Anisotropic viscoelastic phase separation in polydisperse hard rods: non-sticky gelation

Abstract

Spinodal demixing of systems into two phases having very different viscosities leads to viscoelastic networks, i.e. gels. Here we consider demixing in a colloidal system where one phase is a nematic liquid crystal with a strongly anisotropic viscosity. We combine real space analysis of a sepiolite clay system with molecular dynamics computer simulation. We find a long-lived network with many of the characteristics of a colloidal gel. Remarkably the anisotropic viscosity means that flow is possible within the nematic network, but only along the network, which thus preserves its structure, leading to a new form of anisotropic gel. Our system presents a further novel property, in that it is comprised of hard particles. Thus our dynamically anisotropic gels form in the absence of attraction between the particles. Thus we show that our new system exhibits the ingredients of gelation and conclude that it represent a new class of material, \emph{non-sticky} gels in which attractions are not present.