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We report the study of the self-diffusion coefficient for strongly interacting polystyrene latex particles in a water solution, where aggregation processes are present. The reported data, obtained by measuring the contribution in the intensity-intensity correlation function of the occupation fluctuation number of particles in the scattering volume, agree with the current models of kinetic growth for random aggregation. [ABSTRACT FROM AUTHOR]

Divalent (2-ethyl hexyl) sulfosuccinate surfactant is used to form water in oil aggregates. By increasing the water content pronounced structural changes are observed. At low water content spherical droplets are formed. By increasing the water content, cylindrical aggregates are formed. The maximum amount of water solubilized using divalent surfactants is relatively low (the limit value of the ratio of water over AOT concentration w is less than 7, using divalent surfactants, and is equal to 60 using sodium AOT). At higher water content a phase transition is observed with two isotropic phases, with the lower phase containing mainly the surfactant. [ABSTRACT FROM AUTHOR]

We have investigated, by means of radiowave dielectric spectroscopy measurements, the ripple phase of two different phospholipid — water mixtures (DPPC and DMPC), each of them containing different amounts of DPPE or DMPE, respectively, up to 7% wt/wt of total lipid. — Addition of DPPE or DMPE to the phospholipid aqueous systems should reduce the effective head group area and, hence, the orientational head group dipole correlation. The results, showing a marked damping of the dielectric increment at the pretransition in relation to the DPPE or DMPE concentration, provide further evidence that the anomalous polarization observed in these systems at the pretransition temperature must be attributed to the bilayer ripple modulation. [ABSTRACT FROM AUTHOR]

The passive electrical properties of human lymphocyte membranes incubated with different gangliosides have been measured by means of radiowave dielectric spectroscopy in the frequency range where the Maxwell-Wagner effect occurs. — The alterations of the membrane structure and functionality reflect in an increase of the membrane conductivity σs and membrane permittivity εs, depending on the chemical composition of the ganglioside employed. The possible relation to the structural changes of the cytoplasmatic membrane are briefly discussed. [ABSTRACT FROM AUTHOR]

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]

The formation of lyotropic mesophases in systems of tetradecyldimethylaminoxide/water/aliphatic alcohol was examined in dependence on alcohol concentration and alcohol chain length (heptanol, octanol, nonanol, decanol). The ternary phase diagrams were established. The following lyotropic phases were detected by microscopic texture observation: hexagonal phase (H), lamellar phase (La), rodlike nematic phase (NC), and disklike nematic phase (ND). The positions of the corresponding regions in the phase diagrams were determined. In particular, the NC- and ND-phase were of special interest. — Lyotropic-cholesteric phases were induced in the lyotropic-nematic phase region by adding optically active components such as cholesterol, tartaric acid, lithocholic acid. When subjected to the influence of a magnetic field, these cholesteric phases show the socalled spaghetti-like texture. The textures have been used for determining the pitch length. A linear relation between pitch length and concentration of the optically active components was established. [ABSTRACT FROM AUTHOR]

Rod formation is primarily governed by the characteristic Gibbs free energy of rod formation, ΔGrod. Geometrically, a rod-shaped micelle consists of a central cylindrical part of hydrocarbon radius rc and of more or less hemispherical parts at the ends of hydrocarbon radius rs. To smooth out the transition region between the spherical part of an endcap and the cylindrical part a catenoid is introduced. The model includes hydrophobic, electrostatic, and steric interactions, and allows direct adsorption of counterions to the micelle surface. It is used to calculate the optimal radius of the cylindrical part and to determine the according equilibrium configuration of the endcaps. The theoretical results are compared with empirical data for cetylpyridinium salts. Direct counterion adsorption is found to amount to about 50%. A strong steric influence on counterion adsorption is given. [ABSTRACT FROM AUTHOR]

The effect of methanol, ethanol, and 1-propanol on the critical micelle concentration (CMC) of several surfactant aqueous solutions has been studied in the 10-40°C temperature range by surface tension and conductivity measurements. Experimental parameters such as the standard free energy, enthalpy and entropy of micellization weere also determined. — The results show that on increasing alcohol concentration the CMC first reaches a minimum at an intermediate cosolvent mole fraction x2 = x*2 typical for each alcohol, and then increases with increasing x2. The value of x*2 is close to that at which structural changes in the mixtures occur as inreferred from compressibility, UV, IR absorption spectra, and neutron and x-ray scattering measurements. — The present experiments support the assumption that the dominant mechanism by which 1-alcohols affect the micellization process is through their effect on the structure of solvent. It is suggested that the same conclusion could be valid for a number of other systems of biological and chemical interest. [ABSTRACT FROM AUTHOR]

The concentration dependence of the infrared spectra of CCl4 solutions of AOT [bis(2-ethylhexyl)sodium sulfosuccinate] has been determined in a concentration range (0-1.6 mM) encompassing the critical micelle concentration (CMC ≃ 0.2 mM). — Effects detected on the molar extinction coefficients of the bands due to C-H stretching vibrations can be used as indicators of micelle formation. — The same spectroscopic technique has also been used to investigate the structure of water in oil microemulsion. The interaction of water with reversed micelles of AOT has been studied as a function of the ratio W = [H2O]/[AOT] in the range 0-12 by using the absorption band due to O-H stretching mode, in the 3800-3000 cm−1 range, and the absorption band in the range 1700-1500 cm−1, arising from the H-O-H bending vibration. Our results indicate that at low W values (W < ∼4) the water in micellar core is structurally and motionally different from unperturbed bulk water. On increasing W, water displays more marked "bulk" properties, and the absorption bands approach that of bulk water. [ABSTRACT FROM AUTHOR]

The model for multicomponent nonideal mixed micelles used via the regular solution approximation allows accounting for the critical micelle (CMC) of binary or ternary mixtures obtained with nΦCm (anionic surfactant), TTAB (cationic surfactant), and OP(EO)8 (nonionic surfactant). The anionic/cationic interaction is much higher than the ionic/nonionic interactions; this is probably due to the high electrostatic attraction between molecules which have opposite charges. We have found that anionic/cationic interaction appears to depend very slightly on the anionic surfactant structure, while anionic/nonionic interaction increases with the length of the alkyl chain of the anionic surfactant, but does not depend significantly on the position of the polar and head branching. — The introduction in the model of the pair interaction parameters, determined from the CMC of the binary mixtures, gives valuable predictions for the CMC and for the micelle compositions of the ternary mixtures. CMC of the ternary mixture are lower than the CMC of each component of the mixture. Contrary to that which is expected for an ideal mixing, the mixed micelles are principally composed of ionic surfactant molecules. Our results seem to show that these behaviors could depend slightly on the position of the polar head branching and on the length of the alkyl chain of the anionic surfactant. [ABSTRACT FROM AUTHOR]

Conductivities of the AOT and nonionic C12E5 systems are reported. A preculiarity of the AOT system is the possibility to prepare w/o microemulsions with more than 50 wt% of water, which show, however, a low conductivity. In contrast, a nonionic system with comparable amounts of water and oil displays a conductivity several orders of magnitude larger. Upon addition of salt the conductivity pattern of the AOT system resembles that of a nonionic with opposite temperature dependence. [ABSTRACT FROM AUTHOR]

We report a dynamic (QLS) and static (SLS) light scattering and small-angle neutron scattering (SANS) investigation of lecithin reverse micellar solutions with novel polymer-like properties. We present evidence for a water-induced transition from small colloid-like to giant polymer-like cylindrical aggregates. Under suitable conditions, we can determine the overall dimension, the flexibility, and the local cylindrical structure of these reverse micelles using SLS and SANS. This permits us to directly confirm the existing structural model and verify the postulated analogy between the structural properties of polymer chains and lecithin reverse micelles. [ABSTRACT FROM AUTHOR]

The phase behavior of ternary mixtures of water, hydrocarbons, and nonionic amphiphiles is, by now, well known. In this paper the effect of replacing water by formamide is studied. This polar protic solvent reduces the hydrophobic effect and, thereby, the repulsive interactions with surfactant tails. The result is a higher mutual solubility of formamide and surfactant, a weaker adsorption at the internal interface and, hence, a lower solubilization capacity of the amphiphile. The reduced amphilphilic strength of surfactants in formamide corresponds to Ci-4E in aqueous systems. As with aqueous systems the present mixtures form microstructures, namely oil-droplets in formamide and formaide-droplets in oil. For equal volumes of formamide and oil, small-angle neutron scattering (SANS) spectra indicate the existence of bicontinuous structures. [ABSTRACT FROM AUTHOR]

FT-IR spectra in the hydroxyl region in reversed micelles where the sodium counterions of the surfactant Aerosol-OT have been replaced by Ca2+ and Zn2+ ions are presented. The IR spectra, taken as a function of the molar ratio R = [H2O]/[surfactant], are analzyed in the framework of a twostate model for the water molecules in which the O-H vibration can be split into two contributions: one originated by the water "tightly-bonded" to the surfactant ions, and the other induced by the "bulk" water of the micellar water pool. We also evaluate the percentage a(R) of the bond water in the micellar growth process. Furthermore, an explanation of the O-H stretching band features is suggested by comparison between our spectra and those simulated through an MD "experiment". [ABSTRACT FROM AUTHOR]

Lecithin/isooctane/water gel is investigated by means of different experimental techniques, namely, depolarized light scattering, ultrasonic and dielectric measurements. Pure isooctane and lecithin/isooctane solution are also tested for comparison. A relaxation process, taking place in the 10−13 s time scale was revealed from the light-scattering experiment, both in the gel and in the solution. This is attributed to the reorientational relaxation of the solvent that keeps its bulk properties. The comparison between the activation enthalpies for the detected process in the gel and in the solution, together with the behavior of the relaxation times vs frequency showed the existence of some influence of the entangled network on the isooctane dynamics. Data from ultrasonic measurements show the existence of the same relaxation process, both in the gel and in the solution, with a relaxed value very near to the one obtained for pure isooctane. The observed dynamics were interpreted as due to the existence of the same elementary microspheres of lecithin in the bulk of the solvent in both systems. The relaxation phenomenon revealed by the dielectric data was analyzed in the frame of a Cole-Cole phenomenological law and associated to the role played by water molecules on lecithin reorientation. The temperature dependence of the observed phenomenon is in agreement with the existence of an entangled polymeric-network. [ABSTRACT FROM AUTHOR]

Alkyl monoglycosides and polyglycosides (APG) are characterized in terms of their interfacial properties which exhibit a dependence on alkyl chain length and degree of polymerization. A comparison is drawn to other nonionic and anionic surfactants. In hard water, clouding phenomena are observed for C8/10 and C12/14 APG. The critical micelle concentrations (CMC) of the alkylglycosides are similar to those of other nonionic surfactants and show a decrease with increasin galkyl chain length. The degree of polymeriization has only a minor influence on the CMC. Above the CMC, alkylglycosides exhibit very low interfacial tensions against mineral oil compared to C12/14 fatty alcohol sulfate (C12/14 FAS). In contrast to C12/14 FAS and C12/14 fatty alcohol hexaglycol ether, respectively, C12/14 APG shows remarakbly high dynamic surface tensions even at a concentration far above the CMC. For mixtures of C12/14 APG and C12/14 FAS the static surface tensions and the CMC lie close to those of C12/14 APG, whereas the dynamic surface tension behavior is dominated by the anionic surfactant. [ABSTRACT FROM AUTHOR]

The preparation of oriented protein samples is an attractive goal, e.g., to gain more detailed information from spectroscopic experiments. Our approach towards this aim was to prepare monolayers of phospholipids at the air-water interface and to incorporate the proteins into these ordered structures. Subsequently, we used the Langmuir-Boldgett (LB) transfer technique to obtain samples of oriented proteins on solid supports. — Incorporation was achieved by spreading the proteins from a detergent solution onto a prespread lipid monolayer on the water surface. We characterized successful incorporation by in situ fluoresence microscopy and by electron microscopy, and investigated the topology of transferred monolayers. — Our results show that the choice of the lipid matrix is pivotal. We present an optimized lipid matrix system that facilitates protein incorporation, while enabling LB transfer at the same time. — Fluorescence microscopic investigations revealed that the lateral phase structure of the lipid films remains qualitatively unaffected by the reconstitution, with the proteins incorporated into the fluid phases. Quantitative evaluations of the protein content of the thin film samples indicated that ∼15% of the proteins spread were incorporated, whereas evaluation of the additional area of incorporation (of protein and detergent) showed that a substantial amount of detergent was incorporated as well. [ABSTRACT FROM AUTHOR]

Electronic speckle pattern interferometry (ESPI) can detect micro displacements and deformation of optically rough surfaces. — Experiments have been performed on pure liquid surfaces and Langmuir films at the airwater interface to determine whether ESPI can be implemented to study liquid surface properties. — Mechanically induced resonant modes of liquid surfaces have been visualized as interference patterns similar to Chladni figures. Oscillation amplitudes on the order of a few microns have also been measured. — The resonance frequency depends only slightly on surface tension and surface pressure, while there is greater correlation between vibration amplitude and the characteristics of the liquid surface. — On the basis of these preliminary results it may be possible to use this technique to detect short wavelength oscillations (<1 mm) and to measure the damping of capillary ripples to obtain the viscoelastic parameters of liquid surfaces. [ABSTRACT FROM AUTHOR]

The adsorption behaviour of a homologous series of amphiphilic hemicyanines is studied at the air-water interface. The dyes exhibit an unusual, marked odd-even effect with respect to the standard free energy of adsorption and the minimum surface area demand. The reasons for such strong, hitherto unknown odd-even effect is not yet clear. [ABSTRACT FROM AUTHOR]

Nitronylnitroxides are promising materials for the preparation of unusual magnetic systems, particularly when coordinated with transition metal ions. In this work mono- and multilayers of the amphiphilic radical 2-tridecyl-4,4,5,5-tetramethyl-imidazolidine-1-oxyl-3-oxide radical were characterized from its spreading isotherms and by optical and ESR spectroscopy. The time stability of the films was also studied. [ABSTRACT FROM AUTHOR]

The following two-dimensional binary systems at the W/A interface are studied: stearic acid (SA)-polymethylmethacrylate (PMMA), stearylamine (SAm)-PMMA, SA-valinomycin (VAI), SAm-VAL, methylstearate (MS)-VAL. — The behavior of area, surface compressional moduli, and overall collapse pressure as a function of molar ratios of components shows: i) SA and SAm are compatible with PMMA if the pH of support allows their ionization; ii) SA and SAm are incompatible with VAL at any pH value of the support studied. — The different behavior is attributed to the impossibility of interactions between polar groups of VAL and ionizable groups of the other component. The bidimensional distribution of the VAL is confirmed by transfer of K+ from subphase to monolayers, proved by ATR-FTIR experiments on mono and plurilayers of VAL. — The polar groups are therefore oriented toward the inner molecular cavity of VAL. — The study extended to the MS-VAL system shows compatibility between components with prevalent repulsive interaction between the two components. [ABSTRACT FROM AUTHOR]

We have studied monolayers of a dye containing hydrophobic moieties at the air/water interface and in LB films. In particular, the aims of the present study were to characterize the interfacial behavior of the alkylsubstituted cyanine dye, (N,N′-tetrahexadecylcyanine iodide) to investigate the surface miscibility of the cyanine dye with the matrix molecule (dihexadecylphosphate), and to correlate the results obtained at the air/water interface with the data collected on transferred layers of the same system. For these purposes, mixtures with different molar ratios of matrix and dye were prepared and their interfacial distribution and orientation were studied, both at the air/water interface, and in multilayers transferred on solid substrates. The Monolayers at the air/water interface were studied by measuring surface pressure-area and reflection at constant area or at constant wavelength, whereas absorption spectra were performed on the transferred layer system. [ABSTRACT FROM AUTHOR]

We have investigated photo-induced electron transfer (PET) in monolayers at the water-air interface. The donor was a cyanine dye (di-octadecyl-oxacyanine perchlorate) incorporated in a matrix monolayer of dipalmitoyl-phosphatidic acid. Three different viologens derivatives were used as acceptors, namely methyl-, tetradecyl-, and benzylviologen. The acceptors were dissolved in the aqueous subphase and the process of adsorption at the interface was studied by measuring surface pressure-area isotherms, as well as UW-Vis reflection spectra. In the case of methylviologen, we did not find any evidence for penetration of the acceptor in the monolayer, whereas adsorption of benzyl- and tetradecylviologen led to changes in the arrangement of the molecules in the monolayer. — Photo-induced electron transfer was then monitored by measuring the change in fluorescence of the donor in the monolayer as the quencher was adsorbed at the monolayer/subphase interface. Fluorescence intensity-area isotherms were measured simultaneously with surface pressure-area isotherms. Fluorescence quenching due to the adsorbed acceptor was found to increase with increasing hydrophobicity of the quencher molecule. These results are correlated to the different modes of adsorption of the acceptors. [ABSTRACT FROM AUTHOR]

Two dimensional pattern formation during the phase transitions between the liquid expanded phase and various condensed phases in Langmuir monolayers is observed by fluorescence microscopy. For fatty acids, circular or fractal domains are generated, depending on temperature. The analysis of their geometrical properties yields information on characteristic lengths involved in this diffusion-controlled growth process and on line tension. For acyl-amino-acis, spectacular dendritic grwoth is observed. We have checked the predicted theoretical laws of shape selection (p2V = constant, V: tip growth velocity; p: tip curvature radius). From this, an estimation of the line tension anisotropy can be obtained. [ABSTRACT FROM AUTHOR]

We report a lateral diffusion study of a surface active protein, bacterial lipase from pseudomonas fluorescens, and a vinyl polymer, poly(t-butyl methacrylate) on the air/water interface by the technique of fluorescence recovery after photobleaching. For the validation of our technique and the calibration of the instrument, we relied on a phospholipid system that Peters and Beck used earlier, and found that our results were in accord with theirs within 20% in absolute magnitude. For both the phospholipid and lipase, we analyzed the lateral diffusion data in terms of the free area model of Sackmann and Träuble. We conclude that the results of lipase could be interpreted by invoking a conformational change induced by lateral compression in the monolayer state, and those of the polymer by postulating the quenching of the diffusion process in the dilute region when its surface concentration enters into the semidilute region. [ABSTRACT FROM AUTHOR]

Fluorescence microscopic studies of ester and acid monolayers show the existence of several condensed phases, in accord with recent diffraction measurements. Studies with polarized excitation reveal "star defects," i.e., organized domains of uniform tilt similar to those seen in smectic liquid crystals. The observation of chiral patterns in monolayers composed of achiral molecules is in accord with the proposal that one of the phases is the analog of the smectic L liquid crystal. Monolayers of pentadecanoic acid develop large-scale chiral defect structures. [ABSTRACT FROM AUTHOR]

Surfactant-bentonite complexes (organo-clays) with different amounts of adsorbed dodecyltrimethylammonium bromide (DTAB) were prepared. The adsorption of the pesticides paraquat and biphenyl from aqueous solution on clays was studied by the batch method with radiotracers. — On organo-clays the preferentially adsorbed di-cation paraquat only partially replaces the mono-cationic surfactant. This result was supported by investigations with microcalorimetry and x-ray diffraction. — On the contrary, the adsorption of the hydrophobic biphenyl is enhanced with an increased amount of adsorbed DTAB by hydrophobization of the bentonite. [ABSTRACT FROM AUTHOR]

The interfacial tension isotherms for bis(di-2-ethylhexyl)phosphoric acid and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester in aliphatic hydrocarbon-water systems were interpreted and used to propose an interfacial mechanism for the extraction of copper(II), zinc(II), and calcium(II). The surface excess isotherms were modeled using the Szyszkowski isotherm and spline function. The results suggest an interfacial mechanism of the metal extraction with the formation of the final product solvated by organic acid molecules as the rate-limiting step. [ABSTRACT FROM AUTHOR]

The adsorption of aromatic compounds (2-chlorophenol 2-naphthol) in the presence of cationic C16-surfactants by different clays (kaolin, illite, and bentonite (montmorillonite)) from water was studied. — The cationic surfactants alter the adsorption properties of clays by means of surface hydrophobing, which leads to a drastic increase and acceleration of the adsorption of these aromatic pollutants. If the surface is densely covered by surfactant ions, high exothermic heats of displacement for 2-naphthol are found by microcalorimetry. X-ray diffraction measurements of the basal spacing proved the intercalation of 2-chlorophenol within the hydrophobic interlayers of C16-bentonite. At very high surfactant concentrations (c ≫ CMC) the decreased adsorption of 2-naphthol was explained by a competition for 2-naphthol molecules between micelles and hydrophobic adsorbed surfactant layer. [ABSTRACT FROM AUTHOR]

The adsorption behavior of cetylpyridinium-chloride (CPC) at different oxide surfaces (Al2O3, silicagel, SnO2, TiO2) was characterized by means of liquid-flow adsorption microcalorimetry. The corresponding adsorption isotherms were also measured by a flow method. It was found that all the experimental enthalpies of displacement were exothermic. The plot of the enthalpies of displacement against the amount of CPC adsorbed results in straight lines with approx. the same slope for all oxides, although the surface charge of the oxides is different. Electrostatic and lateral interactions seem to contribute only little to the measured enthalpies of displacement. In apparent contradiction to these results, the investigation of the pH and electrolyte concentration dependence of CPC adsorption onto silica gel suggests an electrostatic adsorption mechanism coupled with hemicellization. [ABSTRACT FROM AUTHOR]

Reversible and persistent optical data storage in Langmuir-Blodgett-Kuhn liquid crystalline systems has been reported recently. Depending on the molecular structure, the trans-cis isomerization in these systems (induced by illumination with UV- and VIS-light) leads to different macroscopic behavior of the chromophore percentage on the photo-induced structural changes in a series of statistical copolymers. [ABSTRACT FROM AUTHOR]

We have recently introduced a new method of creating ultrathin films [1-3] based on the electrostatic attraction between opposite charges. Consecutively, alternating adsorption of anionic and cationic polyelectrolytes leads to the formation of multilayer assemblies. Multilayer buildup is easily monitored by small angle x-ray scattering (SAXS). The total thickness of the multilayer assemblies increases linearly with the number of adsorbed layers, indicating a stepwise and regular deposition process. — Here, we report on the fine-tuning of the total film thickness by changing the ionic strength of the solvent from which the polyelectrolytes are adsorbed. When the anionic polyelectrolyte is adsorbed from solutions containing 1.0, 1.5, and 2.0 mol/l NaCl, the average thickness of each oppositely charged layer pair is precisely adjusted to 17.7 Å, 19.4 Å, and 22.6 Å, respectively. [ABSTRACT FROM AUTHOR]

The dynamic viscosity of the waterless microemulsion glycerol/AOT [sodium bis (2-ethylhexyl)sulfosuccinate]/isooctane has been studied at constant volume fraction φ as a function of temperature. The experimental curves are curious: depending on the value of φ, the viscosity either decrease or goes through a maximum when the temperature increases. The results are interpreted in the framework of the percolation theory. The percolation locus in the φ-T plane has been determined, as well as the cloud-point curve. An approximative model is used in order to fit the percolation line, taking into account the temperature dependence of the interaction strength. [ABSTRACT FROM AUTHOR]

Ammonium-type F-alkylated surfactants characterized by the presence of two tails RF/R′F or RF/R′F have been prepared, and the vesicular behavior of some double-chain surfactants has been studied in ultrasound-treated aqueous dispersions. Stable vesicular aggregates were found which showed unilamellar membrane structures. Their shapes, hydrodynamic radii and size distriubtion were determined by dynamic light scattering and electron microscopy. The phase transition temperatures of aqueous dispersions of double-chain surfactants were measured by differential scannig calorimetry. [ABSTRACT FROM AUTHOR]

We study interbubble gas transfer in liquid foams by measuring the relative decrease of the bubble area from reflectometry. Foams are obtained by independently fixing foaming solution and gas flows through a coarse porous structure. Precise measurements of these flows instantaneously give the gas volume fractions of the foams; real time diffractometry gives their initial bubble size distributions, which we found to be lognormal. — We calculate interbubble gas transfer within such foams on the basis of a theory developed by Lemlich for other bubble size distributions. For a given bubble mean size, we find that the experimentally measured width of the bubble size distribution provides the fastest transfer; then the calculated transfer is close to the one which corresponds to the Lemlich distribution. — Comparison between theoretical and experimental relative decreases of the bubble total area allows to obtain the initial effective permeability of the interbubble medium to gas transfer. We show that this permeability can be drastically lowered by associating an anionic surfactant with an amphoteric one in the foaming solution . [ABSTRACT FROM AUTHOR]

New electrophoretic light scattering (ELS) measurements are reported on aqueous colloidal suspensions down to salt concentrations lower than ns = 10−6 M, where the polyions are liquid-like ordered due to screened Coulomb forces. Mobility data are presented for spherical polystyrene latices of different radius a and rodlike tobacco mosaic virus (TMV) particles (length l = 300 nm and radius a = 9 nm), and they are discussed in relation to the small ion concentration or ka. The salt concentration ns is determined via electric conductivity measurements. Static light scattering (SLS) combined with computer calculations are used to characterize the structure; they also yield the salt concentration of the suspensions. The suspensions of latex spheres show, with decreasing salt concentration, a minimum in mobility. For lowering hte salt content below 10−4 M an increase up to a factor of 3 is observed. The mobility of a dilute suspension of rodlike TMV is found to be about 5 μm/s/V/cm. Increasing the particle concentration leads to a decrease in mobility. In the limit of negligible salt concentration for a particle concentration below 0.1 mg/ml the mobilities lie above 5 μm/s/V/cm. At higher concentrations they are smaller than this value. A qualitative comparison with the theory is made. [ABSTRACT FROM AUTHOR]

Solid particles suspended in a liquid phase can build linear structures when a large enough electric field is applied to the suspension. These structures confer to the suspension a shear modulus G, which is measured with an oscillating plate device. This system allows to simultaneously visualize the change of structure of the suspension. We observe an important decrease of G with the amplitude of the strain, and explain it by the behavior of the forces between two conductive particles at short separations. Striking features relative to stripe formation upon large amplitude strain and subsequent considerable increase of elasticity are reported. [ABSTRACT FROM AUTHOR]

We suggest a method for preparation of large (∼ 15 ÷ 70 μm in diameter), unilamellar, fluctuating, isolated vesicles, allowing us to perform routine measurements of membrane bending elasticity modulus kc by image analysis of thermal fluctuations. The method is based on the effects of AC electric fields on the lipid swelling and liposome formation. We have observed a monotonous decrease of kc for egg phosphatidylcholine (EPC) vesicles from (0.66 ± 0.06) · 10−19 J for 1 day to (0.45 ± 0.05) · 10−19 J for 13 days after vesicle formation. The lipid mixture Chol/PC 37:63 mol/mol led to kc = (1.06 ± 0.15) · 10−19 J, and PE/PC 25:75 mol/mol — to (0.72 ± 0.06) · 10−19 J. — The mechanism of vesicle formation is discussed. It proved that the basic phenomenon is sequences of lateral fusions of smaller vesicles induced by the applied AC electric field. [ABSTRACT FROM AUTHOR]

The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (HMPAA) and surfactants is studied. The hydrophobic groups of the polymer (octadecyl or dodecyl chains) interact with the surfactant molecules to form mixed micellar-type aggregates. In semidilute solution these mixed aggregates act as cross-linkers between the polymer chains, inducing a viscosification or gelation of the system. The strongest effect was observed with a cationic surfactant, because in this case both electrostatic attraction and hydrophobic interactions contribute to the stabilization of the mixed aggregate. However, association occurs even between HMPAA and an anionic surfactant (SDS), despite the unfavorable electrostatic repulsions, indicating that the hydrophobic interactions are the driving force for the formation of the mixed aggregates. [ABSTRACT FROM AUTHOR]

We have measured the coalescence lifetimes of AOT-stabilised oil and water drops with the AOT monolayer present at the planar oil-water interface. Measurements were made as a function of aqueous phase NaCl concentration over the range over which phase inversion of the emulsions occurs and for heptane, dodecane and tetradecane as oil. The drop lifetimes decrease sharply with increasing [NaCl]. Below a crossover [NaCl], the oil drop lifetimes are longer than the water drops, whereas this behaviour is reversed at higher [NaCl]. The [NaCl] at the crossover points for the three oils increases with alkane chain length. This behaviour is compared with that of the corresponding emulsion systems which are water continuous at low [NaCl] but phase invert to give oil-continuous emulsions at high [NaCl]. The NaCl concentrations required for emulsion phase inversion increase with increasing oil chain length but are not identical to the [NaCl] values at the drop coalescence crossover points. [ABSTRACT FROM AUTHOR]

Stability and rheological studies on gel emulsions (w/o high internal phase ratio emulsions, HIPRE) both with pure and commercial polyethyleneglycol alkyl ether surfactants are reported. Stability of gel emulsions at room temperature is increased by addition of NaCl to the internal phase; in contrast, no appreciable effect is found at higher temperatures. Rheological properties are influenced by both NaCl concentration and temperature. Apparent yield stress and elastic modulus are increased either by NaCl addition or temperature increase. Shear modulus as a function of volume fraction is analyzed in terms of droplet size and interfacial tension. [ABSTRACT FROM AUTHOR]

The photoinduced electron transfer reactions from nanosized CdS particles synthesized in micelles of cadmium lauryl sulphate and sodium lauryl sulphate to various dialkyl viologens is measured for a molar ratio of cadmium to sulphide ions equal to 2. — The yield of the reduced viologens obtained by CdS irradiations is miximum in the case of C1 viologen, which decreases gradually with increase in the chaine length of the viologens. Moever, a back electron transfer reaction is observed in the case of C1, C3, and C8 viologens. The addition of sodium lauryl sulphate (NaLS) inhibits the back electron transfer reaction. This is due to strong interactions between methyl viologen and lauryl sulphate, which gives the viologens a hydrophobic character and favors their entrance into the micellar core. This is confirmed by studying the photoelectron transfer from CdS particles to methylviologen laurylsulphate. [ABSTRACT FROM AUTHOR]

Functionalized reverse micelles are used to control the size of the CdS semiconductor particles. We show, in dilute solution, that the use of mixed sodium-cadmium AOT reverse micelles favors the formation of monodispersed particles. By increasing the water content, the size of the particle increases, and it maintains a high monodispersity. The increase of the water pool concentration and the amount of cadmium ions induces an increase in the size and in the polydispersity. [ABSTRACT FROM AUTHOR]

The generalized Langevin equation and the procedure of contraction of the description is employed to study collective diffusion in colloidal suspensions without hydrodynamic interactions. We derive the time-evolution equation for the dynamic structure factor of the system. Our general results turn out to be fully equivalent to those derived on the basis of the many-particle Fokker-Planck equation. In particular, we show that, before taking the overdamped limit, the dynamic structure factor has the exact short-time dependence up to order t4. We explain how our approach could be further extended to derive additional short-time exact conditions. [ABSTRACT FROM AUTHOR]

It is shown that the two exponential modes in the dynamic scattering intensity obtained by scattering experiments from ternary polymer mixtures cannot, in general, be identified with the interdiffusion and cooperative diffusion processes, contrary to recent suggestions in the literature. Conditions under which such an identification is possible are obtained. General expressions for the interdiffusion and cooperative diffusion coefficients associated with a given pair of components a and b in a ternary, or, in general, multicomponent polymer mixture are obtained in terms of the partial mobilities μαβ and partial scattering functions Sαβ(q) of the a and b polymers. In the framework of the random phase approximation, a new expression of the interdiffusion coefficient in an incompressible ternary mixture of a and b homopolymers in a matrix of c homopolymers is found in terms of the tracer diffusion coefficients of the three species. It is shown that the results of the controversional "fast mode" and "slow mode" theories are obtained from this new expression as two limiting cases. [ABSTRACT FROM AUTHOR]

As has been shown for the system poly(ethylene glycol) (PEG-600) — H2O, a gradual change in the number of water molecules per oxyethylene (EO) unit leads to a corresponding change of the wavelength of the absorption maximum of methyl orange (MO). This effect has been used to investigate the alterations of the hydration state of oligoether chains in nonionic surfactans solutions. The measurements have been carried out with polydisperse preparations of p-(1,1,3,3-tetramethylbutyl)phenyoxypoly(oxyethylene glycol) with an average EO-chain length varying from 3.1 (OPE-3.1) to 90 (OPE-90). Special attention has been focused on the influence of lower alkanols on solutions of OPE-9. The shift of the MO peak sometimes parallels the micellization of nonionic surfactants, but not necessarily. The main information obtained by the MO method is about the hydration state of the EO chains, i.e., their aggregation state. By varying the EO degree of the OPEs from low (3.1, 5.4) to medium (9, 10, 13, 18) to high values (70, 90), distinct alterations in the aggregation behavior have been observed. It has also been shown solubilization and the structure-breaking action of alkanols affect the hydration state of the oligoether chains. [ABSTRACT FROM AUTHOR]

We report extensive light-scattering measurements (elastic, quasielastic, and Brillouin) performed in dense micellar or microemulsion systems. The overall analysis of the data, in terms of a static effective-medium approach, indicates that the observed dynamic and structural effects are related to a dynamic percolation regime. [ABSTRACT FROM AUTHOR]

We report depolarized light-scattering measurements on methylmethacrylate (MMA) gels crosslinked with ethylene-dimethylacrylate (ED-MA). The study is performed varying the crosslinking amount of the gels from 0 to 6%, in the range 0-150 cm−1 of the scattered light-spectrum. The obtained data confirm that the micro-phase separation phenomenon takes place in our system. [ABSTRACT FROM AUTHOR]

Static and dynamic light-scattering measurements were performed on water/AOT(sodium di-2-ethylhexylsulfosuccinate)/i-octane(2,2,4-trimethylpentane) w/o-microemulsions with various amounts of block-copoly(oxyethylene/isoprene/oxyethylene). We could show that the blockpolymer causes an aggregation of the microemulsion droplets. The mean size and polydispersity of the aggregates increase as the number of copolymer molecules per nanodroplet is increased. When the formal ratio of nanodroplets and copolymer molecules equals one, the mean aggregation number is three. The relative steepness of the increase of molar mass and hydrodynamic radius with increasing copolymer concentration suggests that the aggregates formed have an elongated shape. [ABSTRACT FROM AUTHOR]

Polymerization in microemulsion allows for the synthesis of latices with sizes of 10 nm ≤ R ≤ 60 nm. In the system styrene/cetyltrimethylammoniumchloride/water, the particle size is controlled by the relative amount of surfactant to styrene and can be predicted by a simple three-phase picture of the microemulsion. Polymeric surfactants reveal a more complex behavior which prohibits an effective size control. — The particle surface is easily modified by addition of functional comonomers or additives which are incorporated in the interface. The additives stabilize or poison the original microemulsions. The results of the sucessful modification are highly reactive particles with a larger inner surface which can be used for different purposes. For example, the synthesis of a material with the ability of selective ion binding is described. [ABSTRACT FROM AUTHOR]