On the friction coefficient of straight-chain aggregates

TL;DR

This paper introduces a new method to accurately calculate the friction coefficient of straight-chain aggregates in the continuum regime, linking it to molecular collision rates and shielding factors, validated by simulations.

Contribution

It proposes a novel methodology relating the friction coefficient to collision rates and shielding factors, validated for straight-chain aggregates.

Findings

Calculated friction coefficients agree with previous results.

Diffusive motion can be modeled with monomer-dependent or average forces.

Shielding factors are crucial for accurate Langevin-dynamics simulations.

Abstract

A methodology to calculate the friction coefficient of an aggregate in the continuum regime is proposed. The friction coefficient and the monomer shielding factors, aggregate-average or individual, are related to the molecule-aggregate collision rate that is obtained from the molecular diffusion equation with an absorbing boundary condition on the aggregate surface. Calculated friction coefficients of straight chains are in very good agreement with previous results, suggesting that the friction coefficients may be accurately calculated from the product of the collision rate and an average momentum transfer,the latter being independent of aggregate morphology. Langevin-dynamics simulations show that the diffusive motion of straight-chain aggregates may be described either by a monomer-dependent or an aggregate-average random force, if the shielding factors are appropriately chosen.