Enhanced Elasticity and Soft Glassy Rheology of a Smectic in a Random Porous Environment

TL;DR

This study investigates how the shear modulus of liquid crystal 8CB confined in a colloidal gel changes with temperature and gel density, revealing enhanced elasticity and glassy rheology in the smectic phase due to defect interactions.

Contribution

It demonstrates the impact of gel confinement on the elastic and rheological properties of smectic liquid crystals, highlighting defect-driven behavior and soft glassy dynamics.

Findings

Shear modulus increases significantly with decreasing temperature in the smectic phase.

Low-temperature modulus exhibits a power-law frequency dependence with an exponent approaching zero.

Defects dominate the low-temperature elastic response in the smectic phase.

Abstract

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 three orders of magnitude the values for pure 8CB. The modulus at low temperatures possesses a power-law component, $G^*(\omega) \sim \omega^\alpha$, 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.