Dynamics of colloidal crystals in shear flow (original) (raw)

Crystal Nucleation of Colloidal Suspensions under Shear

Physical Review Letters, 2004

We use Brownian Dynamics simulations in combination with the umbrella sampling technique to study the effect of shear flow on homogeneous crystal nucleation. We find that a homogeneous shear rate leads to a significant suppression of the crystal nucleation rate and to an increase of the size of the critical nucleus. A simple, phenomenological extension of classical nucleation theory accounts for these observations. The orientation of the crystal nucleus is tilted with respect to the shear direction.

Shear effects on crystal nucleation in colloidal suspensions

Physical Review E, 2008

Extensive two-dimensional Langevin dynamics simulations are used to determine the effect of steady shear flows on the crystal nucleation kinetics of charge stabilized colloids and colloids whose pair potential possess an attractive shallow well of a few k B T's ͑attractive colloids͒. Results show that in both types of systems small amounts of shear speeds up the crystallization process and enhances the quality of the growing crystal significantly. Moderate shear rates, on the other hand, destroy the ordering in the system. The very high shear rate regime where a reentering transition to the ordered state could exist is not considered in this work. In addition to the crystal nucleation phenomena, the analysis of the transport properties and the characterization of the steady state regime under shear are performed.

Crystallization Kinetics of Colloidal Spheres under Stationary Shear Flow

Langmuir, 2005

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.

Stability and fluctuations in sheared colloidal crystals

Physical Review A, 1990

Macroscopic equations of motion describing the coupled dynamics and fluctuations of a dilute colloidal crystal and the underlying fluid in the presence of shear are analyzed for plane Couette flow. The system becomes unstable through a transverse acoustic resonance mechanism at a critical shear rate tu, ". For large system size L, tu, "-[L in(L)]. The lattice displacement fluctuations excited by thermal motion only diverge logarithmically as the instability is approached, but cause the Debye-Wailer factors to become periodic functions of time. The theory is discussed in terms of recent scattering experiments and other theoretical work.

Colloidal lattice shearing and rupturing with a driven line of particles

Physical Review E, 2013

We examine the dynamics of two-dimensional colloidal systems using numerical simulations of a system with a drive applied to a thin region in the middle of the sample to produce a local shear. For a monodisperse colloidal assembly, we find a well defined decoupling transition separating a regime of elastic motion from a plastic phase where the particles in the driven region break away or decouple from the particles in the bulk, producing a shear band. For a bidisperse assembly, we find that the onset of a bulk disordering transition coincides with the broadening of the shear band. We identify several distinct dynamical regimes that are correlated with features in the velocity-force curves. As a function of bidispersity, the decoupling force shows a nonmonotonic behavior associated with features in the noise fluctuations, power spectra, and bulk velocity profiles. When pinning is added in the bulk, we find that the shear band regions can become more localized, causing a decoupling of the driven particles from the bulk particles. For a system with thermal noise and no pinning, the shear band region becomes more extended and the average velocity of the driven particles drops at the thermal disordering transition of the bulk system.

Homogeneous nucleation of colloidal melts under the influence of shearing fields

Journal of Physics: Condensed Matter, 2004

We study the effect of shear flow on homogeneous crystal nucleation, using Brownian Dynamics simulations in combination with an umbrella sampling like technique. The symmetry breaking due to shear results in anisotropic radial distribution functions. The homogeneous shear rate suppresses crystal nucleation and leads to an increase of the size of the critical nucleus. These observations can be described by a simple, phenomenological extension of classical nucleation theory. In addition, we find that nuclei have a preferential orientation with respect to the direction of shear. On average the longest dimension of a nucleus is along the vorticity direction, while the shortest dimension is preferably perpendicular to that and slightly tilted with respect to the gradient direction.

Heterogeneous nucleation of colloidal melts under the influence of shearing fields

Journal of Physics: Condensed Matter, 2004

We study the effect of shear flow on homogeneous crystal nucleation, using Brownian Dynamics simulations in combination with an umbrella sampling like technique. The symmetry breaking due to shear results in anisotropic radial distribution functions. The homogeneous shear rate suppresses crystal nucleation and leads to an increase of the size of the critical nucleus. These observations can be described by a simple, phenomenological extension of classical nucleation theory. In addition, we find that nuclei have a preferential orientation with respect to the direction of shear. On average the longest dimension of a nucleus is along the vorticity direction, while the shortest dimension is preferably perpendicular to that and slightly tilted with respect to the gradient direction.

Theory of Shear-Induced Melting of Colloidal Crystals

Physical Review Letters, 1986

We propose a theory of shear-induced melting of colloidal crystals based on a nonequilibrium generalization of first-order freezing theory. The results agree qualitatively with experiment.

Shear-induced particle migration in binary colloidal suspensions

2008

We present experimental investigations of the spatial and temporal evolution of particle migration in pressure driven flows of Brownian particle suspensions. Binary suspensions of 1.4 and 3.0 m diameter colloidal particles are pumped through a 50ϫ 500 m 2 rectangular-cross-section capillary tube. Shear rate gradients caused by the resulting parabolic velocity profile drive the particles away from the walls toward the center of the channel, where the shear rate is lowest. The flows are directly imaged using high-speed laser scanning confocal microscopy. Size segregation of the particles is observed. Depending on the conditions, either the large or the small particles enrich the center. We measure the development of the size segregation by tracking the evolution of the cross-stream concentrations of the particles.