We show that an enslaved phase-separation front moving with diffusive speeds U = C T^(-1/2) can leave alternating domains of increasing size in their wake. We find the size and spacing of these domains is identical to Liesegang patterns. For equal co
mposition of the components we are able to predict the exact form of the pattern analytically. We also show that there is a critical value for C below which only two domains are formed. Our analytical predictions are verified by numerical simulations using a lattice Boltzmann method.
Enslaved phase-separation fronts that move with a speed just smaller than that of a free front will leave in their wake a morphology of alternating domains that are roughly aligned with the front. However, these alternating domains will typically not
be in phase initially. Instead there are defects. Here we present novel phase-separation morphologies that are formed in such systems where the defects are reminiscent of spiral dislocations in crystal growth.
Simulations of liquid-gas systems with extended interfaces are observed to fail to give accurate results for two reasons: the interface can get ``stuck on the lattice or a density overshoot develops around the interface. In the first case the bulk de
nsities can take a range of values, dependent on the initial conditions. In the second case inaccurate bulk densities are found. In this communication we derive the minimum interface width required for the accurate simulation of liquid gas systems with a diffuse interface. We demonstrate this criterion for lattice Boltzmann simulations of a van der Waals gas. When combining this criterion with predictions for the bulk stability we can predict the parameter range that leads to stable and accurate simulation results. This allows us to identify parameter ranges leading to high density ratios of over 1000. This is despite the fact that lattice Boltzmann simulations of liquid-gas systems were believed to be restricted to modest density ratios of less than 20.
We present a lattice Boltzmann algorithm based on an underlying free energy that allows the simulation of the dynamics of a multicomponent system with an arbitrary number of components. The thermodynamic properties, such as the chemical potential of
each component and the pressure of the overall system, are incorporated in the model. We derived a symmetrical convection diffusion equation for each component as well as the Navier Stokes equation and continuity equation for the overall system. The algorithm was verified through simulations of binary and ternary systems. The equilibrium concentrations of components of binary and ternary systems simulated with our algorithm agree well with theoretical expectations.
Lattice Boltzmann simulations of liquid-gas systems are believed to be restricted to modest density ratios of less than 10. In this article we show that reducing the speed of sound and, just as importantly, the interfacial contributions to the pressu
re allows lattice Boltzmann simulations to achieve high density ratios of 1000 or more. We also present explicit expressions for the limits of the parameter region in which the method gives accurate results. There are two separate limiting phenomena. The first is the stability of the bulk liquid phase. This consideration is specific to lattice Boltzmann methods. The second is a general argument for the interface discretization that applies to any diffuse interface method.
In this article we show that the phase-ordering scaling state for binary fluids is not necessarily unique and that local correlations in the initial conditions can be responsible for selecting the scaling state. We describe a new scaling state for sy
mmetric volume fractions that consists of drops of the one component suspended in a matrix of the other. The underlying reason for the existence of the newly observed scaling state is that the main coarsening mechanism of binary fluids which is the deformation of interfaces by flow is not acting, and this leads to a new scaling law. An initial droplet state can be formed by a number of physical phenomena. In a unified description this can be undestood as local correlations in the initial conditions. Local correlations with length $xi$ are believed to be irrelevant when the typical length scale L of the system is large ($Lgg xi$). Our result shows that these initial correlations, contrary to current thinking, can be important even at late times.
In this letter we show that the late-time scaling state in spinodal decomposition is not unique. We performed lattice Boltzmann simulations of the phase-ordering of a 50%-50% binary mixture using as initial conditions for the phase-ordering both a sy
mmetric morphology that was created by symmetric spinodal decomposition and a morphology of one phase dispersed in the other, created by viscoelastic spinodal decomposition. We found two different growth laws at late times, although both simulations differ only in the early time dynamics. The new scaling state consists of dispersed droplets. The growth law associated with this scaling state is consistent with a $Lsim t^{1/2}$ scaling law.
We use lattice Boltzmann simulations to study the effect of shear on the phase ordering of a two-dimensional binary fluid. The shear is imposed by generalising the lattice Boltzmann algorithm to include Lees-Edwards boundary conditions. We show how t
he interplay between the ordering effects of the spinodal decomposition and the disordering tendencies of the shear, which depends on the shear rate and the fluid viscosity, can lead to a state of dynamic equilibrium where domains are continually broken up and re-formed.
