Anomalous brownian motion of colloidal particle in a nematic environment: Effect of the director fluctuations

Abstract

As recently reported [Turiv T. et al., Science, 2013, 342, 1351], fluctuations in the orientation of the liquid crystal (LC) director can transfer momentum from the LC to a colloid, such that the diffusion of the colloid becomes anomalous on a short time scale. Using video microscopy and single particle tracking, we investigate random thermal motion of colloidal particles in a nematic liquid crystal for the time scales shorter than the expectedtimeofdirector2uctuations.Atlongtimes,comparedtothecharacteristictimeofthenematicdirector relaxation we observe typical anisotropic Brownian motion with the mean square displacement (MSD) linear in time¿ andinverslyproportionaltotheeffectiveviscosityofthenematicmedium.Atshortertimes,however,the dynamics is markedly nonlinear with MSD growing more slowly (subdiffusion) or faster (superdiffusion) than τ. These results are discussed in the context of coupling of colloidal particle's dynamics to the director fluctuation dynamics.