Coupling agent

Silane coupling agents are suitable for fillers and substrates whose surfaces contain hydroxyl groups, silanol groups, metal hydroxyl groups, stable oxide layers, or activatable reactive sites. They are not suitable for all inorganic materials, nor can they be directly applied to all metals, ...

When adding glass fibers to resins, silica (silica gel) to rubber, or various inorganic fillers to coatings/adhesives, the common challenge lies not in "whether fillers are present," but in whether the interface between the inorganic and organic phases is sufficiently stable.