Periodic dynamics, localization metastability, and elastic interaction of colloidal particles with confining surfaces and helicoidal structure of cholesteric liquid crystals
Michael C. Varney, Qiaoxuan Zhang, Mykola Tasinkevych, Nuno M. Silvestre, Kristine A. Bertness, Ivan I. Smalyukh
Although nematic and cholesteric liquid crystals are three-dimensional fluids, they also possess long- range orientational ordering of their constituent molecules, supporting both topological defects and chiral superstructures. Implications of this ordering remain unexplored even for simple dynamic processes such as found in so-called "fall experiments", or motion of a spherical inclusion under the effects of gravity. Here we show that elastic and surface anchoring interactions prompt periodic dynamics of colloidal microparticles in confined cholesterics when gravity acts along the helical axis. We explore elastic interactions between colloidal microparticles and confining surfaces as well as with an aligned ground-state helical structure of cholesterics for different sizes of spheres relative to the cholesteric pitch, demonstrating unexpected departures from the Stokes-like behavior at very low Reynolds numbers. We characterize metastable localization of microspheres under the effects of elastic and surface anchoring periodic potential landscapes seen by moving spheres, demonstrating the important roles played by anchoring memory, confinement, and topological defect transformation. These experimental findings are consistent with the results of numerical modeling which we perform through minimizing the total free energy due to colloidal inclusions at different locations along the helical axis and with respect to the confining substrates. Potential applications may include colloidal sorting based on particle shapes and sizes.
Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)
, Zhang, Q.
, Tasinkevych, M.
, Silvestre, N.
, Bertness, K.
and Smalyukh, I.
Periodic dynamics, localization metastability, and elastic interaction of colloidal particles with confining surfaces and helicoidal structure of cholesteric liquid crystals, Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), [online], https://doi.org/10.1103/PhysRevE.90.062502
(Accessed January 28, 2023)