Investigation of Polymer Association Behaviors in Solvents Using a Coarse-Grained Model

TL;DR

This paper introduces a reaction-controlled model and an efficient sampling method to study polymer association behaviors in solvents, revealing how interactions and cooperativity influence polymer configurations and distributions.

Contribution

It develops a new associative polymer model obeying thermodynamics and an improved configurational bias method for faster sampling, advancing understanding of polymer association mechanisms.

Findings

Association follows Bernoulli process in ideal conditions.

Excluded volume and solvent effects cause inhomogeneous association probabilities.

Cooperative association leads to coexistence of coil and globule states.

Abstract

The associative interaction, such as hydrogen bonding, can bring about versatile functionalities to polymer systems, which has been investigated by tremendous researches, but the fundamental understanding on association process is still lacking. In this study, a reaction-controlled association model is proposed to delve into the polymer association activities in solvents, which is proved to obey the principle of thermodynamics. Additionally, associative polymer chain configurational bias method is developed to improve sampling efficiency, demonstrating a significantly faster relaxation process. First, we set non-bonded interactions to be zero, and only keep the chain connectivity and association. It is found that the association process intrinsically follows Bernoulli process by comparing the simulation results and analytic results. Next, we include non-bonded interactions into the simulation to examine its effects. It emerged that the excluded volume effect and solvents immiscibility effects can result in inhomogeneous associating probability distribution along the chain contour, in contrast to the homogeneity observed in ideal systems, thereby shifting from the binomial distribution to Poisson binomial distribution. At last, the study is extended to cooperative association systems. The incorporation of cooperative association can lead to the coexistence of coil and globule state at the transition point, verified by the potential of mean force calculation. Finally, a mathematical model is proposed, illustrating the changes in statistical weight induced by sequence enthalpy bias, which is the consequence of cooperative behaviors.