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

We report studies of the frequency-dependent shear modulus, G*(ω) = G′(ω) + iG″(ω), 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*(ω) ∼ ω^α, with exponent α 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.