Structural and dynamical properties of dilute gel networks in colloid-polymer mixtures

Formation dynamics of branching structure in the slippery DLCA model

We numerically investigated the aggregation dynamics and resulting network structures of colloidal gels using the slippery diffusion-limited cluster aggregation (DLCA) model. In this model, bonds are irreversibly formed upon the particle contacts, but the angles among them are not fixed, unlike the conventional DLCA. This allows clusters to be deformed in the process of aggregation. By characterizing the aggregation dynamics and using a reduced network scheme, our simulation revealed two distinct branching structure formation routes depending on the particle volume fraction ϕ. In lower volume fraction systems (ϕ ≤ 8%), the deformations of small-size clusters proceed prior to the percolation. When the Maxwell criterion is satisfied and the clusters become mechanically stable, the formation of the branching structure is nearly completed. After forming the branching structures, they aggregate and form a larger percolating network. Then, the aggregation proceeds through the elongation and straightening of the chain parts of the network. In higher volume fraction systems (ϕ > 8%), on the other hand, the clusters percolate, and a fine and homogeneous branching structure is formed at the early stage of the aggregation. In the aging stage, it collapses into a denser and more heterogeneous structure and becomes more stable. Our quantitative analyses of the branching structure will shed light on a new strategy for describing the network formation and elasticity of colloidal gels.

Dilute gel networks vs. clumpy gels in colloidal systems with a competition between repulsive and attractive interactions

Using Brownian dynamics simulations we study gel-forming colloidal systems. The focus of this article lies on the differences of dense and dilute gel networks in terms of structure formation both on a local and a global level. We apply reduction algorithms and observe that dilute networks and dense gels differ in the way structural properties like the thickness of strands emerge. We also analyze the percolation behavior and find that two different regimes of percolation exist which might be responsible for structural differences. In dilute networks we confirm that solidity is mainly a consequence of pentagonal bipyramids forming in the network. In dense gels, tetrahedral structures also influence solidity.

Comment on "Communication: Is directed percolation in colloid-polymer mixtures linked to dynamic arrest?'

In their communication [J. Chem. Phys. 148, 241101 (2018)] Richard et al. misquote and criticize a work of Kohl et al.~[Nature Communications 7, 11817 (2016)] resting on simulations in a regime of the phase diagram that significantly differ from the one that Kohl et al.~consider. In this comment it is shown that both the effective density as well as the rescaled second virial coefficient indicate that the comparison presented by Richard et al.~is invalid. Therefore, the implications with respect to the work of Kohl et al.~are incorrect. There is no indication for a disagreement between the simulations of Richard et al.~and those of Kohl et al.~and I am confident that upon a consistent comparison and interpretation of the results both works can contribute to a more comprehensive picture of gel-forming systems.