Glass fiber-epoxy interactions in the presence of silane: A molecular dynamics study

In this study, the interaction of epoxy resin with the glass fiber in the presence of monolayer glycidoxypropyl-trimethoxy silane is studied using molecular dynamics simulations. To quantify the fiber-matrix adhesion, the interphase traction-separation response is developed by loading the interphase in mode-I and mode-II. The overall composite model is also loaded in tension and shear to predict the stress-strain responses and failure loci. Interphase consisting of different silane-epon-amine connectivity patterns has thickness in the range of 1.3-1.7 nm as determined by the root mean squared fluctuation method. In the absence of silane, fiber-epoxy non-bonded interaction is very weak and failure is at the fiber surface. Simulations indicate that higher fiber surface reactivity (i.e., -SiOH number density) does not improve adhesion unless there is silane in the interphase. Presence of silane introduces covalent bonding interactions in the fiber-epoxy interphase improving the interphase properties. As a result, composite strength and energy absorption capability improves significantly with the number of bond sites at the fiber surface and promotes progressive failure through multiple damage modes. Simulation results suggest that silane number density of 1-2 nm(-2) should be the optimum to achieve high strength and energy absorption for the composite system investigated.