Viscoelastic rheology of colloid-liquid crystal composites.

Gelation in colloidal suspensions is mostly induced by attractive interparticle potentials. Beside these interactions, the mechanical properties of the gel are influenced by morphological aspects like fractality. In suspensions of liquid crystal (LC) and polymeric colloids, solvent-particle interactions dominate and can be changed when the mesogen undergoes phase transition from isotropic to nematic. In case of poly(methyl methacrylate) colloids and 4-pentyl-4′-cyanobiphenyl (5CB), cooling through the isotropic-nematic phase transition results in a cellular network. Such network formation is accompanied by a strong evolution of the mechanical properties. Shear moduli reach values up to 106 Pa for temperatures of 15 K below the transition. Until now, the mechanical response of the gel was attributed to the elastic interactions of the LC with the colloids. However, the dynamic viscoelastic stiffening with decreasing temperature could not be explained satisfactorily. We used a homemade piezorheometer to meas...