① The SiX group connected to the silicon atom is hydrolyzed to generate SiOH;
②Si-OH is dehydrated and condensed to generate Si-OH-containing oligosiloxane;
③ SiOH in the oligosiloxane forms a hydrogen bond with the OH on the surface of the substrate;
④ In the process of heating and curing, it forms a covalent bond with the substrate along with the dehydration reaction.
It is generally believed that only one of the three silanol groups generated by the hydrolysis of the silane coupling agent at the interface is bonded to the surface of the substrate; the remaining two Si-OHs may be condensed with Si-OH in other silanes, or are free state. Therefore, the interface of two materials with very different properties can be coupled by the silane coupling agent, thereby improving the performance of the composite material and increasing the bonding strength, and obtaining a new type of composite material with excellent performance and reliability. Silane coupling agents are widely used in rubber, plastics, adhesives, sealants, coatings, glass, ceramics, metal anticorrosion and other fields. Now, silane coupling agent has become one of the necessary additives in the material industry.
The role and effect of silane coupling agents are recognized and affirmed by people, but why a very small amount of coupling agent on the interface has such a significant impact on the performance of composite materials, there is no complete set of coupling mechanisms to explain it. The mechanism of the coupling agent on the interface between two materials with different properties has been studied a lot, and explanations such as chemical bonding and physical adsorption have been proposed. Among them, the chemical bonding theory is the oldest but is considered to be a relatively successful theory so far.