Spontaneous evolution of self-assembled phases from anisotropic colloidal dispersions

Abstract

We demonstrate spontaneous evolution of various self-assembled phases from a homogeneous aqueous dispersion of high aspect ratio Montmorillonite (MMT, platelet diameter ~250 nm and thickness 1 nm) nanoclay platelets based on the observations made over a period of 4 years. The phase diagram for this system in salt-free suspensions in normal pH conditions using rheology, light scattering, and dilution experiments was established, and we have noticed that these suspensions do undergo nontrivial phase evolution yielding formation of equilibrium fluids and gels and aging dynamics. This observation showed that the yield stress dependence on the concentration of clay followed a power-law behavior similar to low aspect ratio Laponite nanoclay dispersions. During the initial period, all dispersions formed stable sols, and with aging network-like structures were found to form via two routes not reported hitherto: one for below gelation concentration by phase separation and another for above the same, through equilibrium gelation resembling the Laponite nanoclay system, where existence of patchy colloids, equilibrium gels, and empty liquids was observed experimentally.