Clay-organosiloxane hybrids: A route to cross-linked clay particles and clay monoliths

Reaction of bis(trimethoxysilyl)hexane, (CH3O)(3)Si(CH2)(6)Si(OCH3)(3), and the protonated salt of 3-aminopropyltriethoxysilane, (C2H5O)(3)Si(CH2)(3)NH3+Cl-, with different clay aqueous colloidal dispersions produces a network of clay platelets cross-linked on their edges by the corresponding organosiloxanes. In the case of the alpha,omega-bridging organosiloxane, where the surface modification of the clay by the silane proceeds on its outer surfaces, cross-linking results in a gel network that extends to the whole volume of the initial aqueous dispersion. Drying of this gel and grinding of the as-formed, relatively hard specimens affords fine hybrid powders consisting of cross-linked clay particles that inherit the swelling, intercalation, and ion-exchange properties of the starting clay. Controlling both the composition of the initial suspension (clay type, solvent, and concentration) and the drying process, enables the fabrication of monolithic clay hybrids. In the case of the protonated aminosiloxane, the surface modification of the clay takes place both within its interlayer space and at its edges. The former leads to the formation of silsequioxane pillars within the clay galleries. The latter produces stiff yet ductile monoliths upon drying via condensation of edge-modified adjacent clay layers. When Laponite and (CH3O)(3)Si(CH2)(3)N(CH3)(3)Cl-+(-) are used, optically transparent monoliths (or clay glasses) are obtained.