Polymer depletion effects near mesoscopic particles

TL;DR

This paper investigates how long, flexible polymers influence the behavior and interactions of mesoscopic particles, revealing significant differences from ideal chains and providing a systematic framework for understanding many-body effects.

Contribution

It offers explicit calculations of solvation free energies for various particle shapes and demonstrates the limitations of the Asakura-Oosawa approximation for small particles.

Findings

Qualitative differences between self-avoiding and ideal polymer chains.

Validation of Helfrich-type curvature expansion for particle shapes.

Quantitative results for particle-wall and particle-particle interactions.

Abstract

The behavior of mesoscopic particles dissolved in a dilute solution of long, flexible, and nonadsorbing polymer chains is studied by field-theoretic methods. For spherical and cylindrical particles the solvation free energy for immersing a single particle in the solution is calculated explicitly. Important features are qualitatively different for self-avoiding polymer chains as compared with ideal chains. The results corroborate the validity of the Helfrich-type curvature expansion for general particle shapes and allow for quantitative experimental tests. For the effective interactions between a small sphere and a wall, between a thin rod and a wall, and between two small spheres quantitative results are presented. A systematic approach for studying effective many-body interactions is provided. The common Asakura-Oosawa approximation modelling the polymer coils as hard spheres turns out to fail completely for small particles and still fails by about 10% for large particles.