Influence of supercritical carbon dioxide on the morphology of modified clays

This research examines the influence of supercritical CO2 on five different organoclays, coated with either alkyl or phenyl ammonium surfactant. The supercritical fluid was found to alter the surfactant morphology, plasticizing the organic medium leading to further cation exchange within the galleries of the clay. For organoclays with a paraffin complex conformation, this change in the morphology resulted in basal expansion provided the tilt angle of the attached species was not already close to 90°, while for a bilayer conformation, the rearrangement in chain packing led to a decrease in dspacing. The di-tallow-dimethyl ammonium surfactant was found to be the optimal candidate in terms of gallery expansion, while the benzyl trimethyl ammonium surfactant appeared unaffected by the supercritical solvent. Increased temperature and pressure appeared most beneficial for plasticizing the organic surfactant, while pressure release rate had no effect.