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In situ X-ray photon correlation spectroscopy (XPCS) was used to investigate the crosslinking kinetics of a two-component epoxy resin adhesive. The effect of external temperature on the crosslinking reaction was studied by subjecting the epoxy to different curing temperature profiles. The temporally resolved dynamics of fillers was tracked, which conveniently served as a probe of the internal dynamics of the thermoset network and allowed us to study the crosslinking process. The epoxy resins showed different relaxation processes depending on temperature, indicating a complex relationship between applied temperature and the development of stress/relaxation conditions related to the formation of the thermoset network and subsequent vitrification process. The epoxy was found to be highly temperature sensitive, with heating to elevated temperatures promoting gelation, but the vitrification process was not completed during the isothermal curing stage. Instead, cooling the sample to room temperature facilitated the final vitrification process. Finally, this paper contextualizes the results of this epoxy system within the broader field of XPCS on complex polymer systems and further advocates for XPCS as a fundamental technique for the study of complex polymers. 

Abstract The properties of artificially grown thin films are strongly affected by surface processes during growth. Coherent X-rays provide an approach to better understand such processes and fluctuations far from equilibrium. Here we report results for vacuum deposition of C₆₀on a graphene-coated surface investigated with X-ray Photon Correlation Spectroscopy in surface-sensitive conditions. Step-flow is observed through measurement of the step-edge velocity in the late stages of growth after crystalline mounds have formed. We show that the step-edge velocity is coupled to the terrace length, and that there is a variation in the velocity from larger step spacing at the center of crystalline mounds to closely-spaced, more slowly propagating steps at their edges. The results extend theories of surface growth, since the behavior is consistent with surface evolution driven by processes that include surface diffusion, the motion of step-edges, and attachment at step edges with significant step-edge barriers.