Transport of probe particles in polymer network: effects of probe size, network rigidity and probe-polymer interaction

TL;DR

This study uses molecular dynamics simulations to explore how probe size, network rigidity, and interactions affect particle transport in polymer networks, revealing complex behaviors like subdiffusion and caging relevant to biological and material systems.

Contribution

It provides new insights into the microscopic factors influencing probe dynamics in polymer gels, highlighting the roles of flexibility, size, and binding in transport phenomena.

Findings

Increased network rigidity and probe size restrict motion.

Negative dips in velocity autocorrelation indicate viscoelastic caging.

Flexible networks allow large probes to move freely despite size.

Abstract

Fundamental understanding of the effect of microscopic parameters on the dynamics of probe particles in different complex environments has wide implications. Examples include diffusion of proteins in the biological hydrogels, porous media, polymer matrix, etc. Here, we use extensive molecular dynamics simulations to investigate the dynamics of the probe particle in a polymer network on a diamond lattice which provides substantial crowding to mimic the cellular environment. Our simulations show that the dynamics of the probe increasingly becomes restricted, non-Gaussian and subdiffusive on increasing the network rigidity, binding affinity and the probe size. In addition, the velocity autocorrelation functions show negative dips owing to the viscoelasticity and caging due to surrounding network. These observations go with general experimental findings. Surprisingly for a probe particle of size comparable to the mesh size, unrestricted motion engulfing large length scales has been observed. This happens with the more flexible polymer network, which is easily pushed by the bigger probe. Our study gives a general qualitative picture of transport of probes in gel like medium, as encountered in different contexts.