Temperature and Solvent Viscosity Tune the Intermediates During the Collapse of a Polymer

TL;DR

This study investigates how temperature and solvent viscosity influence the collapse dynamics of a polymer, revealing the formation of long-lived intermediates and the role of internal friction in the process.

Contribution

It introduces a simulation framework that tunes solvent viscosity and uncovers the impact of temperature and viscosity on polymer collapse intermediates and relaxation times.

Findings

Identification of sausage-like intermediates during collapse.

Relaxation time of intermediates shows anti-Arrhenius and Arrhenius behaviors.

Internal friction significantly affects collapse dynamics, akin to protein folding.

Abstract

Dynamics of a polymer chain in solution gets significantly affected by the temperature and the frictional forces arising due to solvent viscosity. Here, using an explicit solvent framework for polymer simulation with the liberty to tune the solvent viscosity, we study the nonequilibrium dynamics of a flexible homopolymer when it is suddenly quenched from an extended coil state in good solvent to poor solvent conditions. Results from our extensive simulations reveal that depending on the temperature $T$ and solvent viscosity, one encounters long-lived sausage-like intermediates following the usual pearl-necklace intermediates. Use of shape factors of polymers allows us to disentangle these two distinct stages of the overall collapse process, and the corresponding relaxation times. The relaxation time $\tau_s$ of the sausage stage, which is the rate-limiting stage of the overall collapse process, follows an anti-Arrhenius behavior in the high-$T$ limit, and the Arrhenius behavior in the low-$T$ limit. Furthermore, the variation of $\tau_s$ with the solvent viscosity provides evidence of internal friction of the polymer, that modulates the overall collapse significantly, analogous to what is observed for relaxation rates of proteins during their folding. This suggests that the origin of internal friction in proteins is plausibly intrinsic to its polymeric backbone rather than other specifications.