Local structure of percolating gels at very low volume fractions

Abstract

The formation of colloidal gels is strongly dependent on the volume fraction of the system and the strength of the interactions between the colloids. Here we explore very dilute solutions by the means of numerical simulations, and show that, in the absence of hydrodynamic interactions and for sufficiently strong interactions, percolating colloidal gels can be realised at very low values of the volume fraction. Characterising the structure of the network of the arrested material we find that, when reducing the volume fraction, the gels are dominated by low-energy local structures, analogous to the isolated clusters of the interaction potential. Changing the strength of the interaction allows us to tune the compactness of the gel as characterised by the fractal dimension, with low interaction strength favouring more chain-like structures.

The influence of surface roughness on the adhesive interactions and phase behavior of suspensions of calcite nanoparticles

“…3D. Aggregation into local crystalline structures as opposed to the formation of percolating gels, has also been observed by Griffiths and coworkers 39 using the Morse pair potential with different interaction strengths. Those authors reported local fractal dimensions similar to the ones we find here.…”

“…Relatively low surface roughnesses, ρ = 1.5 Å result in deep energy minima, ∼20-30k B T. This interactions are similar to those considered before in models of adhesive hard-spheres and patchy colloidal potentials, [34][35][36][37][38] which included shortranged attractive wells of the order of 10's k B T. Based on these works, we expect that the effective interaction employed here should lead to irreversible and diffusion-limited cluster aggregation (DLCA), 35 characterized by the formation of a gel phase at low particle packing fractions, likely in the interval ϕ = 0.01-0.10. 39 Surface roughnesses below 1.5 Å should also result in irreversible aggregation.…”

Vitrification and gelation in sticky spheres

“…Another aspect is that at low volume fractions (φ 0.01), percolation takes some time to occur even in the demixing region of the phase diagram. 83,84 Under these conditions, percolation does control gelation.…”

Real Space Analysis of Colloidal Gels: Triumphs, Challenges and Future Directions

“…Later work showed that the dynamics change abruptly at the point of gelation 4(b) [48]. This does not mean that other mechanisms do not contribute and particularly at low volume fractions, there is strong evidence for the role of cluster growth [77,80] (see also the discussion in section 5.1). However such clusters almost certainly lie within the region of the phase diagram where spinodal demixing occurs, with percolation taking longer to occur at these low volume fractions (see the pale blue region where cluster growth is important in Fig.…”