Molecular Modeling of Glass-Epoxy Interphase: Influence of Chemistry and Molecular Weight of Silanes

In this paper, we study the effect of chemistry and molecular weight (MW) of silanes on the glass fiber-epoxy interaction using all-atom molecular dynamics (MD) simulations. Silane with two different end chemistries (Amino and Glycidoxy) and four MWs (Aminopropyl trimethoxysilane (APS, 179 g/mol), 3- Glycidoxypropyl trimethoxysilane (GPS, 236 g/mol), 8-Glycidoxyoctyl Trimethoxysilane (GOS, 306 g/mol) and 16-Glycidoxyhexadecyl Trimethoxysilane (GHS, 418 g/mol)) are considered. For the matrix, Diglycidyl Ether of Bisphenol A (DGEBA) and Jeffamine230 curing agent are considered. In the presence of mono-layer silanes, the interphase forms between glass fiber and epoxy matrix. The silane layer has a 0.98nm-2 silane number density, which covers 25% of the glass fiber reactive sties. The fiber-matrix composite system with mono-layer silane is created through condensation and curing reaction using the general AMBER force field (GAFF). The composite system is then subjected to transverse tensile and shear loadings using reactive force field ReaxFF to predict mechanical properties and damage mechanisms. The interphase thickness is predicted to be in the range of 1.1-1.4nm. Within the interphase various connectivity patterns are identified for the amine and epoxide terminated silanes. The interphase strength exceeds the strength of the bulk epoxy, leading to cohesive failure in the matrix for all silane types investigated.