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

Spinodal demixing into two phases having very different viscosities leads to viscoelastic networks, i.e. gels, usually as a result of attractive particle interactions. Here, however, we demonstrate demixing in a colloidal system of polydisperse rod-like clay particles that is driven by particle repulsions instead. One of the phases is a nematic liquid crystal with a highly anisotropic viscosity, allowing flow along the director but suppressing it in other directions. This phase coexists with a dilute isotropic phase. Real-space analysis and molecular dynamics simulations both reveal a long-lived network structure that is locally anisotropic yet macroscopically isotropic. We show that our system exhibits the characteristics of colloidal gelation and conclude that it represents a new class of material, non-sticky gels.