Silane coupling agents can be used as adhesion promoters for composite materials and coatings. Silane has the ability to form covalent bonds with inorganic substrates and epoxy resins.

The general formula of the silane coupling agent generally shows two types of functional groups. X is a hydrolyzable group, usually alkoxy, acyloxy, halogen or amine. After hydrolysis, a reactive silanol group is formed, which can condense with other silanol groups (for example, the surface of a siliceous filler) to form a siloxane bond. It can also form stable condensation products with other oxides such as those of aluminum, zirconium, tin, titanium and nickel, or form less stable bonds with oxides of boron, iron and carbon. Alkali metal oxides and carbonates do not form stable bonds with Si-O-. The R group is a non-hydrolyzable organic free radical, which may be a functional group with some special functions to produce some expected functions.

Most widely used organosilanes have one organic substituent and three hydrolyzable substituents. In most surface treatment applications, the alkoxy group of trialkoxysilane is hydrolyzed to form silanol. The reaction of these silanes is divided into four steps. Initially, the hydrolysis of three labile groups occurred. This is followed by condensation of oligomers. Then the oligomer is hydrogen-bonded with the OH group of the substrate. Finally, during drying or curing, a covalent bond is formed with the substrate, accompanied by loss of water. Although described in steps, these reactions can occur simultaneously after the initial hydrolysis step. At the interface, usually each organosilane silicon has only one bond to the surface of the substrate. The two remaining silanol groups exist in condensed or free form. The R group can undergo covalent reactions or physical interactions with other phases.

Silane can be vapor-deposited in a single layer under anhydrous conditions to modify the surface. Typical reaction conditions are higher temperature (50°-120°C) and longer reaction time (4-12 hours). Among alkoxysilanes, only methoxysilane can be vapor deposited without a catalyst. The most effective silane for vapor deposition is cyclic azasilane.