Rheological studies on liquid-crystal colloids prepared by dispersing spherical microparticles with homeotropic surface anchoring

Abstract

We report rheological studies on the liquid-crystal colloids prepared by dispersing silica microparticles with homeotropic surface anchoring in 8CB liquid crystal. In nematic colloids, a shear-thickening behaviour is observed in low shear rate region. The apparent yield stress of both the nematic and smectic-A (SmA) phases increases with increasing volume fraction of particles (ϕ). The critical strain amplitude (γc', i.e., crossover of G' and G") in SmA colloids decreases significantly with increasing ϕ. The frequency-dependent storage modulus of SmA colloids show a power-law behaviour (G'(ω)~ωɑ) and the loss modulus (G"(ω)) exhibits a shallow minimum. The optical rheomicroscopy shows that the nematic colloids form a network structure which are stretched and broken at high shear rate. When the temperature is decreased to SmA phase, the networks collapse showing regions of high-density particles. The variation of storage modulus with ϕ indicates that the SmA colloids response is dominated by defects.