Jae Young Sim, Jae-Hoon Choi, Jong-Min Lim, Soojeong Cho, Shin-Hyun Kim, and Seung-Man Yang, "Microfluidic Molding of Photonic Microparticles with Engraved Elastomeric Membranes," Small, accepted for publication (2014).
We report a microfluidic approach to prepare photonic microparticles by repeated molding of photocurable colloidal suspension. We integrate an elastomeric membrane with negative relieves which vertically separates two microfluidic channels; bottom channel is used for suspension flow, whereas water-filled top channel is used for pneumatic actuation of the membrane. Upon pressurization of the top channel, membrane is deformed to confine the suspension into its negative relieves, which is then polymerized by UV irradiation, making microparticles with mold shape. The microparticles are released from the mold by relieving the pneumatic pressure and flows through the bottom channel. This one cycle of molding, polymerization, and release can be repeatedly performed in microfluidic device of which pneumatic valves are actuated in a programmed manner. The microparticles exhibit structural colors when the suspension contains high concentration of silica nanoparticles; the nanoparticles form regular arrays and the microparticles reflect specific wavelength of light as a photonic crystals. The silica nanoparticles can be selectively removed to make pronounced structural colors. In addition, the microparticles can be further functionalized by embedding magnetic particles in the matrix of the microparticles, enabling the remote control of rotational motion of microparticles.
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