Structure and Rheology of the Defect-gel States of Pure and Particle-dispersed Lyotropic Lamellar Phases

TL;DR

This study investigates how shear-treatment and particle additives affect the defect structures and rheological properties of lyotropic lamellar phases, revealing defect networks as primary contributors to elasticity and dissipation.

Contribution

It provides new insights into the defect-gel states of lyotropic lamellar phases with particles, highlighting the role of defect networks in their rheology and how shear and particles influence these structures.

Findings

Shear aligns the phase but leaves a defect network intact.

Particles anchor defect nodes, affecting the defect network persistence.

Adding particles increases moduli and slows their decay under shear.

Abstract

We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of shear-treatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.