitrarily chosen. For example, by selecting appropriate fluid and/or species within the fluid, the absorbance of the substrate to various wavelengths may be controlled as desired. As non-limiting examples, a substrate may be substantially transparent to visible light but not infrared radiation or ultraviolet light, substantially transparent to infrared radiation but not visible light or ultraviolet light, substantially transparent to ultraviolet light but not infrared radiation or visible light, etc., and/or the substrate may be substantially transparent to a specific color or range of colors within the visible light spectrum, for example, substantially transparent to red light but not green light, or green light but not red light, etc.

As a specific non-limiting example, by introducing particles into a fluid contained within a substrate that are large enough to scatter ultraviolet light but do not substantially scatter visible light (for example, particles comprising ZnO, TiO₂, octylmethoxycinnamate, benzophenone-3, or octocrylene), the substrate may be rendered substantially transparent to visible light but not to ultraviolet light. The particles, in some cases, may be able to scatter ultraviolet light, for example, on the basis of size, e.g., if the particles have a characteristic diameter (diameter of a perfect sphere having the same volume as the particle) substantially equal to, or of the same order of magnitude as, the wavelength of ultraviolet light. As another specific, non-limiting example, if the substrate contains a fluid containing colored dyes that absorb certain wavelengths but not other wavelengths, the substrate may be substantially transparent to some colors or wavelengths but not other colors or wavelengths. The specific choice of fluid and/or species within the fluids for a particular application can be selected by those of ordinary skill in the art without an undue amount of experimentation, depending on the particular application and/or absorption required. It should be noted that in some cases, the absorbance of light (e.g., visible, infrared, and/or ultraviolet light) as described above can be combined with other techniques for absorbing light. For example, light may be absorbed using other, non- fluid-based methods, for example, polarizing filters or films, and such methods may be used with or without the use of absorbing components described above. In addition, absorbance can also be controlled, in some embodiments, by varying the alignment of the polarizing components, and/or by varying the number of overlapping components, e.g., overlapping channels, some or all of which may contain absorbing components such as those described above.

Yet another aspect of the invention is generally directed to displays, for example, displays having substrates having a substantially transparent region and a region that is not substantially transparent (for example, the region may be translucent or opaque), displays using fluid within the substrate to create text and/or images (e.g., fluid within channels such as micro fluidic channels), etc. Some non-limiting examples of using a fluid within the substrate to create text and/or images have been discussed above. In other cases, the substrate may include any colored fluid (one, or a plurality of fluids) within a microfluidic channel to create text and/or an image, and in some cases, the text and/or image is non-predetermined, as discussed herein.

In embodiments in which a substantially transparent region is used, the substantially transparent region may be transparent to all, or only a certain range of wavelengths, for example, the substantially transparent region may be substantially transparent to red light but not to blue light (and thus, the substantially transparent region may appear to be red colored). In some cases, the shape, position, and/or color of the transparent region (or substantially transparent region) and/or the region that is not substantially transparent may be controlled as desired. For example, the transparent or substantially transparent region of the substrate may be altered from a first shape to a second shape, altered from a first color to a second color, and/or moved from one location on the substrate to another. Light may be directed at the substrate, such that the region that is not substantially transparent creates a shadow. Accordingly, the shape, position, and/or color of the shadow may be controlled as desired, by controlling the shape, position, and/or color of the transparent or substantially transparent region and/or the region that is not substantially transparent. For example, a shadow may be created in the shape of a logo, an image, a movie, text, etc. In one embodiment, a shadow created using the sun as the source of light may be directed at a specific location (e.g., on the floor), and the substrate controllably altered over time such that the shadow remains in that location throughout the day, e.g., the region that is not transparent is moved across the substrate in response to the movement of the sun (for instance, to block sunlight).

In one set of embodiments, a substrate having a substantially transparent region and a region that is not substantially transparent may be created using a substrate comprising a microfluidic channel. For example, the substrate may have a number of fluidic elements (e.g., as previously described), which may each be filled with a colorless fluid (e.g., creating a substantially transparent region), an opaque fluid (e.g., a fluid containing a dye, particles, etc., creating a region that is not substantially transparent), a colored fluid (creating a colored shadow), etc. By independently controlling the fluidic elements within the substrate, these and other effects may be created, as well as combinations of these effects. Thus, for example, a substrate may be controlled to create a first substantially transparent region where light (e.g., sunlight) can pass, and a second, opaque or translucent region that prevents or at least inhibits light transmission, thereby creating a shadow of a desired image, a movie, text, logo, etc., which may be chosen by a user, and in some cases, altered as desired (e.g., periodically, in response to the movement of the sun, etc.) Other visual effects may be created in other aspects of the invention. For example, in one set of embodiments, by manipulating a plurality of substrates, some or all of which may independently comprise microfluidic channels or regions that are substantially transparent as described above, the plurality of substrates may collectively display a global or combined image. In some cases, each of the substrates may display an image, or text, that is not related to the global image, and each substrate may be manipulated such that the global image emerges from the unrelated image or text of each substrate. A process for producing such effects is discussed in U.S. Pat. No. 6,137,498, issued October 24, 2000, entitled "Digital Composition of a Mosaic Image," by Silvers.

In another set of embodiments, the substrate may be used to produce a non- predetermined perforated image. A "perforated image," as used herein, is an image containing a plurality of holes or gaps, often regularly spaced. Due to the holes, when close to the perforated image, the image can be (at least partially) seen through; but from a distance, the image appears to be solid. Such a perforated image can be used, in some cases, as a "one-way" window, in which an observer close to the window can see through the window, but an observer from far away cannot see through the window.

Such a perforated image can be produced, in one embodiment, using a substrate containing one or more microfluidic channels. For example, the substrate may contain a plurality of fluidic elements, e.g., as previously described, which are spaced such that the image produced using the substrate is perforated. As another example, a substrate having a plurality of fluidic elements may be used to create an image where a certain number or percentage of the fluidic elements within the image are not used for image production (e.g., are not colored, for instance with a fluid), thereby creating a perforated image.

In yet another set of embodiments, a substrate (or plurality of substrates) may have non-predetermined text and/or a non-predetermined image that is not identifiable to an observer who is closer to the substrate, but is identifiable to an observer at a distance further away from the substrate. For example, an image may not identifiable to an observer within about 10 cm, about 50 cm, about 1 m, about 2 m, or about 3 m of the substrate, but is identifiable to an observer at a distance of at least about 5 m, about 6 m, about 7 m, about 8 m, about 9 m, or about 10 m of the substrate. As a non-limiting example, the substrate may be the wall or a series of windows of a building, such that an observer within the building would not be able to see the entire image presented by the substrate(s) simultaneously and hence the image would not be observable to the observer, but an observer outside of the building would be able to see and identify the image presented.

The present invention is not limited to only visual or light effects. Yet another aspect of the invention is directed to control of an environment surrounding a substrate comprising a channel, such as a microfluidic channel. A property of the environment may be controlled by altering a fluid within the channel. For example, the temperature may be controlled using the substrate, or materials may be added to and/or removed from the environment. In some cases, the substrate may be relatively large, for example, having a surface area of at least about 1 ft². In one set of embodiments, at least a portion of the microfluidic channel may be open or otherwise be exposed to the environment surrounding the substrate (e.g., through a membrane, a permeable substrate, or a porous substrate or other material, etc.). For example, a volatile substance (e.g., a perfume, an air freshener, an antimicrobial, a gas, etc.) carried by the fluid may be released into the environment, or a substance in the environment may be absorbed into the fluid and thereby removed from the environment (or the concentration within the environment may be decreased), for example CO₂. In another set of embodiments the temperature of the environment may be controlled, at least partially, using a substrate comprising a channel, such as a microfluidic channel. For example, a fluid may be heated and introduced into the microfluidic channel, and/or heated within the microfluidic channel. For instance, the fluid may be heated via a chemical reaction, via resistive or electrical heating, via heat transfer with another fluid, etc. In some cases, the fluid may be heated upon exposure to light, for example, sunlight. The fluid may contain, for example, a light-absorbing species or a species having a relatively high specific heat capacity (for example, water, ethanol, or solid particles, for example, comprising ceramics, metals, adobe, stone, brick, concrete, etc.). The heated fluid within the substrate may then be used, for example, to store energy for later use, or heat the environment surrounding the substrate, for example, via radiation or heat conduction. Similarly, in another embodiment, an endothermic reaction may occur within the fluid within the substrate, thus causing the substrate to cool the environment.

Thus, in some embodiments of the invention, energy may be transferred from one location to another via the fluid. Accordingly, in some cases, solar energy may be used to heat the fluid, and used for heating, to power an electrical device, or the like. In one set of embodiments, the fluid may absorb energy (such as solar energy) at a first location within the substrate, be moved to a second location within the substrate, and then the energy may be controllably released at the second location, e.g., for heating or to power a device, etc. It should also be noted that the energy stored by the fluid and the energy released by the fluid do not necessarily have to be identical. As a non-limiting example, visible light or ultraviolet energy may be stored by the fluid, and released as infrared radiation or heat, etc.

Accordingly, in another set of embodiments, the fire resistance of a substrate may be altered and/or controlled. For example, energy (e.g., heat or radiation energy) from a fire may be absorbed by a fluid within the substrate, and directed to another location. By altering the fluid and/or species within the fluid, the fire resistance of the substrate can be altered or controlled. In some cases, the channels within the substrate may be at a distance from the surface of the substrate that provides a meaningful or reasonable amount of insulation from conductive heat transfer.

In still another set of embodiments, the substrate may be used as a sensor, e.g., to determine an external stimulus applied to the substrate, for example, temperature, pressure, weight, light, size, shape, or electrical and/or magnetic effects. The external stimulus can be determined by determining a property of the fluid. Interaction of the external stimulus with the substrate may cause a change in a property of the fluid, which may be determined to determine the external stimulus. As an example, heat applied to the substrate may cause a change in temperature of a fluid in a channel within the substrate, and the temperature of the fluid can be determined to determine the temperature of the substrate. As another example, a pressure applied to the substrate may cause a change in the flow of fluid (e.g., flow resistance or flowrate) through the substrate, which may be determined to determine the pressure. As yet another example, light may interact with a fluid in the substrate, or with a species contained by the fluid (e.g., a light-sensitive species), and cause a determinable change in the fluid or species. Detection of the change may then be used to determine the light incident on the substrate. If the substrate comprises a plurality of fluidic elements, which may be arranged in an array, the shape and/or size of the external stimulus may be determined, depending on the density of the fluidic elements, and in some cases, determined as a function of time.

As used herein, the term "determining" generally refers to the analysis of a species or condition, for example, quantitatively or qualitatively, and/or the detection of the presence or absence of the species or condition. "Determining" may also refer to the analysis of an interaction between two or more species or conditions, for example, quantitatively or qualitatively, and/or by detecting the presence or absence of the interaction.

In one embodiment, such a substrate may be used as a touch-sensitive surface, i.e., a surface that can determine contact, pressure, temperature, optical interference, or other measurements. Such contact can be determined as changes in the fluid, the material, or species within the fluid. Such a substrate may be used, for example, for mood recognition, fingerprint recognition, shape recognition, etc. In one set of embodiments, a soft and/or a flexible substrate may be used, optionally including one or more valves that may be deformable, e.g., upon touch contact. By pressing on such valves within the substrate, flow of a fluid along one or more micro fluidic channels may be stopped, diverted, or otherwise altered. The location, amount, time, etc., of contact with the surface may be determined, as discussed above. For instance, in one embodiment, contact with a deformable substrate comprising a channel, such as a microfluidic channel, may disrupt and/or interrupt flow of fluid within the channels. The channels may be arrayed within the substrate in a regular array. By determining which channels had disrupted and/or interrupted flow, the location, amount, time, etc. of contact of a user with the substrate may be determined.

Still another aspect of the invention is directed to a self-cleaning surface. In one set of embodiments, a substrate containing a microfluidic channel may contain a cleaning fluid, for example, alcohol (e.g., ethanol), a surfactant (e.g., soap), or an antimicrobial or other disinfectant. In some embodiments, the microfluidic channels are open to the surface of the substrate (e.g., directly, via a membrane or a porous covering, through a porous substrate, via capillary or "wicking" effects, etc.), and the cleaning fluid may be directed onto the surface to clean it. The cleaning fluid may be left there (e.g., to evaporate, as in the case of alcohol), or may be removed, e.g., via other microfluidic channels in the substrate. It should also be understood that the use of a cleaning fluid in a channel is not limited to only self-cleaning surfaces, but can be used in any of the embodiments described herein.

Other fluids may also be used, in conjunction with the cleaning fluid. For example, the cleaning fluid may contain more than one cleaner, or a rinsing fluid may be used after the cleaning fluid. In another set of embodiments, the fluid within the microfluidic channels (which may or may not be a cleaning fluid) may contain cleaning elements, for example, bubbles, absorptive particles, or the like.

Yet another aspect of the invention is directed to the formation of electrical circuits. For example, in a substrate comprising a channel such as a microfluidic channel, a circuit may be formed by adding a conductive fluid to the channel, and/or altering a nonconductive fluid such that it becomes conductive, such that, in the presence of the conductive fluid, a closed electrical circuit within the substrate is formed. In some cases, the circuit may be one that is not pre-determined, i.e., the substrate may comprise an array of channels, and a closed electrical circuit may be completed, for example, by adding a conductive fluid to one or more appropriate microfluidic channels and/or altering a nonconductive fluid such that it becomes conductive.

In some cases, the substrate will appear to have "invisible" electric circuitry or wiring, i.e., at least a portion of the electrical circuit is not observable to the naked eye. For example, the electrical circuit may be formed using a colorless fluid, and/or the electrical circuit may include microfluidic channels having a cross-sectional dimension such that the microfluidic channel is not observable to the naked eye. In addition, the electrical circuit may be used to connect or complement other electrical components present within the substrate (not necessarily a microfluidic channel), for example, etched semiconductor lines (e.g., produced using conventional techniques such as photolithography), metal electrodes, conducting polymers embedded in the substrate, or the like.

U.S. Provisional Patent Application Serial No. 60/872,806, filed December 4, 2006, entitled "Active Surfaces, Including Microfluidics, Displays, Sensors, Light Interaction and Control," by Edwards, et al., is incorporated herein by reference. The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.

EXAMPLE 1 This example illustrates a fluid applicator technique. In Fig. IA, a display device 10 comprises a plurality of substantially parallel channels, e.g., micro fluidic channels. An applicator 12 can be used to direct fluid into the substantially parallel channels. In Fig. IB, fluidic droplets are applied serially to the substantially parallel channels, which may define pixels of the display. The color of each of the droplets may be independently controlled, for example, by the use of one or more colored fluids in the applicator. In Fig. 1C, a second fluidic droplet 15 has been added to a channel 14 containing a first fluidic droplet 16. In a microfluidic channel, the second fluidic droplet may not readily mix with the first fluidic droplet, e.g., due to the dominance of viscosity in the low Reynolds number regime of the microfluidic channel, or other surface effects. This process can be repeated as desired. The colors added to the droplets by the applicator to each microfluidic channel may be controlled, for example, by a computer program to create meaningful imagery or information, text, a logo, or the like in Fig. ID.

EXAMPLE 2 In this example, a display device of the invention using microfluidic channels is illustrated. Fig. IA shows a series of three fluidic chambers 21, 22, 23, each in fluidic communication with a microfluidic channel 24, 25, and 26, respectively. In some cases, the three fluidic chambers 21, 22, 23 may define a fluidic element or a pixel, e.g., if the first chamber, the second chamber, and the third chamber are not spatially distinguishable to the naked eye. In this figure, the fluidic element would appear to be colorless, as the fluidic chambers each do not contain colored fluids, while the microfluidic channel is sized such that the microfluidic channel is not observable to the naked eye, even when filled with a colored fluid. In Fig. 2B, a device 27, 28, 29 (e.g., a valve or a pump) is used to move fluid from each respective microfluidic channel into each respective fluidic chamber, resulting in visible coloration of the three fluidic chambers 21, 22, 23 (Fig. 2C). Thus, the fluidic element may be perceived as being colored. For example, the fluidic element may be perceived as black if the colored fluids contain dyes such as cyan, magenta, or yellow, or the fluidic element may be white if the colored fluids produce visible light (e.g., fluorescent dyes such as red, yellow, and blue dyes, or if the fluids are backlit). By removing the colored fluid from the fluidic chamber (e.g., by withdrawing the fluid, by adding a colorless fluid to the chamber, etc.), the color can be removed or otherwise altered (for example, if fluidic chamber 21 were altered without altering fluidic chamber 22 or 23). For example, in Fig. 2D, the colored fluids in each of the three fluidic chambers 21, 22, 23 is removed using a device 17, 18, 19 (such as a valve or a pump).

An array of such fluidic elements may be used to define a display device having a plurality of pixels, as is shown in Figs. 2E and 2F. As can be seen in these illustrations, each fluidic element (and each fluidic chamber in each fluidic element) may be independently controlled, thus resulting in the ability to create any suitable pattern, for example, text, an image, a logo, etc.

EXAMPLE 3 This example illustrates various methods to create color within a fluidic element in a substrate (in the below figures, the entire channel network is present within a single substrate).

In Figs. 3A-3C, various materials can be reacted to create color. For example in Fig. 3A, a colorless fluid (e.g., water) flows in channels 30. In Fig. 3B, a colored dye, for example a pH-sensitive dye such as litmus, are introduced into various channels 31 , along with acids and bases. Litmus turns red upon reaction with acids 36, and blue upon reaction with bases 37. Red and blue coloration will thus occur where the litmus-seeded channels intersect the acid- and base-seeded channels, respectively (Fig. 3C). This technique can be used to create other effects that depend on combinations of substances (e.g. fluorescence using molecules that produce light when they interact).

In Figs. 3D-3F, color droplets are moved by the fluid flow without mixing within channels 30. Intersecting or overlapping channels (e.g., where the channels are physically separate, but overlap when viewed together) may be used to create new colors or shades of color. In Figs. 3G-3H, several looped channels are present, each containing a number of colored droplets. As previously discussed, the droplets do not readily mix, e.g., due to the dominance of viscosity in the low Reynolds number regime of the microfluidic channel, or other surface effects. By moving the fluid within each of the channels, various fluidic droplets can be moved to a specific location (e.g., defining a pixel), for example, location 35 (Fig. 3G), and in some cases, additional colors can be created by moving two colored droplets in overlapping channels into the location (e.g., Fig. 3H, showing the overlap of lighter and darker shaded droplets). In combination with polarizing components, additional flexibility in color brightness/darkness can also be achieved (see below). In addition, the colored droplets (or other species present in the channels) may be transferred from one channel to another to create additional visual effects. EXAMPLE 4

This example illustrates a method of creating dynamically-tinting fluidic elements. In Fig. 4A, two sets of polarizing components 41, 42 - one set aligned perpendicularly to the other - are each suspended in two sets of overlapping channels. In Fig. 4A, no overlapping polarizing components are present in the fluidic element. In Fig. 4B, the polarizing components are brought to a region where the channels overlap, such that the polarizing components in one are aligned with the perpendicularly-aligned polarizing components of the other. Light transmitting through the region of overlap can be blocked by the polarizing components, thus creating a reduction in light intensity, or "tinting." In addition, the degree of tinting may be controlled by controlling the concentration of polarizing components in the fluids within the channels.

A similar system can also be used to "hide" or "reveal" colored components. Referring now to Figs. 4C-4E, channel 43 may contain a colored fluid. When channels 41 and 42 contain perpendicularly-aligned polarizing components, light transmission is blocked, thereby "hiding" the colored component (Fig. 4D). In contrast, in Fig. 4E, the colored component is moved, but the polarizing effect remains in the overlap region, thereby allowing the colored component in channel 43 to be observed, e.g., while preserving a tint.

The amount of tinting can also be controlled by varying the number of locations at which overlap occurs, and/or the alignment of the polarizing components. EXAMPLE 5

This example illustrates "trees" that are able to carry fluids in part because of capillary pressure, which may be proportional to surface tension, and/or inversely proportional to channel radius. By subdividing larger channels into numerous smaller ones, each radius can be decreased while maintaining a high volume flow rate overall (Fig. 5A). Fluid may flow from a smaller bubble to a larger bubble (e.g., according to Laplace's Law). This property may be used to drive channel flow using, for example, two elastic balloons of different sizes (B). EXAMPLE 6

In this example, an energy exchange loop, whereby fluid in one location absorbs energy, carries it to an energy exchange site, and recirculates to the original location, is shown. This system can serve as a way to control light and heat, as an energy generator, as a way to improve the fire resistance of materials, etc.

The energy exchange loop can circulate between the material and an external environment (Fig. 6A), or between different parts of the material (Fig. 6B or Fig. 6C). The fluid may contain an energy-absorbing component, such as an infrared-absorbing dye. As energy absorption occurs, the fluid may rise, reach the energy exchange site, then recirculate. This passive system is thus self-powered; an active system, in which the fluid is forced through the channels, can also be created. If the energy released at the exchange site is captured, it can be used meaningfully, to generate electricity, heat, etc. As another example, fire resistance might be improved by the rapid distribution of heat, which could otherwise accumulate in a localized region. EXAMPLE 7

This example illustrates the use of substrates of the invention to minimize heating of a location, for example a greenhouse. In Fig. 7, solar energy is represented by three arrows: visible light 71, infrared and longer- wavelength light 72, and ultraviolet and shorter- wavelength light 73. The substantially transparent walls of the greenhouse contain fluid channels containing infrared- and ultraviolet-absorbent dyes, and are polarized (for example, by the presence of polarizing components in the fluid channels). The floor 77 may also contain fluid channels in some cases, for example polarized with filters perpendicular to those in the walls. Energy accumulated in the dyes, the polarizers, and elsewhere in the wall and floor material is taken by the circulating fluid to an external energy exchange site (not shown) where it can recycle its energy-absorbance capacity before recirculating into the greenhouse (see Example 6 for an example). In other embodiments, polarization may also be due to other, non-fluid-based methods, for example, polarizing filters or films, and such methods may be used with or without the use of polarizing components in the fluid channels described above. As shown in Fig. 7, infrared and ultraviolet light is absorbed upon incidence at the walls by the dyes in the fluid in walls 75. Visible light is able to pass but is filtered by the polarizers. Once inside, visible light that reaches the floor is absorbed by the floor polarizers (in diagram, see lower-left rays). Visible light that is absorbed by other objects inside 79 may be reradiated in the infrared 78, which can then be absorbed by the walls.

EXAMPLE 8 This is an illustration of another example of a fluidic panel. In some cases, panels with widths and heights on the order of centimeters to meters, thicknesses on the order of millimeters to centimeters, and which will be viewed from distances on the order of centimeters to meters, may contain pixels sized on the order of millimeters. This may be useful, for example, for achieving relatively high resolutions. Such panels may also have suitable pressure requirements, and/or refresh rates.

As an example embodiment, a substantially transparent panel 80 cm wide, 70 cm high, and 1 cm thick can contain substantially parallel and substantially coplanar channels into which colored fluid is added to create a meaningful visual image in the orthogonal direction. About 120 horizontal channels, each about 2 mm in width (or "depth" or "diameter") and separated from each other by about 0.5 mm, may extend across the width of the panel (80 cm) and together span about 30 cm of the panel height. To create a rectangular array of pixels, fluid "pixels" in each channel may be about 2.0 mm in length (matching the pixel dimension defined by the channel width) for a total resolution of about 120 x 400, or about 20 pixels/cm². Each such channel would have a volume of about 3.2 mL, and the 120 channels would contain, in total, about 384 mL. Additional fluid may be contained in the applicator or in spaces outside of the display area (for example, a fluid source).

The applicator, or another device associated with the display panel, may produce a pressure to direct fluid flow. Some typical pumps may produce pressures on the order of psi's or tens of psi's (for example, at least about 0.5, at least about 1, at least about 3, at least about 5, at least about 10, at least about 20, at least about 50, at least about 100 psi, etc.), and the pressure may be adjusted, providing one way to control flow. The choice of pressure helps determine, among other parameters, the flow rate in each channel, and whether the flow is laminar. For instance, to maintain a laminar regime, which may be preferable in some displays, an upper limit on the Reynolds number can be selected in some cases, for example choosing a Reynolds number of 1000 or 2000, in order to calculate an appropriate pressure. Given the channel geometry and pressures described above and assuming the fluid is water (which has a viscosity of about 1 centipoise), the fluid in this particular example may flow at speeds on the order of centimeters to meters per second.

If the color of fluid pixels, and the channels into which each flows, is controlled, a meaningful image and/or text may be produced, visible to an observer from a direction substantially orthogonal to the flow direction, from a distance of at least about a centimeter to substantially greater distances (e.g. at least about 50 cm, 1 m, 10 m, 100 m, 500 m, 1 km, etc).

It should be noted that the actual sizes and other parameters of any channels will depend not only on the aesthetic, informational, and other parameters as outlined in this document, but also on other considerations relating to similar panels in general, such as strength, risk of cracking or freezing, energy transmittance, etc.

While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention. AIl definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law. As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. What is claimed is:

Claims

1. An article, comprising a plurality of fluidic elements, each element independently comprising: a fluidic chamber sized so as to be visible to the naked eye; a microfluidic channel in fluidic communication with the chamber, the microfluidic channel being sized such that, when the chamber is filled with a fluid having a color, the microfluidic channel is not observable to the naked eye; and a device for controlling entry of fluid from the microfluidic channel into the fluidic chamber.

2. The article of claim 1 , wherein the fluidic chamber has a smallest dimension of at least about 10 micrometers.

3. The article of claim 1, wherein the microfluidic channel has a largest cross- sectional dimension no larger than about 10 micrometers.

4. The article of claim 1, wherein the device comprises a pump.

5. The article of claim 1, wherein the device comprises a valve.

6. The article of claim 1, further comprising a substrate comprising the plurality of fluidic elements,

7. The article of claim 6, wherein the substrate is flexible.

8. The article of claim 6, wherein the substrate is substantially transparent.

9. The article of claim 6, wherein the substrate is the surface of a vehicle.

10. The article of claim 6, wherein the substrate is the surface of a building.

1 1. The article of claim 1 , wherein the elements are present at a density of at least about 5,000 elements/inch².

12. The article of claim 1, wherein each element independently comprises at least three fluidic chambers.

13. An article, comprising a plurality of fluidic elements, each element independently comprising: a fluidic chamber having a smallest dimension of at least about 10 micrometers; and a microfiuidic channel, in fluidic communication with the chamber, having a largest cross-sectional dimension no larger than about 10 micrometers; and a device for controlling entry of fluid from the microfiuidic channel into the fluidic chamber.

14. The article of claim 13, further comprising a substrate comprising the plurality of fluidic elements.

15. The article of claim 13, wherein the elements are present at a density of at least about 5,000 elements/inch².

16. The article of claim 13, wherein each element independently comprises at least three fluidic chambers.

17. The article of claim 13, wherein the microfiuidic channel has a largest cross- sectional dimension no larger than about 5 micrometers.

18. The article of claim 17, wherein the microfiuidic channel has a largest cross- sectional dimension no larger than about 3 micrometers.

19. The article of claim 18, wherein the microfluidic channel has a largest cross- sectional dimension no larger than about 1 micrometers.

20. The article of claim 13, wherein the fluidic chamber has a smallest dimension of at least about 30 micrometers.

21. The article of claim 20, wherein the fluidic chamber has a smallest dimension of at least about 50 micrometers.

22. The article of claim 21 , wherein the fluidic chamber has a smallest dimension of at least about 100 micrometers.

23. An article, comprising a plurality of fluidic elements, each element independently comprising: a chamber having a smallest dimension of at least about 10 micrometers; and a microfluidic channel, in fluidic communication with the chamber, having a largest cross-sectional dimension no larger than about 10 micrometers; and wherein the elements are present at a density of at least about 5,000 elements/inch².

24. The article of claim 23, wherein the elements are present at a density of at least about 1,000 elements/cm².

25. The article of claim 24, wherein the elements are present at a density of at least about 3,000 elements/cm².

26. The article of claim 25, wherein the elements are present at a density of at least about 10,000 elements/cm².

27. The article of claim 26, wherein the elements are present at a density of at least about 30,000 elements/cm².

28. The article of claim 27, wherein the elements are present at a density of at least about 100,000 elements/cm².

29. An article, comprising: a fluidic chamber sized so as to be visible to the naked eye; a first microfluidic channel, in fluidic communication with the chamber, containing a first fluid having a first color; a second microfluidic channel, in fluidic communication with the chamber, containing a second fluid having a second color distinguishable from the first color; and a third microfluidic channel, in fluidic communication with the chamber, containing a third fluid having a third color distinguishable from the first and second colors.

30. The article of claim 29, wherein the first color is red, the second color is green, and the third color is blue.

31. The article of claim 29, wherein the first color is cyan, the second color is yellow, and the third color is magenta.

32. The article of claim 29, wherein the first color is red, the second color is yellow, and the third color is blue.

33. The article of claim 29, further comprising a fourth microfluidic channel in fluidic communication with the chamber.

34. The article of claim 29, further comprising a device for controlling entry of fluid from the first microfluidic channel into the fluidic chamber.

35. The article of claim 29, the article further comprising an integral light source positioned to direct light at the fluidic chamber.

36. An article, comprising a plurality of fluidic elements, each element independently comprising: a first fluidic chamber; a first microfluidic channel in fluidic communication with the first chamber; a second fluidic chamber; a second microfluidic channel in fluidic communication with the second chamber; a third fluidic chamber; and a third microfluidic channel in fluidic communication with the second chamber, wherein the first chamber, the second chamber, and the third chamber are not spatially distinguishable to the naked eye.

37. The article of claim 36, the article further comprising an integral light source positioned to direct light at at least one of the fluidic chambers.

38. An article, comprising: a display device containing a plurality of pixels, each pixel controllable using a device able to alter a non-electrical property of a fluid contained within the pixel.

39. The article of claim 38, wherein the pixels are present at a density of at least about 5,000 pixels/inch .

40. The article of claim 38, wherein the device is able to alter pH of the fluid.

41. The article of claim 38, wherein the device is able to alter temperature of the fluid.

42. The article of claim 38, wherein the device is able to alter pressure of the fluid.

43. The article of claim 38, wherein each pixel is defined, at least in part, by a microfluidic channel.

44. The article of claim 38, wherein the pixel contains a fluid.

45. The article of claim 44, wherein the fluid is a colored fluid.

46. A method, comprising: providing a display device containing a plurality of pixels; and controllably altering the color of a pixel by chemically reacting a fluid contained within the pixel to produce a color change.

47. The method of claim 46, wherein the act of altering the color of a pixel comprises altering pH of the fluid contained within the pixel.

48. The method of claim 46, comprising altering the color of the pixel from transparent to a color or from a color to transparent.

49. The method of claim 46, comprising altering the color of the pixel from transparent to opaque or from opaque to transparent.

50. The method of claim 46, comprising altering the color of the pixel from transparent to translucent or from translucent to transparent.

51. A method, comprising: providing a display device containing a plurality of pixels; and controllably altering the color of a pixel by introducing a colored fluid into the pixel.

52. The method of claim 51, comprising altering the color of the pixel from transparent to a color or from a color to transparent.

53. The method of claim 51 , comprising altering the color of the pixel from transparent to opaque or from opaque to transparent.

54. The method of claim 51 , comprising altering the color of the pixel from transparent to translucent or from translucent to transparent.

55. An article, comprising: a display device containing a plurality of pixels, each pixel defined, at least in part, by at least one microfluidic channel.

56. The article of claim 55, wherein the microfluidic channel has a largest cross- sectional dimension no larger than about 10 micrometers.

57. The article of claim 55, wherein the pixels are present at a density of at least about 5,000 pixels/inch².

58. The article of claim 55, wherein the microfluidic channel is sized such that the microfluidic channel is not observable to the naked eye.

59. The article of claim 55, wherein each pixel comprises a fluid.

60. A method, comprising: providing a plurality of microfluidic channels that are substantially parallel; and adding a plurality of droplets to one or more microfluidic channels to create text and/or an image.

61. The method of claim 60, wherein at least some of the droplets are colored.

62. A method, comprising: altering the total absorbance of a substrate comprising a microfluidic channel containing a fluid by altering a property of a fluid in the microfluidic channel.

63. The method of claim 62, comprising altering the total absorbance of a substrate with respect to visible light.

64. The method of claim 62, comprising altering the total absorbance of a substrate with respect to infrared light.

65. The method of claim 62, comprising altering the total absorbance of a substrate with respect to ultraviolet light.

66. The method of claim 62, comprising adding a species to the fluid.

67. The method of claim 66, wherein the species is a light-absorbing species.

68. The method of claim 66, wherein the species is a particle.

69. The method of claim 68, wherein the particle has an characteristic diameter that is greater than about 700 nm.

70. The method of claim 68, wherein the particle has an characteristic diameter that is greater than about 400 nm.

71. The method of claim 62, comprising changing color of the fluid.

72. The method of claim 62, wherein the total absorbance is substantially increased.

73. The method of claim 62, wherein the total absorbance is substantially decreased.

74. A method, comprising: altering the total absorbance of a substrate comprising a micro fluidic channel containing a fluid by causing movement of fluid within the channel.

75. The method of claim 74, comprising altering the total absorbance of a substrate with respect to visible light.

76. An article, comprising: a substantially transparent substrate containing a micro fluidic channel; and a fluid, contained within the microfluidic channel, that substantially alters the total absorbance of the substrate, relative to the substrate in the absence of the fluid.

77. The article of claim 76, wherein the total absorbance of the substrate is increased by at least about 50%, relative to the substrate in the absence of the fluid.

78. The article of claim 77, wherein the total absorbance of the substrate is increased by at least about 100%, relative to the substrate in the absence of the fluid.

79. The article of claim 78, wherein the total absorbance of the substrate is increased by at least about 200%, relative to the substrate in the absence of the fluid.

80. The article of claim 76, wherein the substrate has a surface area of at least about 1 ft².

81. The article of claim 76, wherein the fluid comprises a light-absorbing species.

82. The article of claim 76, wherein the fluid comprises particles

83. The article of claim 82, wherein the particles are present at a concentration at least sufficient to substantially alter the total absorbance of the substrate.

84. The article of claim 76, wherein the fluid is a colored fluid.

85. A method, comprising: providing a substrate having a total absorbance to infrared light; and controllably altering the total absorbance of the substrate to infrared light to a second, non-predetermined value.

86. The method of claim 85, wherein the total absorbance of the substrate to infrared light is altered without substantially altering the total absorbance of the substrate to visible light.

87. The method of claim 85, wherein the substrate comprises a microfiuidic channel.

88. A method, comprising: providing a substrate having a total absorbance to ultraviolet light; and controllably altering the total absorbance of the substrate to ultraviolet light to a second, non-predetermined value.

89. The method of claim 88, wherein the total absorbance of the substrate to ultraviolet light is altered without substantially altering the total absorbance of the substrate to visible light.

90. The method of claim 88, wherein the substrate comprises a microfiuidic channel.

91. An article, comprising : a substrate substantially transparent to light having a first wavelength and not substantially transparent to light having a second wavelength, wherein the first wavelength and second wavelength are not predetermined.

92. The article of claim 91, wherein the substrate comprises a microfiuidic channel.

93. The article of claim 91, wherein the light having the first wavelength and the light having the second wavelength are each visible light.

94. A method, comprising: selecting a wavelength range; and altering fluid within a substrate such that the substrate is substantially transparent to the selected wavelength range.

95. The method of claim 94, wherein the substrate comprises a microfluidic channel.

96. The method of claim 94, wherein the selected wavelength range comprises visible light.

97. The method of claim 94, wherein the selected wavelength range comprises infrared light.

98. The method of claim 94, wherein the selected wavelength range comprises ultraviolet light.

99. A method, comprising: selecting a wavelength range; and altering fluid within a substrate such that the substrate is not transparent to the selected wavelength range.

100. The method of claim 99, wherein the substrate comprises a microfluidic channel.

101. A method, comprising: providing a substrate having a substantially transparent region and a region that is not substantially transparent; and controllably altering the shape and/or position of the transparent region of the substrate.

102. The method of claim 101, wherein at least a portion of the region that is not substantially transparent is translucent.

103. The method of claim 101, wherein at least a portion of the region that is not substantially transparent is opaque.

104. The method of claim 101, wherein at least a portion of the substantially transparent region is colored.

105. The method of claim 101, wherein the substrate is a window.

106. The method of claim 101, comprising controllably altering the shape and/or position in response to an external stimulus.

107. The method of claim 101, comprising controllably altering the shape and/or position as a function of time.

108. The method of claim 101, wherein the act of controllably altering the shape and/or position of the transparent region of the substrate comprises forming an image.

109. The method of claim 108, wherein the image is not predetermined with respect to the substrate.

110. The method of claim 101, wherein the image is a perforated image.

111. The method of claim 101, wherein the act of controllably altering the shape and/or position of the transparent region of the substrate comprises forming text.

112. The method of claim 11 1, wherein the text is not predetermined with respect to the substrate.

113. The method of claim 101, wherein the act of controllably altering the shape and/or position of the transparent region is controllable by a user.

114. The method of claim 101, wherein the region that is not substantially transparent is defined by a channel containing a fluid.

115. The method of claim 101, wherein the fluid is colored.

116. The method of claim 101, wherein the fluid is opaque.

117. The method of claim 101, wherein the channel is a microfluidic channel.

118. The method of claim 117, wherein the microfluidic channel has a largest cross- sectional dimension no larger than about 10 micrometers.

119. The method of claim 117, wherein the microfluidic channel is sized such that the microfluidic channel is not observable to the naked eye.

120. An article, comprising: a substrate, a region of which is substantially transparent; and a device able to alter the shape and/or position of the region of the substrate which is substantially transparent.

121. The article of claim 120, wherein the substrate comprises a microfluidic channel.

122. The article of claim 120, wherein the shape and/or position of the region of the substrate which is substantially transparent is not predetermined with respect to the substrate.

123. The article of claim 120, wherein the substrate is a window.

124. The article of claim 120, wherein the device is able to alter the shape and/or position of the region of the substrate which is substantially transparent to display text and/or an image.

125. A method, comprising: providing a substrate having a region that is not transparent; directing light through the substrate to produce a shadow; and controllably altering the shape and/or position of the shadow.

126. The method of claim 125, wherein the substrate comprises a microfluidic channel.

127. The method of claim 125, wherein the shape and/or position of the region of the substrate which is substantially transparent is not predetermined with respect to the substrate.

128. An article, comprising: a substrate able to create a non-predetermined colored shadow.

129. A method, comprising: providing a substrate containing a microfluidic channel; and controlling fluid with the microfluidic channel to produce non- predetermined text and/or a non-predetermined image.

130. The method of claim 129, wherein the non-predetermined text and/or the non- predetermined image is not identifiable to an observer within 3 m of the substrate, but is identifiable to an observer at a distance of at least about 6 m of the substrate.

131. A method, comprising: displaying a plurality of non-predetermined images on a plurality of substrates, at least some of which comprise micro fluidic channels, such that the plurality of substrates collectively displays a global image.

132. A method, comprising: displaying a plurality of non-predetermined images on a plurality of substrates, at least some of which comprise regions that are substantially transparent, such that the plurality of substrates collectively displays a global image.

133. A method, comprising: providing a surface able to display a plurality of non-predetermined images, wherein the surface is the surface of a vehicle.

134. A method, comprising: providing a surface able to display a plurality of non-predetermined images, wherein the surface is the surface of a building.

135. A method, comprising : providing a surface able to display a plurality of non-predetermined images, wherein the surface is the surface of a fabric.

136. A method, comprising: providing a surface able to display a plurality of non-predetermined images, wherein the surface is the surface of furniture.

137. An article, comprising: a vehicle having an integral external surface comprising a microfluidic channel.

138. An article, comprising: a building having an integral external surface comprising a microfluidic channel.

139. An article, comprising: a vehicle having an integral external surface able to display non- predetermined text and/or a non-predetermined image.

140. An article, comprising: a building having an integral external surface able to display non- predetermined text and/or a non-predetermined image.

141. An article, comprising : a substrate controllable to produce a non-predetermined perforated image.

142. A method, comprising : displaying a non-predetermined perforated image on a substrate.

143. A method, comprising : providing a substrate comprising a plurality of microfluidic channels, the substrate comprising a surface having a surface area of at least about 1 ft²; and altering a property of the environment by altering a fluid within the channel.

144. The method of claim 143, comprising altering temperature of the environment.

145. The method of claim 143, comprising altering concentration of a species in the environment.

146. The method of claim 145, wherein the species is water.

147. The method of claim 145, wherein the species is CO₂.

148. The method of claim 145, wherein the species is CO.

149. The method of claim 145, wherein the species is a gas.

150. The method of claim 145, wherein the species is volatile.

151. The method of claim 143, wherein the microfluidic channels are open to the environment.

152. The method of claim 143, wherein the microfluidic channels are separated from the environment by a membrane.

153. The method of claim 143, wherein the substrate is porous.

154. An article, comprising: a substrate comprising a plurality of microfluidic channels, at least a portion of which are in fluidic contact with the environment surrounding the substrate, wherein the substrate comprises a surface having a surface area of at least about 1 ft².

155. The article of claim 154, wherein the microfluidic channels are in direct contact with the environment.

156. The article of claim 154, wherein the microfluidic channels are separated from the environment by a membrane.

157. The article of claim 154, wherein the substrate is porous.

158. A method, comprising: substantially altering the temperature of a substrate comprising a microfluidic channel by altering the concentration of a light-absorbing species contained within the microfluidic channel.

159. A method, comprising: substantially altering temperature of a substrate comprising a microfluidic channel by causing a chemical reaction to occur in the microfluidic channel.

160. A method, comprising: cleaning a surface of a substrate, the substrate comprising a microfluidic channel, by directing a cleaning fluid into the microfluidic channel.

161. The method of claim 160, wherein the cleaning fluid comprises an alcohol.

162. The method of claim 160, wherein the cleaning fluid comprises an antimicrobial.

163. The method of claim 160, wherein the microfluidic channel is open such that fluid is able to flow from the microfluidic channel to the surface.

164. The method of claim 160, wherein the substrate is porous.

165. The method of claim 160, wherein the microfluidic channel further comprises a device for controlling movement of fluid from the microfluidic channel to the surface.

166. An article, comprising: a self-cleaning surface comprising a microfluidic channel.

167. A method, comprising: providing a substrate comprising a microfluidic channel; directing a nonconducting fluid into the microfluidic channel; and altering the conductivity of the fluid in the microfluidic channel such that a closed electrical circuit within the substrate is formed.

168. A method, comprising: providing a substrate comprising a microfluidic channel; directing a nonconducting fluid into the microfluidic channel; and replacing at least a portion of the nonconducting fluid with a conductive fluid such that a closed electrical circuit within the substrate is formed.

169. A method, comprising: producing a non-predetermined electrical circuit in a substrate comprising a microfluidic channel by directing a conducting fluid into the microfluidic channel.

170. A method, comprising: passing a fluid through a substrate comprising a microfluidic channel; and determining an external stimulus applied to the substrate by determining a property of the fluid.

171. The method of claim 170, wherein the external stimulus is temperature.

172. The method of claim 170, wherein the external stimulus is pressure.

173. The method of claim 170, wherein the external stimulus is weight of an object.

174. The method of claim 170, wherein the external stimulus is light incident on the substrate.

175. The method of claim 170, wherein the external stimulus is an electrical stimulus.

176. The method of claim 175, wherein the fluid comprises an electrically-sensitive species.

177. The method of claim 170, wherein the external stimulus is a magnetic stimulus.

178. The method of claim 177, wherein the fluid comprises a magnetically-sensitive species.

179. The method of claim 170, wherein the substrate comprises a plurality of fluidic elements comprising the fluidic channels.

180. The method of claim 179, wherein the external stimulus is size.

181. The method of claim 179, wherein the external stimulus is shape.

182. A method, comprising : providing a substrate comprising a microfiuidic channel containing a fluid; causing the fluid to absorb energy in a first location within the substrate; moving the fluid from a first location to a second location within the substrate; and controllably releasing the energy from the fluid in the second location.

183. An article, comprising a plurality of fluidic elements, each element independently comprising: a fluidic chamber for containing a fluid selected to interact with light in a predetermined manner; at least one access channel in fluidic communication with the chamber for introducing fluid into or removing fluid from the chamber; and a device for controlling entry of fluid from access channels into fluidic chambers, wherein the fluidic elements, or a subset thereof, are together controllable as a series of visual pixels for display of an image resulting from interaction of light with a combination of the fluidic elements, and/or wherein the fluidic elements, or a subset thereof, are together controllable to affect passage of light through and/or reflection of light from a combination of the fluidic elements.

184. An article, comprising: a window comprising microfluidic channels.

185. The article of claim 184, wherein the window comprises glass.

186. The article of claim 184, wherein the window comprises a plastic.

187. The article of claim 184, wherein the window comprises at least 2 panes.

188. The article of claim 184, wherein the window encloses an interior.

189. The article of claim 188, wherein the interior comprises air.

190. The article of claim 188, wherein the interior is at least a partial vacuum.

191. The article of claim 184, wherein the thickness of the window is between about 10 mm and about 3 cm.

192. The article of claim 184, wherein the window has a height of between about 1 m and about 3 m.

193. The article of claim 184, wherein the microfluidic channels are generally parallel to a plane defined by the window.

194. The article of claim 184, wherein the window comprises a plurality of fluidic elements comprising the microfluidic channels.

195. The article of claim 184, wherein the window is able to display text and/or an image that is non-predetermined.

196. The article of claim 184, wherein the microfluidic channel has a largest cross- sectional dimension smaller than the thickness of the window.

197. The article of claim 184, wherein the microfluidic channel contains a colored fluid.

198. The article of claim 184, wherein fluid within the microfluidic channel flows passively.

199. The article of claim 184, further comprising a device for moving fluid within the microfluidic channels.

200. The article of claim 199, wherein the device comprises a pump.

201. An article, comprising: a display device, having microfluidic channels, wherein the display device comprises a pixel having a smallest dimension of at least about 1 cm.

202. The article of claim 201, wherein the smallest dimension is at least about 3 cm.

203. The article of claim 202, wherein the smallest dimension is at least about 10 cm.

204. The article of claim 203, wherein the smallest dimension is at least about 30 cm.

205. The article of claim 204, wherein the smallest dimension is at least about 100 cm.

206. The article of claim 205, wherein the smallest dimension is at least about 300 cm.

207. The article of claim 206, wherein the smallest dimension is at least about 1 m.

208. An article, comprising a plurality of fluidic elements, each element independently comprising: a fluidic chamber sized so as to be visible at a distance of at least about 1 m; a microfluidic channel in fluidic communication with the chamber, the microfluidic channel being sized such that, when the chamber is filled with a fluid having a color, the microfluidic channel is not observable to the naked eye; and a device for controlling entry of fluid from the microfluidic channel into the fluidic chamber.

209. An article, comprising: a fluidic chamber sized so as to be visible at a distance of at least about 1 m; a first microfluidic channel, in fluidic communication with the chamber, containing a first fluid having a first color; a second microfluidic channel, in fluidic communication with the chamber, containing a second fluid having a second color distinguishable from the first color; and a third microfluidic channel, in fluidic communication with the chamber, containing a third fluid having a third color distinguishable from the first and second colors.

210. An article, comprising a plurality of fluidic elements, each element independently comprising: a first fluidic chamber; a first microfluidic channel in fluidic communication with the first chamber; a second fluidic chamber; a second microfluidic channel in fluidic communication with the second chamber; a third fluidic chamber; and a third microfluidic channel in fluidic communication with the third chamber, wherein the first chamber, the second chamber, and the third chamber are not spatially distinguishable to an observer at a distance of at least about 1 m.

211. An article, comprising: a display device containing a plurality of pixels defined by fluid within channels, the channels having an aspect ratio of at least about 10:1.

212. The article of claim 211, wherein the channel is a microfluidic channel.

213. The article of claim 211, wherein the channel has an aspect ratio of at least about 30:1.

214. The article of claim 211, wherein the channel has an aspect ratio of at least about 100:1.

215. A method, comprising : flowing fluid in a channel, wherein the fluid is used to display text and/or an image that is presented orthogonally to the flow of fluid in the channel.

216. An article, comprising a plurality of fluidic elements, each element independently comprising: a fluidic chamber sized so as to be visible to the naked eye; a channel in fluidic communication with the chamber, the channel being sized such that, when the chamber is filled with a fluid having a color, the channel is not observable to the naked eye; and a device for controlling entry of fluid from the channel into the fluidic chamber.

217. A display device, comprising: a fluidic chamber sized so as to be visible to the naked eye; a first channel, in fluidic communication with the chamber, containing a first fluid having a first color; a second channel, in fluidic communication with the chamber, containing a second fluid having a second color distinguishable from the first color; and a third channel, in fluidic communication with the chamber, containing a third fluid having a third color distinguishable from the first and second colors.

218. The display device of claim 127, comprising an array of fluidic chambers.

219. A display device, comprising a plurality of fluidic elements, each element independently comprising: a first fluidic chamber; a first channel in fluidic communication with the first chamber; a second fluidic chamber; a second channel in fluidic communication with the second chamber; a third fluidic chamber; and a third channel in fluidic communication with the second chamber, wherein the first chamber, the second chamber, and the third chamber are not spatially distinguishable at a distance of 3 m.

220. An article, comprising: a display device containing a plurality of pixels, each pixel defined, at least in part, by at least one channel.

221. A method, comprising: providing a plurality of channels that are substantially parallel; and adding a plurality of droplets to one or more micro fluidic channels to create non-predetermined text and/or a non-predetermined image.

222. A method, comprising: altering the total absorbance of a substrate comprising a channel containing a fluid by altering a property of a fluid in the channel and/or by causing movement of fluid within the channel.

223. An article, comprising: a substantially transparent substrate containing a channel; and a fluid, contained within the channel, that substantially alters the total absorbance of the substrate, relative to the substrate in the absence of the fluid.

A method, comprising: providing a substrate containing a channel; and controlling fluid with the channel to produce non-predetermined text and/or a non-predetermined image.