EFFECT OF POLYMER NONIDEALITY IN A COLLOID-POLYMER MIXTURE

We present a theory for the effect of polymer nonideality on the phase behavior of a hard-sphere colloid plus nonadsorbing polymer mixture. Starting from the behavior at the theta temperature, which has been tr eated previously within a mean-field framework. [H. N. W. Lekkerkerker et al., Europhys. Lett. 20, 559 (1992)], we use perturbation theory t o take into the account the polymer-polymer interaction up to the seco nd virial level. Theoretical predictions of the phase behavior are com pared with data obtained in one particular model system: sterically st abilized polymethylmethacrylate particles and random-coil polystyrene dispersed in cis-decahydronaphthalene. Within the same theoretical fra mework the potential of mean force is calculated between a pair of pla tes immersed in a nonideal polymer solution. The result, showing a pot ential barrier in front of an attractive depletion well, is in agreeme nt with a recent calculation by Walz and Sharma