Micro-Rod Particle Dynamics in the Nematic Phase of Liquid Crystals Under Electric Fields

Liquid crystals (LCs) have a wide variety of applications, propelling them to the forefront of electro-optics and displays. In many more recent applications, the behaviour of liquid crystals have reliedon particles suspended within them. Yet, particle behaviour and distribution can be significantly influenced by the application of an electric field. As a result, particles dispersed in the liquid crystal experience forces that can induce motion, change their translational direction, and even alter spatial organization^[1]. Polarizing microscopy enables the examination of alignment quality and facilitates the identification of the electric field frequency stability regimes where particular particle behaviors are observable^[2].

Investigating micro-rods with different aspect ratios leads to a wealth of additional degrees of freedom for motion as compared to the translation observed for spherical particles ^[3]. Insight into their behaviour is crucial for engineering novel materials and devices with specific features to diverse applications. The significance of aspect ratios in influencing the dynamic behavior of micromaterials in various settings is investigated in this work. Our experiments have unveiled novel modes of motion, encompassing both linear and nonlinear dynamics, for rod-shaped particles in a nematic liquid crystal under the influence of an electric field. The observed behaviors included linear translation, circular motion, and a newly characterized pattern involving rotation around both the long and short axes of the rods, obviously absent for spherical microparticles. Additionally, we identified novel macroscopic modes of motion, such as looping and logarithmic spiral trajectories.

The dynamic behaviour depends on particle size, confining cell gap, viscosity via temperature change, and electric field amplitude and frequency. The molecular boundary conditions produced by various cell gaps can alter how the particle in the liquid crystal reacts to outside stimuli, i.e., electric fields in our case. The results are of importance to fundamentally understand the motion of particles of different shape.