Modeling sizing emulsion droplet deposition onto silica using all-atom molecular dynamics simulations

Abstract

Understanding structure–function relationships of the matrix–fiber interphase is important for the future design of composites with enhanced performance. This interphase structure is determined in part by sizing, an emulsion of epoxy film-former, silane coupling agent , and surfactant applied to fibers prior to work-up and resin impregnation . The multicomponent, microphase-separated nature of sizing makes it difficult to study using experiments and continuum-level simulations. In this study, microsecond all-atom molecular dynamics (MD) simulations are used to elucidate the dynamics of complex multicomponent sizing droplets on glass fiber surfaces. We analyze droplet/surface properties such as spreading factor, component density profiles, and spatial distribution of hydrogen bonds. From these observables, we show that the triblock copolymer surfactant enhances wetting of the epoxy resin film former on the glass surface, whereas the silane coupling agent slows down the spreading by pinning the droplet via siloxyl-surface hydrogen bonding. This work takes a step toward systematic understanding of the functionality of sizing in allowing pre-cured resin to wet glass surfaces in the context of composite lay-up. • Spreading dynamics of sizing droplets on silica depend on their composition. • Coupling agents deposit in rings that pin droplet contact lines and slow spreading.