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The dynamic surface tension of surfactant and polymer solutions can be measured by different experimental techniques, each of them having a specific time window, from the range of milliseconds up to seconds, minutes, and hours. In the present paper, the application is described of a new design of maximum bubble pressure instrument for measuring the dynamic surface tension of surfactant solutions in...
The aim of this study was to formulate an aromatic oil-based concentrate stabilized by a non-ionic surfactant with a high ability to solubilize water, i.e., to produce a single-phase water-in-oil (W/O) microemulsion. The oils used were benzene, methylbenzene, 1,4-dimethylbenzene and 1,3,5-trimethylbenzene. The surfactants used were commercial nonyl phenyl polyoxyethylenes, Berol 02 with six ethoxy...
The growth, via Ostwald ripening, of O/W miniemulsions (formed from pentan-1-ol, sodium dodecyl sulphate, and water) has been investigated using a turbidimetric technique. It was found that the ripening rate was linearly dependent upon the interfacial tension within the emulsion below the CMC of the surfactant, as predicted by the LSW theory for Ostwald ripening.
In a system with three coexisting phases (α, β and γ) at equilibrium and having densities in the order ρα < ρβ < ργ, the interfacial tensions (σαβ, σβγ and σαγ) either obey Antonow’s rule, which gives wetting behavior, or conform to Neumann’s inequality, which gives non-wetting behavior. The validity of these implications has...
The surface pressure-area isotherms for a polymer resin spread on an aqueous subphase were invertigated. A time-dependent hysteresis effect was observed on re-expansion of the film. An explanation for this effect is proposed based on the concept of two “welded” monolayers.
Water-soluble polymers containing small amounts of hydrophobic groups have been synthesized in an aqueous medium by free radical copolymerization of a hydrophilic monomer (acrylamide) with a micelle-forming cationic polymerizable surfactant. Such hydrophobically modified water-soluble polymers exhibit particulr aqueous solution properties due to attractive hydrophobic interactions and repulsive electrostatic...
Synthesis of hydrophobic ribonuclease and α-chymotrypsin is performed in AOT reverse micelles in order to covalently bind hydrophobic molecules on to the enzymes’ surface. Enzyme characterization is described using high performance liquid chromatography and electrophoresis. Location of enzyme derivatives within reverse micelles is determined using fluorescence experiments. These indicate that modified...
The surfactant film bending elasticity can be described by a spontaneous curvature C0 and two elastic constants K and K, associated with the mean curvature and the Gaussian curvature respectively. These parameters are very important in the determination of the structure of the dispersions stabilized by the surfactant (droplets or sponge-like structures). They also control the thermal fluctuations...
Small angle x-ray scattering (SAXS) measurements were carried out on w/o microemulsions containing two different enzymatic systems: trypsin or lipase. The results were compared to SAXS measurements in the absence of proteins. When relatively small reverse micelles were used, the presence of enzyme induced a decrease of the aqueous core radius. For larger droplets the presence of the biomolecules did...
The synthesis of a new polymerizable surfactant forming reverse micelles has been performed. The didecyldimethylammonium methacrylate is soluble in aromatic solvents and, by water addition, the solutions remain clear, stable over several months, and low conducting. Structural studies of these microemulsions have been performed by small-angle x-ray and dynamic quasi elastic light scattering. These...
In dilute aqueous solutions of surfactants a succession of phases is generally observed, namely, solutions of globular then elongated flexible micelles (worm-like micelles) followed by the phases of fluid membranes (successively a lamellar phase and the L3 (sponge) phase). This is well accounted for by the continuous decrease of the spontaneous curvature of the surfactant film upon variation of some...
A model is presented that describes the clustering of microemulsion droplets from a thermodynamic point of view. It is based on two assumptions: one assumption is that the microemulsion droplets aggregate linearly. The other assumption is that the chemical potential per droplet is equal for all sizes of aggregates. By means of the fundamental thermodynamic equations of self-association the distribution...
Titanium isopropoxide was hydrolyzed in some water-in-oil microemulsions to produce TiO2 gels. Photophysical methods have been used to follow the evolution of the gels and to compare the effect of the different microemulsions used. Dipcoating of various substrates has also been examined. It was found that the formation of the TiO2 gels is a factor assisting adhesion and spreading of the microemulsions...
Polyethylene glycol of different molecular weights ranging from a few hundred to a few hundred thousand was solubilized in water-in-oil microemulsions made of cyclohexane, pentanol, sodium dedecylsulfate, and water. The effect of the presence of polymer was studied by conductivity, fluorescence probing, and light scattering. We have found that the small size polymer affects only the water-oil interface...
The electrical conductivity σ of aqueous ternary water/AOT/undecane microemulsions (AOT: sodium bis 2-ethylhexyl sulfosuccinate) was studied at constant temperature T versus pressure (up to 200 bar) and the volume fraction φ of dispersed matter (water + AOT). The phase diagram was also determined. The results presented in this paper are given in terms of curves plotted as σ(φ) at a given P and T and...
The localization of Penicillium simplicissimum lipase in AOT/isooctane microemulsions has been investigated by fluorescence energy transfer. This method is based on the nonradiative transfer from the tryptophan residues of the enzyme which act as the donor, to cis-parinaric acid which act as the acceptor molecule. The energy transfer efficiency which depends on the distance separating this pair, was...
Phospholipid vesicles have been prepared from mixtures of dipalmitolyphosphatidylcholine (DPPC) and phosphatidylinositol (PI) covering a range of mole % PI. A theoretical approach to vesicle adsorption as a function of PI content of the vesicles has been developed based on a lattice model for interactions between the bacterium glycocalyx and the inositol head groups in the vesicle surface. The model...
The heat-induced denaturation and aggregation of β-lactoglobulin in water can be quantitatively modeled by analogy with a radical polymerization reaction. The model contains an initiation, a propagation and a termination step and it predicts that linear polymeric aggregates of β-lg monomers will be formed. The β-lg monomers are assumed to be linked together via intermolecular disulphide bonds, which...
Spontaneous formation of vesicles which occurs upon dilution of lecithin-bile salt mixed micellar solutions was studied using static (SLS) and dynamic (DLS) light scattering. Special attention was paid to the properties of the vesicles formed, and also to the mixed micellar precursors, since the structure of these mixed micelles is still controversial. We show how a self-consistent interpretation...
Dynamic light scattering has been employed to study the influence of electrostatic interactions on the thickness and structure of β-casein layers adsorbed onto polystyrene latex particles. The influence of protein charge has been investigated by varying the background ionic strength or by including CaCl2, the calcium ion being a specific binding agent of the protein in solution. Both moderators cause...
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