Unexpected decoupling of stretching and bending modes in protein gels

TL;DR

This study reveals that protein gels exhibit two distinct elastic behaviors at different frequencies, with a surprising decoupling of stretching and bending modes due to their different length scales.

Contribution

It introduces a model explaining the decoupling of stretching and bending modes in protein gels based on their length scales and frequency response.

Findings

Elastic moduli depend strongly on volume fraction.

Stretching and bending modes occur in separate frequency domains.

Decoupling is due to differences in length scales involved.

Abstract

We show that gels formed by arrested spinodal decomposition of protein solutions exhibit elastic properties in two distinct frequency domains, both elastic moduli exhibiting a remarkably strong dependence on volume fraction. Considering the large difference between the protein size and the characteristic length of the network we model the gels as porous media and show that the high and low frequency elastic moduli can be respectively attributed to stretching and bending modes. The unexpected decoupling of the two modes in the frequency domain is attributed to the length scale involved: while stretching mainly relates to the relative displacement of two particles, bending involves the deformation of a strand with a thickness of the order of a thousand particle diameters.