Role of microscopic phase separation in gelation of aqueous gelatin solutions

TL;DR

This study investigates the microscopic mechanisms behind gelatin gelation, revealing that it results from fiber network formation rather than percolation, with implications for understanding gelation processes.

Contribution

The paper introduces impedance spectroscopy to distinguish diffusion and aggregation processes, showing gelation is driven by fiber network formation, not percolation.

Findings

Gelatin solutions exhibit two low-frequency conductivity relaxations.

Self-diffusion of gelatin molecules is unaffected by gelation.

Gelation results from triple helix aggregation into fiber networks.

Abstract

Using a unique home-made cell for four-contact impedance spectroscopy of conductive liquid samples, we establish the existence of two low frequency conductivity relaxations in aqueous solutions of gelatin, in both liquid and gel state. A comparison with diffusion measurements using pulsed field gradient NMR shows that the faster relaxation process is due to gelatin macromolecule self-diffusion. This single molecule diffusion is mostly insensitive to the macroscopic state of the sample, implying that the gelation of gelatin is not a percolative phenomenon, but is caused by aggregation of triple helices into a system-spanning fibre network.