Effect of geometry and surface properties of silicates on nanostructuration of suspension in precursors of an epoxy/amine network

Several lamellar silicates (Montmorillonite, Hectorite, Mica) showing different host structures and aspect ratios were modified with octadecylammonium ions by a cationic exchange process. The resulting organoclays were characterized using thermal gravimetric analysis and X-ray diffraction, which allowed us to estimate the amount of surfactants within the organoclays and their organization in the interlamellar spacing. Some local pseudo-organizations were found and checked by differential scanning calorimetry (DSC). The interactions of organophilic silicates were evaluated, without any shear, with the precursors of a rubbery epoxy/amine network. These silicate/monomers interactions were monitored via the measurements of the interlamellar swelling, the surface energies and the physical gel formation. The organoclays used form gels in the monomers above the percolation threshold if no shear is applied and present a gel/sol transition at a critical shear stress. Gel strength determined from storage modulus and viscosity values determined at high shear rates reveal different organizations of clay in the monomers depending on the silicate aspect ratio and silicate/monomers interactions. (c) 2006 Wiley P.eriodicals, Inc.