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SUMMARY:Design of Liquid Crystals for Microscale Dynamics - 1 - Oleg Lavre
 ntovich (Kent State University\; Kent State University)
DTSTART:20190326T101500Z
DTEND:20190326T111500Z
UID:TALK121642@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Dynamics of small particles in fluids has fascinated scientist
 s for centuries\, since van Leeuwenhoek observed in 1674 tiny creatures\, 
 nowadays known as &ldquo\;bacteria&rdquo\;\, swimming chaotically in a dro
 plet of water. Much later\, Brown found that even inanimate small particle
 s\, when placed in water\, engage in a similar chaotic dynamics. If one co
 uld learn how to control and streamline the chaotic motion of particles su
 ch as bacteria and colloids at the microscale\, that would open technologi
 cal opportunities in areas such as transformation of stored or environment
 al energy into systematic motion\, micro-robotics\, transport of matter at
  microscale\, etc. Remarkably\, bacteria and colloids driven by an externa
 l field do not obey the laws of thermodynamics and can be used to extract 
 a useful work. This set of lecture presents an approach to command microsc
 ale dynamics by replacing an isotropic medium such as water with an anisot
 ropic fluid\, a liquid crystal. The liquid crystals are formed by elongate
 d molecules that tend to align parallel to each other along a common direc
 tion called the director. As a result\, physical properties\, such as elec
 tric conductivity or viscosity depend on the direction of measurement\, wh
 ether it is parallel or perpendicular to the director. Orientational order
  of the medium leads to new dynamic effects\, such as anomalous diffusion 
 [1] and formation of particle-like solitary waves [2]. By using a newly de
 veloped technique of nano-photonic photoalignment\, the liquid crystal dir
 ector can be patterned into any predesigned structure [3]. We demonstrate 
 that the patterned liquid crystals can control microscale dynamics of inan
 imate particles such as solid colloids\, fluid droplets\, through the effe
 cts of nonlinear electrophoresis [4] and electro-osmosis [5]. Moreover\, p
 lasmonic patterning of liquid crystals allows one to command the dynamics 
 of swimming bacteria\, guiding their trajectories\, polarity of swimming a
 nd concentration in space [6]. The patterned director design can also be e
 xtended to liquid crystal elastomers\, in which case the director field co
 ntrols the thickness of elastomer coatings [7]. Some of these systems form
  an experimental playground for the exploration of out-of-equilibrium acti
 ve matter\, in which the levels of activity and degree of orientational or
 der can be controlled separately.The work is supported by NSF DMREF DMS-17
 29509 and by Office of Science\, U.S. Department of Energy\, grant DE-SC00
 19105.[1] T. Turiv\, I. Lazo\, A. Brodin\, B. I. Lev\, V. Reiffenrath\, V.
  G. Nazarenko\, and O. D. Lavrentovich\, Effect of Collective Molecular Re
 orientations on Brownian Motion of Colloids in Nematic Liquid Crystal\, Sc
 ience 342\, 1351-1354 (2013).[2] B. X. Li\, V. Borshch\, R. L. Xiao\, S. P
 aladugu\, T. Turiv\, S. V. Shiyanovskii\, and O. D. Lavrentovich\, Electri
 cally-driven three-dimensional solitary waves as director bullets in nemat
 ic liquid crystals\, Nature Communications 9\, 2912 (2018).[3] Y. Guo\, M.
  Jiang\, C. Peng\, K. Sun\, O. D. Lavrentovich\, and Q.-H. Wei\, High-Reso
 lution and High-Throughput Plasmonic Photopatterning of Complex Molecular 
 Orientations in Liquid Crystals Advanced Materials 28\, 2353-2358 (2016).[
 4] O. D. Lavrentovich\, I. Lazo\, and O. P. Pishnyak\, Nonlinear electroph
 oresis of dielectric and metal spheres in a nematic liquid crystal\, Natur
 e 467\, 947-950 (2010).[5] I. Lazo\, C. H. Peng\, J. Xiang\, S. V. Shiyano
 vskii\, and O. D. Lavrentovich\, Liquid crystal-enabled electro-osmosis th
 rough spatial charge separation in distorted regions as a novel mechanism 
 of electrokinetics\, Nature Communications 5\, 5033 (2014).[6] C. Peng\, T
 . Turiv\, Y. Guo\, Q.-H. Wei\, and O. D. Lavrentovich\, Command of active 
 matter by topological defects and patterns\, Science 354\, 882-885 (2016).
 [7] G. Babakhanova\, T. Turiv\, Y. B. Guo\, M. Hendrikx\, Q. H. Wei\, A. S
 chenning\, D. J. Broer\, and O. D. Lavrentovich\, Liquid crystal elastomer
  coatings with programmed response of surface profile\, Nature Communicati
 ons 9\, 456\, 456 (2018).
LOCATION:Seminar Room 1\, Newton Institute
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