Glass fiber sizing is a thin coating applied to the glass fiber surface during the fiber manufacturing process that protects the fiber from handling damage and enables the level of adhesion between the fiber and matrix. When emulsified sizing mixture from the sizing bath is applied on the glass surface, it is believed that there is preferential adsorption of silane molecules toward the glass surface. Silane molecules react with the glass surface as well as among themselves. Later in composite processing, they make linkage with epoxy or other resins during consolidation and cure to form distinct interphase region. Complex nature of formation and structure of the sizing are not well understood.
In this study, the structure of the Glycidoxypropyl-trimethoxy silane (GPS) based sizing layer and its reactivity/interaction with glass surface will be studied from a Materials-by-Design perspective using molecular dynamics (MD) method. GPS-FF sizing mixture will be placed on top of the hydroxylated silica surface. Silica-sizing system will be equilibrated with non-reactive force field (AMBER) to identify the spatial distribution of silane molecules. Condensation reaction, which forms Si-O-Si linkage, between GPS molecules and between GPS and glass surface will be modeled with cross-linking algorithm. Composition of T0/T1/T2/T3 species (i.e., Si atoms with zero/one/two/three Si-O-Si linkages) will be identified from spatial distribution and close proximity of the GPS molecules. Silica-sizing model will then be studied with reactive force field ReaxFF to develop interphase traction law and to identify deformation and properties tailoring mechanism. Effects of GPS concentration (5-15% wt.) and interphase thickness on interphase properties and damage modes will be identified. Finally, silica-sizing interphase properties will be compared with the baseline silica, sizing and epoxy properties.