STEADY AND DYNAMIC SHEAR RHEOLOGY OF DISPERSIONS OF LYOTROPIC LIQUID CRYSTALS

Abstract

ABSTRACT Biphasic dispersions of aqueous solution and lamellar liquid crystal of sodium bis(2-ethyl-hexyl)sulfosuccinate (AOT) were examined at 25°C from 7 to 20 wt% AOT by cone-and-plate or parallel-plate rheometry. In this concentration range the liquid crystalline phase is continuous. The materials were found to be viscoelastic. Their behavior was linear for strain amplitudes γo ≤ 1% at oscillatory shear frequencies ω = 10−2 to 102 rad/s. Measurement of the dynamic elastic modulus spectrum Gq(ω) at γo = 1% provided a good probe of the material structure without perturbing the structure. After oscillatory shear above γo ≡ 2%, or after steady shear, the dispersions become less elastic and more viscous. There is a slow trend (hours and days) for a partial recovery of the initial structure, although no unique reference state is obtainable The results help explain large increases with time of the apparent viscosity (rheopexy) observed with a capillary viscometer. The steady shear viscosities decrease with s...