Trapped and Alone: Clay-Assisted Aqueous Graphene Dispersions.

Abstract

Dispersing graphene sheets in liquids, in particular water, could enhance the transport properties (like thermal conductivity) of the dispersion. Yet, such dispersions are difficult to achieve since graphene sheets are prone to aggregate and subsequently precipitate due to their strong van der Waals interactions. Conventional dispersion approaches, such as surface treatment of the sheets either by surfactant adsorption or by chemical modification, may prevent aggregation. Unfortunately, surfactant-assisted graphene dispersions are typically of low concentration (<0.2 wt %) with relatively small sheets (<1 μm lateral size) while chemical modification is punished by increased defect density within the sheets. We investigate here a new approach in which the concentration of dispersed graphene in water is enhanced by the addition of a fibrous clay mineral, sepiolite. As we demonstrate, the clay particles in water form a kinetically arrested particle network within which the graphene sheets are effectively trapped. This mechanism keeps graphene sheets of high lateral size (∼4 μm) dispersed at high concentrations (∼1 wt %). We demonstrate the application of such dispersions as cooling liquids for thermal management solutions, where a 26% enhancement in the thermal conductivity is achieved as compared to that in a filler-free fluid.