Derek L. Ho and Charles J. Glinka Div. 856, MSEL
Understanding the structure of organophilic clays and the interaction between clay platelets dispersed in organic solvents is important to characterizing nanocomposites formed by organophilic clays and polymers. In order to understand and optimize potential processing conditions, organically modified montmorillonite clays were dispersed in a number of organic solvents covering a range of solubility parameters and characterized using small angle neutron scattering and wide angle x-ray scattering techniques. The organic modifier was dimethyl dihydrogenated tallow ammonium. Both as-received (unextracted) and purified (extracted) organically modified clays were studied. The scattering profiles and dispersion behavior in organic solvents of the dry powder of unextracted and of extracted dimethyl dihydrogenated tallow montmorillonite are significantly different confirming that the organic modifiers are present in excess in the unextracted material as reported by the industrial provider. The scattering data show that both unextracted and extracted organically modified clay platelets were fully exfoliated in chloroform while the platelets retain their lamellar structure and swell to a similar extent in benzene, toluene and p-xylene, but the extracted material has a stronger tendency to gel. The scattering profiles indicate that the swollen tactoids of extracted material are thinner, and therefore more numerous, which may account for the bulk suspension behavior. The extracted clay dispersion exhibited a concentration dependence to the scattering for all the organic solvents studied except chloroform while the unextracted clay dispersion did not. Neither the extracted nor the unextracted dispersions exhibited any temperature dependence to the scattering. The thickness of unmodified montmorillonite platelets was found to be 9.9 Å while that of organically modified montmorillonite platelets was determined to be 24.3 Å using wide angle x-ray scattering. The lateral size of organically modified montmorillonite platelets was observed to be in the range of 0.4 m m to 1.0 m m using atomic force microscopy.