Effect of chain length distribution on the phase behavior of polyglycerol fatty acid ester in water

The effect of the chain length distribution on the phase behavior, the structure of liquid crystals, and physicochemical properties was investigated in water/ polyglycerol fatty acid ester. Polyglycerol fatty acid esters with sharply distributed polyglycerol (10G*0.7L) and with broadly distributed polyglycerol (10G0.7L) were used. Unreacted polyglycerol in both surfactants was removed. 10G*0.7L forms hexagonal liquid crystals at a higher concentration than 10G0.7L. The effective cross-sectional area of the lipophilic parts in the hexagonal phase of 10G0.7L is smaller than that of 10G*0.7L owing to the difference in the chain length distribution. Evidently, 10G0.7L molecules are tightly packed in aggregates; therefore, 10G0.7L decreased the surface tension more strongly and promoted emulsification. Received: 11 January 2000 Accepted: 8 March 2000     

Phase behavior of ethylene oxide-dimethylsiloxane PEO-PDMS-PEO triblock copolymers with water

Linear ethylene oxide-dimethylsiloxane PEO-PDMS-PEO triblock copolymers have been synthesized by hydrosilation of ,-dihydropoly(dimethylsiloxane) ) and -methyl--propargylpoly(ethylene oxide) . Studies by optical microscopy, complementary small-angle x-ray scattering (SAXS), and differential scanning calorimetry (DSC) have shown that the copolymers mixed with water are characterized by lyotropic liquid crystalline phases according to composition and temperature. The binary phase diagrams with varying copolymer composition are reported.     

Phase behavior of ternary mannosylerythritol lipid/water/oil systems

Due to the great importance of new therapeutic routes for morphine in pain treatment, several investigations are under development. In this way, the design of a liquid system for the oral administration of morphine would be of great help, especially in patients with difficulties in swallowing (children and elderly people). The systems studied in this work are kollidon^® SR microparticles, a biodegradable polymer classically used as excipient in the design of solid dosage forms, as vehicles for morphine. A detailed investigation of the capabilities of the polymer particles to load this drug at their surface is described. Electrophoretic mobility and optical absorbance determinations were used with this aim. The main factors determining the drug incorporation, after incubation of the microparticles in the morphine solutions, were the adsorption time, the type of electrolyte and its concentration, and the drug concentration. The optimum loading conditions were used to perform morphine release evaluations, finding that the release profiles were biphasic since the drug adsorbed was slowly released during 24 h after an initial burst release phase.     

Phase and rheological behavior of the polymerizable surfactant CTAVB and water

The phase and rheological behaviors of the polymerizable surfactant, cetyltrimethylammonium benzoate (CTAVB), and water as a function of surfactant concentration and temperature are investigated here. The critical micelle concentration (cmc) and the (cmc(2)), as well as the Krafft temperature (T(K)), are reported. A large highly viscous micellar solution region and hexagonal- and lamellar-phase regions were identified. The micellar solutions exhibit shear thickening in the dilute regime, below the overlapping or entanglement concentration. At higher concentrations, wormlike micelles form and the solutions show strong viscoelasticity and Maxwell behavior in the linear regime and shear banding flow in the nonlinear regime. The linear viscoelastic regime is analyzed with the Granek-Cates model, showing that the relaxation is controlled by the kinetics of reformation and scission of the micelles. The steady and unsteady responses in the nonlinear regime are compared with the predictions of the Bautista-Manero-Puig (BMP) model. Model predictions follow the experimental data closely.     

Phase equilibria and surfactant behavior of fluorinated ionic liquids with water

This work studies the phase equilibria and surfactant behavior of fluorinated ionic liquids (FILs) containing fluorinated chains equal to four carbons with water. The knowledge about the phase behavior is crucial for the applications of these novel FILs with tuneable properties. The phase equilibria of the binary mixtures FILs with water were studied at atmospheric pressure in a temperature range from (298.15 to 353.15) K. In this study, FILs containing ammonium, pyrrolidinium and imidazolium cations and the perfluorobutanesulfonate anion were included. The Non-Random Two Liquid (NRTL) thermodynamic model was successfully applied to rationalize the phase behavior of the binary (water + FILs) mixtures. Furthermore, the critical micelle concentrations (CMCs) of these FILs, which present cations and/or anions with surfactant properties were also performed at T = 298.15 K by measurements of the ionic conductivity. Finally, the Dynamic Light Scattering (DLS) was used with aim to determinate the size of the aggregates of these FILs in water.     

Phase behavior of capillary bridges: towards nanoscale water phase diagram

Water capillary bridges often condense at contact spots between small particles or asperities. The capillary adhesion force caused by these bridges is a major component of the attractive adhesion force, and thus it significantly affects the nanotribological performance of contacting surfaces. Recent atomic force microscope (AFM) measurements indicate that phase behavior of water in these tiny bridges may be different from macroscale water behavior. In particular, a metastable state with a deeply negative pressure, boiling at low temperatures, and ice at room temperature have been reported. Understanding these effects can lead to a modification of the traditional water phase diagram by creating a scale-dependent or nanoscale phase diagram.     

Phase behavior of a DNA-based surfactant mixed with water and n-alcohols

The self-assembly behavior of a cationic surfactant (dodecyltrimethylammonium, DTA) with DNA as counterion in mixtures of water and n-alcohols (decanol, octanol, hexanol, butanol, and ethanol) was investigated. The phase diagrams were established and the different regions of the phase diagram characterized with respect to microstructure by (2)H NMR, small-angle X-ray scattering (SAXS), and other techniques. The DNA-DTA surfactant is soluble in all of the studied alcohols, showing increased solubility from decanol down to ethanol. All of the phase diagrams are analogous with respect to the occurrence of liquid crystalline (LC) regions, but the area of the LC region increases as one goes from decanol to ethanol. In all phase diagrams, hexagonal phases (of the reversed type) for the alcohol-rich side and lamellar phases for the other side were detected. For balanced proportions of the components, there is a coexistence of the lamellar and the hexagonal phase, here detected with a double quadrupole splitting in the (2)H NMR spectra. The correctness of the phase diagrams is confirmed by the fact that along the tie-lines the splitting magnitude remains nearly constant. All of the alcohols except for ethanol act as cosurfactants penetrating the DNA-DTA film. Adding salt to the ternary mixtures causes an increase in the unit cell dimension of the lamellar and the hexagonal phases. The phase diagram becomes more complicated when butanol is used for the alcohol phase. Here, there is the occurrence of a new isotropic phase with some properties analogous to those of the disordered sponge (L3) phase obtained for simple surfactant systems.     

Phase behavior of n-octadecane in the form of water dispersion by the optical method

An aqueous dispersion of n-octadecane (n-C₁₈H₃₈) with a dispersed phase particle size of ～100 nm was prepared by ultrasonic dispersion method without the addition of surfactants. The temperatures of melting, crystallization and transitions to rotator phases were determined by the optical method (light scattering). The effect of surface crystallization was observed experimentally.     

Phase behavior of the quasiternary system N-methylmorpholine-N-oxide,water, and cellulose

The crystallization and melting behavior of the system N-methylmorpholine-N-oxide (MMNO)–H₂O–cellulose has been studied by differential scanning calorimetry, optical and electron microscopy, and x-ray scattering. The phase diagram of the MMNO–H₂O solvent system is reported up to a water content of 28% w/w. MMNO forms two crystalline hydrates, namely a monohydrate (13,3% w/w H₂O) and a hydrate comprising five molecules of crystal water per two MMNO molecules (28% w/w H₂O), which melts at 78°C and 39°C, respectively. The melting points of the various diluent crystals are strongly depressed in the presence of cellulose. For example, the solvent liquidus curve in the quasibinary system MMNO.1H₂O–cellulose can be described very well using the simple Flory–Huggins expression with an interaction parameter χ = ?3. Finally, the MMNO-rich part of the melting point/composition diagram of the quasiternary MMNO–H₂O–cellulose system is constructed and discussed.     

Phase behavior of charge stablized colloid dispersion with added water soluble polymers

Demixing and colloidal crystallization in the mixture of charge stabilized colloidal poly(methyl methacrylate) particles and soluble poly(ethylene oxide) were investigated by means of synchrotron small-angle X-ray scattering (SAXS) technique. Phase diagram of the mixture was obtained based on visual inspection and SAXS results. The phase behavior is determined as a function of the concentration of the polymer as well as the volume fraction of the colloidal particles. The system shows a one phase region when the concentration of the polymer is low, whereas a two-phase region is present when the concentration of the polymer is larger than a critical concentration at certain volume fraction of the colloids. Interestingly, a face centered cubic colloidal crystalline structure was formed under certain conditions, which has been rarely observed in experiments of colloid-polymer mixtures with competing interactions.     

Phase behavior of the lecithin/water/isooctane and lecithin/water/decane systems

The isothermal pseudo-ternary-phase diagram was determined at 25 degrees C for systems composed oflecithin, water, and, as oil, either isooctane or decane. This was accomplished by a combination of polarizing microscopy, small-angle X-ray scattering, and NMR techniques. The lecithin-rich region of the phase diagram is dominated by a lamellar liquid-crystalline phase (Lalpha). For lecithin contents less than 60% and low hydration (mole ratio water/lecithin = W0 < 5.5), the system forms a viscous gel of branched cylindrical reverse micelles. With increase in the water content, the system phase separates into two phases, which is either gel in equilibrium with essentially pure isooctane (for lecithin < 25%) or a gel in equilibrium with Lalpha (for lecithin > 25%). These two-phase regions are very thin with respect to water dilution. For 8 < W0 < 54 very stable water-in-oil emulsions form. It is only after ripening for more than 1 year that the large region occupied by the emulsion reveals a complex pattern of stable phases. Moving along water dilution lines, one finds (i) the coexistence of gel, isooctane and Lalpha, (ii) equilibrium between reverse micelles and spherulites, and, finally, (iii) disconnected reverse micelles that fail to solubilize water for W0 > 54. This results in a Winsor II phase equilibrium at low lecithin content, while for lecithin > 20% the neat water is in equilibrium with a reverse hexagonal phase and an isotropic liquid-crystalline phase. The use of the decane as oil does not change the main features of the phase behavior.     

Phase behavior for ternary systems composed of ionic liquid+saccharides+water

In this work, we proposed a new aqueous biphasic system composed of hydrophilic ionic liquids (IL, 1-butyl-3-methylimidazolium tetrafluoroborate) and saccharides, forming an upper IL-rich phase and a lower sugars-rich phase. It was found that that the distance between binodal curves and the origin is the increasing order of sucrose相似文献   

Phase behavior and viscoelastic properties of trisilanolcyclohexyl-POSS at the air/water interface

A trisilanol polyhedral oligomeric silsesquioxane (POSS), trisilanolcyclohexyl-POSS (TCyP), has recently been reported to undergo a series of phase transitions from traditional Langmuir monolayers to unique rodlike hydrophobic aggregates in multilayer films that are different from "collapsed" morphologies seen in other systems at the air/water interface. This paper focuses on the phase transitions and morphology of films varying in average thickness from monolayers to trilayers and the corresponding viscoelastic properties of trisilanolcyclohexyl-POSS molecules at the air/water interface by means of surface pressure-area per molecule (Pi-A) isotherms, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) measurements. The morphology studies by BAM reveal that the TCyP monolayer can collapse into different 3D structures by homogeneous or heterogeneous nucleation mechanisms. For homogeneous nucleation, analysis by Vollhardt et al.'s nucleation and growth model reveals that TCyP collapse is consistent with instantaneous nucleation with hemispherical edge growth at Pi = 3.7 mN.m(-1). Both surface storage (Gs') and loss (Gs") moduli obtained by ISR reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms: (A) A viscous liquidlike "monolayer"; (B) a "biphasic regime"between a liquidlike viscous monolayer and a more rigid trilayer; and (C) an elastic solidlike "trilayer". These observations provide interesting insights into collapse mechanisms and structures in Langmuir films.     

Phase behavior of a phospholipid/fatty acid/water mixture studied in atomic detail

Molecular dynamics simulations have been used to study the phase behavior of a dipalmitoylphosphatidylcholine (DPPC)/palmitic acid (PA)/water 1:2:20 mixture in atomic detail. Starting from a random solution of DPPC and PA in water, the system adopts either a gel phase at temperatures below approximately 330 K or an inverted hexagonal phase above approximately 330 K in good agreement with experiment. It has also been possible to observe the direct transformation from a gel to an inverted hexagonal phase at elevated temperature (approximately 390 K). During this transformation, a metastable fluid lamellar intermediate is observed. Interlamellar connections or stalks form spontaneously on a nanosecond time scale and subsequently elongate, leading to the formation of an inverted hexagonal phase. This work opens the possibility of studying in detail how the formation of nonlamellar phases is affected by lipid composition and (fusion) peptides and, thus, is an important step toward understanding related biological processes, such as membrane fusion.     

Phase behavior of an extended surfactant in water and a detailed characterization of the concentrated phases

The formation of microemulsions with triglycerides at ambient conditions can be improved by increasing the surfactant-water and surfactant-oil interactions. Therefore, extended surfactants were developed, which contain hydrophilic/lipophilic linkers. They have the ability to stretch further into the oil and water phase and enhance the solubility of oil in water. In this work, the phase behavior of a chosen extended surfactant (C(12-14)-PO(16)-EO(2)-SO(4)Na, X-AES) in H(2)O/D(2)O at high surfactant concentrations (30-100 wt %) and at temperatures between 0 and 90 °C is studied for the first time. The lyotropic liquid crystals formed were determined by optical microscopy, small-angle X-ray scattering (SAXS), and (2)H and (23)Na NMR, and a detailed phase diagram of the concentrated area is given. The obtained mesophases are a hexagonal phase (H(1)), at low temperatures and small concentrations, a lamellar phase (L(α)) at high temperatures or concentrations, a bicontinuous cubic phase (V(2)) as well as a reverse hexagonal phase (H(2)). To our knowledge, this is the first surfactant that forms both H(1) and H(2) phases without the addition of a third compound. From the (2)H NMR quadrupole splittings of D(2)O, we have examined water binding in the L(α) and the H(2) phases. There is no marked difference in the bound water between the two phases. Where sufficient water is present, the number of bound water molecules per X-AES is estimated to be ca. 18 with only small changes at different temperatures. Similar results were obtained from the (23)Na NMR data, which again showed little difference in the ion binding between the L(α) and the H(2) phases. The X-ray diffraction data show that X-AES has a much smaller average length in the L(α) phase compared to the all-trans length than in the case for conventional surfactants. At very high surfactant concentrations an inverse isotropic solution (L(2)), containing a small fraction of solid particles, is formed. This isotropic solution is clearly identified and the size of the reversed micelles was determined using (1)H NMR measurements. Furthermore, the solid particles within the L(2) phase and the neat surfactant were analyzed. The observed results were compared to common conventional surfactants (e.g., sodium dodecyl sulfate, sodium lauryl ether sulfate, and sodium dodecyl-p-benzene sulfonate), and the influence of the hydrophilic/lipophilic linkers on the phase behavior was discussed.     

Phase behavior studies of quaternary systems containing N-lauroyl-N-methylglucamide/alcohol/alkane/water

The three-phase behavior of quaternary systems comprising N-lauroyl-N-methylglucamide (MEGA-12)/alcohol/alkane/water has been studied using epsilon-beta fishlike phase diagrams. From the epsilon-beta fishlike phase diagrams a series of phase inversions Winsor I (2) --> III (3) --> II (2) were observed, and the hydrophilic-lipophilic balanced (HLB) plane equation for the quaternary system was deduced. Some physicochemical parameters, such as the mass fraction of alcohol in the HLB interfacial layer, A S, the coordinates of the start (beta B, epsilon B) and end points (beta E, epsilon E) of the middle-phase microemulsion, the mass fractions of MEGA-12 and alcohol in the total system (C S and C A), and the solubilities of MEGA-12 and alcohol in oil phase (S O and A O), were calculated. The effects of different alcohols, alkanes, and NaCl concentrations in the aqueous phase on the phase behavior and solubilization capacity were investigated, which indicates that alcohol with longer and alkane with shorter hydrocarbon chains have a larger solubilization capacity. NaCl concentration has little influence on the phase behavior.     

Phase behavior of bile acid/lipid/water systems containing model dietary lipids

Dietary lipids are solubilized in bile acid micelles in the small intestine. In the present study, we investigate the phase behavior of bile acid/model rapeseed oil (or model beef tallow)/water systems to predict interfacial phenomena during consumption of a variety of foods. The structures of molecular assemblies are identified based on polarizing microscope images, wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). The results of in vitro tests suggest that an increase in the intake of model rapeseed oil causes the formation of multi-lamellar vesicles and lamellar liquid crystals. The molecules in the lamellar liquid crystal are formed highly ordered layer structure with the spacing of 8.8 nm along the c-axis, while monoclinic packed structure is constructed as two-dimensional structure in ab-plane due to bulky molecular structures of bile acid and unsaturated fatty acid. When the model beef tallow composition in the model system is more than several wt.%, stearic acid crystals are extracted. Moreover, bicarbonate ions are important ingredients to solubilize >10 wt.% of the model lipids. These phase transitions might be induced by the addition of dietary lipids in vivo during the consumption of oil or meat. Our findings are significant for understanding the lipid absorption process in the small intestine, and for developing medical and healthcare products.