Characterization of organically modified clays using scattering and microscopy techniques

Understanding the structure of organophilic clays and the interaction betwe en clay platelets dispersed in organic solvents is important for characteri zing nanocomposites formed by organophilic clays and polymers. To understan d and optimize potential processing conditions, organically modified montmo rillonite clays were dispersed in a number of organic solvents covering a r ange of solubility parameters and characterized using small-angle neutron s cattering 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 scat tering profiles and dispersion behavior in organic solvents of the dry powd er of unextracted and of extracted dimethyl dihydrogenated tallow montmoril lonite are significantly different, confirming that the organic modifiers a re present in excess in the unextracted material as reported by the industr ial provider. The scattering data show that both unextracted and extracted organically modified clay platelets were fully exfoliated in chloroform whi le the platelets retain their lamellar structure and swell to a similar ext ent in benzene, toluene, and p-xylene, but the extracted material has a str onger tendency to gel. The scattering profiles indicate that the swollen ta ctoids of extracted material are thinner, and therefore more numerous, whic h may account for the bulk suspension behavior. The extracted clay dispersi on exhibited a concentration dependence on the scattering for all the organ ic solvents studied except chloroform while the unextracted clay dispersion did not. Neither the extracted nor the unextracted dispersions exhibited a ny temperature dependence on the scattering. The thickness of unmodified mo ntmorillonite platelets was found to be 9.9 Angstrom while that of organica lly modified montmorillonite platelets was determined to be 24.3 Angstrom u sing wide-angle X-ray scattering. The lateral size of organically modified montmorillonite platelets was observed to be in the range of 0.4-1.0 mum us ing atomic force microscopy.