The surface treatment of spherical silica particles with silane coupling agent having mercapto group was carried out and structure and amount of silane nanolayer formed on silica surface were analyzed using H-1 pulse nuclear magnetic resonance (NMR) and thermogravimetric analysis, respectively. Effects of loading amount and number of alkoxy groups of silane on the structure were investigated. Silanes with dialkoxy and trialkoxy structures were used as silane coupling agents and the loading amount of the silane on the silica surface was varied from one to nine times the amount required for monolayer coverage. The relaxation time was longer in the dialkoxy type than in the trialkoxy type of silane. The relaxation time increased with increase of the loading amount of silane for the dialkoxy type; on the other hand, there was no influence of the loading amount of silane for the trialkoxy type. It was found that the silane structure was flexible for the dialkoxy type, whereas it was rigid for the trialkoxy type. Effect of mixing ratio of silane coupling agents having di- and trialkoxy groups on the silane nanolayer structure was also investigated, and H-1 pulse NMR studies confirmed that the relaxation time measured for the mixed silane-treated system was between those for the dialkoxy and the trialkoxy structures and depended on the mixing ratio. It was found that the network density of silane-treated layer on silica particles could be controlled by varying the molar ratio of dialkoxy/trialkoxy silane coupling agents. (C) Koninklijke Brill NV, Leiden, 2011