Adsorbed behavior of spin-labeled silane coupling agent on colloidal silica studied by electron spin resonance

The adsorption mechanism of silane coupling agent on the colloidal silica surface is studied with spin-labeled silane coupling agent using ESR method. The density of the adsorbed silane molecules was determined to be approximately 1.5-2 molecules per 100 A2 of the silica surface in 95% ethanol solution. In addition, ESR signal of spin-labeled agent adsorbed on the colloidal silica surface was composed of two components; slow component attributable to the agents adsorbed directly on the Si--OH groups of the silica surface through hydrogen bond formation and rapid one attributable to the agents interacted with such adsorbed silane molecules.