2. Wetting effect and surface energy theory
In 1963, when reviewing the known aspects of surface chemistry and surface energy related to adhesion, ZISMAN concluded that in the manufacture of composite materials, the good infiltration of liquid resin into adherends is of paramount importance. If complete wetting is achieved, the physical adsorption of the resin on high-energy surfaces will provide a cohesive strength that is higher than the cohesive strength of the organic resin.

3.Deformable layer theory
In order to alleviate the interfacial stress caused by the difference in thermal shrinkage between the resin and the filler when the composite material is cooled, it is desirable that the resin interface adjacent to the treated inorganic material is a flexible deformable phase, so that the toughness of the composite material maximum. The surface of the inorganic substance treated by the coupling agent may preferentially absorb a certain complexing agent in the resin, and the uneven curing of the interphase regions may result in a much thicker molecular layer than the coupling agent between the polymer and the filler. Flexible resin layer. This layer is called a deformable layer. This layer can relax the interface stress and prevent the interface cracks from expanding, thus improving the bonding strength of the interface and the mechanical properties of the composite.

4. Constraint layer theory
In contrast to the deformable layer theory, the constrained layer theory states that the resin in the region of the inorganic filler should have a certain modulus between the inorganic filler and the matrix resin, and the function of the coupling agent is to "tighten the polymer structure" "In the interphase area. From the point of view of the properties of the reinforced composite material, to obtain maximum adhesion and hydrolysis resistance, a constraining layer is required at the interface.
As for the titanate coupling agent, its combination with organic polymers in thermoplastic systems and filler-containing thermosetting composites is mainly based on the compatibility and intertwining of long-chain alkyl groups, and forms a common with inorganic fillers. Price key. The above assumptions reflect the coupling mechanism of the coupling agent from different theoretical sides. In the actual process, it is often the result of the joint action of several mechanisms.