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 (SiO₂) particles in hexagonal (H₁) liquid crystal (LC) phase of water and non-ionic surfactant C₁₂E₉ is investigated by varying particle concentration and cooling rate. The rheology data shows that both SiO₂/H₁ and FeOOH/ H₁ LC composites exhibit a higher G^′ when compared to the particle-free H₁ phase, with increasing particle loading and cooling rate. FeOOH particles improve G^′ of the H₁ phase more significantly than SiO₂ particles due to the formation of an interconnected network at H₁ 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 H₁ phase. Dynamic strain sweep and creep experiments show a non-linear stress–strain relationship attributed to the alignment of micellar cylindrical rods under shear.