Viscous Isotropic Phase Research Articles

Effect of ionic surfactants on the phase behavior and structure of sucrose ester/water/oil systems

The phase behavior and structure of sucrose ester/water/oil systems in the presence of long-chain cosurfactant (monolaurin) and small amounts of ionic surfactants was investigated by phase study and small angle X-ray scattering. In a water/sucrose ester/monolaurin/decane system at 27 °C, instead of a three-phase microemulsion, lamellar liquid crystals are formed in the dilute region. Unlike other systems in the presence of alcohol as cosurfactant, the HLB composition does not change with dilution, since monolaurin adsorbs almost completely in the interface. The addition of small amounts of ionic surfactant, regardless of the counterion, increases the solubilization of water in W/O microemulsions. The solubilization on oil in O/W microemulsions is not much affected, but structuring is induced and a viscous isotropic phase is formed. At high ionic surfactant concentrations, the single-phase microemulsion disappears and liquid crystals are favored.

Lyotropic liquid crystalline phase behavior and structure of cesium n-tetradecanoate-water mixtures

The compositional sequence and microstructure of liquid crystalline phases formed by binary mixtures of cesium n-tetradecanoate (CsTD) and water (deuterium oxide) were studied from 297 to 338 K and from 35 to 95 wt% surfactant. The experimental methods used were deuterium ( 2H) quadrupole nuclear magnetic resonance (NMR) spectroscopy and optical polarizing microscopy. The Krafft boundary in the CsTD-water system is about 2–5°C, more than 45° lower than that in the comparable sodium n-tetradecanoate-water system. The structured surfactant phases observed were micellar; normal hexagonal; ribbon, a viscous birefringent phase of biaxial symmetry; viscous isotropic; and lamellar. The ribbon phase structure was deduced from the biaxial deuterium NMR spectral lineshape and by the contiguity of hexagonal and ribbon phases. This phase has not been observed previously by quadrupole NMR spectroscopy in a simple binary surfactant-water system. The phase transition from hexagonal to ribbon (ca. 65 wt%) is apparently second order as indicated by the lack of an observable two-phase region. A higher order transition is consistent with the proposed continuous variation in microstructure from rodlike aggregates to those of ribbonlike symmetry. The viscous isotropic phase, which has been observed in mixtures of potassium dodecanoate or sodium octanoate with water, was stable at temperatures above 310 K, at a composition of about 70 wt% CsTD. The lamellar phase is stable to very high surfactant concentrations at modest temperatures, >95 wt% CsTD at 338 K. The change in counterion from sodium to cesium lowers the Krafft temperature, enabling the study of liquid crystalline phase behavior from 5 to 100°C.

A structural study of the mesophases of two oxyethylene alkyl ether-decane-water systems, a comparison between technical grade C12EO〈7〉 and pure C12EO6

As part of a study polyoxyethylene alkyl ethers (C m EO n ), water and decane, the phase diagram and the structures of the mesophases of pure C12EO6 and technical grade C12EO〈7〉 were compared. The constructed phase diagrams of the two systems show a great resemblance except for one difference: the viscous isotropic phase is only present in the C12EO6 phase diagram. The swelling behavior of the lamellar and hexagonal phases was studied with smallangle x-ray scattering. Both the lamellar and hexagonal phases showed an ideal swelling behavior and no differences between the lamellar and hexagonal phases of the two systems were detected. With freeze-fracture electron microscopy the hexagonal and lamellar phases were visualized. No differences in the textures of the lamellar phases were found, however, the micrographs of the hexagonal phases of the two systems clearly showed different textures. While in the hexagonal phase of the C12EO6 system only infinite long rods were visualized, short interrupted rods were found in the hexagonal phase of the C12EO〈7〉 system.

Viscoelastic properties of paracrystalline phases appearing in water‐surface agent‐oil diagrams

Synopsis The ternary mixtures investigated were obtained from water, mineral oil and ether-linked non-ionic surfactants (polyoxyethylene derivatives of oleic alcohol). The examination of the rheological properties of these mixtures, particularly the viscoelastic properties of the various phases encountered in these diagrams, was expanded. The phases examined were: - anisotropic paracrystalline phases: hexagonal phase and lamellar phase; - the isotropic paracrystalline phase: type I viscous isotropic phase. The measurement instrument used for this work was a creep rheometer. The paracrystalline phases were subjected to very low shear stresses, and the strains induced were recorded as a function of time. The analysis of creep functions obtained enabled us to construct a viscoelastic model and obtain the value of its parameters for each particular case. This analysis of the viscoelastic properties provides an accurate identification of each of the paracrystalline phases: the lamellar and isotropic viscous phases show respectively a Newtonian fluid nature with a yield value (Bingham model), and a perfect elastic solid. The hexagonal phase on the other hand shows an intermediate type of behaviour which is characterized by a well-defined retarded elasticity. This study could also lead to a microscopic interpretation of their structure.

Phase behavior and molecular motion of aerosol OT in liquid-crystalline phases with water

The phase diagram and molecular motion of sodium di-2-ethylhexylsulfosuccinate, or Aerosol OT, or AOT, with water mainly at 37 and 25°C, are explored. Results are reported on visual observations, polarizing microscopy, and 1H and 13C NMR. At 25°C the solubility limit of AOT in water is 1.4 ± 0.2 wt%, in agreement with the recent literature. Above the solubility, uniaxial negatively birefringent lamellar liquid crystals form. The biphasic region extends up to 20 ± 4 wt%, as determined from visual observations, microscopy, and mainly from 1H NMR linewidths. From 20 to about 75 wt% there is a lamellar liquid crystal whose birefringence changes to positive around 40 wt%. The phase behavior results are qualitatively consistent with those of Rogers and Winsor (1969) and Fontell (1973), although there are some quantitative differences. The surfactant molecular motion is quite fast below the solubility, becomes quite restricted in the lamellar liquid-crystalline phase, becomes fast again in the viscous isotropic phase (∼75 to ∼80 wt%), and becomes much more restricted above 80 wt%, where the phase is hexagonal inverse middle liquid crystalline. 13C T 1 values for the lamellar liquid crystal show a motional gradient common in isotropic lamellar liquid crystals. The water molecular motion becomes increasingly restricted in the lamellar liquid crystal. The water resonance broadens substantially in the viscous isotropic and is not seen in the hexagonal liquid crystal.

Stable Emulsion Regions of Surfactant-Oil-Water and Surfactant-Oil-Water-Long Chain Alcohol Systems

A ternary diagram for nonionic surfactant-oil-water system was studied and the region of stable and strongly opaque emulsion (the region E1) was determined on the diagram. It was found that the E1 region existed only within the two-phase region consisting of a viscous isotropic phase and an oil phase, and that at least 10% surfactant was necessary to obtain this region.The quarternary system containing cetostearyl alcohol in addition to the ternary system was also examined. Addition of the alcohol produced a new stable region of strongly opaque emulsion (the region E2) besides E1. The appearance of the region E2 reduced the minimum surfactant concentration to obtain the stable and strongly opaque emulsion to about 2%. Similar effect was observed for behenyl alcohol of cosmetic grade, which is also a mixture of alcohols. However, pure alcohols of carbon numders from 12 to 16 lacked the ability to form the E2 region. Those of carbon numbers of 18 and 20 gave the E2 region but only above the surfactant concentration of 5%.

Study on Polymorphism of Monoglycerides. V.

Liquid crystal obtained from a mixed system of monopalmitin and water was examined for phase diagram, growth mechanism of liquid crystal and morphological changes during phase transition, using a polarizing microscope and DSC.1) With concentration of monoglyceride in the range of 9973%, a reversed middle phase was formed, and it became a neat phase with 8030% concentration. At concentrations below 70%, a viscous isotropic phase appeared in the high temperature region and this transited to a neat phase with lowering of temperature. With monoglyceride concentration below 40%, the stable range of the neat phase and viscous isotropic phase transited gradually to a lower temperature side, and the liquid crystal disappeared at about 23% concentration of monoglyceride.2) The reversed middle phase observed in the region of high concentration of monoglyceride grew by the crossed aggregation of a rod-like pattern. It was similar to the growth of usual smectic liquid crystal.On the other hand, the neat phase served in the low concentration range is considered to grow, as the nuclei was generated from the monomolecular film and micelle formed in the viscous isotropic phase.

Cubic Mesomorphic Phases

LOW-ANGLE X-ray diffraction has shown the existence of a viscous isotropic (cubic) mesomorphic phase in a number of surface-active agent plus water systems1–4 at concentrations between those required for the formation of neat (lamellar) and middle (hexagonal) mesomorphic phases. Initially, a face-centred cubic (fcc) lattice was proposed1 for this viscous isotropic phase and several possible model structures have been advanced5. Luzzati et al. have recently proposed6, however, that all reported cubic mesomorphic phases are based, not on an fcc lattice, but on the same body-centred cubic (bcc) lattice, space group Ia3d in the International Tables7.

Phase equilibria and structure of dry and hydrated egg lecithin

The behavior of purified egg lecithin in water has been investigated in relation to the quantity of water present and the temperature. The complete binary phase diagram of egg lecithin-water is presented as well as X-ray diffraction data on selected mixtures. Dry egg lecithin is present in at least partially crystalline form until about 40 degrees C. Above this temperature it forms a "wax-like" phase up to about 88 degrees C. From 88 to 109 degrees C it forms a viscous isotropic phase which gives face-centered cubic spacings by X-ray analysis. Above 110 degrees C its texture is "neat" and the structure is assumed to be lamellar until its final melting point at 231 degrees C. Hydrated lecithin forms (except for a small zone of cubic phase at low water concentrations and high temperature) a lamellar liquid crystalline phase. This phase contains up to 45% water at 20 degrees C. Mixtures containing more water separate into two phases, the lamellar liquid crystalline phase and water. In the melting curve of hydrated lecithin a eutectic is noted at about 16% water and the cubic phase seen when less water is present disappears at this composition of the mixture. These facts, along with previous vapor pressure measurements, suggest that there is a structural change at about 16% water. X-ray diffraction studies of lecithin at 24 degrees C and calculations from these data suggest that the reason for this may be the presence of a "free water layer" when more than 16% water is present.