Directional freezing of binary colloidal suspensions: a model for size fractionation of graphene oxide.

Abstract

The performance of graphene oxide (GO)-based materials strongly depends on the lateral size and size distribution of GO nanosheets. Various methods are employed to prepare GO nanosheets with a narrow size distribution. One promising method was proposed recently, directional freezing of a GO aqueous dispersion at a controlled growth rate of the freezing front. We develop a theoretical model of a binary colloidal suspension, incorporating both the moving freezing boundary and the preferential adsorption of colloidal particles to the ice phase. We numerically solve the coupled diffusion equations and present state diagrams of size fractionation. Selective trapping of colloids according to their size can be achieved by a suitable choice of the experimental parameters, such as the adsorption rates and the freezing speed.