Different mechanisms for dynamical arrest in largely asymmetric binary mixtures

Abstract

Using confocal microscopy we investigate binary colloidal mixtures with large size asymmetry, in particular the formation of dynamically arrested states of the large spheres. The volume fraction of the system is kept constant, and as the concentration of small spheres is increased we observe a series of transitions of the large spheres to different arrested states: an attractive glass, a gel, and an asymmetric glass. These states are distinguished by the degree of dynamical arrest and the amount of structural and dynamical heterogeneity. The transitions between two different arrested states occur through melting and the formation of a fluid state. While a space-spanning network of bonded particles is found in both arrested and fluid states, only arrested states are characterized by the presence of a space-spanning network of dynamically arrested particles.

Gelation in mixtures of polymers and bidisperse colloids

“…The asymmetric and non-uniform variations with r of the rheological and microstructural properties are qualitatively similar to those noted in earlier studies of the rheology [34,38] and phase behavior [39] of binary hard sphere PMMA suspensions. At a constant total volume fraction φ T ≈ 0.65 and a particle size ratio α ≈ 0.15, replacing a minor fraction of large particles with small particles (r near 1) significantly altered the low-shear storage modulus; by contrast, replacing a minor fraction of small particles with large particles (r near 0) produced little change in these metrics [34].…”

“…This asymmetry in rheology was attributed to the deformation of the steric stabilizing layer on the surface of the particles [34]. In highly size-asymmetric mixtures of large and small particles (α = 0.1 -0.2) formulated at a constant total volume fraction φ ≈ 0.6, distinct repulsive glass and asymmetric glass states were observed at the extreme compositional ratios [38,39]. Changes in dynamics, localization length, and cluster sizes were attributed to depletion interactions induced by the small particles [39]; these microstructural changes were in turn reflected in the ratio of the elastic and viscous moduli in the linear viscoelastic regime [38].…”

“…Most studies of phase behavior have focused on particles with hard-sphere or repulsive interactions [32,[34][35][36][37][38][39]. Small particles can induce a depletion attraction [40] between large particles; the resulting interplay between the largelarge and small-large interactions generates a multitude of phases, which may exhibit nonmonotonic dependence on system parameters [38,39,41].…”

“…Most studies of phase behavior have focused on particles with hard-sphere or repulsive interactions [32,[34][35][36][37][38][39]. Small particles can induce a depletion attraction [40] between large particles; the resulting interplay between the largelarge and small-large interactions generates a multitude of phases, which may exhibit nonmonotonic dependence on system parameters [38,39,41]. For example, when the ratio of the radii of the small and large particles α = a S /a L is sufficiently high, suspensions can macroscopically phase separate or fractionate into regions of small and large particles [35,42]; fractionation is also theoretically predicted for continuous distributions of particle size dispersity [43].…”

Communication: Probing the existence of partially arrested states in ionic liquids

“…[1][2][3] Despite much research having been done in recent years, 4 the possibility of observing mixed arrested states, in which only one of the components becomes glass while the rest of the system remains fluid, has received less attention. 5 Recently, the Self-Consistent Generalized Langevin Equation (SCGLE) theory was used to investigate the dynamically arrested states in the context of the primitive model (PM) of molten salts. 6 The most important result of the cited work was the prediction of low-temperature regions where the larger ions are fluid and the smaller ions are arrested.…”