Turbulence and coarsening in active and passive binary mixtures

Phase separation between two fluids in two dimensions is investigated by means of direct numerical simulations of coupled Navier-Stokes and Cahn-Hilliard equations. We study the phase ordering process in the presence of an external stirring acting on the velocity field. For both active and passive mixtures we find that, for a sufficiently strong stirring, coarsening is arrested in a stationary dynamical state characterized by a continuous rupture and formation of finite domains. Coarsening arrest is shown to be independent of the chaotic or regular nature of the flow.     

Phase separation of highly dissymmetric binary ionic mixtures

We study the phase separation of binary ionic mixtures involving two species of classical point ions in a rigid uniform neutralizing background of degenerate electrons. The thermodynamic properties of the ionic fluid are calculated on the basis of the HNC integral equation for the three partial pair distribution functions. We develop a systematic technique which allows the properties of mixtures of arbitrary composition to be expressed in terms of infinitely dilute solutions. Phase diagrams and critical parameters are determined for 12 different binary systems involving ionic charge ratios between 2 and 8. The dependence of the critical temperature on the ionic charges, on the pressure and an ionic quantum corrections is examined in detail.     

Phase separation of liquid binary mixtures containing metals under pressure

We have measured the pressure variations of the two-phase regions of liquid binary mixtures of metal with metal (LiNaandGaBi), metal with semiconductor (TlSe) and metal with salt (BiBiI₃andBiBiBr₃) up to 28 kbar. It was found that in the mixtures of LiNa and GaBi the two-phase regions enlarge at higher pressures, while in the mixtures of TlSe, BiBiI₃ and BiBiBr₃ the two-phase regions disappear at low pressures.     

Phase separation in strongly coupled binary ionic mixtures at zero temperature

The ground-state energy of strongly coupled binary ionic mixtures is evaluated by solving the hypernetted-chain (HNC) equations for the pair distribution functions. The point ions are immersed in a rigid and uniform neutralizing background of relativistic electrons. We have calculated the equation of state and the pair structure of these binary fluids for three concentrations and over a rather extensive range of densities. The miscibility essentially depends on the statistics of the species and on the coupling. We show that the phase separation is very sensitive to the choice of the wave function used to describe the mixture.     

Phase separation of binary systems

In this paper, three physical predictions on the phase separation of binary systems are derived based on a dynamic transition theory developed recently by the authors. First, the order of phase transitions is precisely determined by the sign of a nondimensional parameter K such that if K>0, the transition is first order with latent heat and if K<0, the transition is second order. Here the parameter K is defined in terms of the coefficients in the quadratic and cubic nonlinear terms of the Cahn-Hilliard equation and the typical length scale of the container. Second, a phase diagram is derived, characterizing the order of phase transitions, and leading in particular to a prediction that there is only a second-order transition for molar fraction near 1/2. This is different from the prediction made by the classical phase diagram. Third, a TL-phase diagram is derived, characterizing the regions of both homogeneous and separation phases and their transitions.     

Phase separation dynamics in binary systems containing mobile particles with variable Brownian motion

In this paper, we consider a particular form of coupling, namely \(B=\sigma (\dot{\rho _m}-\dot{\rho _\phi })\) in spatially flat (\(k=0\)) Friedmann–Lemaitre–Robertson–Walker (FLRW) space–time. We perform phase-space analysis for this interacting quintessence (dark energy) and dark matter model for different numerical values of parameters. We also show the phase-space analysis for the ‘best-fit Universe’ or concordance model. In our analysis, we observe the existence of late-time scaling attractors.     

Micellization and phase separation in binary amphiphile mixtures

Grand canonical Monte Carlo simulations with histogram reweighting are used to examine the micellization and phase separation of a lattice model for binary amphiphile mixtures in an implicit solvent. The model amphiphiles consist of a neutral, rigid head group that occupies seven lattice sites and solvophobic tail chains of varying length and number. It is found that the critical micelle concentration of the mixtures closely matches theoretical values obtained by assuming that the components form an ideal mixture. The solubility of amphiphiles which undergo a first-order transition to form a disordered liquid phase can be increased by adding an amphiphile that forms micelles, and the phase transitions in these mixtures are between a dense liquid state and a low concentration phase that contains aggregates. In both micelles and dense liquids, the amphiphiles mix indiscriminately and the micelle size and shape depends on the concentration ratio of the two species.     

Phase diagram of two-dimensional binary Yukawa mixtures

We have used Ramakrishnan–Yussouff (RY) density functional theory (DFT) to explore the topology of the phase diagram of two-component charge stabilised colloidal suspensions confined to a two-dimensional plane. The particles of the system interact via purely repulsive soft core Yukawa potential. Pair correlation functions (PCFs) used as input informations in DFT were calculated by solving both the hypernetted chain (HNC) and Percus–Yevick (PY) integral equation theories. To test the relative performance of the HNC and PY theories in the context of phase transitions, we have also studied the corresponding one-component systems. We found that RY DFT with HNC PCFs does not stabilise solid in both the one- and two-component cases, whereas the PY theory does. By considering the freezing into the substitutionally disordered triangular solid, we found that the temperature-composition phase diagrams of the binary mixture are narrow spindles whose thickness depends on the symmetry of the mixture components and the value of the screening constant of the Yukawa potential. Although the phase diagram obtained by RY DFT with structural inputs calculated by the PY theory is found to be shifted to higher temperature region in the temperature-composition plane, however, it captures qualitatively all the essential features of the phase diagram. Our results are in principle verifiable through computer simulations and experiments.     

Crystallization and phase separation in nonadditive binary hard-sphere mixtures

We calculate for the first time the full phase diagram of an asymmetric nonadditivehard-sphere mixture. The nonadditivity strongly affects the crystallization and the fluid-fluid phase separation. The global topology of the phase diagram is controlled by an effective size ratio y(eff), while the fluid-solid coexistence scales with the depth of the effective potential well.     

Coarsening of self-organized clusters in binary mixtures of particles

Experiments on patterned particle segregation in binary granular mixtures which are subjected to horizontal shaking have been performed. A novel mechanism for separation is found, where random forcing of one species by the other causes clustering. A pattern is formed which contains a series of stripes aligned orthogonal to the direction of the periodic forcing. The pattern coarsens with time and shows a power law behavior which is consistent with simple models of the geological process of "stone striping."     

Phase behavior of binary hard-sphere mixtures from perturbation theory

Using a first-order perturbation theory, we have studied the phase diagram of a binary mixture of hard spheres for different values of the size ratio. Recent models for the two-body depletion potential between large spheres are used to take into account the role of the small spheres. The theory predicts a complex phase diagram including a fluid-solid transition at high packing fraction of small spheres, metastability of fluid-fluid demixing, an isostructural solid-solid transition at high packing fraction of the large spheres for sufficiently small values of the size ratio q of the spheres, and the tendency to sticky-sphere behavior in the limit q-->0. The agreement with recent simulation results is quite good. We also show that this phenomenology was already implicit in the pioneering work of Asakura and Oosawa.     

Phase separation in mixtures of hard core bosons

A theoretical investigation of boson versions of the t-J and t-J(z) models on the square lattice is carried out. In the t-J(z) model, phase separation between a hole-rich and a hole-free phase occurs, at sufficiently low hole doping, for arbitrarily small values of J(z). The boson t-J model, instead, features a uniform ground state at any doping for J/t< or =1.5. No evidence of a striped ground state is found. Relevance of this study to the corresponding fermion models is discussed. Fermi statistics is found to enhance the tendency toward phase separation; in particular, phase separation is predicted, at low doping, in the fermion t-J(z) model, at all values of J(z).     

Phase behaviors of binary mixtures composed of banana-shaped and calamitic mesogens

In this work, five mixtures with different concentrations of banana-shaped and calamitic compounds have been prepared and subsequently studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction on non-oriented samples. The phase sequences and molecular parameters of the binary systems are presented.     

Phase transitions in binary mixtures of rodlike colloids and stiff polymers

A suspension of long rodlike colloids and long stiff polymers is modelled as a mixture of hard rods. The diameter of the colloid particle is finite, while the polymer is considered in the limit of zero diameter. Two types of first-order phase transition may occur in such mixtures: an isotropic-nematic phase transition if the density (or the pressure) is high enough, and a demixing transition involving two isotropic phases. The demixing transition has a critical point, and a triple point with one nematic and two isotropic phases may also exist. Phase diagrams are calculated. For the demixing isotropic-isotropic transition to be observed the ratio between the polymer length and the colloid length must exceed 0.36.     

Controlling the motion of interacting particles: homogeneous systems and binary mixtures

We elaborate on recent results on the transport of interacting particles for both single-species and binary mixtures subject to an external driving on a ratchetlike asymmetric substrate. Moreover, we also briefly review motion control without any spatial asymmetric potential (i.e., no ratchet). Our results are obtained using an analytical approach based on a nonlinear Fokker-Planck equation as well as via numerical simulations. By increasing the particle density, the net dc ratchet current in our alternating (ac)-driven systems can either increase or decrease depending on the temperature, the drive amplitude, and the nature of the inter-particle interactions. This provides an effective control of particle motion by just changing the particle density. At low temperatures, attracting particles can condense at some potential minima, thus breaking the discrete translational symmetry of the substrate. Depending on the drive amplitude, an agglomeration or condensation results either in a drop to zero or in a saturation of the net particle velocity at densities above the condensation density-the latter case producing a very efficient rectification mechanism. For binary mixtures we find three ways of controlling the particle motion of one (passive) B species by means of another (active) A species: (i) Dragging the target particles B by driving the auxiliary particles A, (ii) rectifying the motion of the B particles on the asymmetric potential created by the A-B interactions, and (iii) dynamically modifying (pulsating) this potential by controlling the motion of the A particles. This allows to easily control the magnitude and direction of the velocity of the target particles by changing either the frequency, phase and/or amplitude of the applied ac drive(s).     

外噪声场对二元混合物相分离的驱动作用

采用蒙特卡罗法研究了外高斯噪声场对二元混合物体系相分离的驱动作用.研究发现，高斯噪声场的引入可以加快体系畴的生长，驱动体系形成沿着［1,1］取向的条状畴结构.在噪声强度一定、噪声作用的概率小于0.015时，高斯噪声场消除了深度淬火引起的体系畴的冻结，畴的生长因子随噪声作用概率线性增加.对足够强的高斯噪声场，存在一个最佳的作用概率区域，其间体系能形成取向性好的条状畴结构. 关键词： 高斯噪声 二元混合物 相分离