Enhanced elasticity and soft glassy rheology of a smectic in a random porous environment

We report studies of the frequency-dependent shear modulus, G(*)(omega)=G(')(omega)+iG('')(omega), of the liquid crystal octylcyanobiphenyl (8CB) confined in a colloidal aerosil gel. With the onset of smectic order, G(') grows approximately linearly with decreasing temperature, reaching values that exceed by more than 3 orders of magnitude the values for pure 8CB. The modulus at low temperatures possesses a power-law component, G(*)(omega)similar to omega(alpha), with exponent alpha that approaches zero with increasing gel density. The amplitude of G(') and its variation with temperature and gel density indicate that the low temperature response is dominated by a dense population of defects in the smectic. In contrast, when the 8CB is isotropic or nematic, the modulus is controlled by the elastic behavior of the colloidal gel.