31. Experimental study of dynamics of topological defects in nematic polymer liquid crystals-wangwei

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.

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