CRUMPLED AND COLLAPSED CONFORMATIONS IN GRAPHITE OXIDE MEMBRANES

MEMBRANES composed of bilayers of amphiphiles such as phospholipids generally exhibit two-dimensional liquid-like structure within the layers. When the constituent molecules of such a membrane are permanently cross-linked to each other, the membrane becomes less flexible, forming a two-dimensional solid. Solid membranes are expected to exhibit very different behaviour from their liquid counterparts 1-3, including transitions between a two-dimensional flat phase, a crumpled phase of fractal dimension 2.5 and a compact, three-dimensional phase. Experimental evidence for the crumpled phase has, however, been lacking. As this phase was not observed in computer simulations 4-6, it has been suggested that it may always be absent for self-avoiding (and therefore all real) membrane 4-6. To the contrary, we report here the experimental observation of the crumpled conformation in an aqueous suspension of graphite oxide membranes. Static light scattering measurements indicate the presence of membrane conformations with a fractal dimension of 2.54 +/- 0.05. As the intra-membrane affinity is enhanced by changing the composition of the solvent, the membranes collapse to a compact configuration.