Delamination of graphite oxide in a liquid upon cooling.

Graphite oxide (GO) in liquid acetonitrile undergoes a transition from an ordered phase around ambient temperature to a gel-like disordered phase at temperatures below 260 K, as demonstrated by in situ X-ray diffraction. The stacking order of GO layers is restored below the freezing point of acetonitrile (199 K). The reversible swelling transition between a stacked crystalline phase and an amorphous delaminated state observed upon cooling provides an unusual example of increased structural disorder at lower temperatures. The formation of the gel-like phase is attributed to the thermo-responsive conformational change of individual GO flakes induced by stronger solvation. Scanning force microscopy demonstrates that GO flakes deposited onto a solid substrate from acetonitrile dispersions at a temperature below 260 K exhibit corrugations and wrinkling which are not observed for the flakes deposited at ambient temperature. The thermo-responsive transition between the delaminated and stacked phases reported here can be used for sonication-free dispersion of graphene oxide, micro-container applications, or the preparation of new composite materials.