Controlling Solvent Quality by Time: Self-Avoiding Sprints in Nonequilibrium Polymerization

TL;DR

This paper shows that during nonequilibrium polymerization, polymers can behave like self-avoiding walks in poor solvents, due to reaction-driven diffusion and local monomer depletion, challenging traditional equilibrium scaling laws.

Contribution

It reveals a new nonequilibrium self-avoiding walk behavior in polymer growth, supported by reaction-diffusion simulations, with implications for polymer processing techniques.

Findings

Polymers exhibit self-avoiding walk behavior in poor solvents during nonequilibrium growth.

Reaction-driven diffusion causes local monomer depletion, leading to directed growth.

Chain relaxation times exceeding reaction times enable this nonequilibrium scaling behavior.

Abstract

A fundamental paradigm in polymer physics is that macromolecular conformations in equilibrium can be described by universal scaling laws, being key for structure, dynamics, and function of soft (biological) matter and in the materials sciences. Here, we reveal that during diffusion-influenced, nonequilibrium chain-growth polymerization, scaling laws change qualitatively, in particular, the growing polymers exhibit a surprising self-avoiding walk (SAW) behavior in poor and theta-solvents. Our analysis, based on monomer-resolved reaction-diffusion computer simulations, demonstrates that this phenomenon is a result of i) nonequilibrium monomer density depletion correlations around the active polymerization site, leading to a locally directed and self-avoiding growth, in conjunction with ii) chain (Rouse) relaxation times larger than the competing polymerization reaction time. These intrinsic nonequilibrium mechanisms are facilitated by fast and persistent reaction-driven diffusion (sprints) of the active site, with analogies to pseudo-chemotactic active Brownian particles. Our findings have implications for time-controlled structure formation in polymer processing, as in, e.g., reactive self-assembly, photo-crosslinking, and 3D printing.