Depletion theory and the precipitation of protein by polymer

TL;DR

This paper reinterprets depletion theory for nanoparticles in polymer solutions, deriving explicit expressions for interactions and explaining polymer effects on protein precipitation.

Contribution

It introduces a new interpretation of depletion theory using polymer segment chains and derives explicit interaction formulas for particles of various shapes.

Findings

Derived explicit interaction expressions between small spheres.

Provided a quantitative explanation for polymer influence on protein precipitation.

Discussed limitations and extensions of mean-field depletion theory.

Abstract

The depletion theory of nanoparticles immersed in a semidilute polymer solution is reinterpreted in terms of depleted chains of polymer segments. Limitations and extensions of mean-field theory are discussed. An explicit expression for the interaction between two small spheres is derived. The depletion free energy for a particle of general shape is given in terms of the capacitance or effective Stokes radius. This affords a close to quantitative explanation for the effect of polymer on protein precipitation.