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Fluidic Assembly and Packing of Microspheres In Confined Channels

Christopher R. Iacovella1, Siva A. Vanapalli2, Kyung Eun Sung1, Deshpremy Mukhija, Joanna Mirecki Millunchick, Mark A. Burns1, Michael J. Solomon3, and Sharon C. Glotzer4. (1) Chemical Engineering, University of Michigan, 2350 Hayward Street, 3440 G.G. Brown, Ann Arbor, MI 48109, (2) Physics of Complex Fluids, University of Twente, Enschede, 7500 AE, Netherlands, (3) Chemical Engineering, University of Michigan, Ann Arbor, 3074 H. H. Dow, 2300 Hayward, Ann Arbor, MI 48109, (4) Chemical Engineering and Materials Science and Engineering, University of Michigan, 2300 Hayward Street, Ann Arbor, MI 48109

The fabrication of particles with controlled anisotropy is important for emerging applications in self-assembly ranging from photonics to drug delivery. In previous work, a microfluidics based approach to the continuous assembly of anisotropic colloidal particles was presented for a variety of target building blocks [1]. In this work, we focus on the active fluidic assembly and packing of spherical particles in small 3d rectilinear microchannels using a partially closed membrane valve [2]. In this range we find zigzag morphologies with repeating “bond” angles between spheres. In conjunction with experiment, we utilize Brownian dynamics simulations to predict the packing of confined particles to fully delineate the range of bond angles possible. We further create a compact theory based on trigonometric relationships to predict the relative orientation of particles within the microchannels, finding excellent agreement between experiment, simulation, and theory.

[1] Sung, K. E.; Vanapalli, S. A.; Mukhija, D.; McKay, H. A.; Millunchick,

J. M.; Burns, M. A.; Solomon, M. J. J. Am. Chem. Soc. 2008, 130, 1335-1340.

[2] Vanapalli, S. A.; Iacovella, C. R.; Sung, K. E.; Mukhija, D.; Millunchick,

J. M.; Burns, M. A.; Glotzer, S. C.; Solomon, M. J. Langmuir, 2008, 24(7), 3661-3670.