Solvent effects on osmotic second virial coefficient studied using analytic molecular models. Application to solutions of C-60 fullerene

Osmotic second virial coefficients (OSVC's) are calculated analytically for some molecular models in which the solvent is taken into account explicitl y. The basic effect of solvent packing is examined first by applying the me thod to the reference case of a binary hard sphere mixture. Then, cohesion forces for the solvent and solute-solvent attractive forces are introduced successively into the description. The results are applied to interpret rec ent experimental data on solutions of C-60 in nonaqueous solvents. With a p lausible assumption in the model, a very good agreement is obtained with th e experimental OSVC value for C-60 in CS2. In the case of benzene as the so lvent, the theoretical result is consistent with the experimental observati on (formation of aggregates). No specific adjustable parameter was needed i n the model to interpret the experimental results. The description suggests that the solute-solvent interaction has a determinant influence on the obs erved OSVC value.