Pair-wise additivity for potentials of mean force in dilute polymer solutions

Standard Monte Carlo techniques were used to compute the potential of mean force between pairs and between triplets of freely jointed hard-sphere poly mers in dilute solutions. Segment-segment interactions at poor solvent cond itions were represented by square-well potentials. Well width equaled half a segment diameter and well depth was either zero or -0.30 k(B)T. Polymer c hains contained 25 segments. For polymer triplets at a set of selected two-body distances, the pair-wise additivity of the potential of mean force provides a reasonable approximat ion for the three-body potential of mean force. At athermal conditions, the error introduced by assuming additivity is generally less than 10-15% of t he total three-body interaction, while for well depth -0.30 kBT, the error rises, but is still generally less than 20-30%. Deviations from the calcula ted three-body potential of mean force are a function of solvent conditions and of relative positions of the interacting polymers. For polymer chains containing 15, 25 or 30 segments, simulation results do not depend signific antly on polymer length. (C) 2001 Elsevier Science Ltd. All rights reserved .