# Depletion force between disordered linear macromolecules

## TL;DR

This paper investigates the depletion force between disordered linear macromolecules by combining analytical calculations, molecular dynamics simulations, and theoretical approaches to understand how disorder affects entropic interactions.

## Contribution

It introduces a method to calculate the depletion force for disordered macromolecules modeled as random hard sphere arrangements, combining analytical and simulation techniques.

## Key findings

- Depletion force depends on the position along the macromolecule.
- Disorder influences the magnitude and profile of the depletion force.
- Comparison shows differences between stiff and flexible disordered polymers.

## Abstract

When two macromolecules come very near in a fluid, the surrounding molecules, having finite volume, are less likely to get in between. This leads to a pressure difference manifesting as an entropic attraction, called depletion force. Here we calculate the density profile of liquid molecules surrounding a disordered rigid macromolecules modelled as a random arrangement of hard spheres on a linear backbone. We analytically determine the position dependence of the depletion force between two such disordered molecules by calculating the free energy of the system. We then use molecular dynamics simulations to obtain the depletion force between stiff disordered polymers as well as flexible ones and compare the two against each other. We also show how the disorder averaging can be handled starting from the inhomogenous RISM equations.