Unwinding dynamics of double-stranded polymers

TL;DR

This study models the unwinding process of double-stranded polymers, revealing how they separate over time and providing scaling laws for unwinding duration based on polymer length.

Contribution

It introduces a theoretical and simulation-based analysis of unwinding dynamics, highlighting the non-equilibrium nature of loose strand formation during separation.

Findings

Unwinding proceeds from the ends inward.

Loose strands grow as l~t^0.39.

Total unwinding time scales as N^2.57.

Abstract

We consider the unwinding of two lattice polymer strands of length N that are initially wound around each other in a double-helical conformation and evolve through Rouse dynamics. The problem relates to quickly bringing a double-stranded polymer well above its melting temperature, i.e., the binding interactions between the strands are neglected, and the strands separate from each other as it is entropically favorable for them to do so. The strands unwind by rotating around each other until they separate. We find that the process proceeds from the ends inward; intermediate conformations can be characterized by a tightly wound inner part, from which loose strands are sticking out, with length l~t^0.39. The total time needed for the two strands to unwind scales as a power of N as tu~N^(2.57+-0.03). We present a theoretical argument, which suggests that during this unwinding process, these loose strands are far out of equilibrium.