Excess Water Phases Research Articles

Two Types of Phase Behavior in a Water/Nonionic Surfactant/Triglyceride System

Two types of phase behavior were observed in a water/nonionic surfactant/triglyceride sys-tem. One type was the same as that noted in a water/nonionic surfactant/hydrocarbons system in which a surfactant phase, D, coexists with excess water and oil phases at a certain temperature. The other type was typically observed in a water/nonionic surfactant/amphiphilic oil such as long-chain alcohols. That is, a lamellar liquid crystal coexists with an oil phase at lower tem-perature. With increase in temperature, liquid crystals melt and the melted phase (another sur-factant phase, D') forms a three-phase region together with the water and oil phases. Each of these two types of phase behavior is dependent on the types of surfactant and triglycerides and can be changed by addition of propanol.

An Empirical Model for Microemulsion Phase Behavior

Summary An empirical model for microemulsion phase behavior has been developed that is based on proper choice of pseudocomponents. Previous attempts to represent phase behavior of surfactant/oil/brine systems with three pseudocomponents have been unsuccessful. One of the problems has been salt fractionation between the microemulsion and excess water phases. It was found that through the use of a sulfonate/water pseudocomponent, this effect could be handled, and the system then exhibited true ternary behavior. When this pseudocomponent was used, a single set of Vo/VS and Vw/Vs-vs.-salinity curves was found to be valid for a wide range of overall compositions. These solubilization-parameter curves were fit with empirical equations, and it is these that comprise the model. The basis for a sulfonate/water pseudocomponent is discussed using electrical double-layer theory. In addition, solubilization-parameter curves generated from spherical microemulsion models are compared with the experimental curves.

Phase Behavior of Two Types of Isotropic Surfactant Phases in a Brine/Sodium Dodecyl Sulfate/Hexanol/Hexadecane System

Two types of isotropic surfactant phases (microemulsions) were found in a brine/sodium dodecyl sulfate (SDS) /hexanol/hexadecane system, and their phase behavior was systematically investigated.In the system of water/SDS/hexanol, lamellar liquid crystals (L.C.) coexisted with excess water (W) and oil (alcohol; Om) phases under the condition of an exact balance between hydrophile-lipophile constituents of the mixed surfactant (SDS+hexanol). The addition of salt caused the L.C. to turn into an isotropic surfactant phase (D') coexisting with W and Om, a reversed micellar solution phase. With the addition of hexadecane, the Om phase split into an excess oil phase (O) and surfactant phase (D) in which large amounts of oil and water, were solubilized; the latter is known as a middle-phase microemulsion. The solubilization of hexadecane in the D' phase was only slight, and its composition remained in the vicinity of brine-SDS-hexanol plane. Two three-phase regions, W+D+O and W+D'+Om (or D) were formed independently at higher temperature, but they overlapped and four coexisting phases (W+D'+D+O) were observed in a certain range of lower temperature.L.C., D', and D phases appeared at an exact balance of hydrophile-lipophile constituents of the surfactant in a diluted region, but the order of surfactant molecular assembly reverted from the L.C. to D phase by way of the D' phase.

Partitioning of Nonionio and Anionic Surfactant Mixtures Between Oil/Microemulsion/Water Phases

Summary Mixtures of different surfactant types have been proposed for application in polymer/micellar flooding processes. In some cases, severe fractionation of such mixtures is found even in short core experiments. In this paper, a new theory of surfactant partitioning between phases is developed and tested. Polydisperse nonionic surfactants blended with an anionic surfactant are considered. Important parameters in the theory are the critical micelle concentrations (CMC's) of surfactant mixtures in water and the partition. coefficients of the surfactant between oil and water measured at total surfactant concentrations less than the CMC. From these simple experiments, surfactant fractionation in microemulsion systems can be modeled. We also show that the fractionation of polydisperse ethoxylated nonionic surfactants between excess oil and water phases is not as severe in the presence of anionic surfactants as it is in systems containing only nonionic surfactants.

2H-nuclear magnetic resonance investigations on phospholipid acyl chain order and dynamics in the gramicidin-induced hexagonal HII phase

The following results are reported in this paper: The interaction of gramicidin with [11,11-2H2]dioleoylphosphatidylcholine (DOPC) and [11,11-2H2]dioleoylphosphatidylethanolamine (DOPE) at different stages of hydration was studied by 2H- and 31P-nuclear magnetic resonance. In the L alpha phase in excess water the acyl chains of phosphatidylethanolamine (PE) are more ordered than phosphatidylcholine (PC) most likely as the result of the lower headgroup hydration of the former lipid. In excess water gramicidin incorporation above 5 mol % in DOPC causes a bilayer----hexagonal HII phase change. In the HII phase acyl chain order is virtually unaffected by gramicidin but the peptide restricts the fast chain motions. At low water content gramicidin cannot induce the HII phase but it markedly decreases chain order in the DOPC bilayer. Increasing water content results in separation between a gramicidin-poor and a gramicidin-rich L alpha phase with decreased order of the entire lipid molecule. Further increase in hydration reverts at low gramicidin contents the phase separation and at high gramicidin contents results in a direct change of the disordered lamellar to the hexagonal HII phase. Gramicidin also promotes HII phase formation in the PE system but interacts much less strongly with PE than with PC. The results support our hypothesis that gramicidin, by a combination of strong intermolecular attraction forces and its pronounced cone shape, both involving the four tryptophans at the COOH-terminus, has a strong tendency to organize, with the appropriate lipid, in intramembranous cylindrical structures such as is found in the HII phase.

Metabolic changes of membrane lipid composition in Acholeplasma laidlawii by hydrocarbons, alcohols, and detergents: arguments for effects on lipid packing.

The packing of lipids into different aggregates, such as spheres, rods, or bilayers, is dependent on the hydrophobic volume, the hydrocarbon-water interfacial area, and the hydrocarbon chain length of the participating molecules, according to the self-assembly theory [Israelachvili, J. N., Marcelja, S., & Horn, R. G. (1980) Q. Rev. Biophys. 13, 121-200]. The origin of the participating molecules should be of no importance with respect to their abilities to affect the above-mentioned parameters. In this investigation, Acholeplasma laidlawii, with a defined acyl chain composition of the membrane lipids, has been grown in the presence of three different classes of foreign molecules, known to partition into model and biological membranes. This results in an extensive metabolic alteration in the lipid polar head group composition, which is expressed as changes in the molar ratio between the lipids monoglucosyldiglyceride (MGDG) and diglucosyldiglyceride (DGDG), forming reversed hexagonal and lamellar phases in excess water, respectively. The formation of nonlamellar phases by A. laidlawii lipids depends critically upon the MGDG concentration [Lindblom, G., Brentel, I., Sjölund, M., Wikander, G., & Wieslander, A. (1986) Biochemistry (preceding paper in this issue)]. The foreign molecules tested belong to the following groups: nonpolar organic solvents, alcohols, and detergents. Their effects on the gel to liquid crystalline phase transition temperature (Tm), on the order parameter of the acyl chains, and on the phase equilibria between lamellar and nonlamellar liquid crystalline phases in lipid-water model systems are known in several instances.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between surfactant phase behavior and the creaming and coalescence of macroemulsions

Macroemulsions are inherently thermodynamically unstable systems which exhibit lifetimes which depend on the initial state of the system and the rates of creaming and coalescence. A previous study has shown an apparent relationship of emulsion stability to the thermodynamic equilibrium) phase behavior of systems containing surfactant/hydrocarbon/water M. Bourrel, A. Graciaa, R. S. Schechter, and W. H. Wade, J. Colloid Interface Sci. 72, 161 (1979)) . It was found that macroemulsions are most stable at the boundaries which separate two phase systems from those which form three phases consisting of a microemulsion in equilibrium with excess hydrocarbon and water phases. The present investigation shows that on approaching the three-phase boundaries those factors, such as the density difference between phases, the continuous phase bulk viscosity, and the surface viscosity, which tend to influence the rate of creaming, all act to decrease it. Hence at the phase boundary creaming is shown to be a slow step, thereby causing the emulsion to appear to be stable. It was also found that, despite the fact that the surface viscosity is maximum at the boundaries, coalescence becomes more rapid as the boundaries are approached. Thus, while the time scale for creaming increases, that for coalescence decreases. Overall, then, macroemulsions formed well away from the phase boundaries cream first, but persist longest. Within the three-phase region where the surfactant system is balanced equal concentrations of surfactant in the excess phases) coalescence proceeds at a remarkable, but unexplained, speed. In this region macroemulsions coalesce before they cream and emulsion stability is least. These observations are shown to apply to systems in the presence of varying quantities of alcohol. The phase behavior was adjusted by varying the electrolyte concentrations.

Phase Behavior and Properties of a Petroleum Sulfonate Blend

Abstract A sulfonate system composed of Stepan Petrostep™ 465, Petrostep 420, and 1-pentanol was investigated. The system was found to give ultralow interfacial tension against crude oil in a reasonable range of salinity and sulfonate concentrations. It also was found that sulfonate partitioned predominantly into the microemulsion phase. However, a significant amount also partitioned into water and, at high salinity, into the oil phase. On the other hand, the oil-soluble 1-pentanol partitioned mostly into oil and microemulsion phases. The interfacial tension between excess oil and water phases was ultralow, in the range of 10−3 mN/m. The tensions were close to and paralleled those between the middle and water phases. The trend remained the same even when the alcohol content changed. This means that in the salinity range that produces a three-phase region, below the optimal salinity, the water phase effectively displaces both oil and middle phases, even though the oil may not be displaced effectively by the middle phase. The implication is that, from an interfacial tension point of view, the oil recovery would be more favorable in the salinity range below the optimal salinity with the mixed petroleum sulfonate system used here. This was confirmed by oil recovery tests in Berea cores. It also was concluded that the change in viscosity upon microemulsion formation might have a significant influence on the surfactant flood performance.

Mixing Rules for Optimum Phase-Behavior Formulations of Surfactant/Oil/Water Systems

Abstract Many formulations used in surfactant flooding involve blends of surfactants designed to glue the best oil-recovery efficiency. Because oil-recovery efficiency usually is presumed to relate closely to surfactant/brine/oil phase behavior, it is of interest to understand the effect of mixing surfactants or of mixing oils on this phase behavior.We show that a correlation defining optimal behavior as a function of salinity, alcohol type and concentration, temperature, WOR (water/oil ratio), and oil type can be extended to mixtures of sulfonated surfactants and to those of sulfonates with sulfates and of sulfonates with alkanoates, provided the proper mixing rules are observed. provided the proper mixing rules are observed. The mixing rules apply to some mixtures of anionic and nonionic surfactants, but not to all. These mixtures exhibit some properties that may be of practical interest, such as increased salinity and practical interest, such as increased salinity and temperature tolerance. Introduction Recent studies have shown that formulation of the surfactant/brine/oil system is a key factor governing the performance of microemulsions designed to recover residual oil. These studies demonstrate that all optimal formulations exhibit characteristic properties that are remarkably similar. In general, properties that are remarkably similar. In general, the optimal microemulsion can solubilize large quantities of oil and connate water; in the presence of excess quantities of oil and water, a third surfactant-rich middle phase is formed. The interfacial tensions (IFT's) between the excess phases and the surfactant-rich phase are both low - about 10 dyne/cm (10 mN/m). Given an oil/brine system from a particular reservoir, one can achieve this formulation by varying the surfactant or the cosurfactant. Different oils, brines, or temperatures require formulations correspondingly altered to maintain optimal conditions. Previous studies have shown that the three-phase region exists over a range of values when one parameter, such as cosurfactant concentration, parameter, such as cosurfactant concentration, salinity, temperature, etc., is varied systematically (often called a scan). Thus, some ambiguity may exist with regard to the selection of those parameters representing the optimal formulation. Clearly, the optimum is that which recovers the most oil. However, tests are laborious, difficult to reproduce precisely, and sensitive to other factors, such as precisely, and sensitive to other factors, such as mobility, surfactant retention, wettability, etc. Therefore, it is desirable to impose an alternative definition that can be used for screening, though the final design still is dictated by core floods.Healy and Reeds have shown that the optimal formulation for oil recovery closely corresponds to that for which the IFT's between the excess oil and water phases and the surfactant-rich phase are equal. An almost equivalent criterion also was shown to be that point in the three-phase region for which the volume of oil solubilized into the middle phase equals the volume of brine. Furthermore, Salager et al. have used still another criterion that seems to be essentially equivalent to those used by Healy and Reed - an optimal salinity is defined as the midpoint of the salinity range for which the system exhibits three phases.These criteria are useful because they permit the screening of microemulsion systems using simple laboratory tests. SPEJ P. 271

Effects of salinity on the viscosity and birefringence of a microemulsion system

Oil/water/surfactant systems form complex equilibrium phases which are sensitive to a number of parameters, including amount and concentration of cosurfactant (often an alcohol), salinity, and temperature. If one of these variables is changed systematically as, for example, the salinity, an interesting transition may be observed in which at low salinities a microemulsion is in equilibrium with an excess oil phase, at moderate salinities a middle phase microemulsion is in equilibrium with both excess oil and excess water phases, and at higher salinities brine is in equilibrium with a microemulsion phase. To help elucidate the structure of the microemulsion, studies of viscoelasticity and streaming birefringence in oscillatory shear flow have been conducted of a middle phase-forming system as a function of salinity. It is found that the viscoelastic properties of the microemulsions are unchanged for shear rates varying from 0.1 to 100 sec −1. Both the birefringence and the viscosity maximize near the salinity marking the transition from lower phase to middle phase microemulsion. Further inflections in these properties occur at a salinity marking the midrange of the middle phase microemulsion. For all cases the dominent relaxation time is near 3 to 5 msec while the birefringence changes by two orders of magnitude. The birefringence is a sensitive indicator of the elastic structure of the microemulsion.

Ternary Phase Diagram for Aerosol OT/Water/Oil System

The ternary phase diagram for purified Aerosol OT (AOT) /water/benzene system has been studied at 25 and 50°C. Aqueous micellar solution phase (Wm), lamellar liquid crystalline phase and nonaqueous reversed micellar solution phase (Om) can solubilize a large amount of oil or water respectively at 50°C but small at 25°C. This marked change occured discontinuously around at 40°C in benzene system. HLB of AOT is almost unchanged with temperature, but becomes lipophilic with increasing the water/AOT ratio. On the other hand, in the presence of added salt (NaCl), Wm+excess oil phase exists at higher temperature, and Om+excess water phase exist at lower temperature. At an optimum temperature, brine containing 0.5 wt% of NaCl and 2, 2, 4-trimethyl pentane can dissolve each other in arbitrary ratios with only 3.5 wt%/system of AOT. In this case, AOT becomes relatively hydrophilic with increasing temperature.

Structure des phases liquide-cristallines de différents phospholipides, monoglycérides, sphingolipides, anhydres ou en présence d'eau

X-Ray diffraction studies have been carried out on some lipids of various chemical compositions: two monoglycerides (glyceryl-monodecanoate and glyceryl-monododecanoate), several phospholipids (synthetic di-palmitoyllecithin, egg lecithin, lysolecithin derived from the latter, egg phosphatidylethanolamine) and sphingolipids (sphingomyelin and cerebrosides isolated from beef brain) have been studied. The structure of these lipid-water systems depends on concentration and temperature: crystalline phases are formed at low temperatures, whereas higher temperatures and high lipid content promote the formation of liquid-crystalline phases. At low lipid content and high temperature, only lysolecithin forms a micellar solution in water; for the other lipids, a suspension of a liquid-crystalline phase in excess water is observed. Four liquid-crystalline phases, already described in other soap or lipid systems, have been observed here. 1. (a) A lamellar phase occurs in the following systems: water-monoglyceride (monodecanoate: 25 °C; monododecanoate: 45 °C); water-sphingomyelin (45 °C); water-cerebrosides (72 °C); water-phosphatidylethanolamine (20 °C); water-egg lecithin (5 to 35 °C) and anhydrous lecithin at high temperature. 2. (b) A hexagonal phase, made of a regular array of lipid cylinders, is observed in the water-lysolecithin system at 35 °C. 3. (c) An inverted hexagonal phase (cylinders made of water) occurs in the water-phosphatidylethanolamine system at 55 °C. 4. (d) A cubic phase is observed in anhydrous lecithin at high temperature. The structural parameters of these phases and the polymorphism of the various lipids are discussed.