| Nanocomposites consisting of highly anisotropic layered silicates have received a great deal of attention owing to the potential for unprecedented increases in mechanical properties, barrier properties, and flame retardant properties. They key challenge is to disperse/exfoliate the layered silicates into individual sheets in order to take advantage of their large available surface area (∼760 m2/g). In this research, a novel supercritical carbon dioxide (scCO2) processing method was utilized to disperse nano-clays. The structure and properties of the clays and the resultant nanocomposites are characterized using a combination of wide-angle X-ray diffraction (WAXD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and rheology. Significant dispersion was achieved with Cloisite 93A clay, whereas relatively poor dispersion was achieved with Cloisite Na+ (natural clay). The extent of clay dispersion appears to be dependant on the 'CO2-philicity', which in turn depends on the surface modifications and inter gallery spacing. The presence of an acidic-hydrogen on the Cloisite 93A surface appears to play a strong role on its 'CO2-philicity'. We further demonstrate that CO2-phobic Cloisite Na+ (natural clay) can be dispersed with scCO2, using a CO2-philic polymer, polydimethylsiloxane (PDMS). The dispersed clay-PDMS nanocomposite shows an order of magnitude increase in the dynamic storage modulus at low frequencies, accompanied by the emergence of a 'solid-like' plateau, characteristic of dispersed nanocomposites with enhanced clay-polymer interactions. |
