Design of nematic liquid crystals to control microscale dynamics

ABSTRACT

Dynamics of small particles, both living and inanimate, has fascinated scientists for centuries. Learning how to control it could open technological opportunities in the transformation of stored or environmental energy into systematic motion. This review presents an approach to command microscale dynamics by using liquid crystals as an environment and liquid crystal elastomers as substrates. The orientational order of liquid crystals and associated properties, such as elasticity, surface anchoring, and bulk anisotropy, enable new dynamic effects, ranging from the propagation of particle-like solitary waves to steady directional self-locomotion of active droplets.  Liquid crystals could be photoaligned into patterns with varying molecular orientations.  In the presence of an electric field, these patterns transport solid and fluid particles by nonlinear electrokinetics rooted in anisotropy of conductivity and permittivity. Patterned lyotropic liquid crystal environment commands the dynamics of swimming bacteria by mediating their hydrodynamic interactions, rectifying active flows, and producing collective polar modes of swimming. Patterned elastomer coatings demonstrate a pre-programmed topography that is effective in shaping the morphology of living tissues. The liquid-crystal guidance holds a major promise in achieving the goal of commanding microscale active flows.

KEYWORDS:

• Active matter
• liquid crystals
• solitons
• patterned director
• electrophoresis
• microswimmers

Acknowledgements

I dedicate this review to the memory of Maurice Kleman, a mentor and a friend. I am thankful to the former and current Ph.D. graduate students G. Babakhanova, H. Baza, V. Borshch, Y.-K. Kim, R. Koizumi, I. Lazo, B.X. Li, Yu. A. Nastishin, V.G. Nazarenko, C. Peng, I.I. Smalyukh, M. Rajabi, T. Turiv, D. Voloschenko, S. Zhou, collaborators N. L. Abbott, I.S. Aranson, D.J. Broer, M. C. Calderer, J. de Pablo, A. Doostmohammadi, M.M. Genkin, D. Golovaty, A.P.H.J. Schenning, A. Sokolov, S.V. Shiyanovskii, J. Selinger, R. Selinger, K. Thijssen, J. Viñals, N.J. Walkington, Q.-H. Wei, J.M. Yeomans, whose contributions made the presented research possible. I also thank the organizers of the Spring School on The Mathematical Design of Materials A. Zarnescu, X. Chen, M. Ravnik, and V. Slastikov for the opportunity to present at the Isaac Newton Institute for Mathematical Sciences.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work supported by NSF grant DMR-1905053 and by Office of Science, U.S. Department of Energy, grant DE-SC0019105. A part of this review was written during participation in KITP Active 20 program, supported in part by the NSF grant PHY-1748958 and NIH grant R25GM067110.