Raft Instability of Biopolymer Gels

TL;DR

This paper investigates the instability of biopolymer gels, revealing that anisotropic depletion attractions cause heterogeneities and invalidate traditional theories like percolation and Onsager's virial method.

Contribution

It applies Onsager theory to biopolymer gels with cross-linkers, uncovering raft-like heterogeneities and challenging existing theoretical frameworks.

Findings

Anisotropic depletion attraction causes gel heterogeneities.

Breakdown of percolation theory in these gels.

Failure of Onsager's second-order virial method.

Abstract

Following recent X-ray diffraction experiments by Wong, Li, and Safinya on biopolymer gels, we apply Onsager excluded volume theory to a nematic mixture of rigid rods and strong ``$\pi/2$'' cross-linkers obtaining a long-ranged, highly anisotropic depletion attraction between the linkers. This attraction leads to breakdown of the percolation theory for this class of gels, to breakdown of Onsager's second-order virial method, and to formation of heterogeneities in the form of raft-like ribbons.