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Sedimentation velocity and synthetic boundary diffusion studies have been undertaken for aqueous solutions of the branched microbial polysaccharide welan gum. Centrifugation and filtration to remove insoluble material from the crude gum is shown also to remove a proportion of soluble high molar mass material. Purified welan which has been dialysed exhaustively against distilled water to remove low molar mass impurities exhibits typical polyelectrolyte behaviour in saltfree solution: an enhanced apparent diffusion coefficient and diminished sedimentation coefficient at modest polymer concentrations, and a dramatic drop in apparent diffusion coefficient at concentrations below 0.6 g dm−3. In the presence of a salt, welan solutions exhibit ‘weak gel' behaviour. At NaCl concentrations greater than about 0.1 mol dm−3, sedimentation velocity shows no evidence of charge effects or conformational change. The solution behaviour may reflect a stable double-helical structure, stabilized by interactions between side chains and carboxylate groups in the polysaccharide backbone, coupled with weak association between double-helices. [ABSTRACT FROM AUTHOR]

The coalescence stability of n-decane-in-water emulsions stabilized by native and highly (>90%) acetylated legumin, the 11 S main storage protein from faba beans (Vicia faba L.) has been investigated by analytical ultracentrifugation. The method is based on centrifugation at constant rotor speeds (sufficiently high to produce a detectable amount of separated oil) up to (pseudo-) equilibrium values for all layers. Coalescence pressures are calculated as a measure of coalescence stability. Acetylation of legumin results in a significant increase of the coalescence stability (about three-fold). The coalescence pressure of the emulsion with the native legumin decreases after a storage period of about 2 months. By contrast, the emulsion prepared from the acetylated legumin shows a higher coalescence pressure, even after about 8 months. This observation is in agreement with the storage stability. Initial results from applying sedimentation velocity experiments in connection with the method for characterizing the coalescence stability have provided the following results: i) only the 11-12 S protein component in the starting native legumin solution occurred in the separated continuous phase after (incomplete) demulsification. A 15 S aggregate (11%) could no longer be detected in the separated continuous phase. ii) The 16-17 S aggregation component and a lower molecular weight dissociation product (≤2 S, 25-30%) present in the starting solution of acetylated legumin did not occur in the separated continuous phase, but only an aggregated 22-26 S component. This supports the conclusion for a preferred adsorption of low molecular components during preparation of the emulsion. [ABSTRACT FROM AUTHOR]

Protein-protein recognition and protein oligomerization functions are among the important roles played by the α-helical coiled coil motif. As part of a study into the equilibrium and kinetic aspects of the folding of model coiled coils, an investigation into the stoichiometry and magnitude of the associative constants by sedimentation equilibrium in the ultracentrifuge has been initiated. A series of interrelated model peptides, with sequence lengths of about 30 residues, has been designed, synthesized and characterized. Each of the peptides has been subjected to conventional sedimentation equilibrium analysis under a variety of conditions. The stoichiometry of self-association has been established and it has been shown that, contrary to the expected result, most of the peptides formed trimeric systems of varying stability. The effect of substituting large hydrophobic constituents of the interacting interfaces of the systems with other similar residues has been shown to have minimal effect on trimer formation. However, substitution of such residues in the central sequence positions with either alanine or asparagine leads to a marked decrease in the stability of the trimeric state. [ABSTRACT FROM AUTHOR]

This mini-review shows how complementary techniques (light, neutron and x-ray scattering, analytical centrifugation, density measurements) have been used in the study of the solvation of halophilic proteins, proteins which are only stable at high salt. The halophilic proteins studied so far are all solvated by large amounts of salt, compared to non-halophilic proteins. [ABSTRACT FROM AUTHOR]

The repressor gene from the Streptomyces phage φC31 expresses three N-terminally different, in-frame protein isoforms of polypeptide molecular masses 74, 54 and 42 kDa. Their precise role in the lysis versus lysogeny decision is currently being investigated and a study of their structural and interactive properties was considered an important aid in this investigation. The preliminary data presented here shows that the native 42 kDa isoform and a Histidine (His-)-tagged form exist as dimers or tetramers, depending on the conditions as determined by sedimentation equilibrium in the analytical ultracentrifuge. [ABSTRACT FROM AUTHOR]

The E. coli heat shock proteins DnaK (Hsp70), DnaJ and GrpE constitute a cellular chaperone system for protein folding. In the context of a rigorous investigation of the structure-function relationships within this complex system we investigated the quaternary structure of DnaJ by analytical ultracentrifugation under conditions of sedimentation equilibrium. DnaJ appeared heterogeneous under all tested conditions. The observed heterogeneity depended mainly on the pH of the preparation. At pH 5.5 the sedimentation profiles were well fitted by two exponential functions, indicating the presence of a low and a high mole mass component. The distribution of the two components was independent of the protein concentration. [ABSTRACT FROM AUTHOR]

The self-association properties of the molecular chaperone HSC 70 have been assessed by analytical ultracentrifugation. Sedimentation velocity analysis indicates the presence of three species, whose proportions were dependent on protein concentration, but whose sedimentation coefficients, s20, w, of 4.3 S, 6.6 S and 8.5 S did not vary with concentration, which is indicative of a slowly equilibrating system. Sedimentation equilibrium studies indicate a dissociation into monomers at low HSC 70 concentrations and an association into dimers and trimers at high concentrations. Multiple sets of sedimentation equilibrium data, obtained at various initial loading concentrations and rotor speeds, were adequately fitted to a single set of equilibrium constants by a monomerdimer-trimer association model in which the association constants for the monomer-dimer and dimer-trimer equilibrium. K1−2=1.1.·105 M−1 and K2−3=0.9·105 M−1 respectively, were nearly identical. Interestingly, na isodesmic, indefinite type of association describes the data almost equally well with a single constant of 1.2·105 M−1. These results might have important implications for the chaperone function of HSC 70. [ABSTRACT FROM AUTHOR]

Some recent results from the scanning force microscopy activity at our laboratory are presented. A brief description of attractive mode force microscopy is followed by a discussion of the following examples: O2/H2-induced morphology changes in thin palladium films, structure of spin cast polysulfone films, fibrinogen adsorption on hydrophobic SiO2, and force measurements on hydrophobic/hydrophilic substrates. [ABSTRACT FROM AUTHOR]

The surface force apparatus developed by Israelachvili, and variants thereof, rely on the measurement of the deflection of a weak spring in order to detect the force between two surfaces. Mechanical instabilities occur when the gradient of the surface force overcomes the spring constant and regions of the force curve become inaccessible. We report here a technique which partly overcomes thisrestriction. It is based on a combination of the bimorph force sensor (Parker, to be published) and a magnetic force transducer (Stewart and Christenson, 1990) which allows the deflection of the sensor to be both controlled and measured with a resolution of 0.05 nm and a force sensitivity of 10−8 N. A force is applied to the spring with the magnetic ttransducer in order to compensate the surface force. This has been achieved with a simple feedback system which allows the spring constant to be increased and strong attractive and repulsive forces to be measured easily. [ABSTRACT FROM AUTHOR]

The application of electron spectroscopy for chemical analysis (ESCA) to liquid phase samples is described. The surface sensitivity of this technique allows structures within the first few molecular layers to be investigated. In particular, the study of electron spectra in angular resolved mode provides a means to perform depth profiling of the surface region. Applications are presented for solutions of fatty acid salts and phase transfer catalysts. In these solutions details of the electric double layer at the surface have been investigated. [ABSTRACT FROM AUTHOR]

We describe the first examples of liposomes and vesicles in formamide, a structured non-aqueous medium. Bilayer membranes were obtained after dispersion of lecithin (for liposomes) and dodecylalkyl-dimethylammonium bromide (for vesicles) in formamide. The structures of these systems are discussed and compared to those obtained in water. [ABSTRACT FROM AUTHOR]

The Π-A isotherms and relaxation behavior of monomolecular films at the air/aqueous solution interface of a copolymer of styrene and allylalcohol (PSAA), mean molecular weight 1500 g/mol) have been investigated as a function of the subphase surfactant concentration. The surfactants were sodium dodecylsulphate (SDS), cetyltrimethylammonium bromide (CTAB) or cetylpyridinium chloride (CPC). At low surfactant concentrations (≲0.3 CMC), the PSAA film is penetrated by surfactant molecules and undergoes a relaxation consistent with conformation changes of the polymer without dissolution into the subphase. At higher concentrations (≈ CMC) the PSAA film is lsowly dissolved into the subphase; Π-A isotherms show a plateau and the films relax by a gradually decreasing surface area. The dissolution of PSAA is probably brought about by adsorption of surfactant molecules onto the polymer chain, giving rise to a water-soluble polymer-surfactant "complex" of poly-electrolyte nature. At medium concentrations, hydrophobic interactions between the neutral polymer and the ionic surfactant increase the hydrophilicity of the film and, thereby, probably lead to the formation of loops of polymer segments into the subphase. All the surfactants seem to interact with the PASS film in similar ways. PASS monolayers are good model systems for emulsion-stabilizing monolayers in North Sea crude oils. The monolayers of both the PSAA and the interfacially active crude oil system respond similarly to the presence of ionic surfactants, indicating anogous dissolution mechanisms. Thus, specific surfactant-monolayer interactions of the type observed will be of importance for an understanding of water-in-crude oil emulsion stability. [ABSTRACT FROM AUTHOR]

Fluorocarbon emulsions have considerable potential as injectable oxygen carriers (blood substitutes, in particular), contrast agents for diagnosis, and drug-delivery systems. One approach to reducing the interfacial tension which opposes the dispersion of fluorocarbons in water, and to contributing to the stabilization of their emulsions, is to use fluorophilic surfactants. Several families of perfluoroalkylated, sugar-derived surfactants with modular molecular structures, including maltosides, trehalose fatty acid monoesters, and glucose phosphate esters were investigated to this end. Relatively minor structural differences were found to cause widely different behaviors. Very stable emulsions of perfluorodecalin (FDC) and perfluorooctylbromide (PFOB, perflubron) were obtained with some of them; the neutral ones led to considerable synergistic stabilization of such emulsions when a polaxomer (Pluronic F-68) was used as the primary surfactant, while the anionic ones developed such a synergistic effect with egg-yolk phospholipids (EYP). Some also had a significant impact on particle sizes. [ABSTRACT FROM AUTHOR]

The structure of human stratum corneum was investigated with small-angle x-ray scattering (SAXS). At room temperature the scattering curve was characterized by a strong intensity at low scattering vector (Q<0.8 nm−1) and two complicated diffraction peaks originating from a lamellar structure of the lipids. The lamellar lipid structure in the stratum corneum transformed to a disordered structure between 65° and 75°C, the same temperature region at which a thermal lipid transition occurred. After cooling down to room temperature a recrystallization of at least a part of the lipids took place, after which only one unit cell with a repeat distance of 13.4 nm could be detected. Comparison of the scattering curve of the stratum corneum after crystallization with the scattering curve of the stratum corneum before recrystallization leads to the conclusion that, in the original curve, the lipids are arranged in two unit cells with repeat distances of 6.4 and 13.4 nm. From model calculations it appears that the latter unit cell consists of more than one bilayer. The scattering curves of stratum corneum hydrated to various levels were measured. A change in the water content of stratum corneum between 6% w/w and 60% w/w (fully hydrated) did not result in swelling of the bilayers, but the scatterin g curve obtained with stratum corneum hydrated to 60% w/w differed from those at lower hydration levels: the scattering curve at 60% w/w showed only the diffraction peaks corresponding to a unit cell with a repeat distance of 6.4 nm. [ABSTRACT FROM AUTHOR]

Infrared reflection absorption spectroscopy (IRAS) and x-ray photoelectron spectroscopy (XPS) have been used to study the adsorption of potassium p-methyl benzyl xanthate and potassium p-trifluoromethyl benzyl xanthate on gold surfaces. Monolayer structures were formed by adsorption from 1 to 10 μM aqueous solutions of the xanthates for different adsorption times. The reflection-adsorption (R-A) spectra are compared with calculated R-A spectra, which are based on the optical constants n(v) and k(v) derived from KBr transmission spectra of the corresponding Au(I) salts. The experimentally obtained peak positions are in good agreement with the calculated ones, indicating that the chemical structure of the surface complexes are closely related to those of the metal salts. However, the relative intensities vary considerably between experimental and calculated R-A spectra. We discuss these intensity changes in terms of molecular orientation and packing. A detailed comparison of the relative ratios for the peaks belonging to the OCS2 and CF3 groups reveals that ordered structures are formed on the gold surface, and that a reorientation from a flat to an almost vertical orientation occurs with increasing immersion time and concentration of the xanthate solution. These observations are confirmed with angle-dependent XPS(Θ). [ABSTRACT FROM AUTHOR]

The adsorption of fibrinogen to a hydrophilic quartz surface was studied by transmission electron microscopy using a negative staining technique to visualize the protein. The distribution of adsorbed fibrinogen was random at low surface concentrations and low bulk concentrations (0.29 nM) when analyzed as the pair correlation function g(r). At higher concentration (0.73 nM) an end-to-end polymer polycrystalline structure was seen at the surface, indicating attractive interaction between the ends of the rod-shaped molecule. The polycrystalline pattern was broken up at higher concentrations and snowflake-like crystals were formed. The results indicate the presence of weak attractive forces between the ends of fibrinogen molecules. [ABSTRACT FROM AUTHOR]

The paper presents a summary of our results of the supported liquid membrane extraction of a polydisperse polyelectrolyte, lignosulfonate. Trilaurylamine dissolved in decanol was found to be a suitable liquid membrane. The smallest molecules are transported first. A simple model for the transport of lignosulfonate is outlined and the results of the experiments are presented. [ABSTRACT FROM AUTHOR]

Adsorption of ferritin to a hydrophobic solid surface was studied by transmission electron microscopy. At low bulk concentrations adsorption is initiated at a few sites and continues by growth of clusters at these sites. The nucleation-and-growth-like kinetics gives an acceleration of the apparent binding rate which is damped by mass transport limitation. The clusters grow to a critical size and dissociate rapidly from the surface. This process of accelerated binding and critical dissociation can be seen repeatedly during adsorption of the protein. At high bulk concentrations, the surface is covered with protein during the first seconds of incubation, but the adsorbed layer then becomes unstable and dissociation is seen within the first minute of incubation, resulting in a clustered spatial distribution of adosrbed protein. These findings suggest that protein adsorption reaches an equilibrium, but that the kinetics of the process is discontinuous. [ABSTRACT FROM AUTHOR]

The interactions between layers of two hydrolyzable surfactants, dodecylamine (DA) and tetraoxyethylene dodecylamine (TEDA), adsorbed on negatively charged muscovite mica have been investigated. It was found that the variation of the interaction and adsorption as a function of pH was similar, but not identical, for the two kinds of surfactants. At a concentration of 10−4 M at low pH (below 8) both types of surfactants adsorb electrostatically to form a monolayer. The resulting surfaces have a hydrophobic character, particularly in the case of dodecylamine. A series of events takes place as the pH is increased. For DA the first event is that uncharged molecules adsorb within the monolayer. This does not occur to any significant degree for TEDA due to steric hindrance within the adsorbed layer. In the next step a bilayer builds up on the surface. The binding of the outer layer is stronger for DA than for TEDA. The DA bilayer becomes uncharged at pH 10.3, and liquid dodecylamine droplets, which phase separate from the bulk solution at this pH-value, precipitate on the surface. At pH-values above 11∔12 the affinity between both types of surfactants and the surface decreases significantly, resulting in a less ordered first layer. In addition, a strong surface charge develops that prevents multilayer build-up. [ABSTRACT FROM AUTHOR]

This paper briefly reviews a new adsorption theory particularly applicable to surfactant adsorption. A one-step model of surface micellization is first introduced. By using the mass-action law treatment, an S-type isotherm equation is derived which explains the adsorption of nonionic surfactants from aqueous solution onto polar adsorbents. However, the adsorption of ionic surfactant generally shows two-step character. First the surface-active species are adsorbed through electrostatic attraction and/or van der Walls interaction. The second step involves hydrophobic interaction if the adsorption is from aqueous solution, and hydrogen bonding or other polar interaction if from non-polar solvent. Under these conditions a general adsorption isotherm equation is derived. The model indicates that the size of surface micelles is usually much smaller than that of corresponding bulk micelles. From thermodynamics of adsorption, it is evident that when dealing with adsorption from aqueous solution, the second step, i.e. surface micellization, is an entropy-driven process similar to the bulk micellization. [ABSTRACT FROM AUTHOR]

The competitive adsorption of sodium p-octylbenzenesulfonate (SOBS) and benzyl alcohol (BzOH) onto solid α-alumina at 35°C with and without 0.1 M NaCl has been studied using high-performance liquid chromatography (HPLC). Calculations of the individual area requirements of SOBS and BzOH in the adsorbed film were undertaken at the saturation level (plateau) of the SOBS adsorption isotherm. The lamellar liquid crystalline D phase of the system SOBS/BzOH/water was investigated by means of x-ray measurements in order to determine the area requirements. The discrepancies found between the area requirements in the D phase and on the α-Al2O3 reveal that the electrostatical headgroup repulsion will, on the solid surface, prevent the SOBS molecules to pack as in the D phase. [ABSTRACT FROM AUTHOR]

Small-angle neutron scattering provides a valuable technique for the study of adsorption at interfaces. It is particularly valuable for particles in nonaqueous media where the surfactant is present during particle formation and, hence, is an essential factor to ensure colloid stability of the dispersion. The method of contrast variation, using mixtures of hydrogenated and deuterated solvents can be used and from the data obtained an analysis of the amount adsorbed estimated. This technique is also applicable to micelles and work is described on 6-(eicosyldimethylammonio) hexanoate. In addition, neutron reflectivity studies on the latter material at the air-water interface are described; these studies allow a comparison to be made of the area occupied at a micelle surface and at a planar interface. [ABSTRACT FROM AUTHOR]

Acidic nonionic microemulsions have been used for gelation of tetraethyl orthosilicate (TEOS). It is shown that the release of ethanol will expand the microemulsion region after reaction. The gelation in the nonionic microemulsion (without hydrocarbon) is strongly dependent on surfactant and water. The gelation time strongly increases when surfactant is in excess of 22% by weight. The NMR spectra revealed only a minor reorganization during 4 months of the ethoxy attached to the Si atom for solutions with insufficient amount of water for gelation. This did not change with time (up to 4 months). All-in-all, the reactions with TEOS in acidic microemulsions are similar to those in organic solvents. [ABSTRACT FROM AUTHOR]

Ionic microemulsions, stabilized by sodium dodecylsulfate and alcohol cosurfactants, have been characterized with respect to phase behavior, particularly the composition of the different phases in Winsor type I, II, and III systems. The system containing brine, octane, sodium dodecylsulfate and 1-butanol shows a regular phase behavior, in conformity with the anticipated behavior, i.e., 2-3-2 phases. The phase transitions with increasing 1-butanol concentration are analogous to those occurring with increasing salinity, when compared with previous investigations. For the system containing brine, cyclohexane, sodium dodecylsulfate and benzyl alcohol, the behavior becomes more complex, even at low surfactant contents. The transitions are 2-3-2-3-2 phases over a wide composition range. The compositions of the phases at equilibrium are discussed in relation to structural considerations, as determined by conductivity and NMR self-diffusion measurements. [ABSTRACT FROM AUTHOR]

The phase limits were determined for W/O microemulsions and the lamellar lyotropic liquid crystal in the system of cyclohexane/aqueous solutions of aluminum and calcium nitrates/commercial tetraethylenegly-coldodecylether. Visual observation, optical microscopy, and small-angle x-ray diffraction were used. The results showed an increase of the maximum amount of aqueous solution in the microemulsions with enhanced salt concentration as well as an enlargement of the area for the lamellar liquid crystal. The penetration of water into the surfactant layers of the liquid crystal was significantly increased after addition of salt. [ABSTRACT FROM AUTHOR]

The solvatochromic acid-base indicator 2,6-diphenyl-4-(2,4-6-triphenyl-1-pyridinio)phenooxide, ET(30), is employed to determine the effective surface potentials of micelles (Ψ0expt) in relatively concentrated aqueous dodecyltrimethylammonium chloride (DTAC) systems (i.e. up to 40 wt% DTAC). Ψ0expt decreases with increasing DTAC concentration, This is attributed to a concomitant increase in the amount of dissociated chloride ions in solution when the DTAC micellar concentration is increased. The effective surface potentials are compared with the electrostatic surface potentials obtained in relatively dilute micellar DTAC/NaCl systems and with the electrostatic surface potentials calculated from the non-linearized Poisson-Boltzmann (P-B) equation and a cell model (Ψ0cell). The P-B cell model, which incorporates a Langmuir adsorption constant in order to categorize the association of Cl− to the surfactant headgroups, adequately describes Ψ0expt up to 7 wt% DTAC. Beyond 7 wt% Ψ0expt and Ψ0cell progressively diverge. The divergence is primarily considered to be a result of the fact that the P-B cell model neglects the ion-ion correlations and the finite size of the ions. [ABSTRACT FROM AUTHOR]

Partial binary phase diagrams for different alkanolammonium carboxylates with water have been determined. The alkanolamines employed were monoethanolamine, triethanolamine and triisopropanolamine, while the fatty acid has been varied with respect to chain length (C8-C22) and saturation. The phase diagrams show two features that distinguish them from ordinary soap-water phase diagrams. First, multi-phase regions and miscibility gaps occur at low concentrations of surfactant, in particular, for triethanolammonium carboxylates. Secondly, the stability regions of the liquid crystalline phases are different, and in general smaller,compared to those formed by the corresponding alkali carboxylates. It is suggested that the first feature is due to that alkanolamines are weak bases and, thus, that any surfactant aggregate comprises a few percent of unhydrolyzed acid, while the second feature is attributed to the larager size of the counterion compared to alkali ions, which tends to destabilize ordered structures. [ABSTRACT FROM AUTHOR]

The force as a function of separation is measured between two mica surfaces coated with adsorbed bilayers of cetyltrimethylammonium bromide (CTAB) and immersed in aqueous ionic micellar solutions of CTAB at different ionic strengths. At short separations, the interaction profile is a double-layer repulsion, arising solely from the dissociated counterions, free CTA+, and added salt. At larger separations, the repulsion is reduced and a secondary minimum in the interaction potential due to the depletion of the micelles from the diffuse double-layer is observed. Finally, at further separations, structural effects superimpose an oscillatory force profile. Addition of electrolyte reduces the thickness of the diffuse double-layers. In addition to the shift of the position of the secondary minimum towards smaller separations, the depletion and structural contributions are depressed progressively as the hard-sphare effective volume of micelles decreases. Finally, at high ionic strength, the structural effects are completely removed, but not the depletion one, as the micelles become highly anisotropic. [ABSTRACT FROM AUTHOR]

The phase diagrams for mixtures of ethyl(hydroxyethyl) cellulose and sodium dodecyl sulfate in water and in 0.03% aqueous NaCl solutions have been determined for the water rich part of the system. The obtained phase diagram is characterized by a two-phase region in the water-rich corner with tielines almost parallel to the water-polymer axis. It is demonstrated that the ratio of polymer to surfactant has a critical effect on the phase behavior. Model calculations based on the Flory-Huggins polymer theory are presented. The close agreement between theoretical and experimental phase behavior gives strong support to a molecular interpretation of the observed phase behavior, implying that there is a relatively strong attraction between the polymer and the ionic surfactant. [ABSTRACT FROM AUTHOR]

A hydrophilic, non-ionic surface was prepared by grafting polyethyleneoxide (PEO) onto polyethylene (PE) and mica substrates. Monofunctional PEO-aldehyde was coupled by means of reductive amination to primary and secondary amino groups of polyethyleneimine (PEI) adsorbed on oxidized polyethylene (PE) and on mica. Optimum values of the reaction parameters influencing the reductive amination in this heterogeneous system were sought in order to achieve complete coverage of the surface by covalently linked PEO chains. Carrying out the coupling reaction at 60 °C, pH 6 and ck2so4 over 40 h resulted in a PEO surface characterized by a maximal ESCA — C-O-/-CH2-ratio and, simultaneously, complete wetting by water. A PEO surface with a high degree of coverage was also obtained by means of adsorption from solution of a PEO-amine compound on mica. [ABSTRACT FROM AUTHOR]

Binary and ternary phase diagrams have been determined for systems containing sodium di-2-ethylhexylsulfosuccinate (Aerosol OT); a polar solvent, formamide, methylformamide, dimethylformamide or ethanediol; with and without hydrocarbon, toluene or dodecane. In formamide, Aerosol OT forms a lamellar, a viscous isotropic (cubic) and a reverse hexagonal liquid crystalline phase. The swelling of the lamellar phase, as well as its temperature stability, is considerably reduced compared to the corresponding aqueous system. In the other solvents, only the reverse hexagonal phase forms. The ternary systems with toluene are generally dominated by an extensive solution region, i.e. a non-aqueous microemulsion, while with dodecane, the solution phase has a considerably reduced extension. [ABSTRACT FROM AUTHOR]

A surface wettability gradient method for the investigation of some quantitative aspects of protein adsorption on solid surfaces has been developed. The method has been used in studies of protein exchange reactions on silicon surfaces. The proteins used were human fibrinogen and γ-globulin and specific detection of these proteins was made using corresponding antibodies. By the gradient method, the protein exchange reactions could continuously be related to the wettability of the solid surface. [ABSTRACT FROM AUTHOR]

Microemulsions based on aliphatic hydrocarbon, surfactant and aqueous buffer have been used as reaction medium for the lipase catalyzed transesterification of a triglyceride and a fatty acid. Both AOT (sodium bis (2-ethylhexyl)sulfosuccinate) and certain alcohol ethoxylates could be used as surfactant to produce a triglyceride having a fatty acid composition similar to that of natural cocoa butter from a palm oil distillation fraction. The non-ionic surfactant gave a higher reaction rate than AOT, presumably due to a more favourable association of water in the microemulsion. Recovery of the enzyme was facile with the former surfactant. However, the ethoxylate was found to participate in an unwanted side reaction, viz, formation of esters with free fatty acids in the solution. [ABSTRACT FROM AUTHOR]

Electromotive force and conductivity measurements have been used to study the counter ion association to micelles of sodium dodecyl sulfate, sodium dodecanoate, and sodium octanoate. The conductivity and electromotive force measurements match very well as both is mainly a measure of the amount of free counter ions in the solutions. Addition of alcohols to these micellar solutions show some differences between octanoate micelles on one hand, and dodecyl sulfate and dodecanoate on the other. Propanol and pentanol addition lead to an increase in the sodium activity for dodecyl sulfate and dodecanoate solutions that are well above the c.m.c. while a decrease is observed for octanoate. Addition of higher alcohols show that the counter ion activity and the conductivity go through a maximum at low alcohol contents and then decreases. At high surfactant contents alcohol addition may induce a shape transition from small spherical micelles to larger rod- or disc-like micelles. It appears that the degree of counter ion association increases when these larger micelles form. [ABSTRACT FROM AUTHOR]

Precipitation processes, solubility and phase behaviour in aqueous solutions of ferric nitrate—dodecyl benzene sulphonic acid (HDBS)—nitric acid, were investigated in various pH regions. Precipitation diagrams were made using light scattering. The solubility product and the enthalpies of precipitation were calculated taking into account the hydrolytic constants of Fe+3, Fe(OH)+2, Fe(OH)2+ species and the dissociation constant of HDBS. The solubility product of ferric dodecyl benzene sulphonate (Fe(DBS)3) was calculated to be Ks0=(1.23±0.80)x10−24 for pH 2.2 at 293 K. The slope of the straight line from which the solubility product was calculated, (0.317) is close to the theoretical value for 3∶1 electrolyte. Using a polarization microscope and X-ray diffraction different phases were characterized: the solid crystal, the lamellar liquid crystal and the mixtures of solid and liquid crystalline phases. The enthalpies of crystallization and liquid crystal formation were determined as ΔH=−33 kJ mol−1 and ΔH=23 kJ mol−1, respectively. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of an inhomogenous fluid confined to a narrow slit with attractive walls have been studied using a simple mean field theoretical approach. The pair-wise interaction assumed is a truncated Lennard-Jones potential with a repulsive hard core. Density profiles of the fluid in the slit, the excess grand potential per unit surface area and the pressure tensor components pN and pT have been calculated. The lack of consistency among these variables, as well as the degree of agreement with the generalized Gibbs surface tension equation and with the Kelvin equation, is discussed. It is concluded that the (hard sphere) local density appproximation is a major source of the discrepancies noted. [ABSTRACT FROM AUTHOR]

The rate of spreading of non-volatile liquids on smooth and on rough surfaces was investigated. The radius of the wetted spot was found to agree with recently proposed scaling laws (t1/10 for capillarity driven and t1/8 for gravity driven spreading) when the surface was smooth. However, the crossover between these regimes was not observed at a constant value of the radius. Rough surfaces exhibited at least four spreading regimes which could be rationalized in terms of a macroscopic contact angle and macroscopic deviations thereof. An interesting feature is the appearance of a wetted rim around the central drop. This rim follows a diffuce spreading law (t1/2). Partially wetting liquids followed the same dynamics provided the spreading conditions was fulfilled. [ABSTRACT FROM AUTHOR]

When a liquid containing surface active molecules advances on a hydrophilic solid surface, specific instabilities are observed. They are due to the diffusion of the surface active molecules which adsorb on the surface, increasing the contact angle. These instabilities appear as waves travelling along the contact line and are visible only in a limited range of liquid edge velocities. [ABSTRACT FROM AUTHOR]

Triplet energy transfer from 9-methylanthracene to azulene or guajazulene has been used to probe the migration of azulenes between micelles in aqueous solution. The migration of the hydrophobic solutes between small ionic and nonionic micelles had the temperature dependence expected for a process controlled by diffusion through the intermicellar solution, although the rate in some cases was substantially less than calculated from the Smoluchowski equation. Under conditions in which the micelles grow into large, probably rod-like structures, there are severe difficulties in separating the inter- and intramicellar deactivation processes. The intermicellar migration was enhanced under these conditions, in cetyltrimethylammonium surfactants on addition of chlorate ions, and in hexaethylene glycol dodecylether at temperatures approaching the cloud-point. The mechanism of this migration is discussed and compared with pertinent results from micelle relaxation kinetics and surfactant self-diffusion measurements. [ABSTRACT FROM AUTHOR]

Results from direct force measurements between mica surfaces and modified mica surfaces immersed in aqueous electrolyte solutions are reported. In particular, experimentally observed attractive and repulsive deviations from force curves, calculated from conventional DLVO theory, are discussed. Such "additional" forces are present in most systems. Even in cases where the measured interaction appears to be well described by conventional DLVO theory, the values of, for example, surface charge densities obtained by fitting calculated forces to measurements should not be viewed as true values. [ABSTRACT FROM AUTHOR]

Employing the theoretical approach and computational methods described previously [9], calculations have been made on the two-dimensional size/composition distribution of spherical micelles composed of sodium dodecylsulphate (SDS) and dodecylalcohol (DOH) monomers. These calculations show fair agreement with experimental CMC and solubilization capacity results. For rod-shaped micelles our calculations indicate that the critical condition for the formation of rods, i.e. β=0, where βkT is the difference in molecular free energy per SDS/DOH unit between the middle part of the micelle and the solution, is approached at significantly lower salt concentrations upon raising the DOH/SDS ratio. The incorporation of DOH in the SDS micelles is driven by the free energy of mixing the monomers within the micelles and by the reduction obtained of their electrostatic free energy. Since a slight swelling is noted, there is a counteracting increase in chain conformational free energy. Moreover, the hydrophobic driving force of aggregation is considerably weaker for DOH than for SDS because the monomer concentration of DOH is comparatively low. [ABSTRACT FROM AUTHOR]

The electrostatic contribution to the force across the apolar region in a lamellar liquid crystal is considered. For an ionic surfactant consisting of one small hydrophilic ion and one larger hydrophobic ion, a microscopic charge separation occurs. If the hydrophobic ion has a finite solubility in the apolar region a double layer force will be generated across the apolar region. It is shown that under realistic conditions this force can overcome the attractive van der Waals force and it is suggested that the extensive swelling of a lamellar phase in hydrocarbon, recently reported by Larché et al. [11] might be explained in terms of this double layer repulsion. It is also concluded that this type of double layer forces can be of important for the stability of microemulsions and water in oil emulsions. [ABSTRACT FROM AUTHOR]

A review is presented about research on surface forces and surface interactions conducted over the past half-century, with some emphasis on the pioneering contributions of the Department of Surface Phenomena at the Institute of Physical Chemistry of the USSR Academy of Sciences. [ABSTRACT FROM AUTHOR]

Experimental results of measurements of refractive index and light scattering yield interesting information about the structure of the L2-phase. In accordance with previously presented studies they show that one, with respect to the role of water, has two main regions, one extending from the water-free phase up to a content of water of about 40% and the other at water contents above about 55%. An intermediate transition region lies between about 40% and 55% of water. In the first main region the incorporation of water into the acid octanoate molecules influences the magnitude of the refractive index decrement and light scattering intensity. In the latter region, the partial contributions of water and the amphiphilic substance for the magnitude of the refractive index remain almost unchanged, but here it seems to be the distribution into different domains, bordering each other, of the two types of water, that in the domains with hydrated polar groups and that in the domains with unbound bulk-water, which causes the changes in the intensity of the light scattering. The structure of the L2-phase, among others, the diversity on the molecular level and the very high concentrations of the active amphiphilic components in large parts of the phase, render quantitative estimations of particle size impossible on the basis of light scattering measurements. Information about phase structure obtained from other experimental investigations, however, makes it possible to show the connection between phase changes on the molecular level and changes in the light scattering intensity. This has also created a basis for some, although partially hypothetical, explanations of which factors play a role in the changes mentioned, as with information about the structure. Among the latter it may be mentioned that the amphiphilic substance, up to very high water contents, retains some of the properties that the first 40% of water have caused. The differences in properties between unbound bulk-water and water bound to the polar groups are considerable; the influence of the bulk-water on the phase properties seems to vary with the manner of its distribution and the properties of the bound water are different, depending on whether it belongs to the solvation water shell of the sodium ion, or whether it is bound via hydrogen bridges. [ABSTRACT FROM AUTHOR]

Electro-optical experiments have been performed on a poly (styrene-co-N-ethyl-4-vinylpyridinium bromide) graft copolymer in water-methanol mixtures and in the absence of added salt. A positive electric briefringence was observed for the graft copolyme while the birefringence of the corresponding polyvinylpyridinium homopolymer was negative. This change of the sign of the optical anisotropy was discussedon the basis of the orientation of the pyridinium ring with respect to the main backbone and hence to the applied electric field. We determined the electric polarizability parameter and the relaxation time of the birefringence. It was shown that the graft copolymer does not display the so-called polyelectrolytic effect, i.e. the pronounced extension of the chain with dilution. The conformation of the graft copolymer remains rather compact and much less extended than the corresponding homopolymer. The influence of the solvent composition was also investigated and the effects discussed in terms of preferential solvation of the styrene units by methanol. [ABSTRACT FROM AUTHOR]

Electron Spectroscopic Imaging (ESI) was performed on a polyethylene specimen and on the poly(styrene-b-2-vinylpyridine) blockcopolymer to obtain information about the microstructural organization. Polyethylene samples were treated with CiSO3H or RuO4 prior to cutting ultrathin specimens. The local distribution of different staining agents was investigated by electronic micrography of specific, inelastically scattered electrons. Ultrathin sections of poly(styrene-b-2-vinylpyridine) were quaternized with CH3I-vapour to yield specific countrasts. [ABSTRACT FROM AUTHOR]

The granule structure that occurs when a polyethylene melt is stained with chlorosulfonic acid by a rapid technique, e.g. at 150°C, cannot be ascribed to nodules. In Part I of this study, it was unmasked as an artifact caused by microdemixing [1]. However, demixing can be prevented by first crosslinking the melt by electron beams. In this case, the melt appears to be homogeneously black after staining. If melting of crystalline polyethylene is arrested exactly at 134°C by the rapid method, not only can the granule structure of the original melt be recognized in the ultrathin section, but also very thin black layers can be seen on the surfaces of the lamellae. Their character is apparently that of a crosslinked melt and they, therefore, conform more to the switchboard model than to the regularly adjacent re-entry model. [ABSTRACT FROM AUTHOR]

The gas permeability of styrene-butadiene block copolymers has been examined for mixtures of CO2 and CH4. The permeated gas has been analyzed using a mass spectrometer as detector. The diffusion coefficient of CH4 depends on the composition of the gas mixture and on the composition of the block copolymer. In comparison to the pure CH4 the permeation of CH4 in mixtures with CO2 increases with increasing CO2-content and ioncreasing butadiene content in the block copolymer. Besides the plastification of the polymer by CO2, the diffusion rate of CH4 increases according to the high solubility of CO2 in polystyrene. [ABSTRACT FROM AUTHOR]

The diffusion process of polymer dissolution in liquid solvents and the kinetics of the surface swollen layer formation have been studied. The following fundamental kinetic paraeters of the dissolution and swelling processes have been presented: the rate of dissolution uOC and its relevant thermodynamic and kinetic parameters (ΔHd≠ and ΔHD,d≠); the induction period of dissolution tQ and its apparent activation energy values in the swelling process (ΔHs≠); and, in the diffusion process connected with swelling (ΔHD,s≠). Both the kinetic and thermodynamic activity of individual solvents for given polymers (carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC) and polyvinyl chloride (PVC)) have been expressed through the internal quantities RAδ,s and RAδ,d, i.e., expansion work of the polymeric coil accomplished by action of the internal pressure Pi. [ABSTRACT FROM AUTHOR]

The rheological properties of a homoglucan produced by Schizophyllum commune were investigated in water and dimethylsulfoixde (DMSO). Aqueous solutions of the polymer showed non-Newtonian character at concentrations of about 0.1% (w/v), and thixotropic behavior was observed. The apparent viscosity of aqueous solutions was not influenced by high salt concentrations and also showed high stability from pH=2−12. The solutions showed Newtonian character in DMSO at polymer concentrations of about 0.1% (w/v). Moreover, the dependency of the apparent viscosity on the polymer concentration was investigated in water and DMSO. The intrinsic viscosities of the polymer in these two solvents were determined by graphic extrapolation of the reduced viscoisty to polymer concentration=0. From these intrinsic viscosities the average molecular weight of the polysaccharide in water and DMSO was calculated. [ABSTRACT FROM AUTHOR]