Linking slow dynamics and microscopic connectivity in dense suspensions of charged colloids

Abstract

The quest to unravel the nature of the glass transition, where the viscosity of a liquid increases by many orders of magnitude, while its static structure remains largely unaffected, remains unresolved. While various structural and dynamical precursors to vitrification have been identified, a predictive and quantitative description of how subtle changes at the microscopic scale give rise to the steep growth in macroscopic viscosity is missing. It was recently proposed that the presence of long-lived bonded structures within the liquid may provide the long-sought connection between local structure and global dynamics. Here we directly observe and quantify the connectivity dynamics in liquids of charged colloids en route to vitrification using three-dimensional confocal microscopy. We determine the dynamic structure from the real-space van Hove correlation function and from the particle trajectories, providing upper and lower bounds on connectivity dynamics. Based on these data, we extend Dyre's model for the glass transition to account for particle-level structural dynamics; this results in a microscopic expression for the slowing down of relaxations in the liquid that is in quantitative agreement with our experiments. These results indicate how vitrification may be understood as a dynamical connectivity transition with features that are strongly reminiscent of rigidity percolation scenarios.

Exploring the validity of time-concentration superposition in glassy colloids: Experiments and simulations

“…In contrast, the value of n α is larger than n β in the mode coupling theory (MCT) prediction [32]. We also remark that the weak to zero dependence of the τ β on the concentration is similar to qualitative observations from other works [11,30,31,97,98].…”

Local structure in deeply supercooled liquids exhibits growing lengthscales and dynamical correlations

“…Thus supercooling is analogous to increasing density for colloidal hard spheres and we use the terms interchangeably throughout. To date, particle-resolved studies with colloids of diameter 1.5–3.5 μm 15 , 25 , 32 , 33 rarely exceed 4 decades of supercooling. Crucially, the mode-coupling crossover is thought to occur after at least 5 decades of supercooling 34 .…”

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

“…Suspensions of particles with nearly hard-sphere interactions exhibit equilibrium fluid and crystal phases, in agreement with the behavior expected for hard spheres, and form a non-equilibrium glass when rapidly concentrated [6]. Microscopic imaging experiments on hard-sphere colloidal suspensions have therefore been used to explore processes involved in transitions to or from crystals [7][8][9][10][11][12], and to test theoretical predictions for the glass transition [13][14][15][16][17][18]. Inducing an attraction between particles, for example by adding a non-adsorbing depletant [19], shifts the equilibrium phase boundaries [20].…”