New insight into kinetics behavor of the structural formation process in Agar gelation

TL;DR

This study investigates the kinetics of agar gelation using a torsion resonator, revealing three distinct stages with different relaxation behaviors and activation energies, enhancing understanding of gel formation mechanisms.

Contribution

It provides a detailed kinetic analysis of agar gelation, identifying multiple relaxation processes and their temperature-dependent behaviors, which were not previously characterized in such detail.

Findings

Agar gelation occurs in three stages with distinct kinetic behaviors.

The relaxation processes follow multiple-order Gaussian-like equations.

Different Arrhenius laws govern the temperature dependence in each stage.

Abstract

A time-resolved experimental study on the kinetics and relaxation of the structural formation process in gelling Agar-water solutions was carried out using our custom-built torsion resonator. The study was based on measurements of three naturally cooled solutions with agar concentrations of 0.75%, 1.0% and 2.0% w/w. It was found that the natural-cooling agar gelation process could be divided into three stages, sol stage (Stage I), gelation zone (Stage II) and gel stage (Stage III), based on the time/temperature evolutions of the structural development rate (SDR). An interesting fluctuant decaying behavior of SDR was observed in Stage II and III, indicative of a sum of multiple relaxation processes and well described by a multiple-order Gaussisn-like equation: . More interestingly, the temperature dependences of the fitted values of Wn in Stage II and Stage III were found to follow the different Arrhenius laws, with different activation energies of EaII= 39-74 KJ/mol and EaIII~7.0 KJ/mol. The two different Arrhenius-like behaviors respectively suggest that dispersions in Stage II be attributed to the relaxation of the self-assembly of agar molecules or the growth of junction zones en route to gelation, in which the formation or fission of hydrogen bonding interactions plays an important role; and that dispersions in Stage III be attributed to the relaxation dynamics of water released from various size domains close to the domain of the viscous flow of water during the syneresis process.