Tuning the mechanical properties of organophilic clay dispersions: particle composition and preshear history effects

TL;DR

This study investigates how preshear history and particle composition influence the mechanical properties of organophilic clay dispersions in synthetic oil, revealing tunable viscoelastic behavior without significant structural changes.

Contribution

It demonstrates that preshear conditions and particle mixture ratios can be used to precisely tune the mechanical properties of organoclay gels.

Findings

Preshear can induce hardening or softening depending on conditions.

Elastic modulus follows a concentration power law of approximately c^3.9.

Structural analysis shows minimal changes despite mechanical tuning.

Abstract

Clay minerals are abundant natural materials used widely in coatings, construction materials, ceramics, as well as being a component of drilling fluids. Here, we present the effect of steady and oscillatory preshear on organophilic modified clay gels in synthetic oil. Both platelet and needle-like particles are used as viscosifiers in drilling fluid formulations. For both particles the plateau modulus exhibits a similar concentration dependence, G_P ~ c^3.9, whereas the yield strain is {\gamma}_y ~ c^(-1) for the platelets and {\gamma}_y ~ c^-1.7 for the needles. Mixtures of the two follow an intermediate behavior: at low concentrations their elasticity and yield strain follows that of needle particles while at higher concentrations it exhibits a weaker power law dependence. Furthermore, upon varying the preshear history, the gel viscoelastic properties can be significantly tuned. At lower (higher) clay concentrations, preshear at specific oscillatory strain amplitudes or steady shear rates, may induce a hardening (softening) of the dispersions and, at all concentrations, a lowering of the shear strain. Hence, in needle dispersions preshear resulted in changes in the volume fraction dependence of the elastic modulus from G_P ~ c^3.9 to G_P ~ c^2.5 and of the yield strain from {\gamma}_y ~ c^-1.7 to {\gamma}_y ~ c^-1. However, small angle X-ray scattering showed not much structural changes, within the q-range covered. Our findings indicate ways to design colloidal organoclay dispersions with a mechanical response that can be tuned at will.