Dynamics of equilibrium linked colloidal gels

TL;DR

This study uses a coarse-grained model to analyze the dynamics of equilibrium linked colloidal gels, revealing how bond persistence time and network connectivity influence their slow relaxation and re-entrant formation without phase separation.

Contribution

It introduces a model linking macroscopic valence constraints to gel dynamics and demonstrates how bond persistence and stoichiometry control network formation and relaxation behaviors.

Findings

Bond persistence time governs slow relaxation.

Re-entrant network formation occurs without phase separation.

Dynamic properties depend on effective network bonds, predictable by Wertheim's theory.

Abstract

Colloids that attractively bond to only a few neighbors (e.g., patchy particles) can form equilibrium gels with distinctive dynamic properties that are stable in time. Here, we use a coarse-grained model to explore the dynamics of linked networks of patchy colloids whose average valence is macroscopically, rather than microscopically, constrained. Simulation results for the model show dynamic hallmarks of equilibrium gel formation and establish that the colloid-colloid bond persistence time controls the characteristic slow relaxation of the self-intermediate scattering function. The model features re-entrant network formation without phase separation as a function of linker concentration, centered at the stoichiometric ratio of linker ends to nanoparticle surface bonding sites. Departures from stoichiometry result in linker-starved or site-starved networks with reduced connectivity and shorter characteristic relaxation times with lower activation energies. Underlying the re-entrant trends, dynamic properties vary monotonically with the number of effective network bonds per colloid, a quantity that can be predicted using Wertheim's thermodynamic perturbation theory. These behaviors suggest macroscopic in situ strategies for tuning the dynamical response of colloidal networks.