Depletion interaction between spheres immersed in a solution of ideal polymer chains

The depletion interaction between two spheres due to nonadsorbing ideal pol ymers is calculated from the polymer concentration profile using the excess (negative) adsorption. Computer simulations show that the polymer concentr ation profiles around two spheres are well described by the product functio n of the concentration profile around a single sphere. From the interaction potential between two spheres the second osmotic virial coefficient, B-2, is calculated for various polymer-colloid size ratios. We find that when th e polymers become smaller than the spheres, B-2 remains positive in the dil ute regime. This shows that the depletion interaction is ineffective for re latively small spheres. (C) 2000 American Institute of Physics. [S0021-9606 (00)50247-5].