Influences of the alkoxy group number and treatment condition on the structure of glycidoxy functional silane-treated layer on silica particles analyzed by ¹H pulse NMR

Abstract

The surface treatment of spherical silica particles using a silane coupling agent with a glycidoxy group was conducted and the effect of the alkoxy group number on the molecular mobility of the silane chain was investigated by ¹H pulse nuclear magnetic resonance (NMR). Silanes with di-alkoxy and tri-alkoxy structures were used, and the silica particles were treated with 2-propanol solution and heated at 120 °C for 24 h after solvent evaporation. The surface coverage of the silica surface was in the range from two to three layers. For multilayer coverage, linear chain and network structures were expected to form on the surface by polycondensation reaction using the di- and tri-alkoxy structures, respectively. However, the relaxation times for silane chains with both di- and tri-alkoxy structures measured by pulse NMR were short, which indicates that both silane chains formed rigid network structures. Fourier transform infrared spectroscopic analysis revealed that ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the di-alkoxy structure. Ring opening of the epoxy group could be reduced by setting the heating temperature at 80 °C. There was a significant difference in flexibility between the silane-layers with di- and tri-alkoxy structures after heating at 80 °C, as reflected by the relaxation time.

Keywords:

• silane coupling agent
• glycidoxy group
• surface treatment
• epoxy resin
• fracture toughness

Acknowledgements

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