Investigating the Structure of CVD Deposited Amino Silane on Silica Substrate via High Resolution Characterization Methods

Abstract

The interphase between glass fiber and an epoxy matrix is a nanometer scale region that governs the load transfer between these constituents in composites. Traditionally, sizing packages are multifunctional and are applied to a fiber surface to protect fibers during handling and weaving while improving wettability and adhesion through covalent bonds between the fiber surface and the matrix. The most conventional sizing application approach is to use epoxy emulsion of silanes and surfactants; however, it leads to non-uniform coating (i.e., coverage and thickness) and a structure that is not well understood. An adhesion promoter like organofunctionalized silanes is often a part of these sizing packages, and they can help achieve desirable interphase properties. Molecular dynamics (MD) simulation studies have shown that these glass-silane-epoxy interphase strength and energy absorption is highly dependent on bond density, interphase-coating thickness, and strain rate (monolayer and full saturation of bond density resulted in highest interphase strength). To create such thin coatings, a chemical vapor deposition (CVD) approach may be well suited since it can achieve both a uniform silane coating and control of the thickness range as low as a monolayer. A CVD method developed previously to deposit the silane coating on glass fiber surfaces, has shown improvements to the interphase strengths, though the deposited coating morphology was not well understood nor optimized. Quantifying/characterizing the uniformity and thickness of coating on a fiber surface is an experimental challenge due to its cylindrical shape. Hence, a Si substrate with an oxide layer was used as a surrogate. The current study focuses on understanding the relationship between CVD process exposure time (5 min, 30 min and 60 min) and structure of the amino silane coating on Si substrate to develop an approach for depositing a uniform and thin coatings.