PARTITIONING OF BINARY SOLVENTS ON CHARGED EXPANDABLE CLAYS

The present paper represents an extension of recent work that consider ed the partitioning response of binary solvents placed into contact wi th charged, expandable clays. Previous theoretical work yielded a mode l of partitioning by performing a thermodynamic analysis, involving th e work of polarization, on a binary solvent, treated as a continuum an d residing within the interlayer space of a layered aluminosilicate cl ay. Partitioning, or the tendency for sorbed and bulk phases to have d ifferent compositions, was shown to be sensitive to the dielectric pro perties of the 2 solvents of the binary mixture and to the surface cha rge density on the clay, among other factors. Although previous experi mental work has helped to validate the theory, additional work is repo rted here that looks at hysteresis effects, the role of the exchangeab le cation (usually organic), the prediction of adsorption isotherms an d the contribution that partitioning, or sorption, makes to the disjoi ning pressure that develops in binary solvent systems. In this current study, 3 different organo-clays were considered: Cetyltrimethylammoni um (CTMA), Isopropanolammonium (IPA), and Benzylammonium (BA) montmori llonite. Solvent systems under study included: acetone/chloroform (a-c ), acetone/quadricyclane (a-q) and acetonitrile/chloroform (an-c). Whi le partitioning of the a-c system on CTMA-clay follows theory quite we ll, theory tends to over-predict partitioning for the a-q system on th e same clay and under-predict partitioning for the an-c system on all clays. Predicted adsorption isotherms range from highly nonlinear to n early linear. Finally, the delamination and subsequent swelling proces ses of BA-clay in a water/acetonitrile binary solvent system are very sensitive to composition, a result that is directly linked to the part itioning process.