Coarsening Kinetics of Complex Macromolecular Architectures in Bad Solvent

TL;DR

This paper investigates the out-of-equilibrium coarsening kinetics of various complex polymer architectures in bad solvent using molecular dynamics simulations, revealing universal scaling laws and architecture-dependent growth behaviors.

Contribution

It introduces a density field approach to characterize domain growth and demonstrates that coarsening follows a universal scaling law across different architectures.

Findings

Coarsening kinetics exhibit scale-invariant behavior independent of solvent quality.

Flexible and microgel systems show similar power-law domain growth.

Semiflexible chains have steeper growth due to local stiffness effects.

Abstract

This study reports a general scenario for the out-of-equilibrium features of collapsing polymeric architectures. We use molecular dynamics simulations to characterize the coarsening kinetics, in bad solvent, for several macromolecular systems with an increasing degree of structural complexity. In particular, we focus on: flexible and semiflexible polymer chains, star polymers with 3 and 12 arms, and microgels with both ordered and disordered networks. Starting from a powerful analogy with critical phenomena, we construct a density field representation that removes fast fluctuations and provides a consistent characterization of the domain growth. Our results indicate that the coarsening kinetics presents a scaling behaviour that is independent of the solvent quality parameter, in analogy to time-temperature superposition principle. Interestingly, the domain growth in time follows a power-law behaviour that is approximately independent of the architecture for all the flexible systems; while it is steeper for the semiflexible chains. Nevertheless, the fractal nature of the dense regions emerging during the collapse exhibits the same scaling behaviour for all the macromolecules. This, suggests that the faster growing length scale in the semiflexible chains originates just from a faster mass diffusion along the chain contour, induced by the local stiffness. The decay of the dynamic correlations displays scaling behavior with the growing length scale of the system, which is a characteristic signature in coarsening phenomena.