Experimental study of dynamics of topological defects in nematic polymer liquid crystals

Abstract

The dynamics of stringlike defects and the shrinkage and annihilation processes of individual defect loops in a nematic polymer liquid crystal have been experimentally investigated. In 40<t<500 s, the line density of defects ρ scales as ρ(t)∼t−1, as expected by theory and as found in the experimental studies of some low molecular weight (LMW) liquid crystals. For individual loops, they first change their complex shape into a circle, resulting in a rapid decrease in length, and then the circular loops continuously shrink. Before a complete annihilation, the relation between the radius R(t) of the circular loop and time t0−t, where t0 is the time to annihilation, is described by R2(t)=2Γ(t0−t)(t⩽t0). The kinetic constant Γ determined from this polymer liquid crystal is 0.34∼0.38 μm2/s, much smaller than those (200∼300 μm2/s) obtained in some LMW liquid crystals. The small Γ is ascribed to the high viscosity of this polymer liquid crystal, compared with LMW liquid crystals.