Revealing nanoscale dynamics during an epoxy curing reaction with X-ray photon correlation spectroscopy

The evolution of nanoscale properties is measured during the thermally triggered curing of an industrial epoxy adhesive. We use X-ray photon correlation spectroscopy (XPCS) to track the progression of the curing reaction through the local dynamics of filler particles that reflect the formation of a thermoset network. Out-of-equilibrium dynamics are resolved through identification and analysis of the intensity-intensity autocorrelation functions obtained from XPCS. The characteristic time scale and local velocity of the filler is calculated as functions of time and temperature. We find that the dynamics speed up when approaching the curing temperature (T_cure), and decay rapidly once T_cure is reached. We compare the results from XPCS to conventional macroscale characterization by differential scanning calorimetry (DSC). The demonstration and implementation of nanoscale characterization of curing reactions by XPCS proves useful for future development and optimization of epoxy thermoset materials and other industrial adhesive systems.