Directed percolation identified as equilibrium pre-transition towards non-equilibrium arrested gel states.

M Kohl,S U Egelhaaf,R F Capellmann,M Laurati,M Schmiedeberg

doi:10.1038/ncomms11817

M Kohl, S U Egelhaaf + Show 3 more

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https://doi.org/10.1038/ncomms11817

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Abstract

The macroscopic properties of gels arise from their slow dynamics and load-bearing network structure, which are exploited by nature and in numerous industrial products. However, a link between these structural and dynamical properties has remained elusive. Here we present confocal microscopy experiments and simulations of gel-forming colloid–polymer mixtures. They reveal that gel formation is preceded by continuous and directed percolation. Both transitions lead to system-spanning networks, but only directed percolation results in extremely slow dynamics, ageing and a shrinking of the gel that resembles synaeresis. Therefore, dynamical arrest in gels is found to be linked to a structural transition, namely directed percolation, which is quantitatively associated with the mean number of bonded neighbours. Directed percolation denotes a universality class of transitions. Our study hence connects gel formation to a well-developed theoretical framework, which now can be exploited to achieve a detailed understanding of arrested gels.

Highlights

The macroscopic properties of gels arise from their slow dynamics and load-bearing network structure, which are exploited by nature and in numerous industrial products
We show that the slowdown of the particle dynamics and the onset of ageing can be related to the microscopic structure of colloidal gels, namely a directed percolation (DP) transition
This is demonstrated in experiments on charged colloid–polymer mixtures[30,33] and in Brownian dynamics simulations of particles interacting through a combination of coulombic repulsion and depletion-induced attraction modelled by the Asakura–Oosawa potential[34]

Summary

Introduction

The macroscopic properties of gels arise from their slow dynamics and load-bearing network structure, which are exploited by nature and in numerous industrial products. We present confocal microscopy experiments and simulations of gel-forming colloid–polymer mixtures They reveal that gel formation is preceded by continuous and directed percolation. We show that the slowdown of the particle dynamics and the onset of ageing can be related to the microscopic structure of colloidal gels, namely a directed percolation (DP) transition. This is demonstrated in experiments on charged colloid–polymer mixtures[30,33] and in Brownian dynamics simulations of particles interacting through a combination of coulombic repulsion and depletion-induced attraction modelled by the Asakura–Oosawa potential[34]. DP is found to be linked to the onset of ageing effects

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