Function Of Attraction Strength Research Articles

Correlated rearrangements of disordered colloidal suspensions in the vicinity of the reentrant glass transition

We experimentally investigate correlated rearrangements (dynamic heterogeneity) in disordered colloidal suspensions as a function of increasing inter-particle attraction strength across the reentrant glass transition. Attractive interactions between constituent spheres are induced by polymer depletion forces at fixed particle volume fraction. We vary sample inter-particle attraction strength and concurrently measure particle trajectories by confocal microscopy at each attraction strength. The reentrant transition from repulsive glass to ergodic fluid and from ergodic fluid to attractive glass is readily observed. As the inter-particle attraction increases, we find that inter-particle bonding causes an increasing number of particles to undergo cooperative or correlated displacements; the length scale associated with these correlated rearrangements exhibits reentrant behavior. Other dynamical quantities such as the mean square displacement, the long-time diffusion constant, and the non-Gaussian parameter also exhibit changes as a function of attraction strength. Notably, the arrested (glass) states show small particle displacements at long lag times, whereas the fluid states exhibit fast dynamics over large length scales.

Sedimentation of aggregating colloids

We investigate the combined effects of gravity, attractive interactions, and brownian motion in suspensions of colloidal particles and nonadsorbing polymer. Depending on the effective strength of gravitational forces, resulting from a density mismatch between the colloids and the solvent, and the magnitude and range of the depletion interactions induced by the polymer, sedimentation in these suspensions can result in an equilibrium structure or a kinetically arrested state. We employ large-scale molecular dynamics simulations to systematically classify the different regimes that arise as a function of attraction strength and gravitational stress. Whereas strong attractions lead to cluster aggregation and low-density arrested states, moderate attractions can enhance crystallization of the colloidal particles in the sediment. We make direct comparisons to experimental results to infer general conclusions about the mechanisms leading to mechanically stable sediments.

Structural precursor to freezing: An integral equation study

Recent simulation studies have drawn attention to the shoulder which forms in the second peak of the radial distribution function of hard spheres at densities close to freezing and which is associated with local crystalline ordering in the dense fluid. We address this structural precursor to freezing using an inhomogeneous integral equation theory capable of describing local packing constraints to a high level of accuracy. The addition of a short-range attractive interaction leads to a well known broadening of the fluid-solid coexistence region as a function of attraction strength. The appearance of a shoulder in our calculated radial distribution functions is found to be consistent with the broadened coexistence region for a simple model potential, thus demonstrating that the shoulder is not exclusively a high density packing effect.