Probing Colloidal Gels at Multiple Length Scales: The Role of Hydrodynamics

Abstract

Colloidal gels are out-of-equilibrium structures, made up of a rarefied network of colloidal particles. Comparing experiments to numerical simulations, with hydrodynamic interactions switched off, we demonstrate the crucial role of the solvent for gelation. Hydrodynamic interactions suppress the formation of larger local equilibrium structures of closed geometry, and instead lead to the formation of highly anisotropic threads, which promote an open gel network. We confirm these results with simulations which include hydrodynamics. Based on three-point correlations, we propose a scale-resolved quantitative measure for the anisotropy of the gel structure. We find a strong discrepancy for interparticle distances just under twice the particle diameter between systems with and without hydrodynamics, quantifying the role of hydrodynamics from a structural point of view.

Local structure of percolating gels at very low volume fractions

“…On the basis of this analysis, we extended previous phase diagrams 31 , identifying a new region where Brownian dynamics simulations can realise percolating gels if the observation time is longer than the percolation time ( Fig. 1): the obtained gels are however strikingly different from the structural point of view with respect to those found in experiments 31,37,52 , with more compact aggregates and prevalence of five-fold symmetric order.…”

“…The deep energy minima represented by the m = 10 defective icosahedra are then responsible of the mechanical stiffness of the gel and its resistance to thermal fluctuations. It is important to notice that it is precisely this kind of structures that are underrepresented in experimental conditions 31,37,52 , due to the effects of hydrodynamic interactions, excluded from the present study.…”

“…It has been suggested in a previous study 31 (where the observation time was fixed in order to match the experimental conditions) that percolating gels in simulations without hydrodynamics become hard to access for volume fractions below φ * ∼ 0.07. Performing more extensive numerical simulations, we quantify this effect estimating the time needed in order to form a percolating cluster as a function of both the volume fraction and the interaction strength.…”

“…In the present work we investigate the low-volume fraction limit of gelation (neglecting hydrodynamic interactions and their long-range, multi-body effects 31,35 ) a) Corresponding author: f.turci@bristol.ac.uk and its relation with percolation for a system of Brownian particles with tuneable short-range attractions. In particular, we demonstrate that the structural features present at moderately low volume fraction φ ≈ 10 −1 survive at much lower volume fractions, φ ≈ 10 −3 , and allow for the formation of thin percolating structures.…”

Universal Breakup of Colloidal Clusters in Simple Shear Flow

“…However, several publications have demonstrated the importance of including hydrodynamic interactions to properly describe the dynamics of hard spheres 43−45 and of interacting particles, 46,47 as well as the formation of colloidal gels. 48 In recent publications, 49,50 we have investigated the breakage rate of colloidal clusters, covering a broad range of masses and fractal dimensions. To focus only on the breakage rate, we performed simulations only up to the very first binary breakage event experienced by a cluster.…”