Ionic liquid induced surface exclusion and anomalous first-order phase transition in Laponite dispersions

Spontaneous liquid-liquid phase separation occurring in laponite dispersions of ionic liquid (IL) solutions was observed at room temperature driven by surface exclusion of clay platelets at the water-air interface. The water-air interface dependent demixing behavior followed anomalous first-order phase transition kinetics described by a partition reaction CS K <-> S + C with a dernixing partition coefficient K = [S] / [C] where the initial homogeneous dispersion [CS] phase separated into a Laponite-poor [S] and Laponite-rich [C] state. The colloidal aggregates were found to be fractal structures with a mass fractal dimension 135< d(f) <1.75. The demixing process could be described by a droplet splitting model. The settling dynamics was induced by ionic liquids due to their charge specific interaction with clay platelets, and the surface exclusion of clay particles at the liquid-air interface governed the rate of demixing. Interestingly, the time-constant of first-order dynamics was found to be invariant of IL concentration. (C) 2015 Elsevier B.V. All rights reserved.