Crystallization: Colloidal suspense

According to classical nucleation theory, a crystal grows from a small nucleus that already bears the symmetry of its end phase - but experiments with colloids now reveal that, from an amorphous precursor, crystallites with different structures can develop

Grain refinement and partitioning of impurities in the grain boundaries of a colloidal polycrystal

We study the crystallization of a colloidal model system in presence of secondary nanoparticles acting as impurities. Using confocal microscopy, we show that the nanoparticles segregate in the grain boundaries of the colloidal polycrystal. We demonstrate that the texture of the polycrystal can be tuned by varying independently the nanoparticle volume fraction and the crystallization rate, and quantify our findings using standard models for the nucleation and growth of crystalline materials. Remarkably, we find that the efficiency of the segregation of the nanoparticles in the grain-boundaries is determined solely by the typical size of the crystalline grains.Comment: accepted for publication in Soft Matte

Crystallization Kinetics of Colloidal Spheres under Stationary Shear Flow

A systematic experimental study of dispersions of charged colloidal spheres is presented on the effect of steady shear flow on nucleation and crystal-growth rates. In addition, the non-equilibrium phase diagram as far as the melting line is concerned is measured. Shear flow is found to strongly affect induction times, crystal growth rates and the location of the melting line. The main findings are that (i) the crystal growth rate for a given concentration exhibits a maximum as a function of the shear rate, (ii) contrary to the monotonous increase of the growth rate with increasing concentration in the absence of flow, a maximum of the crystal growth rate as a function of concentration is observed for sheared systems, and (iii) the induction time for a given concentration exhibits a maximum as a function of the shear rate. These findings will be partly explained on a qualitative level.Comment: 17 pages, 10 figures, accepted in Langmui

Measuring every particle's size from three-dimensional imaging experiments

Often experimentalists study colloidal suspensions that are nominally monodisperse. In reality these samples have a polydispersity of 4-10%. At the level of an individual particle, the consequences of this polydispersity are unknown as it is difficult to measure an individual particle size from microscopy. We propose a general method to estimate individual particle radii within a moderately concentrated colloidal suspension observed with confocal microscopy. We confirm the validity of our method by numerical simulations of four major systems: random close packing, colloidal gels, nominally monodisperse dense samples, and nominally binary dense samples. We then apply our method to experimental data, and demonstrate the utility of this method with results from four case studies. In the first, we demonstrate that we can recover the full particle size distribution {\it in situ}. In the second, we show that accounting for particle size leads to more accurate structural information in a random close packed sample. In the third, we show that crystal nucleation occurs in locally monodisperse regions. In the fourth, we show that particle mobility in a dense sample is correlated to the local volume fraction.Comment: 7 pages, 5 figure

Colloidal crystal growth at externally imposed nucleation clusters

We study the conditions under which and how an imposed cluster of fixed colloidal particles at prescribed positions triggers crystal nucleation from a metastable colloidal fluid. Dynamical density functional theory of freezing and Brownian dynamics simulations are applied to a two-dimensional colloidal system with dipolar interactions. The externally imposed nucleation clusters involve colloidal particles either on a rhombic lattice or along two linear arrays separated by a gap. Crystal growth occurs after the peaks of the nucleation cluster have first relaxed to a cutout of the stable bulk crystal.Comment: 4 pages, accepted for publication in Phys. Rev. Let

Dynamics at the crystal-melt interface in a supercooled chalcogenide liquid near the glass transition.

Direct quantitative measurements of nanoscale dynamical processes associated with structural relaxation and crystallization near the glass transition are a major experimental challenge. These type of processes have been primarily treated as macroscopic phenomena within the framework of phenomenological models and bulk experiments. Here, we report x-ray photon correlation spectroscopy measurements of dynamics at the crystal-melt interface during the radiation induced formation of Se nano-crystallites in pure Se and in binary AsSe4 glass-forming liquids near their glass transition temperature. We observe a heterogeneous dynamical behaviour where the intensity correlation functions g2(q, t) exhibits either a compressed or a stretched exponential decay, depending on the size of the Se nano-crystallites. The corresponding relaxation timescale for the AsSe4 liquid increases as the temperature is raised, which can be attributed to changes in the chemical composition of the melt at the crystal-melt interface with the growth of the Se nano-crystallites

Electrostatic repulsion-driven crystallization model arising from filament networks

The crystallization of bundles in filament networks interacting via long-range repulsions in confinement is described by a phenomenological model. The model demonstrates the formation of the hexagonal crystalline order via the interplay of the confinement potential and the filament-filament repulsion. Two distinct crystallization mechanisms in the short- and large- screening length regimes are discussed, and the phase diagram is obtained. Simulation of large bundles predicts the existence of topological defects within the bundled filaments. This electrostatic repulsion-driven crystallization model arising from studying filament networks can even find a more general context extending to charged colloidal systems.Comment: 6 pages, 8 figure