A structural description of liquid particle dispersions: Ultracentrifugation and small angle neutron scattering studies of microemulsions

Abstract:The dielectric properties of the system water/AOT/dodecane are studied as a function of volume fraction ~ of the dispersed phase and molar ratio n (water/surfactant). Data shows that the spherical model is valid only at low n values or low ~ values. At high concentrations of dispersed phase, one has to consider micellar aggregation or deformation.Key words: Microemulsions, dielectric relaxation, permittivity.Solubility of water in hydrocarbon may be obtained using one or more interface agents. One then obtains a low viscosity, isotropic liquid, usually called "microemulsion". In the case of two interface agents, an ionic surfactant is mostly used with an alcohol partly soluble in water and oil. The use of alcohol may be avoided with non ionic surfactants (in that case microemulsions are obtained in a limited range of temperature) or with two-chain ionic surfactants like sodium-di-2-ethylhexylsulfosuccinate (AOT) or sodium-di-2-pentylsulfosuccinate (AY). In the later case, microemulsions may be obtained in a wide range of temperature.Microemulsions have been widely studied in the last few years because of practical interest in the fields of oil recovery, biotechnology and pharmacochemistry. A wide range of techniques have been used, and are becoming more and more sophisticated: light scattering, neutron scattering, conductimetry, magnetic and electric birefringence, positron anhihilation... Depending on the nature of components, composition and temperature, the structure of microemulsions may be very different. Following some conditions, they are dispersions of very small droplets of water in oil (w/o) or oil in water (o/w), the stability beingensured by a mixed layer of surfactant and co-surfactant. It has already been demonstrated that more complex structures may be found. For example, a bicontinuous structure [1] may be detected from a percolation-type W 977 conductive behaviour in some four-component systems [2][3][4]. In the same way, in the vicinity of the demixion curve, the behaviour of static permittivity [5] has been qualitatively attributed -either to highly anisotropic dispersed elements -or to spherical globule aggregation.The present work deals with the electric properties of w/o microemulsions obtained from a mixing of water, AOT and dodecane. In this particular case of ternary system, the volume fraction of dispersion (AOT + water) may be measured. When using alcohol, this would be possible only along the demixion curve [6], because of the alcohol distribution occurring between the continuous and micellar phases. Then a quantitative discussion of data reported in [5] is not possible. The main feature of the samples is their n ratio, number of water molecules over the number of AOT molecules. We may derive the volume fraction ~0 of dispersed components, assuming that all surfactant is located at the interface, and neglecting oil penetration within the layer. These microemulsions behave like ideal solutions in.the way that volumes of water, AOT, and oil are additive [7,8],The structure of th...

show abstract

“…This conclusion is in agreement with light and neutron scattering data on highly diluted microemulsions [26].…”

Section: -supporting

confidence: 92%

Structure of microemulsions of AOT and water in dodecane

Peyrelasse

Boned

Marin

1986

Colloid & Polymer Sci

View full text Add to dashboard Cite

show abstract

“…In this manner the chemical properties of the system change only very little, although the effect is not always completely negligible, as was shown by Chou et al [10]. Furthermore the contrast variation does not have to be confined to the solvent; sometimes it is very revealing to change the contrast of a specific part of the particle, as was shown by e. g. Dvolaitzky et al [4].…”

Section: Introductionmentioning

confidence: 71%

“…It has been used to study the internal structure of a variety of macromolecules and colloidal particles in diluted solution, such as biological macromolecules [1,2], latex particles [3], microemulsions [4] and block copolymers [5]. The method is based on a variation of the scattering power of the particles by varying the scattering length density of the solvent.…”

Section: Introductionmentioning

confidence: 99%

Small-angle neutron scattering of colloidal silica dispersions in a non-polar solvent

Moonen

Kruif

Vrij

et al. 1988

Colloid & Polymer Sci

View full text Add to dashboard Cite

Small-angle neutron scattering studies were performed on dilute dispersions of colloidal silica spheres in mixtures of hi2-and d12-cyclohexane. The particles consisted of a SiO2-core and a layer of stearyt alcohol molecules terminally attached with a chemical bond (Si-O) to the particle surface. The contrast variation method was applied to reveal the internal structure of the particles. The matchpoints determined with this method were in accordance with those calculated from the mass density of the particles and the "atomic composition", as determined with elemental analysis.For a detailed interpretation of the scattering curves, we assumed that the particles were spherosymmetrical and consisted of two concentric layers. With the relation we derived between the radius of gyration and the reciprocal contrast for such a model, it was possible to determine all the parameters characterizing the particle in terms of this model. The model calculations performed using these parameters fitted very well to the experimental intensities for high contrasts. For lower contrasts, the fit was somewhat less good. This is probably due to random fluctuations in the scattering length density within the particle core.The different radii as found by neutron scattering, agreed very well with those determined using other techniques, such as light scattering (static and dynamic) and electron microscopy.

show abstract

“…The water is thus surrounded by an interfacial film of surfactant and cosurfactant molecules; the hydrodynamic radius is in the lo-' m range [23,371. This is compatible with the protein size (4.5 x 6.0 x 11 nm3) [2].…”

Section: Discussionmentioning

confidence: 99%

Enzymes and microemulsions. Activity and kinetic properties of liver alcohol dehydrogenase in ionic water-in-oil microemulsions

1987

View full text Add to dashboard Cite

The activity and the kinetic properties of horse liver alcohol dehydrogenase have been studied in water-in-oil microemulsions containing sodium dodecyl sulfate (SDS) or hexadecyl trimethylammonium bromide (CTAB), 1-butanol or I-pentanol or 1-hexanol or t-butanol, water and cyclohexane alone o r with octane. In the anionic microemulsions (i.e. containing sodium dodecyl sulfate), the enzyme quickly lost its activity, but was efficiently protected by the coenzyme and some adenine nucleotides. In the cationic microemulsions (i.e. containing hexadecyl trimethylammonium bromide), the enzyme activity was more stable and with higher alcohols was stable for at least 20 min. The Michaelis constant of NAD' calculated with respect to the water content was nearly constant and higher than in water. The maximum velocity in anionic microemulsions depends on the water content whereas in cationic microemulsions, the maximum velocity did not show a clear dependence on the water content and was close to the maximum velocity found in water. The pH dependence of K , and V,,, in these microemulsions was similar to that observed in water. The kinetic data for an hydrophobic substrate, cinnamyl alcohol, showed that this alcohol partitions between the pseudo-phases and thus the apparent Michaelis constant and the concentration at which substrate-excess inhibition appeared were increased. The catalytic properties of the enzyme in microemulsions were illustrated by the preparative reduction of cinnamaldehyde with cofactor recycling. The rate determination of NAD' reduction and of 1-butanol/cinnamaldehyde redox reaction showed that at low water content (2.8%), the NAD' reduction rate was close to zero whereas the redox reaction rate was about half of the rate at higher water content. Probably at low water content the coenzyme binding-dissociation rates are reduced much more than the binding-dissociation rates of the substrates and the rates of the ternary complex interconversion. The cationic microemulsions seemed to be a very favorable medium for enzyme activity, the tetraalkyl ammonium surfactant causing less denaturation than the anionic detergent dodecyl sulfate.The use of water-soluble enzymes for chemical synthesis suffers from several limitations. The most obvious are the low water solubility of many organic substances and the fact that the presence of water makes the reversal of some enzyme reactions for synthetic purposes difficult. In order to overcome these problems, much attention has been paid over the last few years to the solubilization of biological macromolecules in micellar solutions [I -51. Most of the published work deals with three component systems: water, organic solvent and surfactants. Water-soluble enzymes like ribonuclease, peroxidase, a-chymotrypsin, trypsin, lactate dehydrogenase, pyruvate kinase, pyrophosphatase, lysozyme and alcohol dehydrogenase have been solubilized [l -141 in swollen reverse micelles from water, octane or isooctane and di(2-ethylhexy1)sodium sulfosuccinate (AOT). In some instances, other su...

show abstract

A structural description of liquid particle dispersions: Ultracentrifugation and small angle neutron scattering studies of microemulsions

Cited by 125 publications

References 19 publications

Structure of microemulsions of AOT and water in dodecane

Structure of microemulsions of AOT and water in dodecane

Small-angle neutron scattering of colloidal silica dispersions in a non-polar solvent

Enzymes and microemulsions. Activity and kinetic properties of liver alcohol dehydrogenase in ionic water-in-oil microemulsions

Contact Info

Product

Resources

About