# Wet and dry internal friction can be measured with the Jarzynski equality

## TL;DR

This paper proposes a new protocol using the Jarzynski equality to distinguish and measure wet and dry internal friction in polymers through repeated stretching experiments, validated by analytical and simulation models.

## Contribution

It introduces a simple, experimentally feasible method to quantify wet and dry internal friction coefficients in polymers using work measurements and the Jarzynski equality.

## Key findings

- The protocol accurately estimates internal friction coefficients.
- Analytical calculations confirm the method's validity.
- Simulations demonstrate applicability to complex polymer models.

## Abstract

The existence of two types of internal friction wet and dry is revisited, and a simple protocol is proposed for distinguishing between the two types and extracting the appropriate internal friction coefficient. The scheme requires repeatedly stretching a polymer molecule, and measuring the average work dissipated in the process by applying the Jarzynski equality. The internal friction coefficient is then estimated from the average dissipated work in the extrapolated limit of zero solvent viscosity. The validity of the protocol is established through analytical calculations on a one-dimensional free-draining Hookean spring-dashpot model for a polymer, and Brownian dynamics simulations of: (a) a single-mode nonlinear spring-dashpot model for a polymer, and (b) a finitely extensible bead-spring chain with cohesive intra-chain interactions, both of which incorporate fluctuating hydrodynamic interactions. Well-established single-molecule manipulation techniques, such as optical tweezer-based pulling, can be used to implement the suggested protocol experimentally.