Phase Behavior Of Such Systems Research Articles

Robust Phase Behavior of Model Transient Networks

In order to study the viscoelastic properties of certain complex fluids which are described in terms of a multiconnected transient network we have developed a convenient model system composed of microemulsion droplets linked by telechelic polymers. The phase behavior of such systems has two characteristic features: a large monophasic region which consists of two sub-regions (a fluid sol phase and a viscoelastic gel phase) separated by a percolation line and a two phase region at low volume fraction with separation into a dilute sol phase and a concentrated gel phase. From the plausible origin of these features we expect them to be very similar in different systems. We describe here the phase behavior of four different systems we prepared in order to vary the time scale of the dynamical response of the transient network; they consist of the combination of two oil(decane) in water microemulsions differing by the stabilizing surfactant monolayer (Cetyl pyridinium chloride/octanol or TX100/TX35) and of two telechelic polymers which are end-grafted poly (ethylene oxide) chains, differing by the end-grafted hydrophobic aliphatic chains (C12H25 or C18H37).

Phase behavior of three-component ionic fluids

We study the phase behavior of solutions consisting of positive and negative ions of valence z to which a third ionic species of valence Z>z is added. Using a discretized Debye-Hueckel theory, we analyze the phase behavior of such systems for different values of the ratio Z/z. We find, for Z/z>1.934, a three-phase coexistence region and, for Z/z>2, a closed (reentrant) coexistence loop at high temperatures. We characterize the behavior of these ternary ionic mixtures as function of charge asymmetry and temperature, and show the complete phase diagrams for the experimentally relevant cases of Z/z=2 and Z/z=3, corresponding to addition of divalent and trivalent ions to monovalent ionic fluids, respectively.

Equilibrium conditions for the hydrogen sulfide hydrate formation in the presence of electrolytes and methanol

AbstractNatural gas industry encounters systems that consist of gases like CO2 and H2S, and aqueous solutions of methanol and mixed electrolytes. A knowledge of the phase behavior of such systems, including hydrate formation, is essential in gas production and the design of facilities for gas transportation and processing. Recently, Dholabhai et al. (1997, 1996) and Bishnoi and Dholabhai (1998) described equilibrium conditions for CO2 and gas mixtures containing CO2 in the presence of methanol, electrolytes and ethylene glycol. In the present work aqueous three phase (aqueous liquid solution, vapor and incipient hydrate) equilibrium conditions of H2S hydrate formation in aqueous solutions of electrolytes and methanol are measured in the temperature range of 272 to 294 K and pressure range of 0.3 to 1.0 MPa. A ‘full view’ sapphire variable volume cell with a movable piston is used to obtain the experimental data.

Aqueous two-phase systems containing urea: influence on phase separation and stabilization of protein conformation by phase components.

During recombinant Escherichia coli fermentation with high expression levels, inclusion bodies are often formed. Aqueous two-phase systems have been used in the presence of urea for the initial recovery steps. To investigate phase behavior of such systems we determined phase diagrams of poly(ethylene glycol) (PEG)/sodium sulfate/urea/water and PEG/dextran T-500 (DEX)/urea/phosphate buffer/water at different concentrations of urea and different molecular weight of PEG. PEG/Na2SO4 aqueous two-phase systems could be obtained including up to 30% w/w urea at 25 degrees C and PEG/dextran T-500 up to 35% w/w urea. The binodial was displaced toward higher concentrations with increasing urea concentrations. The partition coefficient of urea was near unity. An unstable mutant of T4-lysozyme with an amino acid replacement in the core (V149T) was used to analyze the effect of phase components on the conformation of the enzyme. We showed that partitioning of tryptophan was not dependent on the concentration of urea in the phase system.

Thermodynamics of polymer solutions and blends

AbstractPolymerization reactions are quite often accompanied by liquid‐liquid phase separations. Processing of polymer blends is commonly also based on the phase behaviour of the system; for some applications homogenous blends are to be obtained while for other two‐phase systems are desired. Experimental methods suitable for gaining insight into the thermodynamic behaviour in such viscous systems will be discussed and some relevant measurements, performed by equilibrium methods, will be shown.Classic thermodynamic equilibrium considerations, based on simple molecular models lead to useful descriptions and predictions of the phase behaviour of partially miscible polymer systems. Depending on the amount of experimental information and on the complexity of the polymeric system, predictions will be more or less quantitative. Solubility parameter and group contribution approaches present the first level, and such predictions indicate whether a system is miscible or not.The second level of description is given by Flory‐Huggins‐Staverman approaches. These models call for some experimental evidence but permit estimation of the location of miscibility gaps and their dependence on the polymer molar mass. The concentration ranges of the demixed region are usually not well presented by these models.The quality of the description is improved considerably when the disparity of size and shape between the repeat units of the polymer and solvent constituents are taken into account. On this third level the influence of pressure can be included in the model and reasonable descriptions of the P‐T‐x space can be obtained.Extensions to copolymer systems are being developed nowadays, but still fail to give quantitative representation of the actual complex phase behaviour of such systems.

The phase behavior of systems of the type H 2O-oil—nonionic surfactant—electrolyte

In a recent publication we have suggested to study “simple” systems of the type H 2O-oil-nonionic surfactant-electrolyte as a model for the pseudoquaternary systems relevant in tertiary oil recovery, in order to make qualitative predictions for the phase behavior of such systems. In this paper the first part of the results of such investigations is presented. It is shown in detail how the formation of a three-phase triangle emerges from the change of the phase diagrams of such systems with temperature. The predictions are compared with experiments using simple surfactants. It turns out that these studies can lead to an understanding of the phase behavior of the more complicated real systems.

Thermodynamics of spreading from binary systems

An exact thermodynamic analysis of the equilibrium spreading behavior of binary systems of insoluble monolayer-forming substances has been developed. The analysis includes consideration of most types of possible phase behavior for such systems. The derived equations relate the equilibrium spreading pressures of binary systems to the equilibrium spreading pressures of the pure components and the surface pressure vs area isotherms for the pure and mixed monolayers. The extreme sensitivity of measurements of the spreading pressures of crystalline material to the presence of impurities is also discussed and is illustrated by an experimental example.

Phase behavior of multicomponent fluids

The phase behavior of a system of five or more components cannot be totally represented in three dimensional space. The most common method of projection representing the phase behavior of such systems employs a smaller number of ’’pseudocomponents.’’ Such a representation must be chosen with care because the multiphase region is less well defined than that of the corresponding true component system. Several examples are discussed in which ambiguous results are obtained when a system is treated as if it consisted of an incomplete set of pseudocomponents. The ordinary lever rule has been generalized to apply to three-phase systems, making it possible to calculate the mass fractions of three phases from their compositions. For true ternary systems this lever rule can be inverted to yield the compositions of the three phases in terms of the mass fractions at three observation points. For more than three observations on pseudoternary systems the deviations from true component behavior can be estimated from the spread in the calculated phase compositions obtained from different triplets. The method is illustrated for a true ternary system and two pseudoternary systems. The lever rule and its inverse may also facilitate an approach to a tricritical point where three fluid phases become identical.

Some recent studies on the structural arrangements of lipids in surface layers and interphases

The surface chemistry studies carried out in our laboratory can be traced back to the Department of Colloid Science in Cambridge, England, where one of the present authors spent a year as a student just thirty years ago, working with Prof. (now Sir) E. K. Rideal and Dr. J. H. Sehulman. The original aim was to explore the possibilities of the monolayer technique in the elucidation of the structure of some complex lipid molecules of bacterial origin, viz., phthiocerol (1), the so-called phthioic acid (2), and certain other fatty acids (3). These structure problems were later solved by mass spectrometry (cf. 4) but the monolayer work led to the discovery of new phases in condensed monolayers (5, 6), and the use of the surface phase diagram for the deterruination of the composition of mixtures of fatty acids was demonstrated (7). The relation between the different twodimensional monolayerphases observed and the arrangement of the molecules in the three-dimensional crystal has been the subjeer of discussion (8-10). These problems have been studied in our laboratory in recent years (11). Detailed monolayer studies together with X-ray crystal structure studies have now led to a fairly complete correlation between monolayer states and three-dimensional crystalline arrangements of long-chain molecules. The extension of previous X-ray single crystal structure studies of glycerides carried out in this laboratory (12) to glyceridewater systems (13) has given new infermarion about the phase behavior of such systems. The newly developed electron spectroscopy of nonbinding electrons in the inner shells (14) has recently been applied to Langmuir-Blodgett multi]ayers (15). It seems likely that this technique will become a very important tool in studies of surface layers.

Volumetric Behavior of Oil and Gas From a Louisiana Field I

Abstract An experimental investigation was conducted upon five different pairedsamples of oil and gas from a field in Louisiana. The study, with each pair ofsamples, included the measurement of the formation volume and the volume of theliquid phase for three mixtures of the oil and gas. The gas-oil ratio variedfrom approximately 200 to over 40,000 cu ft per bbl and measurements were madeat temperatures between 40' and 250'F. The gravity of the tank oil for the fivesamples under investigation varied between 38.0? and 55.8? API. The composition of the oil and gas samples and their mixtures is submitted intabular form. A number of diagrams depicting the effect of temperature andgas-oil ratio upon retrograde dew-point pressure are presented. Introduction During the past two decades a fairly large number of investigations were madeof the volumetric behavior of naturally occurring hydrocarbon mixtures. Theearlier work of Beecher and Parkhurst and a more recent report on samples fromDominguez Field are typical of research of this nature. Such studies have beenused in estimating the volumetric behavior of fluids in producing fields otherthan those from which samples were taken. Progress has been made in correlatingthe influence of pressure, temperature, and composition upon the specific andformation volume of hydrocarbon mixtures of relatively low gas-oil ratios, butattempts to extend this correlation to higher ratios have not been particularlysuccessful. The influence of composition upon the volumetric behavior of suchsystems cannot be simply related to a single parameter such as gas-oil ratio.In order to aid in the extension of the correlation, of the volumetric behaviorof mixtures of oil and gas to higher ratios, a rather complete study was madeof five different pairs of samples from a Louisiana field. The complexity ofthe influence of composition upon the volumetric and phase behavior of suchsystems in the regions of retrograde condensation was indicated by earlierwork, and it is doubtful if simple correlations can be established in theseregions with the information currently available. The terminology employed inthis paper is identical to that utilized earlier. T.P. 2950