Liquid-solid transition of Laponite suspensions at very low ionic strength: Long-range electrostatic stabilisation of anisotropic colloids

Abstract

We study suspensions of synthetic clay Laponite at very low ionic strength. We show the existence, for these charged disk-like particles, of a liquid-soft solid transition mainly driven by electrostatic repulsive interactions. Such a process defines a re-entrant transition line in the phase diagram. Location of this line is predicted using basic arguments. The structure is characterized by ultra-small-angle X-ray scattering (USAXS). Soft-solid suspensions show a correlation peak compatible with long-range electrostatic stabilization. Such a result strongly contrasts with the evolution of the scattering spectra for solid-like suspensions of Laponite at high ionic strength (above 10−4 M). Close inspection of this correlation peak reveals that individual particle distribution is not homogeneous in space.