Rheological properties of lyotropic liquid crystals

Abstract

Rheological studies of liquid crystalline systems based on sodium decylsulphate are reported. It was verified that for low shear rates, disk-like (N d ) micellar nematic mesophases show typical pseudo-plastic rheopectic behaviour, associated with a favourable orientation of anisometric micelles in the flow field. The existence of a recovery time was observed, probably due to an orientational competition between flow effects and intermicellar interactions. The same sample observed at higher shear rates exhibited Newtonian behaviour, acting as a “dilute” system in which the interactions between the components are not sufficiently strong to prevent free diffusion. For rod-like (N c ) micellar nematic mesophases at low shear rates, rheopectic behaviour was observed. Additionally, a typical structural viscosity was detected, attributable to a superstructure break down arising from the shearing flow. For N c systems, the existence of a recovery time was observed only for low shear rate values, indicating that for higher values the flow completely orients the sample.