Transport of microparticles in electrohydrodynamic convection of a twisted nematic liquid crystal

Abstract

The dynamics of spherical dielectric particles of micron-sized silica (3 µm) in an electric field in twist structures of nematic liquid crystals (NLC) has been investigated. To improve the solubility of these particles in nematic, a technique has been developed for the functionalization of the surface of microparticles with a surfactant n, n-dimethyl-n-octadecyl-3aminopropyltrimethoxysilyl chloride (DMOAP). The liquid crystal cell was assembled according to the standard scheme. Glass substrates with a conductive coating ensured homogeneous (planar) orientation of nematic molecules. The axes of the preferred orientation of molecules at the boundaries of the NLC layer were 90 degrees, so that, the structure corresponded to a quarter of the full rotation period of the director field. When an alternating voltage was applied and the threshold value was reached, a convective roll structure was formed, in which helicoidal flows of the liquid crystal were realized. Here the velocity of the axial component of the velocity of the nematic liquid reached its maximum value at the boundary of an individual roll. Two types of transport of spherical particles are observed experimentally. The first is a linear motion along the roll axis and the second is a spiral motion, which actually corresponds to the helicoidal flow of a nematic liquid. This behavior is explained by the competition between the electrophoretic mechanism and the helicoidal flow of the nematic.