Liquid Crystals

2Control of Micro-Particles with Liquid Crystals

Chenhui PENG¹ and Oleg D. LAVRENTOVICH²

¹ Department of Physics and Materials Science, University of Memphis, Tennessee, USA

² Advanced Materials and Liquid Crystal Institute, Department of Physics, Kent State University, Ohio, USA

2.1. Introduction

This chapter deals with the dynamics of living and inanimate micro-particles controlled by a liquid crystal (LC) environment. The first theme is nonlinear liquid crystal-enabled electrokinetics (LCEK) in an LC electrolyte. Director gradients created either by colloidal particles or by patterning of surface alignment in the presence of an externally applied electric field produce space charges that trigger flows with velocities proportional to the square of the electric field. As a result, an LC electrolyte enables transport of colloids of any shape and composition (including fluid droplets and gas bubbles), even when the particles show neither bulk nor surface charges. Various potential applications of LCEK, such as microscale sorting and guided transport, are discussed. The second theme focuses on non-toxic lyotropic chromonic liquid crystals (LCLCs) to control the individual and collective dynamics of microswimmers such as flagellated bacteria. The LC environment controls the spatial distribution of microswimmers, a transition from bidirectional apolar swimming to unidirectional polar swimming, and the geometry of swimming trajectories. The system represents an experimental realization ...