Silylation of laponite clay particles with monofunctional and trifunctional vinyl alkoxysilanes

We report in this work the grafting of laponite clay particles with monofunctional gamma-methacryloxypropyl dimethyl methoxy silane (gamma-MPTDES) and trifunctional gamma-methacryloxypropyl trimethoxy silane (gamma-MPTMS) coupling agents. The evolution of the grafted amount and of the grafting yield was monitored as a function of the reaction time and of the initial silane concentration. We showed that the grafted amount increased with time and with the silane content up to a plateau value. The amount of chemisorbed silane at saturation varied from 0.56 to 1.9 mmol g(-1) depending on the nature of the coupling agent, the reaction time and the grafting conditions. While the trifunctional silane was capable of both reaction with the clay edges and formation of complex polysiloxane oligomers in the bulk which were further deposited on the particulate surface, the monofunctional silane formed a monolayer coverage on the border of the clay plates with the carbonyl groups being directed toward the surface as attested by Fourier transform infrared (FTIR) spectroscopy. The properties of the organosilane-modified laponite were examined by various analytical techniques such as wide-angle X-ray diffraction (WAXD), nitrogen adsorption and thermogravimetric analysis (TGA). The monofunctional silane exhibited nearly no effect on the physicochemical properties of the clay whereas grafting of the trifunctional silane resulted in decreased porosity, increased interlamellar distance and higher hydrophobicity.