Structure, Adsorptive Separations, and Characterization of Surfactant/Clay Complexes

C.D. Muzny, T.J. Bruno, and H.J.M. Hanley

Objective: To exploit the unique characteristics of clay platelets in the production of organic-inorganic composite materials with revolutionary material properties and in the development of novel chemical separation techniques.

Problem: Clay is the key inorganic substance in applications ranging from pollution prevention and remediation, enhanced oil recovery, the treatment of petroleum liquids, the manufacture of cosmetics and pharmaceuticals, and the synthesis of polymer nanocomposite materials. An understanding of clay-organic chemical interactions and the effects these interactions have on the structure of clay complexes is a key issue for future developments in all of these applications.

Approach: Our approach is twofold. First, in order to understand the structural changes induced by clay surface treatments, we are undertaking a small-angle neutron scattering and dynamic light scattering investigation of the complexes formed in mixture suspensions of clay mineral and cationic surfactants. These techniques allow us to monitor the changes in the nanoscale structural properties of clay and organoclay complexes in a variety of situations. Second, in order to understand the chemical kinetics of the clay-organic interaction, we have advanced the application of physicochemical gas chromatography by devising stable clay- and organoclay-coated capillary columns. The capillary column approach that we have developed is more efficient, requires lower column temperatures, and produces values of the enthalpy of adsorption (H_ads) with a much lower uncertainty than the conventional techniques.

Results and Future Plans: Our results are wide ranged. For example, they include elucidation of the surface structure of synthetic clay Laponite with cetyltrimethylammonium bromide (CTAB) complexes; determination of the effect of a mineral surface on micelle formation; investigation of the effect of shear on colloidal gel formation using an adapted Couette cell of a constant stress rheometer which is placed in the neutron or light beam; investigation of the formation and structure of complexes of organic macromolecule adsorbed on an inorganic substrate; and investigation of dispersion and flocculation in aqueous mineral systems. We have also determined H_ads for a family of hydrocarbons on Laponite and Laponite complexed with CTAB by application of the organoclay-coated capillary column gas chromatography technique. The CTAB-coated Laponite is especially significant in the environmental context in that it represents a surrogate soil system and can be used to understand the interaction of pollutants on soils.

Future plans are to investigate further the relationship between the structure and rheology of gelling systems; to attempt to construct and characterize clay nanocomposites formed in an organic medium; and to understand better the role of an organic surface on flocculation mechanisms. We would also like to co-ordinate the structure surface studies with the thermodynamic information obtained from the coated capillary column. In addition, our future plans include extending the chromatographic technique to the measurement of the diffusion of pollutants into the clay and organoclay system.

Publications:

Bruno, T.J., Lewandowska, A., Tsvetkov, F., and Hanley, H.J.M., "Determination of Heats of Adsorption on a Synthetic Clay by Gas-Solid Chromatography Using a Wall Coated Open Tubular Column Approach," J. Chromatogr. A 844, 191 (1999).