Complexation of graphene oxide (GO) and cetyltrimethylammonium bromide (CTAB), a model amphiphile, was quantitatively studied to elucidate the governing forces and resulting structures of their self-assembly. We systematically varied pertinent self-assembly parameters, including GO size, mixing ratio, salt, and osmotic stress, and quantified the nanoscale structures of GO:CTAB using x-ray diffraction (XRD). Multilamellar stacking of GO and CTAB layers persists in all GO:CTAB assemblies exhibiting structural order. While driven by hydrophobic interactions between the hydrocarbon tails, the CTAB layer displays a series of structural transitions from a bilayer with in-plane ordering to a more fluidic bilayer and to an interdigitated monolayer. Interaction between GO and CTAB layers shows to be dominated by electrostatics, and osmotic stress studies indicate the absence of continuous hydration layers in GO:CTAB assemblies. Adding salt increases the inter-layer spacing by intercalating between GO and CTAB layers, and this ion layer can be expelled by high osmotic stress. These studies provide quantitative knowledge of the structure and interaction of GO:CTAB complexation, which lays foundation for precise control and rational design of their nanoscale self-assemblies.

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