Ultrafast Self-Assembly of Microscale Particles by Open-Channel Flow
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1196-C02-05
Ultrafast Self-Assembly of Microscale Particles by Open-Channel Flow Sun Choi1,2, Albert P. Pisano1,2 and Tarek I. Zohdi2 1
Berkeley Sensor and Actuator Center (BSAC), 2Department of Mechanical Engineering,
ABSTRACT We developed an ultrafast microfluidic approach to self-assemble microparticles in threedimensions by taking advantage of simple photolithography and capillary action of microparticle-dispersed suspensions. The experimental verifications of the assembly of various sizes of silica microspheres and silica gel microspheres within thin and long open microchannels by using this approach have been demonstrated. We anticipate that the presented technique will be widely used in semiconductor and Bio-MEMS (microelectromechanical Systems) fields because it offers a fast way to control 3D, microscale particle assemblies and also has superb compatibility with photolithography, which can lead to an easy integration of particle assembly with existing CMOS (complementary metal-oxide-semiconductor) and MEMS fabrication processes. INTRODUCTION The microparticles are crucial building blocks for numerous applications such as bioassays1-4, photonics5-6 and microelectronic devices7-8. The self-assembly of microparticles is very favorable in microfabrication because it provides easier, faster and more convenient way to construct functional microstructures. A number of self-assembly techniques of microparticles have been developed on the basis of electrostatic forces,9 electrochemical reactions,6,10 surface functionalization11 and microfluidics.12-14 Especially, fluidic self-assembly is emerging as a promising pathway to guide and assemble microstructures because of its high yield and great simplicity.15 It is reported that particles in milimeterscale,16 and microscale17 in fluid can be assembled and structured by lateral capillary forces between the particles in suspension, and the mechanism of the 2D crystallization of microparticles was also explained.18 There have been several attempts to control the 2D microparticle assembly from the liquid suspension of microparticles.12-13,19-23 In particular cases, the assembly of the microparticles has been achieved in confined geometries by either receding a contact line21-22 or electrostatic forces,23 and the particles have been transported from the suspension to fill the trenches. These approaches require the fine control of the receding speed of the contact line and the contact angle of the meniscus of the fluid with respect to substrates. Also, the release of particle structure in the confined geometries, a crucial issue in the integration of on-chip particle assemblies with other microscale electronic devices, has not yet been demonstrated. Here, we describe a simple, ultrafast microfluidic approach to self-assemble microparticles in three dimension on the basis of the photolithography and capillary action of microparticle-dispersed suspensions. Various sizes of silica microspheres and silica gel microspheres have been successfully assembled within open micro chan
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