Temperature Dependence of Polymer Network Diffusion

TL;DR

This study investigates how the diffusion coefficient of polymer gels varies with temperature, revealing a linear relationship with a negative intercept, and draws parallels to recent findings on negative energy elasticity in polymer networks.

Contribution

It provides the first detailed measurement of the temperature dependence of polymer network diffusion coefficients using dynamic light scattering, highlighting a novel linear relation with a negative constant term.

Findings

Diffusion coefficient increases linearly with temperature.

The increase in diffusion coefficient is a linear function of temperature.

The observed behavior parallels the concept of negative energy elasticity.

Abstract

The swelling dynamics of polymer gels are characterized by the (collective) diffusion coefficient $D$ of the polymer network. Here, we measure the temperature dependence of $D$ of polymer gels with controlled homogeneous network structures using dynamic light scattering. An evaluation of the diffusion coefficient at the gelation point $D_{\mathrm{gel}}$ and the increase therein as the gelation proceeds $\Delta D\equiv D-D_{\mathrm{gel}}$ indicates that $\Delta D$ is a linear function of the absolute temperature with a significantly large negative constant term. This feature is formally identical to the recently discovered "negative energy elasticity" [Y. Yoshikawa et al., Phys. Rev. X 11, 011045 (2021) (arXiv:1912.13191)], demonstrating a nontrivial similarity between the statics and dynamics of polymer networks.