This talk will present a few new classes of "smart" microfluidic materials. Microfluidic systems have recently found wide application in bioanalysis, drug and nanoparticle synthesis. The potential of microfluidics in making materials with extraordinary properties has only begun to be realized and explored. The microfluidic materials that we have developed are in the form of flexible sheets that can be solidified by light or that can repeatedly change their color on demand. These materials are based on engineered microfluidic channel networks embedded into a matrix of thin sheets of polydimethylsiloxane (PDMS). The macroscopic properties of the elastomer are determined by the stiffness or color of the material in the microchannels. The microfluidic networks in the shape-locking sheets are filled with liquid photocurable polymer. The materials formed in this way possess the unique ability to "memorize" and retain user-defined shapes upon illumination. When the microchannel networks are deformed and exposed by UV light, the photoresist inside the channels is solidified and subsequently acts as endoskeleton within the PDMS layer, locking in the programmed shape. The bending and stretching moduli of the materials with solidified endoskeleton increase drastically. The permanent locking in of the shape of the microfluidic sheets could be used in making instant containers, creating "exoskeletons" for delicate devices, rapid prototyping and multiple other applications. We will also present new microfluidic materials that can switch controllably their color and transmittance in the visible and infrared range. The optical characteristics of these materials change when colored solutions with different compositions displace each other by virtue of the laminar flow in the microchannel networks. Such "chameleon" microfluidic sheets can find applications in smart windows and energy management. Finally, we will discuss the potential applications of such liquid-containing polymer composites in novel biomimetic photovoltaic cells.
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