Self-assembly and cooperative dynamics of a model colloidal gel network

Abstract

We study the assembly into a gel network of colloidal particles, via effective interactions that yield local rigidity and make dilute network structures mechanically stable. The self-assembly process can be described by a Flory-Huggins theory, until a network of chains forms, whose mesh size is on the order of, or smaller than, the persistence length of the chains. The localization of the particles in the network, akin to some extent to caging in dense glasses, is determined by the network topology, and the network restructuring, which takes place via bond breaking and recombination, is characterized by highly cooperative dynamics. We use N V E and N V T Molecular Dynamics as well as Langevin Dynamics and find a qualitatively similar time dependence of time correlations and of the dynamical susceptibility of the restructuring gel. This confirms that the cooperative dynamics emerge from the mesoscale organization of the network.

Correlated Rigidity Percolation and Colloidal Gels

“…where r is the interparticle distance rescaled by the particle diameter and A and a are dimensionless constants. In particular we have fixed A = 6.27, a = 0.85 to obtain a short-ranged attractive well of depth and range 0.3σ [50,51]. We adopt periodic boundary conditions and, using the particle diameter σ, we define an approximate volume (surface) fraction φ g = π(σ/2) 2 N/L 2 , where L is the side length of the square simulation box (in units of σ).…”

Network Topology in Soft Gels: Hardening and Softening Materials

“…In spite of its simplicity, our model captures important physical features of real colloidal gels and can be used as a prototypical soft amorphous solid. Starting from this elementary information, we have used anisotropic interactions to introduce local rigidity and stabilize selfassembled thin open structures at low volume fraction [27,33], in the same spirit as recent works [34,35]. Our system consists of N identical particles with position vectors {r i } , i = 1 .…”

“…The potential energy (1) depends parametrically on the dimensionless quantities A, a, B,θ, w. We have chosen these parameters such that for k B T ∼ 10 −1 the particles start to self-assemble into a persistent particle network. The data here discussed refer to A = 6.27, a = 0.85, B = 67.27,θ = 65 • , w = 0.30, one convenient choice to realize this condition.This model has been used to perform a spatially resolved analysis of cooperative dynamics in colloidal gel networks, of their aging and mechanical response [20,21,27,33]. The network structure is characterized by the cohexistence of poorly connected regions, where major structural rearrangements take place and densely connected domains, where internal stresses tend to concentrate.…”

Relaxation dynamics in a transient network fluid with competing gel and glass phases

“…It is designed to capture the spatiotemporal correlations of particle nobilities and provides, from its peak value, an estimate of the dynamic correlations [50,52]. Such functions have also been analyzed for gels with permanent bonds [53] or low density gels [54].…”