Correlation between microstructure and properties of graphene oxide/waterborne polyurethane composites investigated by positron annihilation spectroscopy

A quantitative description of microstructure is highly desirable for the precise construction of high performance graphene based polymer composites. In this paper, the effects of doping graphene oxide (GO) on the microstructure, thermal and mechanical properties of the obtained graphene oxide/waterborne polyurethane (GO/WPU) composites were systematically investigated. In order to give a deep insight into the microstructure of GO/WPU composites, especially for the relative free volume fraction (f(r)) and interfacial interaction intensity (β), positron annihilation lifetime spectroscopy (PALS) was employed for its quantitative characterization. With the increase of GO content, the f(r) decreased first and then increased, the lowest value was observed for the composites containing 0.5 wt% GO. This can be ascribed to the change in the dispersed state of GO and interfacial interactions, which agree well with the results of SEM. The correlation between microstructure and properties was established with the PALS results, the values of f(r) and β give a good explanation of the variation in glass transition temperature and tensile strength, respectively.