Effect of polymer nonideality in a colloid-polymer mixture

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Abstract
We preesnt 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 θ temperature, which has been treated previously within a mean-field framework [H. N. W. Lekkerkerker et al., Europhys. Lett. 20, 559 (1992)], we use perturbation theory to take into the account the polymer-polymer interaction up to the second virial level. Theoretical predictions of the phase behavior are compared with data obtained in one particular model system: sterically stabilized polymethylmethacrylate particles and random-coil polystyrene dispersed in cis-decahydronapthelene. Within the same theoretical framework the potential of the mean force is calculated between a pair of plates immersed in a nonideal polymer solution. The result, showing a potential barrier in front of an attractive depletion well, is in agreement with a recent calculation by Walz and Sharma [J. Y. Walz and A. Sharma, J. Colloid Interface Sci. 168, 485 (1994)].