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The structure of water in aqueous solutions of polyoxyethylene nonionic amphiphiles C10E5, is studied by Raman, depolarized Rayleigh, and Brillouin scattering along an isothermal path crossing the isotropic one-phase region from 0 to 1 amphiphile volume fraction φ. [ABSTRACT FROM AUTHOR]

The structure of water in aqueous solutions of polyoxyethylene nonionic amphiphiles C10E5 is studied by Raman scattering along an isothermal path crossing the isotropic one-phase region from 0 to 1 amphiphile volume fraction φ. The isotropic OH stretching vibration spectrum evidences a behavior that depends on the amphiphile concentration. The interpretation of such scattering data leads to the following structural picture for the water in the systems; for φ lower than 0.75, water is partially bound to the oxyethylene groups of the amphiphile; above φ=0.75 all water present in the system is bound. The structure of such bound water presents a local, low dense, four coordinated environment. [ABSTRACT FROM AUTHOR]

A theory is given for scattering by disc-like clay particles coated with organic layers of uniform thickness. A comparison of theoretical expectations is made with small-angle neutron scattering results obtained on hexadecyltrimethylammonium montmorillonite in an aqueous environment and dioctadecyl dimethylammonium montmorillonite in a non-aqueous medium, toluene. [ABSTRACT FROM AUTHOR]

A new cyclic deionization method for charged colloidal particles is presented. Charge numbers evaluated from four different, simultaneously performed experiments for two species of PS — latex spheres at different, in situ controlled, salt and particle concentrations are presented. [ABSTRACT FROM AUTHOR]

Lipase can catalyze the synthesis of various specific esters, under mild conditions, provided that the water content is low in the reaction medium. Such reactions can take place in water in oil microemulsions, since in these systems i) the substrates can be solubilized in the continuous phase, ii) the enzyme molecule is hosted in the dispersed phase, iii) the water concentration can be controlled, and iv) the interface for these heterogeneous reactions is considerably increased. Nonionic microemulsions formulated with C12E4 in decane, were used for the enzymatic synthesis of fatty acid esters. The effect of various parameters on the reaction rate was studied. These systems were also used for transesterification reactions of triglycerides with free fatty acids. [ABSTRACT FROM AUTHOR]

Two populations of non-ionic surfactant vesicles (NVS) with mean diameter (MD) of 322 and 72 nm, and based on diglycerol hexadecylether (C16G2), cholesterol (CHOL), and dicetylphosphate (DCP) (47.5/47.5/5 wt%) were prepared by detergent dialysis and sonication, respectively. The solubilization of NSV, performed by the continuous and controlled addition, at different rates, of a 100 mM OG solution to vesicles was examined at 25°C by monitoring turbidity at 350 nm. The molecular composition of aggregates ([OG:lip]agg) and the OG concentration in the continuous phase ([OG]bulk) were determined from relation between total OG and lipid concentration at the break points observed on the solubilization curves. At the fastest rate of OG addition, no insertion of OG occurs until [OG]bulk = 13 mM, and when [OG]bulk = 23 mM, the solubilization mechanism of large and sonicated NSV involves a unique process through the formation of the same aggregates. At the slowest one, sonicated NSV membranes exhibit impermeability properties until [OG]bulk = 11 mM and the insertion of the detergent and, most likely, its lateral diffusion in the lipidic structures are time-dependent. Nevertheless, the amounts of OG required to solubilize the NSV membranes indicate that bilayers are particularly resistant to the action of OG molecules, probably due to the C16G2-CHOL association. [ABSTRACT FROM AUTHOR]

In the present work some characteristic properties of aqueous solutions of biological macromolecules are presented. — Experimental results (obtained by means of rheological measurements, ultrasonic techniques, elastic and quasi-elastic light scattering and neutron scattering) reveal the presence of long-ranged structures exhibiting a thixotropic behavior. Such structures, built-up gradually in the course of time, consist of clusters of macromolecules regularly spaced. Moreover, macromolecules inside the cluster show the same ordering on a smaller scale. Occurrence of such thixotropic structure considerably modifies the properties of the solvent (water). [ABSTRACT FROM AUTHOR]

Polarized Maandelstam-Brillouin scattering data in lysozyme 10% by weight aqueous solutions are presented. The hypersound velocity νhs is measured as a function of the exchanged wavevector k. — The experimental results indicate that the hypersonic velocity values, greater than the ones of "bulk" water, behave like the structure factor S(k), giving evidence of a greater rigidity of the system for the k values that correspond to the long-lived Fourier components of the structure factor. [ABSTRACT FROM AUTHOR]

The osmotic coefficients of N-nonyl and N-decyl nicotinamide chlorides, synthesized in our laboratory, have been determined by means of a OSMOMAT vapor pressure osometer. In the precision limits of the method used, they agree as a trend with those previously measured for octyl and dodecyl compounds. If interpreted by means of a pseudo-phase transition model, they could suggest the presence of a phase transition involving a change in the number of particles present in solution, as was already supposed in the case of octyl and dodecyl compounds from measurements of heat capacities vs concentration. — The experimental trends can be fitted by using different theoretical approaches, allowing for the determination of the ionic interaction parameters. — The determination of osmotic coefficients allows the evaluation of the excess free energies of the surfactant solutions and of the entropic contributions once the enthalpic ones are known. Analyzing the behavior of the excess free energies for the homologous series of alkyl-nicotinamide surfactants, a group contribution for each −CH2 group of −2.9 kJ mol−1 can be evaluated in the postmicellar region. [ABSTRACT FROM AUTHOR]

The highly hydrated phospholipid bilayers often exhibit the so called Pβ or ripple phase, which is not yet clearly understood. We have associated the ripple phase to a thermally fluctuating ripple deformation of the bilayer that may be Fourier decomposed into a set of spatial modes. These modes, called ripplons or capillary waves, are driven by the viscoelastic properties of the membranes at the interface with the solvent. The model we proposed is applied on experimental results of radiowave dielectric measurements in DPPC- and DMPC-water mixtures, where the polarization contribution in the ripple phase is supposedly originated by the ripple modulation, and in DPPE-water mixture, where the pretransition disappears. The prediction of the model shows a good qualitative agreement with the experimental results in a wide frequency range. [ABSTRACT FROM AUTHOR]

Using small-angle neutron scattering (SANS), we have studied Scoh(Q) patterns from agarose gels as a function of concentration, H/D contrast, and temperature. Four characteristic regions become apparent in logS vs logQ plots as C increases up to ∼0.5 g agarose/g water. In the intermediate Q region (0.005 ⩽ Q ⩽ 0.075 Å−1), we find extended linear segments in log-log plots. The slopes of these, i.e., the exponents D in S(Q) ∞ Q−D, can be related to scaling parameters which reflect both the (limited) fractal structure of such gels and their inherent polydispersity. Comparison of measured SANS curves with computer simulations has also been done for model gels. − To address questions relating to the network dynamics, we have measured quasi-elastic spectra at μeV resolution (IN10 at ILL) for fully H2O-exchanged gels. Most of the lines observed can be separated into a central, slightly broadened peak superimposed on a broad, background-like Lorentzian reflecting mainly water translational modes. The observed behaviour can be related to the current description of the dynamics of polymeric chains in solution and shows a crossover from a Rouse-like behaviour (Q<0.5 Å−1) to a higher Q region where the broadening mainly reflects Brownian motions of local segments, as well as limited diffusion of the water of hydration. [ABSTRACT FROM AUTHOR]

The kinetics of the spontaneous phosphophatidylglycerol (PG) transfer between equimolar amounts of DC15PG vesicles and equal-sized DMPG magnetoliposomes (i.e., Fe3O4 cores which are coated by a phospholipid bilayer (see De Cuyper & Joniau (1988) Eur Biophys J 15:311-319)) was monitored at pH 7.0. The total PG content of the magnetic vesicle population at first drastically decreases, but later on restores. This complex behavior can be explained in terms of an asymmetric, bidirectional lipid flux: at 41°C the halftime values equal 9 and 91 min for the DMPG efflux and DC15PG influx, respectively. In the temperature zone between 32° and 41°C the temperature dependency of the DC15PG transfer rate is expressed in the Arrhenius plot by a straight line from which an activation energy of 27.3 kcal/mol is calculated. In the presence of 1.5 M DMSO which is known to be a "water-structure breaker", the transfer rates increase by a factor of 6. Further thermodynamic treatment, based on the classical transition-state theory, reveals that the major differences in the transfer rates are reflected in the value of ΔS≠, which in the DMSO-containing medium is increased from 8.8 to 16.9 entropy units. However, ΔH≠ values, which do not differ significantly, represent the main contribution to ΔG≠. [ABSTRACT FROM AUTHOR]

The effect of variations in pH and in concentration of four different amino acids (alanine, glycine, lysine, and threonine) on the electrical properties of the nitrofurantoin/aqueous solution interface is first investigated by the microelectrophoresis method. pH appears to be a determinant factor in the way amino acids interact with the negatively charged nitrofurantoin particles. The fact that alanine (with a non-polar R-group in its molecule) is the amino acid with the smallest effect on the zeta potential of the particles suggests that the polarity of the group is essential in accounting for such interaction. These data are used to interpret experimental results on the stability of the suspensions, as detected from the rate of change of their turbidity with time. [ABSTRACT FROM AUTHOR]

We report changes in the percolation threshold of AOT water droplets by solubilizing cytochrome c, a water-soluble protein. The change of the critical percolation factors (volume fraction, temperature, water content) is attributed to the increase in the attractive interactions between droplets by solubilizing cytochrome c in water droplets. The critical exponents determined from percolation theories are compared using filled and unfilled micelles. [ABSTRACT FROM AUTHOR]

The effect of the presence of the sphingolipid ceramide (CER) on the properties of vsicles of dioleoxylphosphatidylcholine (DOPC) has been investigated by electron paramagnetic resonance (EPR) of doxyl stearic acid (DXSA) with the oxazolidinyl ring in different positions on the alkyl chain. CER acted as a condensing agent at temperature near the gel-liquid crystal phase transition temperature (Tc), whereas it acted as a fluidizer at T well above Tc. This occurred in the double-layer region from the water-lipid interface down to the double-bond system of the oleoyl residues of DOPC. Spreading isotherms of DOPC and DOPC/CER mixtures at T ∼ Tc confirmed the ESR results. [ABSTRACT FROM AUTHOR]

Viscosity measurements as a function of the volume fraction on a dilute colloidal water solution of polystyrene particles are performed in deionized water suspensions at several ionic strengths. The analysis of the data confirms the idea that in such systems their rheological behavior can be completely explained in terms of the interparticle potential energy of interaction. [ABSTRACT FROM AUTHOR]

Negatively charged polystyrene latexes with relatively high surface charge density have been prepared by the emulsifier-free method. Three samples of approximately the same particle size and different surface charge density have been obtained. The effect of pH and ionic strength on electrophoretic mobility has been studied and the experimental mobility converted into ζ-potential according to the O'Brien-White and Dukhin-Semenikhin theoretical treatments. — The ζ-potential values obtained by D-S equation are reasonably in agreement with the predictions of the Gouy-Chapman model. Thus, the passage of mobility and, correspondingly, ζ-potential through a maximum at low ionic strengths of the solution is due to the influence of surface conductance on electrophoresis. Also, primary electroviscous effect has been measured. An approximate equation derived from Booth theory explained the variation of the relative viscosity with the electrokinetic radius. The agreement between theory and experimental data was very good. Finally, critical coagulation concentration values were obtained experimentally. No significant differences were found, whcih is in agreement with the similar ζ-potential values obtained with the three samples of polystyrene latex. [ABSTRACT FROM AUTHOR]

Counterion distributions around-like polyelectrolytes in solution are measured directly using small-angle rod-like x-ray scattering (SAXS). Two systems are studied: cylindrical micelles formed by a comb-shaped copolymer poly-(1-octadecene-co-maleic anhydride) (PODMA), neutralized by CsOH, in aqueous solution; and 500 Å persistence length DNA fragments in aqueous solution having Na+ or Cs+ as counterions, respectively. Method of SAXS data analysis is presented. The Poisson-Boltzmann (P-B) equation in the cell model is used to compute the counterion distributions. Comparison of SAXS data for the PODMA case with the theory shows that the P-B solution overestimates the charge accumulation on the micellar surface due to the very high linear charge density parameter ζ (= 33) of the micelle, while for the case of CsDNA one needs to assume a considerable amount of counterions present in the major and minor grooves of the double helices. [ABSTRACT FROM AUTHOR]

There is now considerable experimental support for the occurrence of thermal anomalies in the physical properties of aqueous colloidal systems in small temperature ranges at about 15°, 30°, 45°, and 60°C. These anomalies are believed to be caused by structural transitions of higher order in water near the particle surfaces. These processes obviously lead to the formation of extended hydration layers. — By using photon correlation spectroscopy, we have determined the coagulation kinetics of hydrosols containing differently sized silica particles in the presence of KCl, KF, MgCl2, and BaCl2. Particularly the earth alkali chlorides generate strong hydration forces conctributing to the overall repulsion effects in the temperature range 25°-45°C. [ABSTRACT FROM AUTHOR]

In this work, forced Rayleigh scattering is combined with a new deionization technique to measure the self-diffusion coefficient of strongly interacting charged polystyrene particles. For each measurement the, actually continuous, deionization process is stopped, allowing the suspension to relax from a sheared state to an equilibrium state. Conductivity and diffusion coefficient are monitored, both during this relaxation to equilibrium, and in dependence of the total deionization time. Relaxational behavior in the diffusion coefficient is observed in samples of both fluid and crystalline equilibrium state, while the conductivity remains unchanged. With increasing total deionization time the conductivity reaches a minimum and rises again to a stable plateau. The self-diffusion coefficient in equilibrium (i.e., at rest) also drops with increasing deionization time for monodisperse samples to unmeasurably low values. On the other hand, a finite, but small diffusion coefficient is found for the charge bidisperse sample. [ABSTRACT FROM AUTHOR]

We have used Monte Carlo simulations to study the interaction of two uniformly charged colloidal particles with adsorbed oppositely charged polyelectrolytes. A predominantly attractive net force is found. The force consists of an attractive term due to bridging and electrostatic correlations and a repulsive term of direct entropic origin. At large separations the force is found to be determined by electrostatic interactions, but at shorter separations the bridging by polyelectrolytes stretching between the colloids is the dominant contribution. This bridging attraction is large and significant in comparison with the ordinary van der Waals interaction. [ABSTRACT FROM AUTHOR]

Mixtures of charged-spherical Yukawa particles are investigated in a regime of size, charge, and density typical of charged colloidal dispersions. We used the thermodynamically self-consistent approximation of Rogers-Young (RY) to calculate the distribution fucntions, gaβ(r), and the partial structure factors, Saβ(k). Mixtures of two different Yukawa particles are studied over the whole concentration range changing the size ratio and the charge ratio. The role played by the charge and the size asymmetry is visualized by the Bhatia-Thornton structure factors. It is found that charge ordering grows as the charge asymmetry (or charge polydispersity) is increased, whereas the opposite behavior in found for the concentration ordering. We also studied mixtures of up to five different species of Yukawa particles in order to understand polydispersity effects in charged colloidal suspensions. [ABSTRACT FROM AUTHOR]

In a previous communication [1], we presented a theory for tracer-diffusion phenomena in binary mixtures of highly charged spherical macroparticles in the limit of zero concentration of one of the species. In this work, we report results of the extension of such a theory for the case of finite concentrations of both species, and discuss the effect of bidispersity when different parameters (charges, diameters, etc.) are varied. The input static correlation functions are calculated within the extended rescaled mean spherical approximation for DLVO interactions. [ABSTRACT FROM AUTHOR]

The Brownian dynamics of a colloidal suspension is measured in the immediate vicinity of a rigid surface by the evanescent quasi-elastic light-scattering technique. A net decrease of the measured diffusion coefficient is observed, due to the hydrodynamic slowing down of the particles very close to the wall. This effect is all the more important when the particles are allowed to get close to the wall, i.e., when the range of the static wall/particle repulsive interaction decreases. It thus provides a mean for testing the particle/wall static interactions via a dynamic light-scattering measurement. The data are analyzed by Brownian dynamic simulations which are proven to be quite valuable to interpret light-scattering data from "hindered" scatterers, such as particles confined in the neighborhood of a wall, or trapped in a porous media or a gel. [ABSTRACT FROM AUTHOR]

Structural properties of colloidal suspensions of charged rodlike particles are studied by computer simulation and several perturbation theory schemes. As a model for the interaction, we consider a repulsive screened Coulomb potential between two interaction centers on each rod. — MonteCarlo simulations were performed for both the dilute (c<1/L3) and the semidilute (c>1/L3) regimes. Results for the pair correlation function, the static structure factor SM(k) and the angular correlation of rod axes were obtained. It turns out that the concentration dependence of the peak position of SM(k) shows a shift from a c1/3-dependence in dilute suspensions to a c1/2 behavior for higher concentrations as observed in light scattering experiments on suspensions of rodlike viruses. — In applying perturbation theory the full interaction potential is expanded with respect to a spherically symmetric reference potential. The latter has been determined according to several averaging schemes: mean potential, median potential, reference averaged Mayer potential (RAM) and the blip function method. A comparison of the results of these schemes with simulation data shows that perturbation theory provides a good description of the structure of this system only in the dilute regime. [ABSTRACT FROM AUTHOR]

Investigations of solubility/precipitation equilibria of aluminum-dodecylbenzensulfonate in sea water have been performed by light scattering and polarizing microscopy. The solubility with respect to surfactant has been found to be 10−10 mol dm−3. [ABSTRACT FROM AUTHOR]

We use a stochastic model to predict the droplet size distribution of emulsions generated in a mixer. The emulsions are made of two immiscible liquids, and do not contain surfactants. The intensity of mixing is measured by the speed of rotation of the propeller stirrer. - The model depends on the two extreme diameters (dmin, dmax) of the states in which the droplets are classified during the formation of the emulsion. It predicts a lognormal stationary distribution, the two independent parameters of which can be analytically related to dmin and dmax, by assuming that during the emulsification the breaking/coalescence probabilities of the droplets are time independent and linear functions of the droplet diameter. It can also be related to the speed of rotation of the stirrer by means of the isotropic turbulence theory. — The predicted volume median diameters and standard deviations of the lognormal stationary distributions are in agreement with experiments especially designed to test the model. [ABSTRACT FROM AUTHOR]

The enzyme Chromobacterium viscosum lipase has been immobilised in a microemulsion-based organogel. Kinetic studies have been performed using HPLC on the synthesis of octyldecanoate from n-octanol and decanoic acid. Catalytic efficiency of the lipase-containing gel is significantly improved by increasing the surface area per unit volume of gel in contact with the substrate-containing, external oil phase. Large amounts of enzyme can be entrapped within the gel — in our case, an enzyme concentration of 600 µg per ml of organogel was easily achieved. The catalytic activity is essentially unaffected over a wide range of gelatin concentration and w0-values of the gel, though in terms of purely practical considerations, compositions giving rise to "hard" gels are the most appropriate for manipulation. The low apparent activation energy of ∼20kJ mol−1 for the reaction is believed to indicate a low energy barrier for diffusion of material between phases and through the enzyme-containing gel. [ABSTRACT FROM AUTHOR]

The microelectrophoretic behavior and colloid stability of dilute dispersions of calcium oxalate monohydrate (COM) in solution have been studied. The COM crystals were precipitated at different experimental conditions of the nucleation process. In a first step, we have investigated the influence of predominant cations or anions on the sign of the COM surface charge. In a second step, the effect of addition of several inhibitors (D-glutamic acid and sodium heparin) during the nucleation process was also investigated. The i.e.p. of the COM particles depends on the excess of calcium or oxalate ions during the nucleation process. The electrokinetic behavior of the COM particles precipitated in the presence of D-glutamic acid show a similar behavior to that of the standard COM particles, as regards the pH and pCa. The ζ-potentials of the COM particles precipitated in the presence of sodium heparin are negative for the entire pH range due to the specific adsorption of this mucopolysaccharide. When the heparin concentration in solution is higher than 3 · 10−3 g/l the COM surface is completely covered by this macromolecule and the precipitated samples display the same electrokinetic behavior. — The colloid stability of a calcium oxalate sol has been studied using the empirical relationship between the ζ-potential and the coagulation behavior provided by Eilers and Korff. The EK index shows that from a colloidal point of view the COM dispersions are very unstable when the COM crystals are preciptated in the presence of 10 p.p.m. of D-glutamic acid. However, the COM crystals precipitated in the presence of 100 p.p.m. of D-glutamic acid present the greater EK index values, which indicates the inhibitory character of D-glutamic acid at this concentration. For the COM dispersions prepared from crystals precipitated in the presence of low and high contents of sodium heparin, the EK index reveals that the COM dispersions become more stable as the heparin concentration in solution increases, which indicates the possible inhibitory character of the heparin. [ABSTRACT FROM AUTHOR]

This paper deals with the electrokinetic study of the solid components of the washing process, such as carbon black and polyester and polyester-cotton fabrics, under the influence of the cellulose ethers as antiredeposition agents and surfactants in the washing solution to explain the deposition results presented in a former paper by the same author. The components of the wash liquor studied were various cellulose ethers, used as antiredeposition agents (CMC, HPMC, HBMC and MHEC), and the anionic surfactant sodium dodecylbenzene sulfonate and the non-ionic surfactant Triton X-100 by separate and in different mixture ratios with a builder such as nitrilotriacetic (sodium salt) (NTA). The potential energy between carbon black particles and fabrics (polyester and polyester-cotton) was assessed by the theory of heterocoagulation, in an attempt to explain the different behavior of the antiredeposition agent during the washing process. [ABSTRACT FROM AUTHOR]

Homopolymer steric stabilization of aqueous mineral particle suspensions is generally brought about by adsorption and formation of a polymer layer at the solid-liquid interface. Hence, with homopolymers arise the problems of efficient adsorption on the solid surface and also satisfactory compatibility or dispersibility of the polymer in the liquid. These problems may be solved by using diblock copolymers, presenting a lyophobic adsorbing block on the one hand, and a lyophilic dispersing block on the other. However, with block copolymers the adsorption process becomes more complicated on account of micelle formation. Competition between micellization and adsorption may exist (theory of Munch and Gast, 1986). We studied the adsorption of alkyl ethoxylate diblock copolymers of medium molecular weights on titanium dioxide as a function of the polyethylene oxide chain length. We simultaneously followed as a function of the copolymer concentration, the size of the molecule (or micelle) in the solution by small-angle x-ray diffraction, and the thickness of the adsorbed copolymer layer by microelectrophoresis. The results depend on the ratio (R) between the molecular weight of the hydrophilic chain (PEO) and that of the hydrophobic chain (alkyl). With R equal or above 4.2, unimolecular micelles developed adsorption more or less flat onto the surface, whatever the copolymer concentration. With R below or equal to 1.9, neat spherical or lamellar micelles are formed, depending on copolymer concentration. Then, we observe a series of adsorptions and desorptions of individual molecules or micelles according to the copolymer concentration. For instance, spherical micelles desorption from the oxide surface takes place when lamellar micelles are developing in the solution. Finally, with R between 1.9 and 4.2, different complicated intermediary situations are observed. [ABSTRACT FROM AUTHOR]

We have investigated the salt-induced fast aggregation of monodisperse polystyrene spheres by means of an elastic light-scattering instrument covering almost two decades of the scattering wave vector. The measurements have been taken at 31 scattering angles as a function of time during the reaction kinetics. This allows to simultaneously determine the average cluster radius as the reaction proceeds, as well as the fractal dimension df of the aggregates. Runs have been made at fixed salt concentration and varying the monomer concentration. — We find that for the larger values of the concentration the fractal dimension is df = 1.6 ± 0.02 and the determination is quite reproducible. However, runs for concentrations below 1010 cm−3 tend to give more erratic results, but a definite trend towards larger values of df is observed. [ABSTRACT FROM AUTHOR]

BEDT-TFF derivatives, labeled 1a and 1b are used to build Langmuir-Blodgett films. — In the first step, oxidation by iodine vapor leads, in both cases, to the formation of radical cation dimers: (1a·+)2 and (1b·+)2. However, the subsequent behavior of films strongly depends on the way the aliphatic substituents are grafted onto the electroactive nucleus. Built-up films of 1b go back reversibly to their initial insulating state, and those of 1a undergo a solid state reorganization leading to a permanent conducting phase. These differences are explained in terms of steric hindrance. Spectroscopic arguments are used to derive the stoichiometry of the conducting films of 1a, which is likely to be that of conducting bulk crystals of (BEDT-TFF)2I3. [ABSTRACT FROM AUTHOR]

An ultrasonic technique based on attenuation measurements is used to characterize suspensions of solid or liquid spherical objects in a fluid. The theory of the propagation of sound in such systems provides an expression of the attenuation that depends strongly on the particle radius. An oil-in-water emulsion and some polystyrene latexes swollen by styrene were studied. For each system, the fit of the ultrasonic theory to the attenuation data provided a value of the radius of the droplets that was found to be in very good agreement with values obtained with either PCS or electron microscopy techniques. The effect of ageing and aggregation of the dispersed particles is also investigated. [ABSTRACT FROM AUTHOR]

The tensio-active properties of different types of polymerizable diesters can be used to synthesize two-dimensional model networks at the interface between oil and water. — The adsorbed monolayers can be polymerized and crosslinked by UV-irradiation. — The kinetics of surface gelation were systematically investigated by measuring the two-dimensional shear modulus and the surface viscosity as a function of the reaction time. The two-dimensional so-gel transition can be describedi n the framework of percolation theories. The rheological properties of the polymerized films exhibit typical features of rubber-elastic systems. — The interfacial polymerization was applied to create a new type of microcapsule, which can be used as a simple model system in order to simulate the flow behavior of biological cells. We have investigated the influence of the membrane elasticity on the deformation process of the droplets using the experimental technique of optical microscopy. [ABSTRACT FROM AUTHOR]

Inverse gas chromatography (I.G.C.) was applied to the characterization of the surface properties (dispersive component (γsD) of surface energy, and acid/base interaction parameter (Isp)) of a series of aluminas differing in specific surface area, but also in contents of impurities (Si, Ca, Na, Mg). This method was extended to a series of barium titanates varying in Ba/Ti ratios. It is shown that both γsD and Isp are very sensitive to the presence of impurities or to the Ba/Ti ratios. [ABSTRACT FROM AUTHOR]

Liquid foams are obtained by independently fixing foaming solution and gas flows through a coarse porous structure. Precise measurements of these flows immediately give the gas-volume fractions of the foams; real-time diffractometry gives their initial bubble-size distributions and these are found to be lognormal. — The proposed methods provide reproducible foams and are sensitive. They will be useful to test the interbubble gas transfer theory and to grade surfactants according to their ability to form persistent foams. [ABSTRACT FROM AUTHOR]

The phase behavior of ternary systems made from alkyldimethylaminoxide as zwitterionic surfactant, long-chain alcohols as cosurfactant, and water was investigated with respect to the occurrence of a L3 phase. In almost all of the systems, it was possible to verify the existence of such a phase in the vicinity of a corresponding lamellar phase. In addtion, in the case of C14DMAO with heptanol and its higher homologues, it was possible, not only to obtain a conventional L3 phase, but also a principally similar phase at lower cosurfactant concentrations (L′3 phase) that differs from the first one mainly by its much higher viscosity and by a much more pronounced streaming birefringence. All the L3 phases investigated were characterized by means of electrical birefringence experiments, dynamic light-scattering, and viscosity measurements. [ABSTRACT FROM AUTHOR]

Fluorescence spectra indicate that pyrene is solubilized in a non-polar region in lead(II) decanoate. The local fluidity of the probe in the La and liquid phases, monitored by excimer formation, is comparable to that of aliphatic hydrocarbons at the same temperature, and the microviscosity is an order of magnitude lower than the bulk viscosity of the soap. [ABSTRACT FROM AUTHOR]

This paper deals with the study of the influence of shear rate and surfactant concentration on the transient flow of a lamellar liquid crystal. A polyethylene glycol (EO=10) nonylphenyl ether has been used. Rheological studies have been carried out with a rotational viscometer, using a Mooney-Ewart sensor system. Shear rate ranged between 0.3 and 18 s−1. All measurements were made at 20°C. A stress overshoot can be observed in transient flow. Time at the overshoot decreases as shear rate or surfactant concentration increases. A power law equation can be used to fit the experimental results of peak and equilibrium viscosities vs shear rate. Shear rate has much more influence on peak than on equilibrium viscosity. The amount of overshoot decreases as shear rate increases. This decay is more significant for systems with less surfactant content. Time-dependent stress decay and fall in viscosity with shear rate have been related to the orientation of crystallites. The decrease of the amount of overshoot with shear rate indicates the formation of metastable defects that lead to an increase in viscosity with rate and shear time. [ABSTRACT FROM AUTHOR]

Monolayers and Langmuir-Blodgett (LB) multilayers were studied in order to prepare mimetic membranes permeable to gases and ions. In particular, valinomycin (Val) monolayers were studied on subphases containing K+ and Na+. Spreading isotherms were indipendent from temperature and from the subphase and showed prevalently a liquid-expanded phase. Monolayer thickness was measured ellipsometrically and it showed a conformation of Val almost planar at the interface. Collapsed films, trnasferred on solid support, were characterized with SEM. Bidimensional mixture of Val and stearic acid (SA) were studied in mono and LB plurilayers. The Val and SA are immiscible in bidimensional phase and their immiscibility does not vary with the ions used in the subphase. ESCA spectra were recorded for LB films of Val alone and Val/SA mixtures. The results showed the presence of K+ in LB multilayers. [ABSTRACT FROM AUTHOR]

In this study, we present the dependence of the relaxation processes from the size cation and thermal history in complexes of polyethylene oxide (PEO) and alkali metal salts (sodium and potassium thiocyanates). The internal friction behavior as a function of temperature and frequency reveals the presence of local (γ) and cooperative (aa) molecular relaxations. The region of the γ-relaxation, which shows a single mechanical loss peak in pure PEO and in PEO-NaSCN, is strongly modified by the addition of potassium salt to PEO and two close peaks are present. Samples, prepared by a slow evaporation of the solvent, have a semi-crystalline structure. A "quenching" procedure imposed on them gives rise to the same structure, but enhances the amorphous phase and shifts the glass transition to lower temperatures, probably as an effect of decreasing constraints of the crystalline phases on the amorphous regions. Finally, different thermal histoires also produce changes on the low temperature γ-relaxation, which are discussed accordingly with the revealed phase behavior. [ABSTRACT FROM AUTHOR]

Electron transfer reactions of photoexcited ruthenium(II) complexes with quenching agents were studied by steady-state and time-resolved luminescence spectroscopy in the presence of a new class of polyelectrolytes: Starburst dendrimers. The polymers are spherical in shape with a highly packed hydrophobic shell, in particular three different generations of carboxylate sodium salts with different size and surface charge density were used. The experiments were performed using Ru(bpy)3+, Ru(phen)32+ as luminescent probes, whereas Co(phen)33+ and methylviologen were used as quenchers. Comparative results were obtained for the same redox couples in the presence of micelles having different polar groups. Stern-Volmer constants were obtained from luminescence emission intensities as a function of quencher concentration. The results showed an enormous increase of the quenching efficiency in the presence of Starburst dendrimers compared to micellar solutions. Further information was obtained from analysis of the emission decays of the probes by means of an adequate kinetic scheme. The results showed that electron transfer took place at the Starburst-water interface with a mechanism strongly dependent on the structure of the quencher and the hydrophobicity of the probe. [ABSTRACT FROM AUTHOR]

The mechanical characteristics (internal friction and dynamic elastic modulus) of polyethylene oxide (PEO)-KSCN complexes are studied as a function of temperature (120-300 K) and frequency. The mechanical spectrum is characterized by the presence of the γ-relaxation at low temperatures and of the aa-relaxation at high temperatures, respectively arising from local and cooperative molecular motions. The salt addition modifies the γ-relaxation region, which consists of a single loss peak in pure PEO, and gives rise to two close low temperature relaxations. The behavior of the relaxation strengths with the salt content permits to assign them to local motions within the amorphous regions of the polymer. — The aa-relaxation shifts to higher temperatures by increasing the KSCN content. Moreover, an enhancement of the amorphous phase of the polymer has been revealed in the low concentration region. [ABSTRACT FROM AUTHOR]

Cationic surfactants are adsorbed in double layers on low-charged layer silicates. The amount adsorbed is determined by the swelling capacity of the layer silicates and the structure of the cationic surfactant. The swelling ability of the surfactant-layer silicate complex correlates with model concepts assuming densely packed pseudotriple layers. Higher packing densities are achieved in particular by a benzyl substituent in the surfactant. The reaction enthalpies increase in proportion to the quantity of surfactant adsorbed. This suggests that cationic surfactant adsorption takes place due to a high affinity for the interlayer surface. The differential molar reaction enthalpy is identical for the surfactants investigated, but depends on the layer silicate used. Additional heat tinting is observed in a calorimeter with increasing surfactant concentration in the interlayers of highly swelling Na hectorite. This is caused by the transition to pseudo-triple layers after double layers have been formed. [ABSTRACT FROM AUTHOR]

The aging of aqeusous ethyl(hydroxyethyl)cellulose (EHEC) solution and mixed solutions of polymer and sodium dodecyl sufate (SDS) in contact with cyclohexane was studied by measurement of interfacial tension, using the pendant drop method. Studies were performed over the concentration ranges 0-18 mM SDS with fixed concentration 0.2% w/w EHEC, and 0-16 mM SDS with no polymer added. EHEC was found t be very surface active, and the kinetics of polymer adsorption to the water/cyclohexane interface is extremely slow. The mixed solutions of polymer and surfactant showed a more typical timescale for adsorption. The variation in the equilibrium interfacial tension of the mixed polymer-surfactant solutions was assumed to reflect the variation of the activity of polymer, and the interactions between the polymer and other particles in the system. The observed effects were explained as due to the changes in polymer-solvent and polymer-surfactant interactions, resulting in a changed conformation of the polymer, as well as the formation of micelle-like clusters and free micelles. [ABSTRACT FROM AUTHOR]

We present some recent optical experiments on plane monolayers at liquid interfaces that allow study of their structure and measurement of their bending elasticity. [ABSTRACT FROM AUTHOR]

This paper presents a critical phenomenon involving a sharp increase in conductance at a critical value of the electric field applied to a bilayer lipid membrane (BLM). By varying the density and the sign of the charge on the BLM at various pH values, the critical potential changes. These changes are related to the variations in the surface potential and indicate that the reorganization of the external polar surface under the action of the electric field always starts on the side in which the electric field is directed from the inner to the outer surface of the monolayer. [ABSTRACT FROM AUTHOR]

We describe the effect of subphase pH on the stability of insoluble monolayers of a range of ionisable materials. Maximum stability occurs at approximately half ionisation of the film. We discuss measurements of the transfer ratio and dynamic contact angle for the deposition of docosanoic acid monolayers onto mica as a function of subphase pH in the absence of added electrolyte. Deposition changes from Z-type of Y to no net deposition as the pH is increased. In general, deposition occurs on OUT strokes when the contact angle is <90°, and on IN strokes when the contact angle is >90°. [ABSTRACT FROM AUTHOR]