Coil dimensions of macromolecules in the presence of crowding colloids: Impact of crowder size

Abstract

Hypothesis

The size of a macromolecule in solution is strongly influenced by the size and concentration of added colloidal particles. Previous experimental and computer simulation studies have shown conflicting results regarding the influence of colloid size on coil compaction. We suggest the coil size depends on the Kuhn segment / nanoparticle size ratio and argue its subtle influence on the shrinking and expansion of a polymer chain.

Methods

Based upon the work of van der Schoot (1998) [42] we propose theory that predicts how the colloid size mediates the compaction of macromolecules in crowded environments. The theoretical predictions are compared to self-consistent field (SCF) lattice computations and scattering experiments on polymer solutions exposed to crowders.

Findings

The theoretical approach predicts that the shrinking of a polymer coil upon adding colloidal particles varies with the size of the colloids. We find coil shrinking is weakest when the colloidal particles are approximately the same size as the Kuhn segment length. The extent of coil shrinking passes a minimum at a specific colloid size relative to the Kuhn segment length, which is confirmed by SCF computations.

Comparison with scattering experiments reveals that these experiments corroborate the extent of polymer shrinking at a given volume fraction of colloids. Our theoretical approach reproduces the functional dependence of the collapse on the crowder volume fraction.