Effect of silica colloids on the rheology of viscoelastic gels formed by the surfactant cetyl trimethylammonium tosylate

TL;DR

This study investigates how adding silica colloids influences the flow and deformation behavior of surfactant-based viscoelastic gels, revealing concentration-dependent rheological changes linked to micelle entanglement and bilayer formation.

Contribution

It provides new insights into the rheological effects of silica colloids on surfactant gels, highlighting the role of electrostatic screening and surfactant adsorption in modulating gel properties.

Findings

Viscosity peaks at specific silica and surfactant concentrations.

Enhanced micelle entanglement increases rheological moduli.

High silica concentrations lead to surfactant bilayer formation.

Abstract

The effects of the addition of sub-micrometer sized colloidal silica spheres on the linear and nonlinear rheology of semi-dilute solutions of a viscoelastic gel are studied. For a 1.4 wt.% solution of the surfactant CTAT, a peak in the zero shear rate viscosity $\eta_{\circ}$ is observed at approximately equal weight percents of silica and CTAT. This peak shifts to lower silica concentrations on increasing either the CTAT concentration or the surface charge on silica and disappears when the CTAT concentration is increased to 2.6wt%. The increases in $\eta_{\circ}$ and the high frequency plateau modulus G$_{\circ}$ on the introduction of SiO$_{2}$ are explained by considering the increasingly entangled wormlike micelles that are formed due to the enhanced screening of the electrostatic interactions. The observed decrease in the values of G$_{\circ}$ and $\eta_{\circ}$ at higher concentrations of silica particles is explained in terms of the formation of surfactant bilayers due to the adsorption of the positively charged cetyl trimethylammonium to the negatively charged silica.