Length-scale discrepancy in the properties of epoxy resin specimens

In studies of the fibre-matrix interphase with microscale single fibre methods, the dependence of results on conversion of the thermoset resin – or degree of cure as it is often called – remains an issue. In the microbond method specifically, the curing of picolitre volume drop-on-fibre systems differs significantly from that of macroscale resin batches. The surface-to-volume ratio and vapour pressure can cause volatile components of the resin to evaporate, potentially limiting the degree of cure. Atomistic scale modelling along with experimental thermal analysis were used to understand the curing process and how it translates to resin properties, while nanoindentation was used to experimentally compare the mechanical performance of samples prepared in different length-scales. The evaporation is experimentally verified. Comparable variation in mechanical properties is shown in atomistic scale models of the epoxy network with no evaporation. The origin is in the network morphologies created by varying the curing process. Thus attributing the length-scale discrepancy solely to conversion is likely an oversimplification and understanding the network morphology from different curing conditions is also needed.