Direct monitoring of silane/epoxy interphase chemistry

Evanescent wave spectroscopy has been used to directly monitor the interactions between an epoxy resin and an amino silane coupling agent, gamma-aminopropyltrimethoxy silane (gamma-APS) adsorbed on silica fibers. First, it was shown that reactions of the adsorbed silane molecules could be monitored as a function of drying at elevated temperature. Next, the silane surface treated fibers were embedded in the epoxy resin and the primary amine reactivity of the silane at 70 degrees C was measured by the decrease from the initial absorbance height of the combination band at 4925 cm(-1). It was found that there was a decrease of 13% in band absorbance when the silane was adsorbed from a 5% gamma-APS solution. The percent decrease was 22% and 38% when the silane was adsorbed from 2% and 1% gamma-APS solutions, respectively. The results show that a significant fraction of the amine groups remain unreacted, even in the presence of excess epoxy. Also, it was discovered that in no instance was there any indication of silane diffusion from the interphase during the course of the experiment, even when the adsorbed silane was not dried at elevated temperature, prior to placement in the epoxy resin. (C) 1998 Elsevier Science Limited. All rights reserved.