Ranking Silane Molecules for Interphase Performance In S-Glass/Epoxy Composites

In our past work, molecular dynamic (MD) simulation of interphases between S-glass and epoxy matrices have been conducted to predict strain rate dependent mixed-mode cohesive traction surface for bridging to the micromechanics length scale. Silane is an important component of a composite material which binds inorganic glass fiber to the organic resin material through covalent bonds. This study uses MD for ranking the silanes based on the strength and energy absorption as a function of the silane chemistry, chain length, orientation (straight/relaxed state) and number of connections of silane with the glass fiber surface.
From the single silane system analyses, it was found that the silanes breaking at Carbon-Nitrogen bond gave better peak force and higher energy absorption before failing as compared to the silanes which broke at Carbon-Oxygen bond. Peak force being 6.43 nN for the Carbon-Nitrogen silanes and 4.99 nN for the Carbon-Oxygen silanes – representing an increase of 29%. The simulations with the relaxed molecules sitting on the glass fiber surface showed that the peak force was the same as straight molecules oriented normal to the fiber surface since the bond breakage mechanism were identical. However, the simulation revealed that the non-bonded interactions contribute to the overall energy absorption during deformation of the relaxed molecules versus the straight molecules. In this case the energy absorption of the relaxed silanes exhibiting Carbon-Nitrogen bond failure can be increased by 80% over the straight silanes exhibiting Carbon-Oxygen bond breakage. Increasing the molecular weight of the silanes was shown to further increase energy absorption by 48%. For the single silane molecule systems, MD simulation shows that the silanes are strain rate independent. The effect of different bond site densities will be studied for the strain rate dependent energy absorption and strength of silane arrays.