Determination of thermodynamic interaction in mixed polymer solutions by a rapid and precise osmotic method. The system dextran/polyvinylpyrrolidone/water

An accurate and simple osmotic method for determination of thermodynamic interaction in ternary solutions (polymer A/polymer B/solvent) is described. The equipment consists of a membrane osmometer of a special design with small chambers and a pressure-sensing device to monitor the pressure difference across the membrane. A procedure has been developed to measure osmotic pressures up to rather high concentrations in both quasi-binary and quasi-ternary systems. The osmotic method is compared with results from light scattering. Different methods are utilized to extract ordinary virial coefficients as well as mixed virial coefficients from the primary data. The system dextran/polyvinylpyrrolidone/water (two different molecular weights of dextran) was chosen as a model.