Aqueous dispersions of silane-functionalized laponite clay platelets. A first step toward the elaboration of water-based polymer/clay nanocomposites

Mono-and trifunctional organo alcoxysilane derivatives carrying a terminal reactive methacryloyl group have been used as reagents for the chemical modification of synthetic Laponite clay platelets in toluene. Qualitative evidence of the presence of chemically attached silane molecules was provided by Fourier transform infrared and Si-29 and C-13 solid-state NMR spectroscopies. Quantitative data (grafted amount and grafting yield) were also obtained by means of elemental and thermogravimetric analysis. While the trifunctional coupling agent was grafted on the clay edges in the form of oligomers pillaring the clay stacks, the monofunctional derivative selectively attached to the individual clay sheets as confirmed by X-ray diffraction and Brunauer-Emmett-Teller measurements. In agreement with these findings, only the clay stacks grafted using the monofunctional coupling agent could be satisfactorily redispersed into water. The aqueous suspensions of the grafted colloidal disks were characterized by small-angle X-ray scattering, dynamic light scattering, and cryogenic transmission electron microscopy. Emulsion copolymer latexes, the surface of which was decorated by individual Laponite platelets, were finally produced using the grafted clay particles as seeds. This new method provides an efficient way for constructing water-based polymer/exfoliated clay nanocomposites.