On the Validity of Effective Potentials in Crowded Solutions of Linear and Ring Polymers with Reversible Bonds

TL;DR

This study uses simulations to evaluate the effectiveness of potential models for reversible polymers with different topologies and reactive site sequences, revealing their applicability and limitations in predicting real system behaviors, including phase separation.

Contribution

It provides a systematic assessment of effective potentials for reversible linear and ring polymers, highlighting their validity range and limitations in crowded solutions.

Findings

Effective potentials accurately predict linear polymer behavior at high concentrations.

Ring polymers show less agreement, with clustering behavior not captured by the potential.

Phase separation occurs in two-component mixtures with orthogonal chemistry, preventing interpenetration.

Abstract

We perform simulations to compute the effective potential between the centers-of-mass of two polymers with reversible bonds. We investigate the influence of the topology of the unbonded precursor (linear or ring) and the specific sequence of the reactive groups (from purely random to periodic), establishing that both have a strong impact on the effective potential. When the reactive sites of both polymers are chemically orthogonal so that only intramolecular bonds are possible, the interactions become more repulsive the closer to periodic the sequence is. The opposite effect is found if both polymers have the same type of reactive sites and intermolecular bonds can be formed. We test the validity of the effective potentials in solution, from high dilution to far above the overlap concentration, by comparing simulations of the effective fluid with those of the real all-monomer system. Very good agreement is found for the reversible linear polymers, indicating that unlike in their non-bonding counterparts many-body effects are minor even far above the overlap concentration. The agreement for the reversible rings is less satisfactory, and at high concentration the real system does not show the clustering behavior predicted by the effective potential. Results similar to the former ones are found for the partial self-correlations in ring/linear mixtures. Finally, we investigate the possibility of creating a gel of two interpenetrated reversible networks. For this purpose we simulate a 50/50 two-component mixture of reversible polymers with orthogonal chemistry for the reactive sites, so that intermolecular bonds are only formed between polymers of the same component. As predicted by both the theoretical phase diagram and the simulations of the effective fluid, the two networks in the all-monomer mixture do not interpenetrate and phase separation (demixing) is observed instead.