Structure of silane layer formed on silica particle surfaces by treatment with silane coupling agents having various functional groups

Abstract

The surface treatment of spherical silica particles with silane coupling agents having various organic functional groups was conducted and the effect of the alkoxy group number on the molecular flexibility of the silane chain with multilayer coverage was investigated using ¹H-pulse nuclear magnetic resonance spectroscopy. The silica particles were treated with 2-propanol solution and heated at 120 °C for 24 h after solvent evaporation to accelerate the polycondensation reaction of silanol groups. For multilayer coverage, flexible linear chain and rigid network structures were expected to form on the surface from the di- and trialkoxy structures, respectively. However, the rigid network structure was formed from both the di- and trialkoxy structures with glycidoxy, amino, and methacryloxy functional silanes. Ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the dialkoxy structure of the glycidoxy functionality. Ring opening of the epoxy group could be reduced by pH adjustment of the treatment solution and the linear chain structure was formed from the dialkoxy structure. In the case of amino and methacryloxy functional groups, hydrogen bonds were formed between the amino or methacryloxy groups and the silanol groups on the silica surface or silane molecules.

Keywords:

• silane coupling agent
• surface treatment
• glycidoxy group
• amino group
• methacryloxy group
• ¹H-pulse NMR

Acknowledgments

The authors are grateful to Denki Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan and Shin-Etsu Chemical Co., Ltd., Tokyo, Japan for kind donation of the silica particles and silane coupling agents, respectively.