Highly Ordered Graphene Oxide and Reduced Graphene Oxide Based Polymer Nanocomposites: Promise and Limits for Dynamic Impacts Demonstrated in Model Organic Coatings

Graphene oxide (GO) dispersed in water has been combined with a mixture of aqueous polymer dispersions and melamine formaldehyde resin (MF). Stable low viscous fluids with no obvious signs of mesoscale ordering at 0.3 wt % yield transparent films with GO loadings up to one weight percent in the form of homogeneously aligned double strands, each comprising few individual layers of the carbon allotrope. While baking of the films at 160 °C results in minor thermal reduction of GO, in situ reduction with excess hydroxylamine (HA) in the presence of the polymer colloids yields stable dispersions in which amphiphilic graphene like flakes temporarily encapsulate gaseous reaction products. Depending on the parameters in the time-temperature domain, the hollow spheres may be transferred into solid material or disassemble during film formation, the latter case providing black, smooth, and transparent films with up to eight magnitudes increased electrical conductivity and an oxygen permeability 30-fold higher compared to the neat polymer matrix. In contrast, GO reduces oxygen permeability by that factor, while water permeability stays unchanged. Thermo-mechanical measurements reveal matrix stiffening by the platelets as well as by HA, the latter via modifying the MF reactivity. Excellent stone chip resistance and ballistic impact tests demonstrate efficient energy dissipation and crack deflection provided by the laminate like morphology of GO based composite. On the contrary, the same material only provides moderate substrate protection in rain erosion tests.