Immiscible Mixtures Research Articles

Effects of a Cationic and Hydrophobic Peptide, KL4, on Model Lung Surfactant Lipid Monolayers

We report on the surface behavior of a hydrophobic, cationic peptide, [lysine-(leucine) 4] 4-lysine (KL4), spread at the air/water interface at 25°C and pH 7.2, and its effect at very low molar ratios on the surface properties of the zwitterionic phospholipid 1,2-dipalmitoylphosphatidylcholine (DPPC), and the anionic forms of 1-palmitoyl-2-oleoylphosphatidylglycerol (POPG) and palmitic acid (PA), in various combinations. Surface properties were evaluated by measuring equilibrium spreading pressures ( π e) and surface pressure-area isotherms ( π- A) with the Wilhelmy plate technique. Surface phase separation was observed with fluorescence microscopy. KL4 itself forms a single-phase monolayer, stable up to a surface pressure π of 30 mN/m, and forms an immiscible monolayer mixture with DPPC. No strong interaction was detected between POPG and KL4 in the low π region, whereas a stable monolayer of the PA/KL4 binary mixture forms, which is attributed to ionic interactions between oppositely charged PA and KL4. KL4 has significant effects on the DPPC/POPG mixture, in that it promotes surface phase separation while also increasing π e and π max, and these effects are greatly enhanced in the presence of PA. In the model we have proposed, KL4 facilitates the separation of DPPC-rich and POPG/PA-rich phases to achieve surface refinement. It is these two phases that can fulfill the important lung surfactant functions of high surface pressure stability and efficient spreading.

Lattice-Gas Automata Methods for Engineering

Modern lattice-gas automata (LGA) methods have now existed since the mid-1980s. They have been widely used in a non-engineering context to study multiphase systems, reactive flows, flow and reaction within porousmedia and turbulence. LGA methods for simple fluids have now developed to a point where they may be applied with confidence in an engineering context. Application of LGA in an engineering context to complex fluids such as immiscible mixtures and emulsions can also be contemplated with some further work. In order to assist such application, the basics of LGA are outlined here along with a brief overview of current applications. Thermal LGA methods are also discussed with the hope of stimulating their development for application in an engineering context.

Molecular dynamics simulations of the thermal degradation of nano-confined polypropylene: Comp. Theor. Polymer Sci., 1997, 7, 191

Summary Recent work conducted in this laboratory has demonstrated that nanocomposites consisting of polymer and montmorillonite clay exhibit a significant reduction in flammability, as compared to immiscible mixtures of these components, even in compositions that contain as little as 3 to 5% clay. This increase in fire resistance is not achieved at the expense of compromising other physical properties. Indeed, in most cases, a dramatic improvement in the important thermal and mechanical properties is also observed. Furthermore, the cost of producing these nanocomposites from the constituent polymer and clay are expected to be almost negligible. Although research in this area is just getting underway, preliminary results suggest that it is possible to make nanocomposites from a wide range of commodity polymers, thereby opening the way for the development of an entirely new generation of low cost, ultra fire resistant, high performance materials.

Synchrotron X-ray Absorption Studies of Atomic-Level Alloying in Immiscible Mixtures

ABSTRACTAn X-ray absorption beamline has been developed recently at the electron storage ring of the LSU Center for Advanced Microstructures and Devices. Using Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES), we have studied the local atomic environments in immiscible mixtures processed by high-energy ball milling, a mechanical alloying technique involving heavy deformation. By examining the local coordination and bond distances, it is concluded that atomic-level alloying can indeed be induced between Cu and Fe through milling at room temperature, forming substitutional fcc and bcc solid solutions. In addition to single-phase regions, a two-phase region consisting of fcc/bcc solutions has been found after milling at both room temperature and liquid nitrogen temperature. In contrast to the Cu-Fe system, solid solution formation is not detectable in milled Ag-Fe and Cu-Ta mixtures. This work demonstrates the power of synchrotron EXAFS/XANES experiments in monitoring nonequilibrium alloying on the atomic level. At the same time, the results provide direct experimental evidence of the capability as well as limitations of high-energy ball milling to form alloys in positive-heat-of-mixing systems.

Crevice corrosion of 316l caused by chloride partition in water-butanone mixtures

Chloride-induced crevice corrosion of a 316L pump was found to have occurred in what was nominally a very dilute solution of sodium chloride in a single-phase solution of water in butanone at 25°C. The hypothesis formed was that water had entered the system in a sufficient amount to form an immiscible mixture of a water-rich phase and a butanone-rich phase. This separation into two liquids was followed by preferential partition into the water-rich phase of the sodium chloride to give a brine. A simple test demonstrated that the hypothesis was tenable.

Chemical freezing of phase separation in immiscible binary mixtures

We discuss the thermodynamic and kinetic conditions under which chemical reactions may prevent the coarsening terminating spinodal decomposition and freeze the unmixing of binary mixtures at some early, pattern forming, stage of evolution. Under very general conditions, we establish that (i) this pattern freezing phenomenon can only occur in nonequilibrium systems the level of dissipation of which exceeds a finite, nonzero threshold value; (ii) at least two independent chemical processes must take place; (iii) chemistry must be destabilizing, which requires that at least one of these processes must be autocatalytic; (iv) pattern formation is possible even outside of the spinodal region, i.e., without involving a phase separation phenomenon, in unsymmetrical mixtures where the potential energies between pairs of identical particles are sufficiently different. This latter condition replaces for nonideal chemically reacting binary mixtures the unequal diffusion coefficients condition which governs the appearance of Turing patterns in the classical reaction-diffusion theory.

Two-dimensional magnetic liquid froth: Coarsening and topological correlations

We present an experimental study of a cellular system which may be formed in a two-dimensional ~2D! layer made of an immiscible mixture of a magnetic fluid and an oil. We obtain a wet or a dry 2D froth, the characteristics of which are determined by the strength of an externally applied magnetic field. The froth is formed in an equilibrium state; the topological and geometrical features of the froth are fixed by the value of the applied field. The cellular pattern of the froth is stable in time, and a coarseninglike behavior is observed on decreasing the amplitude of the field. This cellular system can be used as a model to study topological processes in the equilibrium state, contrary to soap froths which are nonequilibrium systems because gas diffusion occurs. We show that the topological characteristics are statistically reversible after a magnetic-field cycle, and we present a statistical study of the froth features as a function of the amplitude of the field. The topological correlations between neighboring cells are well described by the Aboav-Weaire law. Finally, we consider the area of an n-sided cell, and show that its growth rate ~magnetic field dependent! is, in a surprising manner, proportional to n26, similarly to the Von Neumann law. @S1063-651X~97!10009-5#

Phase behaviour of polyamide—polyester blends: the influence of aromaticity

Miscibility in blends of semi-aromatic polyamides and random aliphatic co-polyesteramides, derived from ϵ-caprolactam, ϵ-caprolactone and laurolactam has been investigated by calorimetric methods. Dilution of ϵ-caprolactam by ϵ-caprolactone in PA-6 transforms miscible blends based on PA-6I and PA-TMDT, respectively, to immiscible mixtures at approximately 35 and 46 mol%, respectively, of ϵ-caprolactone in the copolymer. The data have been found to conform to an analysis provided by a binary interaction model incorporating segmental interaction parameters, χ ij , derived from related blends. Extension of the treatment to polyamide/polyester blends whose constituents contain aromaticity, e.g. PA-66/poly(ethylene terephthalate), PET and PA-6I/polyarylate, PAr, has also been explored. The results confirm the gross immiscibility, indicated by a large unfavourable interaction parameter, typically encountered in these blends.

Macro-Organized Patterns in Ferrofluid Layer: Experimental Studies

We present some experimental results concerning the conformational instabilities observed in a thin layer made of an immiscible mixture of a magnetic fluid and another liquid submitted to an external magnetic field. We observed macroscopic domains with stripe or bubble shape. The transition bet~~een the two morphologies is observed and a coexistence of the two phases is visualized in a variable thickness layer. Furthermore, we give other results about the instabilities of the parallel stripe pattern: by increasing the external field the stripe pattern becomes a chevron structure, which also becomes unstable for higher values of the magnetic field and gives a hairpin pattern. Finally, we present a new system: a magnetic liquid froth in two dimensions which is analogous to soap froths with an additional external control parameter, the magnetic field.

Adsorption from binary immiscible liquid mixture

AIChE JournalVolume 42, Issue 4 p. 1191-1194 R&D Note Adsorption from binary immiscible liquid mixture M. B. Rao, M. B. Rao Air Products and Chemicals, Inc., Allentown, PA 18195Search for more papers by this authorS. Sircar, Corresponding Author S. Sircar Air Products and Chemicals, Inc., Allentown, PA 18195Air Products and Chemicals, Inc., Allentown, PA 18195Search for more papers by this author M. B. Rao, M. B. Rao Air Products and Chemicals, Inc., Allentown, PA 18195Search for more papers by this authorS. Sircar, Corresponding Author S. Sircar Air Products and Chemicals, Inc., Allentown, PA 18195Air Products and Chemicals, Inc., Allentown, PA 18195Search for more papers by this author First published: April 1996 https://doi.org/10.1002/aic.690420434Citations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume42, Issue4April 1996Pages 1191-1194 RelatedInformation

An evaluation of the Doi–Ohta theory for an immiscible polymer blend

The theory developed by Doi and Ohta was evaluated for its ability to predict the rheology of an immiscible polymer blend. The theory describes the additional stresses arising as a consequence of interfacial tension in two phase systems in which the constituents consist of Newtonian fluids and have equal viscosities. The blend considered in this paper consisted of an immiscible mixture of poly(ethylene terephthalate) (PET) and nylon 6,6 at a composition ratio of 25/75 w/w PET/nylon 6,6. The rheological properties of this blend were found to be stable for the time frame required for the rheological experiments used in this work (e.g., <5 min). The Doi–Ohta theory was found to be capable of qualitatively predicting the extra stresses arising as a result of the interfacial tension as observed in the steady state viscosity and steady state first normal stress difference. The transient shear stress and first normal stress difference at the start up of steady shear flow were qualitatively predicted by the Doi–Ohta theory while the recovery of the initial overshoot observed experimentally was not. The overshoot observed experimentally during step‐up experiments and the undershoot observed during step‐down experiments were not predicted by the theory in which it was predicted that the stresses change monotonically with a stepwise change of the shear rate to the final steady state value. While the shear thinning behavior observed for this blend was not predicted by the theory, the scaling relation for the transient stresses predicted by the theory was found to hold for the blend using stepwise changes of shear rate at a constant step ratio.

Phase-stability lines, spinodals and distribution functions for binary immiscible mixtures

The phase-stability lines, the spinodals and the pair distribution functions for simple binary immiscible mixtures obtained from perturbation theory are improved by using Guggenheim's quasichemical approximation. The stability lines are compared with Gibbs ensemble simulations for corresponding systems of coexisting bulk phases. The quasichemical approximation is found to lead to a quantitative agreement with the Gibbs ensemble data, for three-dimensional as well as two-dimensional systems, away from the critical regions. The analytical quasichemical corrections to the pair distribution functions show a significant change in distribution, especially for the solute-solute particle distribution. The results are used to characterize the phase growth.

Growth kinetics in multicomponent fluids

The hydrodynamic effects on the late-stage kinetics in spinodal decomposition of multicomponent fluids are examined using a lattice Boltzmann scheme with stochastic fluctuations in the fluid and at the interface. In two dimensions, the three- and four-component immiscible fluid mixture (with a 1024{sup 2} lattice) behaves like an off-critical binary fluid with an estimated domain growth of t{sup 0.4 +/= 0.03} rather than t{sup 1/3} as previously estimated, showing the significant influence of hydrodynamics. In three dimensions (with a 256{sup 3} lattice), we estimate the growth as t{sup 0.96 +/= 0.05} for both critical and off-critical quenches, in agreement with phenomenological theory.

Kinetic Peculiarities of Adsorption Behavior of Polymer Mixtures

The adsorption kinetics of thermodynamically immiscible polymer mixtures on nonporous adsorbent, viz, fumed silica and fumed silica modified by diethylene glycol from a common solvent (CCl4), have been studied for a wide concentration range, including the crossover from dilute to semidilute regions (C < C*, C = C*, C >C*). Polystyrene (PS) and polybutyl methacrylate (PBMA) with different crossover concentrations have been studied. The structure of the adsorption layer has been characterized by the value of the fraction of bound segment (P) that provides insight into the conformation of adsorbed macromolecules. Comparison of these results with adsorption isotherms shows a reverse correlation between adsorption value and P, both for solutions of pure polymers and for their mixtures, for the case of a molecular aggregative mechanism of adsorption. It has been shown that the establishment of adsorption equilibrium in solutions of polymer mixtures occurs in two stages, namely, a fast stage and a slow stage. The character of kinetic dependencies is determined by the concentrations of components and the nature of the adsorbent. The main factors influencing the adsorption kinetics are the solution mode (diluted or semidiluted) and the thermodynamic compatibility of polymers in solution. For solutions of PS and PBMA mixtures at concentrations above C * the establishment of adsorption equilibrium is more prolonged. The existence of an entanglement network slows the adsorption processes.

Density profiles at a planar liquid-liquid interface

Molecular dynamics of liquid-liquid interface in an immiscible binary mixture of simple particles at low temperature and high pressure reveals stable equilibrium oscillatory structures in the density profiles of both components. The layering vanishes albeit slowly with the increase of the surface area but is not affected by an increase of the depths of bulk liquid layers. A simple Gaussian broadening predicts scaling of the oscillatory portion of the density profiles and good agreement is found. The width of the dip in the total density is also examined.

Thermodynamics of fluid-saturated porous media with a phase change

In the present paper some aspects of the thermodynamics of a fluid-saturated porous solid, taking into account the phase change of liquid into gas, are discussed. Based on the principles of the thermodynamics of irreversible processes, restrictions for the constitutive equations of the constituents are developed, in particular for the phase transition. The porous body is assumed to be incompressible and elastically deformed, and the pore space is filled with an immiscible liquid-gas mixture (moisture). The theory presented here provides some background that can be found suitable, e.g., for drying aspects.

ポリマーアロイ リサイクルのための混合樹脂のアロイ化技術

ポリマーアロイ リサイクルのための混合樹脂のアロイ化技術

Fluid trapping in mid-crustal reservoirs by H2O–CO2 mixtures

A THIN reservoir of free aqueous or carbonic fluids at mid-crustal levels, perhaps in the form of water sills1, has been suggested as the source of fault-transmitted metasomatizing fluids2–4, as the cause of observed deep crustal electrical conductivity and anomalous seismic reflectivity5, and as a lubricated potential detachment zone for thin-skin tectonics6. A problem with this hypothesis is that estimated crustal permeabilities are too high to permit long-term retention of such fluids7,8. Most mechanisms suggested for achieving the required permeability reduction rely on maintaining unusually low porosity 2,6,9,10. Because porosity creation, by tectonic deformation, fluid release or infiltration, is a ubiquitous process, permeability reductions achieved by these mechanisms are hard to sustain for long periods of time. A sealing (permeability reduction) mechanism that can operate in the presence of significant porosity is required. Here I propose that the required mechanism is capillary sealing by immiscible CO2-H2O mixtures derived from rising volatiles.

Morphology and dynamics of a separating immiscible binary liquid mixture under gravity

A homogeneous mixture of a phase separated binary liquid mixture is produced by mechanical mixing and the subsequent demixing process is studied experimentally. It is found that the morphology (e.g. which phase becomes the continuum phase) of the mixing zone depends not only on the relative volume fraction φ but may also depends on the relative affinity of the two coexisting phases at the container wall. We find a volume fraction range (transition range 0.4<φ<0.48) in which the morphology of the mixing zone is very complicated and the demixing rate measured in this range fluctuates from one experiment to another. An explanation, based on the higher affinity of the lower phase at the wall, is suggested to account for the shifted transition range from the symmetric value of φ = 0.5. The temperature dependence of the demixing rate is also investigated. The result is consistent with the diminishing density difference and the vanishing surface tension at the critical point as well as the change in the structure of the mixing zone.

Late stage dynamics of phase separation processes of binary mixtures containing surfactants

Late stage dynamics of phase separation processes of immiscible binary mixtures containing surfactants (amphiphilic molecules) is investigated by computer simulations on the hybrid model proposed by the present authors [T. Kawakatsu and K. Kawasaki, Physica A 167, 690 (1990)]. With use of this hybrid model, one can investigate large scale phenomena while retaining the intramolecular structures of surfactant molecules. Simulations are performed both for irregular bicontinuous and micellar domain formation processes taking the thermal fluctuation effects into account. In the very late stage, the coarsening of the domain structures is considerably slowed down both for bicontinuous and micellar domain formation processes due to the low interfacial tension of the surfactant–adsorbed interfaces. Scaled scattering structure functions are also calculated, which possess the characteristic features of the experimentally observed scattering functions of microemulsions and polymer blends containing amphiphilic block copolymers. We found that the calculated structure function for the system containing surfactants is different from that for the simple binary mixture without surfactant. Also reported are the important effects of thermal fluctuations on micellar domain structures, where the domain formation is considerably accelerated by the thermal fluctuation.