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The bilayer hydrophobic thickness l is estimated from the 2H-NMR spectra of acyl chain perdeuteriated membrane phospholipids. Values obtained from individual quadrupolar splittings and those from the first moment of a powder spectrum are in close agreement. In the fluid (La) phase, the thermal variation of dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidic acid (DMPA) at pH 4.2 and 8.2, and DMPC: cholesterol (7:3) bilayer thicknesses are compared; 30% cholesterol increases the thickness of dMPC by approximately 4-5 Å, whatever the temperature. DMPC and DMPA (whatever the pH) have the same hydrophobic thickness near their respective Tc, the gel-to-fluid phase transition temperature, and display a very similar l decrease when increasing the temperature. However, at high temperatures (60°C) DMPC is thinner than DMPA by approximately 1 Å. Steric, electrostatic, and temperature constraints are therefore seen to modulate the biomembrane hydrophobic thickness , as easily estimated by 2H-NMR. [ABSTRACT FROM AUTHOR]

Most of the properties of the polydimethylsiloxane (PDMS) oils can be deduced from the structure of the linear polymeric chain of the macromolecule, including flexibility and stability of the Si-O-Si backbone, and hydrophobicity of the methyl substituents of the silicon atom. But in fact, the advantages of pure PDMS for industrial application are limited. For the major uses, it is always necessary to either disperse variable amounts of silica in PDMS or to emulsify PDMS in water. The interfacial properties of the water/PDMS/surfactant system were therefore investigated according to phase diagrams, surface tension, and ellipsometric measurements (carried out at CNRS Monpellier), and x-ray and ESR measurements (carried out at Collège de France, Paris). The relationship between the amphiphilic behavior of the PDMS chain and the practical advantages of the PDMS/water system will be discussed. [ABSTRACT FROM AUTHOR]

A quantitative treatment of the influence of sodium dodecyl sulphate, (Na(C12H25SO4)2; NaDS) on the crystal growth and aggregation of calcium oxalates in spontaneously precipitating system is given. The experiments are carried out under the conditions close to those in urine of stone-formers (310 K, pH=6.5, ionic strength I=0.3 mol dm−3, molar ratio cinit (Ca)/cinit (C2O4)=33.3). The formation of solid particles (crystal size distribution, CSD) was followed by Coulter counter. Standard methods for crystal phase identification were applied (thermogravimetric analysis, x-ray diffraction, optical microscopy). NaDS inhibits the crystal growth process; the intensity of the effect seems to be concentration dependent. The order of reaction (p) increases with increasing concentration of NaDS and assumes following values: $$p_{NaDS_1 } = 8.5, p_{NaDS_2 } = 11.4$$ , and $$p_{NaDS_3 } = 11.9$$ . While for the control system (without NaDS) the integration of the growth units into kinks is the rate determining process, in the presence of NaDS crystal growth is controlled by surface adsorption. In systems where NaDS is present at concentrations equal to or below critical micelle concentration (CMC) the overall rate constant of aggregation is not influenced; the addition of NaDS causes no change in the rate controlling mechanism of aggregation. At c (NaDS) significantly higher than the CMC, the overall inhibitory effect compriises, besides inhibition of crystal growth, the retardation of aggregation process as well. [ABSTRACT FROM AUTHOR]

The shape of surface or interfacial tension curves for surfactants able to form micelles can be derived from equilibrium models of the micellization process if monomers only can be adsorbed. The influence of several effects influencing the aggregation equilibrium constants Ks on the shape of the surface pressure curve is examined in light of recently published quasi-chemical models. Some modifications are also considered. The presence of a strong increase of Ks with the intermediate aggregation number s is required for predicting the sharp transition at cmc. However, this effect cannot explain the shape of the distribution curve derived from kinetic studies. Both kinds of curves may be predicted in assuming, in addition, an effect decreasing Ks and a minute formation of dimers. The maximum aggregation number and its dispersity depend on these effects which leads to behaviors similar to those derived in applying the Aniansson et al. theory to kinetic data. The need for an improved description of the influece of electrostatic interactions is stressed. [ABSTRACT FROM AUTHOR]

The analytical model of the adhesive sphere fluid in the Percus-Yevick approximation (ASPY) is analyzed for colloidal systems. To discuss this model we consider the more realistic square well (SW) interaction where the equivalence between the SW and the AS is defined by the equality of the second virial coefficient of the two systems. The main points considered are: the comparison between the distribution functions of the ASPY fluid and the SWPY fluid and the influence of the PY approximation on the results. This approximation is checked with respect to the modified hypernetted chain approximation (MHNC) for the SW system and the simulation data of Season and Glandt for the AS system. We focus on the structure factor and on the small angle behavior. The calculations are done at volume concentrations in the range 0%-40%. The principal conclusions are 1) the ASPY model of the structure factor agrees fairly well with the SWPY model at all volume concentrations if the range of the square well does not exceed 10% of the particles diameter, and 2) away from the critical region in the structure factors of the SW fluid are very close in the PY or MHNC approximation. Similarly, in the same domain there is a reasonable agreement between the ASPY model and the simulation data. Some applications of the ASPY model to particular colloidal suspensions are briefly presented. [ABSTRACT FROM AUTHOR]

The physico-chemical model for extraction of metals by chelating and cationic extractants is discussed. The interfacial tension data are used to simulate relationships between the reaction rate of extraction for various versions of its mechanism and the extractant bulk concentration. The program for microcomputer IBM PC is presented which can be used for routine analyses of various interfacial tension isotherms and different extraction processes. Up to now it was used with success for copper extraction by hydroxyoximes and palladium (II) extraction by dialkyl sulphide in the presence of trialkylamine. [ABSTRACT FROM AUTHOR]

Interfacial tension isotherms were determined for 1-(2′-hydroxy-5′-methyl-phenyl)-octane-1-one oxime in toluene/water and octane/water systems and used to predict extraction orders against hydroxyoxime for various versions of extraction mechanism. It was demonstrated that the formation of the stable 2:1 complex from the intermediate 1:1 complex and the hydroxyoxime molecule present in the aqueous layer near the interface is the slowest step. The interfacial behavior of 1-(2′-hydroxy-5′-methylphenyl)-octane-1-one oxime is similar to those of more hydrophobic oximes, e. g., 2-hydroxy-t-alkylbenzophenone oximes. [ABSTRACT FROM AUTHOR]

Dynamic light scattering measurements on oriented samples of dilute lyotropic smectics have been performed. The hydrodynamics of a two-component smectic A is reviewed and applied to describe the fluctuation spectrum in our multi-component samples. The layer compressibility modulus (at constant chemical potential) $$\bar B$$ is extracted from the anisotropic dispersion relation of the so-called slip mode, which arises from the coupling between concentration and layer displacement fluctuations. The samples, diluted with three different solvents, afford repeat distances of 50-800 Å; the behavior of $$\bar B$$ suggests either undulation or electrostatic repulsions between membranes, depending on the swelling solvent. [ABSTRACT FROM AUTHOR]

The interactions in mixtures of anionic/cationic surfactants were investigated by several methods (conductivity, surface tension, turbidity, electrophoretic mobility, and EMF measurements). The mixtures studied were sodium tetradecylsulfate/tetradecyl pyridinium chloride and sodium dodecyl sulfate/dodecylammonium chloride. At least three different concentration regions can be differentiated in the region of mixed micelles depending on changes in the surfactant molar ratio. A model for their interface between mixed micelles and the surrounding electrolyte is supposed to incorporate the headgroups of both surfactants and pairs of headgroups-counterions of the surfactant in excess. [ABSTRACT FROM AUTHOR]

We report on a surfactant system which is in the liquid crystalline lamellar state and where the spacings between the lamellar layers can be expanded to several thousand Å. As a consequence the solutions show bright iridescent colours when they are illuminated with w hite light against a dark background. The system consists of the zwitterionic surfactant tetradecyldimethylaminoxide in the presence of some cosurfactant and small amounts of hydrocarbon. The system can be swollen with water up to a volume fraction of 0.99 without loss of the liquid crystallinity. The systems are thermodynamically stable and the iridescent colours reappear after the order has been destroyed by shaking the solutions. It is believed that the large spacings are due to electrostatic forces between the surfactant layers. The charges on the layers are due to protonation of the aminoxide groups by water. The existence region of the iridescent phase as a function of surfactant, hydrocarbon and cosurfactant is reported. The spacings for the phases were determined from light transmission and light scattering measurements. [ABSTRACT FROM AUTHOR]

Phase behavior and liquid crystal structures of metal dodecylbenzenesulfonates have been investigated by x-ray diffraction and polarization microscopy. Interplanar distances in the lyotropic lamellae exhibited the differences (D/Å between 35 and 39). It can be assumed that the structures of the lamellar layers have been influenced by various possible reasons, i.e. the hydration of individual metal ions within the water layers of lamellae, the depression of water layers, and the depression of paraffin layers. The types of lamellar organization in the crystalline phases, crystallized from ether or from water solutions, remain in a smectic arrangement with the rigid structure of smaller interplanar distances than those in liquid crystal state. [ABSTRACT FROM AUTHOR]

We report visual observations and preliminary light scattering experiments on the crystallization process in several colloidal systems. The main difference between the colloidal systems studied here is the range of their pair-interaction potential which is varied by changing the stabilizing coating of the particles. This range is found to have a pronounced influence on the rate of crystallization. [ABSTRACT FROM AUTHOR]

A three-component microemulsion system consisting of mixtures of water, decane, and a surfactant AOT (WDA), has been studied by means of extensive light scattering measurements, including the intensity, turbidity and linewidth. The measurements have been performed in the one-phase region over a very large temperature range, along the critical and several off-critical constant microemulsion droplet volume fractions. The standard theory of critical binary fluids, complemented by the linear model equation of state, accounts very well for the intensity data in the vicinity of the lower phase separation temperature Tp using a single value for the short range correlation length, ξ0=(13.5±1.5) Å. We have also been able to fit the dynamic light scatteirng dat by combining a mode-coupling theory including the background effects, and the critical equations of state using a cutoff wavelength qD−1 equal to the constant average diameter of microemulsion droplets. Moreover, we find clear evidence for a crossover from critical to single particle behavior in both static and dynamic light scattering data. A cropssover temperature Tx has been identified for ξ(Tx)=qD−1 so that qD, which can only be measured far away from Tp, plays the most important part in controlling the critical dynamics in the whole temperature range. [ABSTRACT FROM AUTHOR]

In mixing nonionic fluorinated and hydrogenated surfactants, one or several types of mixed aggregated structures can be obtained. Several types of measurements have been performed and combined in order to obtain detailed information on this subject: ternary phase diagram determinations, x-ray diffraction on the liquid crystal phases, small-angle neutron scattering on the isotropic phases, and surface tension measurements on dilute aqueous solutions. It is shown how the surface tension results fully correlate the phase behaviors of these systems. At constant hydrophobic tail, according to the oxyethylene chain length the mixing may be almost ideal or markedly nonideal, although every one phase system (isotroic or liquid crystal) is actually constituted by only one type of mixed aggregate. And it is shown how the mutual oleophoby of these surfactants is enhanced by a marked dissymmetry in the hydrophilic chains but in presence of large amounts of water. The mixing is described by the regular solution formalism, making use of a polynomial representation of the interaction parameter. [ABSTRACT FROM AUTHOR]

A waterless microemulsion (glycerol/AOT/isooctane; molar ratio [glycerol]/[AOT]=3.2) has been studied at T=25°C as a function of the (glyerol+AOT) φ volume fraction. The measured properties are electric conductivity, dynamic viscosity, and dielectric relaxation (time domain spectroscopy). An increase of conductivity σ and dynamic viscosity η are observed as the volume fraction φ increases. The quantities d(ln σ)/dφ and d(ln η)/dφ go through a maximum, as well as static permittivity ɛs. At the same time, the characteristic frequency νR of dielectric relaxation goes through a minimum. The dielectric relaxation may be fitted by a generalized Davidson-Cole distribution of relaxation times. The results are discussed within the framework of the theory of percolation. The minimum of νR at the percolation threshold, and the maximum of ɛs, confirms more specifically the theoretical prediction in the domain of dielectric relaxation. The analogies with microemulsions of the water/AOT/oil type are also discussed. [ABSTRACT FROM AUTHOR]

Dielectric relaxation (102-109 Hz), transient- and phase (1-107 Hz) electric birefringences were carried out cojointly on a W/O ternary microemulsion system from water, benzene, and BHDC as surfactant, for different ratios wo: (water)/(BHDC) and volume fractions φ values. From the Kerr-effect approaches it is possible to distinguish the existence of dimers, trimers, and an unexpected sign-reversal of the Kerr constant as wo decreases, whatever the φ values. Preliminary analysis of the dielectric measurements evidences a freqeuncy power law of the conductivity below 103 Hz. The hypothesis of a quasi dc (i.e., dispersive) transport charge process is proposed and credits the possible presence of temporal self-similar clusters. Four marked dielectric relaxations have been found. The contributions of the Maxwell-Wagner interfacial polarization, the space charge manifestations via a surface resistivity and a double-layer polarization, as well as a possible molecular relaxation process are proposed. [ABSTRACT FROM AUTHOR]

Some common aliphatic hydrocarbons were solubilized in aqueous ionic surfactant micelles. The effect of these additives on ηmic, the microviscosity in the pallisade region of the micelle, was studied. It was found, by means of fluorescence quenching, that ηmic is independent of the nature and quantity of the additive. These findings are discussed in terms of diffusion kinetics and the validity of the Einstein-Stokes equation in micelles. [ABSTRACT FROM AUTHOR]

By means of ion exchange chromatography, a new surfactant was synthesized. Its purity and characteristics, molecular and micellar, were investigated. The originality of this surfactant lies in its counterion, which is a polymerizable group. The polymerization of such direct micellar solution did not lead to precipitation. The use of different techniques like light scattering, NMR, fluorescence spectroscopy, and photoelectron transfer reactions allow us to describe the polymerized aggregates as cylindrical entities which remain in size and shape, even under dilution, below the critical micellar concentration of the unpolymerized micelles. [ABSTRACT FROM AUTHOR]

Rodlike micelles formed by the surfactants N-hexadecylocytldimethylammoniumbromide (C16-C8DAB) and tetradecyltrimethylammoniumsalicylate (TTMA-Sal) were aligned by shear gradients Γ up to 2000 s−1. Small-angle neutron diffraction patterns (SANS) were recorded for different shear gradients. The quiescent solutions show a peak in the scattering intensity distribution having its origin in particle interaction. With increasing shear gradient the scattering intensity becomes very anisotropic. The scattering data are explained on the basis of alignment of rods, taking into account an effective pair correlation function. Both surfactants show evidence for the phenomenon of a shear induced phase transition. Transient SANS measurements on a time scale of 100 ms show two relaxation times for C16-C8DAB. [ABSTRACT FROM AUTHOR]

Anomalous flow birefringent phases, sometimes designated as L3, have been identified in both the water-rich and the oil-rich parts of the phase diagram of the water(-NaCl)-dodecane-pentanol-SDS system. The presence of these phases appear to be associated with that of swollen lamellar phases. Conductivity and neutron-scattering results provide evidence that the structure of these phases consists of a highly connected, sponge-like, random bilayer-continuous surface. The surfactant surface separates, depending upon the system, into either two water-continuous domains or two oil-continuous domains. The data are consistent with a recent theoretical model. [ABSTRACT FROM AUTHOR]

In the present paper a systematic investigation is presented of the phase behavior of perfluoropolyether (PFPE) surfactant, PFPE oil, water and isopropyl alcohol mixtures. Monophasic regions of isotropic, transparent, and fluid samples are identified in the thermal range 20° ÷ 60 °C. Preliminary data by light-scattering investigation support the hypothesis of the presence of O/W and W/O structural aggregates. [ABSTRACT FROM AUTHOR]

The ESR spectra of iodoacetamide, 5-doxyl stearic acid and FDNB derivative spin labels, in nonionic microemulsion systems, formulated with tetraethyleneglycoldodecylether in decane were measured in various amounts of water and surfactant content. At certain microemulsion compositions, the high field line of the ESR spectrum, splits into a doublet, suggesting that the spin probe locates in two different positions, i. e., the water core and the micromembrane which separates the aqueous from the oil phase. The method used for this study is based on i) the partition of spin labels between the microphases of the system expressed as the ratio of the high field peaks (H−1/H*−1) corresponding to the two different spin states; ii) the mobility of the spin labels in the dispersed phase expressed in terms of the degree of anisotropy (H1/H0); and iii) the polarity of the microenvironment of the label expressed in terms of the hyperfine coupling constant αn. The variation of these spectral parameters is discussed in connection with the corresponding structural state of the microemulsions. [ABSTRACT FROM AUTHOR]

Studies of the structure of microemulsions and of Winsor-type systems have emphasized the importance of the properties of the interfacial film through the parameters of spontaneous curvature and of the film curvature elastic modulus. We discuss here the correlations between measured dispersion sizes, surfactant film curvature elasticity (K), and interfacial tensions in several multiphase microemulsion systems. Sizes L are in agreement with simple random-space filling models, the area per surfactant molecule in the film remaining constant. For small values of K, bicontinuous structures are found when the spontaneous curvature of the film is small: the dispersion size is then close to the persistence length of the film. For larger K, more ordered structures appear. Interfacial tensions correlate only approximately with kT/L2. [ABSTRACT FROM AUTHOR]