Rheology of colloidal particles in lyotropic hexagonal liquid crystals: the role of particle loading, shape, and phase transition kinetics

The rheology of self-assembled elongated iron oxyhydroxide (FeOOH) and spherical silica (SiO<inf>2</inf>) particles in hexagonal (H<inf>1</inf>) liquid crystal (LC) phase of water and non-ionic surfactant C<inf>12</inf>E<inf>9</inf> is investigated by varying particle concentration and cooling rate. The rheology data shows that both SiO<inf>2</inf>/H<inf>1</inf> and FeOOH/ H<inf>1</inf> LC composites exhibit a higher G^′ when compared to the particle-free H<inf>1</inf> phase, with increasing particle loading and cooling rate. FeOOH particles improve G^′ of the H<inf>1</inf> phase more significantly than SiO<inf>2</inf> particles due to the formation of an interconnected network at H<inf>1</inf> domain boundaries at cooling rates of 1 and 2 ^∘C/min. We hypothesize that self-assembly of particles at domain boundaries leads to a decreased mobility of defects causing an increase in elasticity of particle-laden H<inf>1</inf> phase. Dynamic strain sweep and creep experiments show a non-linear stress–strain relationship attributed to the alignment of micellar cylindrical rods under shear.