Immiscible Binary System Research Articles

Rheology-modulated contact line dynamics of an immiscible binary system under electrical double layer phenomena.

We investigate the electrically driven contact line dynamics of a binary fluid system constituted by one Newtonian and another non-Newtonian fluid in a narrow fluidic channel with chemically patched walls. We use a power-law model to describe the rheology of the non-Newtonian fluid and a diffuse interface phase-field method to model the dynamics of multiple phases. We bring out the alteration in the interfacial dynamics as attributable to the rheology-driven modifications in the interfacial stress and its interplay with the Maxwell stress originating from electrokinetic effects.

Pulsating electric field modulated contact line dynamics of immiscible binary systems in narrow confinements under an electrical double layer phenomenon.

We investigate the interfacial electro-chemical-hydrodynamics of an incompressible immiscible binary fluid system that moves in a narrow fluidic channel under time-periodic electroosmotic effects. We apply an alternating electrical voltage that sets the binary fluids in motion along the channel, whereas the channel walls are lined with chemical patch to alter the wetting characteristics of the surface. We demonstrate that the pulsating nature of the externally applied electric field in conjunction with the wetting characteristics of the surface may lead to some fascinating behavior of the contact line motion; which, in turn, may affect the capillary filling dynamics in an intriguing manner. Our results also unveil the profound influence of two important governing factors actuating the flow, namely, the frequency and amplitude of the time periodic electric field, on the tunability of the capillary filling rate and power requirement for filling the fluids into the channel.

Suppression of the quantum collapse in binary bosonic gases

Attraction of the quantum particle to the center in the 3D space with potential V/r^2 gives rise to the quantum collapse, i.e., nonexistence of the ground state (GS) when the attraction strength exceeds a critical value (V = 1/8, in the present notation). Recently, we have demonstrated that the quantum collapse is suppressed, and the GS is restored, if repulsive interactions between particles in the quantum gas are taken into account, in the mean-field approximation. This setting can be realized in a gas of dipolar molecules attracted to the central charge, with dipole-dipole interactions taken into regard too. Here we analyze this problem for a binary gas. GSs supported by the repulsive interactions are constructed in a numerical form, as well as by means of analytical approximations for both miscible and immiscible binary systems. In particular, the Thomas-Fermi (TF) approximation is relevant if V is large enough. It is found that the GS of the miscible binary gas, both balanced and imbalanced, features a weak phase transition at another critical value, V = 1/2. The transition is characterized by an analyticity-breaking change in the structure of the wave functions at small r. To illustrate the generic character of the present phenomenology, we also consider the binary system with the attraction between the species (rather than repulsion), in the case when the central potential pulls a single component only.

Nano-Size and Miscibility Gap

Reports on the alloys formed from immiscible atoms when they are contained in a nano-sized system have initiated several research activities in the recent years. Bridging of the miscibility gap at nanoscale is significant as it has the potential to produce novel alloy materials with useful technological applications. Although the literature contains noticeable number of reports on the formation of solid solution between bulk immiscible atoms, several issues related to phase stability and microstructure remain unaddressed. This article discusses some of these issues using examples from the work done by the author’s research group on isolated nanoparticles of bulk immiscible binary systems such as Ag-Ni, Ag-Fe and Ag-Co.

Gibbs free energy approach to the prediction of melting points of isolated, supported, and embedded nanoparticles

By means of the thermodynamic and thermophysical properties of bulk materials, the Gibbs free energies for isolated, supported, and embedded nanoparticles were obtained and used to elucidate the sized-dependent melting phenomenon of the nanoparticles. To account for the substrate effect upon the melting point of nanoparticles, the interfacial energy of binary immiscible systems was studied in detail. It was found that the interfacial energy of a binary immiscible system including carbon can be replaced almost entirely by the contribution from carbon; thus, the reason why the melting model of isolated nanoparticles can be applied to research the melting of the supported nanoparticles was clarified. Moreover, a new approach to achieving the diameter of the smallest crystalline nanoparticles was proposed based on the melting behavior of embedded nanoparticles.

The physicochemical features of binary immiscible metal systems in a new method of synthesis and crystallization

Features of the structure of phase diagrams of immiscible binary metal systems for synthesis and crystallization of various compounds by a new method are considered: temperature and concentration limits of immiscibility, ratio of densities of system components, use of mixed solvents, and processes of hardening of pure immiscible systems. An example of obtaining crystals of refractory compounds is given.

Surface alloying at the nanoscale: Mo on Au nanocrystalline films

Aiming at the physical and chemical mechanisms of surface alloying at the nanometer scalein immiscible binary metallic systems, we have studied the Mo growth mode upondepositing Mo on the surface of Au nanocrystalline films via molecular beam epitaxy.Mo–Au surface alloying was observed when Mo was deposited on Au nanocrystallinefilms at a high temperature. A relevant thermodynamic and kinetic model wasestablished to address the surface alloying at the nanoscale. The size-dependentinterface energy between the Mo particles and the Au nanocrystalline films, as thethermodynamic driving force, is attributed to be the reason behind the physical andchemical mechanisms of the Mo–Au surface alloying on Au nanocrystalline films.

Forced chemical mixing in model immiscible systems under plastic deformation

Molecular dynamics has been employed to investigate forced chemical mixing in binary immiscible systems induced by plastic deformation. Four X matrix-Y precipitate model systems with thermodynamic and structural features almost identical to the ones of Ag–Cu solid solutions but different mechanical properties were generated. With the positive enthalpy of mixing roughly constant, mixing is shown to depend on the precipitate size as well as on the difference between X and Y tetragonal shear moduli.

Critical point dewetting: competition between the gravity and the dispersion force

Near the critical temperature of an immiscible binary liquid system, a solid substrate is usually covered completely by one of the liquid phases. This phenomenon is called the ‘critical point wetting", which is predicted by Cahn in 1977, and have been confirmed for many fluid systems experimentally. However, we found that liquid Se-Tl system on a quartz substrate does not show the critical point wetting near the liquid-liquid critical point. On a contrary, when the temperature goes down from the critical point, a Se-rich wetting film intrudes between the Tl-rich bulk liquid and the quartz wall. This result is a clear evidence of the ‘critical point dewetting’ phenomenon. It is suggested from a theoretical consideration that the critical point dewetting takes place as a result of the competition between the long-range dispersion force and the gravity.

Role of spatial valence charge density on the metastability of an immiscible binary metal system at equilibrium

In the equilibrium immiscible Ag--Ru system, the elastic constants and phonon spectra of the possible ${\mathrm{Ag}}_{3}\mathrm{Ru}$ and $\mathrm{Ag}{\mathrm{Ru}}_{3}$ in $\mathrm{D}{0}_{3},\mathrm{L}{1}_{2}$, and $\mathrm{D}{0}_{19}$ structures, respectively, are first obtained by the lattice dynamics calculation, which shows that only $\mathrm{L}{1}_{2}$ and $\mathrm{D}{0}_{19}\phantom{\rule{0.3em}{0ex}}\mathrm{Ag}{\mathrm{Ru}}_{3}$ phases can relatively be stable. The spatial valence charge density (SVCD) is then acquired by first principles calculation for all the studied structures. It turns out that the high SVCDs distribute mostly between the similar atoms in the relatively stable phases, while located mainly between the dissimilar atoms in all the unstable structures, indicating that the SVCD plays a decisive role in determining the metastability, i.e., the structural stability of the nonequilibrium phase, in an equilibrium immiscible binary metal system.

Elastic modulus and hardness of Cu–Ta amorphous films

Mechanical properties were detected by the nanoindentation method for the Cu–Ta amorphous films with Ta content from 25.6 to 96 at.%. The hardness and elastic modulus are found to vary linearly with the Ta concentration. The incremental change of the elastic modulus is 1.35 GPa per Ta atom and that of the hardness is 0.205 GPa per Ta atom. The samples with Ta content higher than 71 at.% have higher elastic moduli than the crystalline counterparts of the mechanical mixture. This is similar to the supermodulus effect observed in the multilayers in many immiscible binary alloy systems. A model based on the inter-atomic potential is proposed to explain the enhanced modulus and relate it to the additional Gibbs free energy stored in the alloy after amorphization.

Study of mixing of liquid/polymer in twin screw extruder by residence time distribution

The present investigation is an experimental study of the mixing of two phases of strongly different viscosity in a co-rotating twin-screw extruder (TSE). Two cases were considered: a miscible (copolymer of ethylene and vinyl acetate/bis(2-ethylhexyl)phtalate [EVA/DOP]) and an immiscible (EVA/ethylene-glycol [EVA/EG]) binary system. The residence time distribution (RTD) has been determined for each phase of both systems for different screw profiles and different operating conditions. The behavior of the first system is simple: the type of flow is basically the same. However, in the case of nonmiscibility, when the flow rate is high, the shape of the RTD of both phases may be different. We interpret this result with the appearance of a lubrication phenomenon. POLYM. ENG. SCI., 45:926–934, 2005. © 2005 Society of Plastics Engineers

Ion Beam Manipulation to Fabricate Ordered Layered Structures and Amorphous Alloys in Some highly Immiscible Binary Metal Systems

ABSTRACTWe developed a new scheme, namely ion beam manipulation, i.e. interface-assisted ion beam mixing, for fabricating amorphous alloys and artificial solid-state microstructures in metal-metal multilayers, in which the individual layer thickness is down to about 2 nm, differing significantly from the typical thickness of 5–8 nm in conventional ion beam mixing. Employing the scheme, some interesting results were obtained in three highly immiscible systems. In the Ag-W system, which has the largest positive heat of formation among the transition metal alloys, amorphous alloys were obtained, for the first time, through a two-step structural transition, i.e. the initial polycrystalline Ag and W transformed into an intermediate bcc phase, which later transformed into an amorphous state. In the Ru-Pd system, the initial polycrystalline Pd and Ru first transformed into a single crystalline FCC phase, and then turned into a well-ordered structure, which showed an apparent tendency to transform back to the FCC phase upon over-irradiation. In the Ag-Co system, an ordered layered structure was observed and identified to consist of two overlapped FCC lattices, corresponding to a new magnetic state of Co atom with an average magnetic moment measured to be 2.84 μB, which was about twice the equilibrium datum and was the largest value ever observed. We present, in this paper, a brief review concerning the scheme of ion beam manipulation in fabricating the metastable alloys, the structural evolution upon ion irradiation and the associated magnetic properties of some ordered structures obtained by the scheme.

Morphology of Composite Nanoparticles of Immiscible Binary Systems Prepared by Gas-evaporation Technique and Subsequent Vapor Condensation

X–Y composite nanoparticles of four immiscible binary systems (Si–In, Ge–In, Al–In and Al–Pb) were prepared by the condensation of Y vapor onto X nanoparticles produced in advance by a gas-evaporation technique. The nanoparticles, which were observed by electron microscopy, were composed of two or more crystallites of the elements with different morphology. Their growth process is discussed with reference to the phase diagrams.

Surfactant effects and an order-disorder transition in binary gas-liquid nucleation

Density-functional theory is applied to the interaction site model to study gas-liquid nucleation in a partially immiscible binary system consisting of spherical Lennard-Jones atoms (monomers) and dumbbell molecules of two Lennard-Jones atoms (dimers). Increased interaction anisotropy between the dimer sites and monomers is shown to result in mutual enhancement of nucleation. Critical nuclei with a lamellar structure are observed at high dimer activities.

Theoretical Investigation of the Thermal Stability of Nanoscale Layered Systems

The stability of multilayers at elevated temperatures is investigated by simulating the evolution of the concentration profiles within the framework of the Cahn-Hilliard theory. For immiscible binary systems, a permanent layer thickness coarsening perpendicular to individual layers occurs by dissolution of the thinnest layers. With advancing layer coarsening, this one-dimensional coarsening mechanism slows down strongly. Comparatively rapid multilayer decomposition is caused by lateral inhomogeneities in individual layers. Possible mechanisms of the formation of 'holes' consisting of one phase in layers of the other phase are proposed and subsequent hole growth is studied within a two-dimensional model.

Mechanical alloying of immiscible Pb-Al binary system by high energy ball milling

In the present work, mechanical alloying has been applied to the Pb-Al immiscible binary system by using the method of high energy ball milling. The microstructural features of the milled powder, such as grain size, lattice constant and morphology of phases have been studied by X-ray diffraction, analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, energy dispersive spectroscopy was used to analysis chemical composition of phases presented after milling. Differential Scanning Calorimetry measurement was also made on the milled Pb-Al powder. The results show that homogenous blending of Pb and Al can be easily achieved by high energy ball milling in spite of their mutual immiscibility and large difference in density. The obtained alloy exhibits nanocrystalline microstructure. Further more, the experiment result implies the formation of supersaturated solid solution in immiscible Pb-Al system by high energy ball milling.

Computerized prediction of interaction parameters and phase diagrams of the immiscible binary systems of nontransition-nontransition metals

The relationship between the interaction parameters of liquid alloys and the atomic parameters of constituent elements has been investigated by artificial neural network method. The relationship found can be used for the computerized prediction of phase diagrams of liquid-liquid immiscible binary systems between non-transition elements.

The effect of mixing time on the morphology of immiscible polymer blends

The effect of mixing time on the morphology, with the viscosity ratio and composition as parameters in the mixing process, was studied for two immiscible binary polyblend systems, polyamide/polyethersulfone (PA/PES) and poly(butylene terephthalate)/polystyrene (PBT/PS), by selective dissolution followed by macroscopic and microscopic observations. At a short mixing time, the morphology of each phase depends not only on the composition, but also on the viscosity difference of two phases, shown by the results of PA/PES blends with a viscosity ratio of 0.03. The lower viscous phase (PA) forms particles, fibrils, and layers successively with its increasing content and becomes a continuous one at low concentrations as the minor phase, while the high viscous phase (PES) appears mainly in the form of particles and directly becomes a continuous one at high concentrations. With increasing mixing time, the effect of the viscosity ratio becomes less and the morphology is determined mainly by the volume fraction of each phase. Particles are the final morphology of the minor phase. Only at a viscosity ratio of unity is the morphological development of two phases (PBT and PS) with mixing time the same, and any one of these two components is in the form of particles when it is the minor phase. At the composition near 50/50, fibrillar or continuous structure may coexist for both phases. The composition range of co-phase continuity is decided not only by the viscosity ratio but also by the mixing time. With increasing mixing time, this range becomes narrower and finally occurs at volume fraction of 50/50, no longer affected by the viscosity ratio. © 1996 John Wiley & Sons, Inc.

Homogeneous nucleation ahead of the solid—liquid interface during rapid solidification of binary alloys

In recent rapid solidification experiments on Al—5%Be alloys, a Liquid Phase Nucleation (LPN) model was developed to explain the formation of periodic arrays of randomly-oriented Be-rich particles in an Al-rich matrix. In the LPN model, Be droplets were assumed to nucleate in the liquid ahead of the solid—liquid interface, but no justification for this was given. Here we present a model which considers the geometric constraints (imposed by proximity to the interface) on the number of solute atoms available to form a nucleus. Calculations based on this model predict that nucleation of second-phase particles can be most likely a short distance ahead of the interface in immiscible binary systems such as AlBe. As part of the nucleation calculations, a semi-empirical method of calculating solid—liquid surface tensions in binary systems was developed, and is presented in the Appendix.