Dynamical Arrest in Attractive Colloids: The Effect of Long-Range Repulsion

Abstract

We study gelation in suspensions of model colloidal particles with short-ranged attractive and long-ranged repulsive interactions by means of three-dimensional fluorescence confocal microscopy. At low packing fractions, particles form stable equilibrium clusters. Upon increasing the packing fraction the clusters grow in size and become increasingly anisotropic until finally associating into a fully connected network at gelation. We find a surprising order in the gel structure. Analysis of spatial and orientational correlations reveals that the gel is composed of dense chains of particles constructed from face-sharing tetrahedral clusters. Our findings imply that dynamical arrest occurs via cluster growth and association.

Phase behavior and rheological characterization of silica nanoparticle gel

“…At salinities above the CSC but below the upper gelation salt concentration, the unstable solution forms a gel phase. Many authors have proposed that gel formation is due to dynamic arrest of the particle clusters (Campbell et al 2005;Lu et al 2008;de Candia et al 2005). In colloidal suspensions, for longer separation lengths, repulsion is greater than Van der Waals attraction resulting in a long range repulsive barrier.…”

Colloidal dynamics: Influence of diffusion, inertia and colloidal forces on cluster formation

“…Note, that clusters observed in [3][4][5][6][7][8][9][10][11][12][13] are very stable structures, as they did not show any noticeable growth during long periods of observation (from hundreds of hours to months).…”

“…However, comprehensive experimental studies performed during recent years discovered the existence of stable clusters in colloidal suspensions stabilised by electrostatic and/or structural repulsion [3][4][5][6][7][8][9][10][11][12][13].…”

“…The most detailed study of the formation of stable clusters of colloidal particles was undertaken for suspensions of polymethylmethacrilate monodisperse (polydispersity ≤ 5 %) spherical particles with mean radius in the range 212-777 nm in a mixture of cis-decalin and cycloheptyl bromide [3][4][5][6][7][8][9]. The matching densities allowed neglecting the influence of the gravity.…”

“…An increase of both polymer concentrations and solid volume fractions resulted in the increase of the cluster size and finally in formation of gel-like structures [4][5][6]. Using the confocal microscopy allowed the clear visualisation of clustering [3][4][5][6]. According to [3] at polymer concentration 3 g/l and molecular mass 212.4 kDa, the equilibrium cluster aggregation number increased from about 3 at the solid volume fraction of φ=0.025 to more than 20 at the solid volume fraction of φ=0.15.…”