Uptake of silicone oil in the polystyrene matrix of the two phase system polystyrene/silicone oil as detected by NMR

The decrease of the droplet radii of silicone oil dispersed in a polystyrene matrix at a temperature of 140°C with increasing time was measured by NMR dynamic imaging. From this time dependence the diffusion coefficient of the silicone oil into the matrix was calculated to be 7 · 10⁻¹⁸ m² · s⁻¹. The uptake of the silicone oil in the polystyrene matrix was confirmed by broad line NMR measurements.     

Wetting in oil/water/surfactant systems

The behaviour of oils at aqueous interfaces is ubiquitous to many industrially and biologically relevant processes. In this review we consider modifications to the wetting properties of oils at the air/water, oil/water and solid/liquid interfaces in the presence of surfactants. First-order wetting transitions can be induced in a wide range of oils by varying the aqueous surfactant concentration, leading to the formation of mixed monolayers at the interface. In certain cases, these mixed monolayers display novel surface freezing behaviour, including the formation of unusual bilayer structures, which further modifies the properties of the interface. The effects of surfactant on line tension at the three-phase contact line and differences between the air/liquid and liquid/liquid interfaces are discussed.     

Crystalline protein domains and lipid bilayer vesicle shape transformations

Cellular membranes can take on a variety of shapes to assist biological processes including endocytosis. Membrane-associated protein domains provide a possible mechanism for determining membrane curvature. We study the effect of tethered streptavidin protein crystals on the curvature of giant unilamellar vesicles (GUVs) using confocal, fluorescence, and differential interference contrast microscopy. Above a critical protein concentration, streptavidin domains align and percolate as they form, deforming GUVs into prolate spheroidal shapes in a size-dependent fashion. We propose a mechanism for this shape transformation based on domain growth and jamming. Osmotic deflation of streptavidin-coated GUVs reveals that the relatively rigid streptavidin protein domains resist membrane bending. Moreover, in contrast to highly curved protein domains that facilitate membrane budding, the relatively flat streptavidin domains prevent membrane budding under high osmotic stress. Thus, crystalline streptavidin domains are shown to have a stabilizing effect on lipid membranes. Our study gives insight into the mechanism for protein-mediated stabilization of cellular membranes.     

Microemulsions from silicone oil with an anionic/nonionic surfactant mixture

Microemulsion phases have been prepared for the first time from the silicone oil "M(2)" (hexamethyldisiloxane) and a surfactant mixture of a nonionic surfactant "IT 3" (isotridecyltriethyleneglycolether) and an ionic surfactant Ca(DS)(2) (calciumdodecylsulfate). For such a surfactant mixture the hydrophilicity of the system can be tuned by the mixing ratio of the two components. With increasing IT 3 content, the surfactant mixtures show a L(1)-phase, a wide L(α)-region and a narrow L(3) sponge phase. For constant temperature, two single phase channels exist in the microemulsion system. The lower channel (low IT 3 content) ends in the middle of the phase diagram with equal amounts of water and oil, the upper channel begins with the L(3)-phase and passes all the way to the oil phase. Conductivity data show that the upper channel has a bi-continuous morphology up to 40% oil while the lower channel consists of oil droplets in water. In contrast to previous studies on nonionic systems, the two single phase channels are not connected and microemulsions with equal amount of oil and water do not have a bicontinuous structure.     

Solid-phase chemical transformations in molybdate systems

The ternary salt systems M₂MoO₄−AMoO₄−Zr(MoO₄)₂ (M=K, Tl; A=Mg, Mn, Ni, Co, Cu, Zn, Cd) in a sub-solidus region were studied. New ternary molybdates with the M₅A_0.5Zr_1.5(MoO₄)₆ and MA_0.5Zr_0.5(MoO₄)₂ compositions were synthesized by solid-phase reactions in these systems. The crystallographic and thermal characteristics of the compounds were found. The electrical properties of potassium—manganese—zirconium molybdates were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1036–1039, June, 1999.     

Thermal transformations in nanodimensional Pb—WO3 systems

Transformations in Pb-WO₃ nanodimensional systems are investigated in dependence on the thickness of the Pb and WO₃ films, temperature, and thermal treatment duration by means of optical spectroscopy, microscopy, and gravimetry. The contact potential difference for Pb and WO₃ films and the photoelectric power of Pb-WO₃ systems is measured. A diagram of the energy bands of Pb-WO₃ systems is constructed. A model of thermal transformation for the WO₃ films in Pb-WO₃ systems is suggested. The model involves the redistribution of equilibrium charge carriers on the contact, formation of the ([(V_a)⁺⁺e]) center during the preparation of a WO₃ film, its transformation into a ([e(V_a)⁺⁺e]) center during the formation of the Pb-WO₃ systems, and thermal ionization of the ([e(V_a)⁺⁺e]) center.     

Dynamics of spontaneous vesicle formation in fluorocarbon and hydrocarbon surfactant mixtures

The spontaneous self-assembly of unilamellar vesicles was investigated by means of time-resolved synchrotron small-angle X-ray scattering. The self-assembly process was initiated by rapid mixing of anionic surfactant micelles with either zwitterionic or cationic surfactant micelles in equimolar ratio using a stopped-flow device. For the zwitteranionic systems, transient disklike mixed micelles are observed as structural intermediates prior to the onset of vesiculation. These disklike micelles display an exponential growth law, and above a critical size they close to form unilamellar vesicles. In the catanionic system, the earliest observable structures within the mixing time of 4 ms are unilamellar vesicles. Nevertheless, in both systems a narrow distribution of the vesicle size was observed at the initial stages of their formation. The subsequent evolution of the vesicle size distribution depends on the subtle differences in the bilayer composition and properties.     

Polyelectrolyte-induced vesicle formation in lamellar liquid-crystalline model systems

 The object of the research was to investigate the influence of a semiflexible polyanion (carboxymethylcellulose) in the absence and presence of a more flexible cationic polyelectrolyte [poly(diallyldimethyl-ammonium chloride)] on structure formation in liquid-crystalline model systems consisting of sodium dodecyl sulfate (SDS)/ decanol/water. Small-angle X-ray measurements in combination with electron microscopic investigations show the adsorption of the polycation on the SDS head groups. These polymer-modified lamellae form multilamellar vesicles. The semiflexible polyanion was embedded into the liquid crystal without macroscopic phase separation and multivesicular vesicles were formed on the supramolecular level. In combination the oppositely charged polyelectrolytes induce the formation of multivesicular structures where two lamellar structures coexist. Received: 15 July 1999/Accepted in revised form: 22 September 1999     

Thermostimulated transformations in nanosized Bi-MoO3 systems

Transformations in Bi-MoO₃ nanosized systems are studied by optical spectroscopy, microscopy, and gravimetry. The contact potential difference for the Bi and MoO₃ films and the photovoltage of the Bi-MoO₃ systems are measured, depending on the thickness of Bi (d = 3–92 nm) and MoO₃ films (d = 5–40 nm) and the temperature (373–673 K) and time of heat treatment. An energy band diagram of the Bi-MoO₃ systems is constructed. A model of the thermal transformation of MoO₃ films in Bi-MoO₃ systems is proposed that involves the redistribution of equilibrium charge carriers on a contact, the formation of a ([(V_a)⁺⁺e]) center during the preparation of a MoO₃ film, the transformation of this center into a ([e(V_a)⁺⁺e]) center during the formation of Bi-MoO₃ systems, and the thermal transition of an electron to the level of a ([(V_a)⁺⁺e]) center to form a ([e(V_a)⁺⁺e]) center.     

Quasi-static electrorheological properties of hematite/silicone oil suspensions under DC electric fields

In this work, a modified rheometer has been used to gain information on the "start-up" of the shear flow of an electrorheological (ER) fluid consisting of hematite particles dispersed in silicone oil. The results show that unelectrified suspensions behave essentially as fluids, continuously deforming upon application of shear. However, this behavior changes in the presence of an electric field. For low fields and low volume fractions of solids, a solidlike (drastic increase in shear stress after the strain is applied) behavior is observed for small deformations. If the strain is increased, the yield starts and a transition to a viscoelastic-plastic nature is observed. Finally, a plastic behavior is characteristic of the post-yield regime. If the field strength and solids content are high, a discontinuous flow profile develops. These results, together with direct structural observations, suggest that the observed behavior is compatible with the formation of layers of particles electrophoretically deposited on the electrodes; the layers turn into rings when the shear field is applied. It is the slip of the fluid between these rings that can be considered responsible for the ER effect in these suspensions.     

Density functional simulation of spontaneous formation of vesicle in block copolymer solutions

The author carries out numerical simulations of vesicle formation based on the density functional theory for block copolymer solutions. It is shown by solving the time evolution equations for concentrations that a polymer vesicle is spontaneously formed from the homogeneous state. The vesicle formation mechanism obtained by this simulation agrees with the results of other simulations based on the particle models as well as experiments. By changing parameters such as the volume fraction of polymers or the Flory-Huggins interaction parameter between the hydrophobic subchains and solvents, the spherical micelles, cylindrical micelles, or bilayer structures can also be obtained. The author also shows that the morphological transition dynamics of the micellar structures can be reproduced by controlling the Flory-Huggins interaction parameter.     

Microinjection into giant vesicles and light microscopy investigation of enzyme-mediated vesicle transformations

Background: ‘Giant vesicles’ have diameters of several micrometers and can be observed by light microscopy. Their size may allow manipulation of individual vesicles and direct observation of the progress of a chemical reaction in real time. We set out to test this possibility using enzymatic hydrolysis of vesicle components as a model system.Results: We describe a novel micromanipulation technique that allows us to microinject femtoliter amounts of a reagent solution adjacent to or into giant vesicles with diameters ranging from 10 to 60 μm. The vesicle transformations can be monitored directly in real time by light microscopy and recorded by video analysis. Snake venom phospholipase A₂ was added to vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine, and the enzymatic hydrolysis of components of the lipid bilayer was observed over time. A specific effect on the targeted giant vesicle was seen and video recorded, while the neighbouring vesicles remained unaffected. Addition of the enzyme to the outside of a vesicle caused it to burst, whereas injection of the enzyme inside a vesicle resulted in a slow and constant decrease in its size, until it eventually disappeared from the resolution power of the light microscope.Conclusions: These results show that it is possible to micromanipulate an individual vesicle, and to follow visually the progress of an enzymatic reaction occurring on the vesicle bilayer over time.     

Formation of reverse vesicles in silicone surfactant systems

This study deals with the formation of reverse vesicles based on the phase behavior of silicone surfactants. The surfactants, polyoxyethylene–polydimethylsiloxane and polyoxyethylene–polyoxypropylene–polydimethylsiloxane copolymer, were found to form lamellar liquid crystal phases in three different types of silicone oil upon the addition of a certain amount of water. A conventional method in which reverse vesicles are prepared by physically dispersing this lamellar liquid crystal phase in oil was employed in addition to a technique based on a temperature-induced phase transition. The particle sizes and stabilities of the resulting reverse vesicles were evaluated.     

Na-caseinate/oil/water systems: emulsion morphology diagrams

The concentrated (dispersed phase 50-70 wt%) composition space of Na-caseinate, a family of milk proteins, stabilised emulsions was investigated for three different oils: soybean oil, palm olein and tetradecane with pH 6.8 phosphate buffer continuous phase. The variation of emulsion stability and microstructure were explored using static light scattering, diffusion nuclear magnetic resonance, cryo-scanning electron microscopy, rheology and the time varying macroscopic phase separation of the emulsions. For soybean oil and palm olein a rich diversity of emulsion microstructures and stabilities are realised. Five emulsion domains, each having a different microstructure and macroscopic stability have been identified within the composition space probed. For the lowest concentrations of emulsifier bridging flocculation is evident and emulsions are of low stability. Increasing Na-caseinate concentration leads to an increased stability and the existence of distinct individual oil droplets, visualised using cryo-scanning electron microscopy. Further increases in Na-caseinate concentration reduce emulsion stability due to depletion flocculation. Na-caseinate self-assembly is then initiated. At sufficiently high Na-caseinate and/or oil concentrations the continuous phase of the emulsion is a three-dimensional protein network and emulsion stability is again enhanced. At the limits of the emulsion composition space a gel-like paste is formed. The diversity of emulsion microstructure is reduced when tetradecane is the discrete phase. Na-caseinate self-assembly is limited and there is no evidence for formation of a protein network.     

Calculation of wetting angles in crude oil/water/quartz systems

A method for the determination of water-advancing wetting angles has been developed and tested. The method allows measurements in black oils, as opposed to traditional techniques which substitute transparent model oils prior to measurements. The method is based on the Laplace equation and axisymmetric drop shape analysis. The main source of error is the determination of the drop volume. Results in transparent systems are comparable to results using other techniques. Wetting angles are determined for water in two different crude oil systems, using quartz as the substrate. The quartz surfaces are water wet over large pH ranges, but it is possible to accurately identify pH intervals where the surfaces are intermediate or oil wet.     

Interfacial tension of alkylglucosides in different APG/oil/water systems

The interfacial performance of pure alkylglucosides (C₈G₁, C₁₀G₁ and C₁₂G₁) and of technical grade alkylpolyglucoside (APG) surfactants was investigated in three different water/oil systems (decane, isopropylmyristate and 2-octyldodecanol). From the dependence of the interfacial tension on the surfactant concentration below the CMC the cross-sectional area of the molecules at the decane/water interface was estimated. The plateau values of the interfacial tension at the CMC _c are independent of temperature and almost independent of added electrolyte in the decane/water system. The ability of the surfactants to lower the oil/water interfacial tension is most pronounced for the nonpolar oil. The partition coefficient of the surfactant between oil and water phase (k _c) was estimated from the CMC and the observed break point of the interfacial tension after equilibration of the two phases. In decane/water,k _c is nearly zero for all surfactants studied. For the polar oils,k _c increases with the chain length of the surfactant up tok _c10 for C₁₂G₁ in octyldodecanol/water. The values of _c in the different oil/water systems appear to be correlated withk _c and exhibit a minimum neark _c=1.     

Studies of synergism/antagonism for lowering dynamic interfacial tensions in surfactant/alkali/acidic oil systems. 1. Synergism/Antagonism in surfactant/model oil systems

Experimental studies are conducted in order to elucidate the mechanisms responsible for synergism/antagonism for lowering dynamic interfacial tension in model oil/surfactant/brine systems. A well-defined model oil is selected for controlled design of experiments, thus enhancing verification of known and unknown mechanisms. The systems examined contain model oils and two petroleum sulfonate solutions. The influence of additives in oil phase, such as carboxylic acids with different chain length, n-octadecanol, and oil soluble surfactant SP-60, on the equivalent alkane carbon number (EACN) values has been examined. The interfacial tensions of different model oils with different EACN values against surfactant solutions with different n(min) values have also been obtained. We find that antagonism has been observed when EACN/n(min) value is far from unity by adding organic components, while synergism has been observed when EACN/n(min) value is close to unity. The results present here suggest that organic additives in oil phase controlled interfacial tension by changing the partition of surfactants in oil phase, aqueous phase, and interface.