Organic modification of layered silicates: structural and thermal characterizations

Abstract Organic modification of natural and synthetic layered silicates namely montmorillonite and laponite is reported in this work. The modified silicates are being subsequently used in the preparation of nano-composite membranes based on ionomers for fuel cells application. Laponite, an entirely synthetic silicate, was modified using organosiloxanes containing imidazole groups. Two different strategies were adopted for modification: (a) swelling of the silicate in 2-butanone followed by functionalization using the siloxane at room temperature, (b) direct reaction between laponite and the organosiloxane in xylene at 120 °C. Montmorillonite, a natural silicate, was supplied in the alkyl-ammonium form containing –OH groups. The modification of this silicate was conducted following the procedure (b). The structures of both plain and modified silicates were investigated by XRD showing that the interlayer distance (around 17 A) was not affected during the functionalization of laponite. However, a noticeable increase in the interlayer distance from 18.0 A to 24.5 A was observed for the modified montmorillonite. This clearly shows the presence of polysiloxane chains in between the silicate layers. Further characterization showed that the modification of these silicates was in the range between 16% and 23% (molar percentage). TGA was done between 25 and 300 °C in order to study the thermal degradation pattern of the silicates. The amount of adsorbed water could be determined from the results. The functionalization reduced the adsorption of water from 13.5% to 6.8% for laponite and from 8.5% to 4% for montmorillonite.

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