The dielec. spectroscopy method (DS) has become a useful technique for the investigation of the structural and dynamic features of the components of both microemulsions and microdroplets over a wide temp. and frequency range. The dielec. parameters obtained by DS det. the geometry of the assocn. structures as well as the overall picture of the dynamics of the different polar groups. aggregates, and assocn. structures representing dipole modes. In this paper the results of a comprehensive study of the different types of microemulsions (ionic and nonionic) DS are presented. The static and dynamic dielec. properties of microemulsions a a function of temp., frequency and concn. of water, oil, surfactant and cosurfactant are considered. The dielec. properties have been investigated in the frequency range 105-1010 Hz using time domain dielec. spectroscopy (TDDS) and over a broad temp. interval enabling us to cover all the man dynamic processes occurring in such systems. The data treatment for the dynamic behavior of the microemulsions was carried out in the time domain in terms of dipole correlation functions and in the frequency domain in terms of complex dielec. permittivity. The correlation functions of the investigated systems exhibit complex nonexponential relaxation behavior, which must be deconvolute into normal modes and represented as a sum of the simple exponential, exp(-t/$\tau$), and nonexponential terms, exp[-(t/$\tau$)v]. The parameter $ν$ characterizes the shape of the relaxation function and the cross-correlation effects, and describes the morphol. of the system. The mol. mechanisms responsible for dielec. polarization in microemulsion of different nature at discussed. Knowledge of the amt. of hydrate water and co-surfactant in the interface can be obtained for nonionic microemulsions. In the case of ionic microemulsions, TDDS is a powerful technique for monitoring the organization of clusters and for investigation of relaxation processes involving rearrangement and movement of the droplets forming the clusters. [on SciFinder(R)]

Multiple emulsions are complex systems, termed "emulsions of emulsions", i.e. the droplets of the dispersed phase contain even smaller dispersed droplets themselves. Each dispersed globule in the double emulsion is sepd. from the aq. phase by a layer of oil-phase compartments. Double emulsions have significant potential in many applications since, at least in theory, they can serve as an entrapping reservoir for active ingredients that can be released from the inner phase to the outer phase by a controlled and a sustained mechanism. Many of the potential applications are in pharmaceuticals. In practice, double emulsions are thermodynamically unstable systems with a strong tendency for coalescence, flocculation and creaming. Most double emulsions consist of relatively large droplets, cannot withstand storage regimes and have a strong tendency to release the entrapped matter in an uncontrolled manner. Much work has been devoted in the last decade in order to the improve the stability of the multiple emulsions and the control of the release rates of the addenda. The most recent achievements are: Use of polymeric emulsifiers to improve interface coverage and to better anchor into the dispersed phases; Reduce droplets size by improving methods of formation: improved understanding of the release mechanisms and use of various additives to control the release via the reverse micellar mechanism. 35 Refs. [on SciFinder(R)]

The effects of free and bound water on the dielec. properties of microemulsions prepd. with the non-ionic surfactant Brij 97 were investigated. For the calcn. of the relative amts. of free and bound water, a simple multi-layered dielec. model was applied. The model considers the microemulsion as a sum of three sep. layers consisting of a "dry" microemulsion, free water and bound water, resp. The method is based on dielec. measurements of microemulsions at a frequency for which the dielec. permittivity and the dielec. losses for bound and free water have significantly different magnitudes. The dielec. contribution of free water to the relaxation spectrum of the microemulsion can be obtained, allowing both fractions to be calcd. In contrast to the traditional procedures used for calcn. of bound water from the relaxation spectrum, this method does not involve analyses of overlapping relaxation processes. [on SciFinder(R)]

Fenugreek gum was extd. from fenugreek seeds and evaluated for its surface activity. This unique galactomannan has a mannose backbone grafted with galactose units at an av. ratio of one. The purified fenugreek gum was found to reduce surface tension to values lower than guar gum (42 and 55 mN/m, resp.). The interfacial activity was surprisingly better than other galactomannans (interfacial tension was reduced to 2 mN/m in vegetable oils) which led to the formation of oil-in-water emulsions with with small droplet size (2-3 $μ$m) and long-term stability. The fenugreek gum was found to adsorb (or 'ppt.') on the oil interface forming a relatively thick interfacial film. The emulsions are more stable than any equiv. emulsions stabilized by other galactomannan gums. No flocculation was obsd. in emulsions stabilized with fenugreek concns. sufficient for a good coverage of the oil interface as expressed by the coverage index (Rc) correlated to the gum/oil wt. ratio (Rc\textgreater12). [on SciFinder(R)]

Self-diffusion of all components in two different microemulsions has been studied by the Fourier-transform pulsed-gradient spin echo 1H NMR technique. The anal. of hydrodynamic and direct droplet-droplet interactions in microemulsions allows the simultaneous application of the Stokes-Einstein equation for surfactant and oil. The result of this anal. is a simple relation connecting self-diffusion coeffs. of components and the size of droplets. It is shown that because of partial solubilization of water in oil the droplet radius can be significantly different from the expected radius. [on SciFinder(R)]

Time domain dielec. spectroscopy of reverse water/acrylamide/Aerosol-OT(AOT)/toluene microemulsions shows that percolation induced by increasing cosurfactant concn. (increasing cosurfactant chem. potential) obeys scaling above and below a percolation threshold. This scaling anal. suggests that the obsd. percolation is close to static percolation limits. Self-diffusion measurements derived from NMR pulsed-gradient spin-echo expts. reveal an increase in water proton diffusion above the percolation threshold. This increase is assigned to water transport through fractally chained assemblies of microemulsion droplets. The diffusion of water, cosurfactant, and surfactant (AOT) below threshold is modeled quant. taking into account the chem. partitioning equil. between the microemulsion droplets and the toluene continuous pseudophase. Above threshold, the apparent increasing water and cosurfactant partitioning into the toluene (continuous) pseudophase suggests facilitated transport through fractal aggregates. Ad dynamic partitioning model is used to est. the vol. of percolating fractal cluster, and yields an order parameter for water-in-oil to percolating cluster microstructural transitions. This same order parameter is also illustrated to derive from self-diffusion data wherein percolation and transformation to sponge phase microstructure are driven by increases in temp. and in disperse phase vol. fraction. For microstructural transitions driven by three different field variables, chem. potential, temp., and disperse phase vol. fraction, this order parameter shows that the onset of percolation corresponds to the onset of increasing water proton self-diffusion, and that the onset of increasing surfactant self-diffusion corresponds to the formation of bicontinuous microstructures and the onset of transformation to middle phase microemulsion. [on SciFinder(R)]

A review with 57 refs. Multiple emulsions are complex systems of emulsion within an emulsion, where the droplets of the dispersed phase themselves contain even smaller dispersed droplets. The two major types are water-in-oil-in-water (W/O/W) and oil-in-water-in-oil (O/W/O) double emulsions. Double emulsions are unstable thermodn. systems, which tend to cream, flocculate and coalesce. Much effort has been made to develop methods of 'better sealing' in the inner and outer interfaces and to reduce the droplet size of the emulsions. Dissolved or dispersed compds. in the inner phase of double emulsions tend to be released to the outer phase primarily via a reverse micellar transport (which is diffusion-controlled) or through the thin lamellae of a surfactant phase migrating to the outer phase via the outer interface. It is difficult to control the release of the solutes unless macromols. are used to improve lamellar stabilization (steric stabilization) forming a rigid surfactant-polymer complex at the interfaces. The review describes recent achievements in the use of BSA, casein, gelatin and other naturally occurring macromols. together with monomeric-amphiphilic mols. for possible future applications in food systems. [on SciFinder(R)]