Silane coupling agents interaction

Silane coupling agents interact with receptive inorganic surfaces forming tenacious bonds at the interface. These receptive inorganic surfaces are characterized by the presence of hydroxyl groups (OH) bonded principally to silicon and aluminum. 

Fig. 20. Schematic representation of the hydrolysis of silane coupling agents and their subsequent interaction with hydroxylated mineral surfaces.

The subject of silane chemistry and its interaction with both glass surface and polymer resins have been studied extensively. Since the silane coupling agent for improving the bond quality has first appeared in the literature (Rochow, 1951), a wide variety of organofunctional silanes has been developed, prominently by Plueddemann and coworkers. An early compilation of this subject for epoxy and polyester matrix composites (Plueddemann et al., 1962, Clark and Plueddemann, 1963 Plueddemann, 1974), and more recent reviews on the use of silane agents and... 

The substrate/silane interphase and the silane/matrix interphase are equally important in considering the mechanism of reinforcement by silane coupling agents in composites. The mineral oxide/silane interphase is more well defined than a metal/silane or a silane/matrix interphase. For example, in the case of a metal substrate, surface oxides may dissolve into the silane layer or form a complex. In the case of the silane/matrix interphase, a diffuse boundary layer may exist due to dispersion of physisorbed silanes in the matrix phase or penetration of the matrix resin into chemisorbed silane layers. Many features of the interaction of a silane coupling agent with a polymer matrix are specific to the system, and thus the chemistry of the silane/matrix interphase must be characterized and defined for each system. 

The results of the research investigations summarized here, and of numerous other recent studies, have contributed greatly to current views of the chemical interactions of silane coupling agents in mineral-reinforced composites. However, concepts and hypotheses based on results of earlier work [1, pp. 16-27] have been confirmed in most instances. 

Several studies of polymer/silane coupling agent interphases have involved the use of scanning electron microscopy (SEM) [5-7]. For example, Vaughan and Peek [6] have used SEM to examine fracture surfaces to determine the mode of failure of composite materials and to draw conclusions about interfacial interactions of various coupling agents and epoxide and polymer resin systems. 

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