Molecular Dynamics Simulations of Fiber-Sizing Interphase

In this study, the structure of the Glycidoxypropyl-trimethoxy silane (GPS) based sizing and its interaction with glass fiber surface and an epoxy film former (FF) are studied using all-atom molecular dynamics (MD) methods. Sizing is formulated with 0-30% wt. concentration of GPS in a GPS-Film Former (FF) mixture. The silica-sizing system is first equilibrated with non-reactive General AMBER Force Field (GAFF) to identify the spatial distribution of silane molecules within the simulation volume. Condensation reactions are simulated using a crosslink algorithm where Si-O-Si linkages form between GPS molecules as well as between GPS and the glass surface. Simulations results show that silane molecules agglomerate as macromolecules and create an inhomogeneous sizing structure. GPS molecules near the glass surface are attracted to the glass surface and form a monolayer of Si-O bonds. Simulations show that a continuous cross-linked silane network is not formed even at the highest GPS concentration levels. However, the atomic structure that evolves during the sizing of the fiber provides insight into the mechanisms of interphase formation that develops during composite processing when the curing agent present in the matrix (e.g. Jeffamine in the case of epoxy matrix) diffuses into the sizing and reacts with both the epoxy FF and the silane through epoxide-amine reactions.