Structured emulsions

Recent investigations have allowed a better understanding of interdroplets interactions, of the impact of protein–polysaccharide interactions on emulsion stability and of the mechanisms involved in the production of emulsion gels. Owing to the possibility of controlling the structural properties, the design of food emulsions with improved kinetic stability and/or novel functional properties becomes possible.     

Solid-stabilized emulsions

The comprehension of bulk properties of solid-stabilized emulsions (stability, compressibility, elasticity) in relation with interfacial properties has progressed. The association of oil, water and particles allows a large set of materials to be obtained, where emulsions are used either as intermediate or end products. The efficiency of some stimulus-responsive particles to stabilize or destabilize emulsions “on demand” has been experimentally evidenced.     

Morphological transformations of native petroleum emulsions. I. Viscosity studies

Emulsions of water in as-recovered native crude oils of diverse geographical origin evidently possess some common morphological features. At low volume fractions varphi of water, the viscosity behavior of emulsions is governed by the presence of flocculated clusters of water droplets, whereas characteristic tight gels, composed of visually monodisperse small droplets, are responsible for the viscosity anomaly at varphi approximately 0.4-0.5. Once formed, small-droplet gel domains apparently retain their structural integrity at higher varphi, incorporating/stabilizing new portions of water as larger-sized droplets. The maximum hold-up of disperse water evidently is the close-packing limit of varphi approximately 0.74. At higher water contents (up to varphi approximately 0.83), no inversion to O/W morphology takes place, but additional water emerges as a separate phase. The onset of stratified flow (W/O emulsion gel + free water) is the cause of the observed viscosity decrease, contrary to the conventional interpretation of the viscosity maximum as a reliable indicator of the emulsion inversion point.     

Surfactant-free emulsions

Recent aspects and advances on surfactant-free emulsions are reviewed: preparation methods (e.g., acoustic emulsification, removal of dissolved gas from water and oil mixtures, utilization of solid particles, near- and super-critical carbon dioxide), colloidal stabilization (e.g., the addition of hydrophobic polymers into oil droplets, utilization of megasonic irradiation), and characterization techniques (single-droplet detection technique) of surfactant-free emulsions.     

Chemical destabilization of crude oil based emulsions and asphaltene stabilized emulsions

A comparison of low and high molecular weight demulsifiers and their effect on both crude oil and asphaltene based water-in-oil emulsions is performed. Physical characteristics are given for crudes and for the chemicals. These parameters were then correlated with the demulsifier performance. Results indicate that a significant lowering of interfacial tension is required, but not sufficient for an efficient demulsification. Addition of the chemicals directly to the oil phase prior to emulsification, i.e., as inhibitors, increased the performance of the chemicals significantly. Received: 3 May 2000 Accepted: 10 July 2000     

Deaggregation of acacia emulsions

Summary Emulsions aggregated by the hydrocolloid potassium arabate through interparticular bridging, are deaggregated by shear and added surface active agent but are unaffected by simple electrolyte. The minimum shear rate for almost complete deaggregation is in the region of 550 sec⁻¹ and the process is irreversible. In terms of critical micelle concentrations (c.m.c), potassium laurate (anionic) is more effective than hexadecyl-trimethylammonium bromide (cationic) which in turn is very much more effective than Tween 20 (non-ionic). The rate of deaggregation by surface active agent is rapid.     

Dielectric properties of emulsions

Summary Dielectric constants of O/W emulsions were measured over a wide range of concentration and at frequencies ranging from 20 cps. to 3 mc. No dielectric dispersion due to the interfacial polarization was observed in the experimental range of frequency, while the electrode polarization was observed below 100 kc. Experimental results were compared with theoretical values for spherical dispersions. It was concluded that the dielectric constants of O/W emulsions were expressed best byBruggeman's equation over the whole range of concentration.

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Zusammenfassung Die DK von ?l/Wasser-Emulsionen wurden über einen weiten Konzentrationsbereich und für Frequenzen zwischen 20 Hz und 3 MHz gemessen. Es war keine dielektrische Dispersion verursacht durch Oberfl?chenpolarisation innerhalb des experimentellen Frequenzbereiches zu beobachten. Dagegen wurde unterhalb 100 kHz Elektrodenpolarisation bemerkbar. Die experimentellen Ergebnisse wurden mit den theoretischen Darstellungen der Misch-DK für Dispersionen mit kugligen Teilchen verglichen. Der Verlauf der DK der ?l/Wasser-Emulsion wird am besten und über den ganzen Konzentrationsbereich durch die Gleichung vonBruggeman dargestellt.

     

NMR studies of emulsions

Application of NMR techniques to characterize colloidal systems has rendered many unique and valuable insights. Here we consider NMR's ability to quantify an emulsion droplet size distribution (DSD) via its ability to measure restricted molecular self-diffusion. The methodology is described along with the advantages and limitations of the technique. Recent highlights and typical applications are then elucidated.     

Crystallization in emulsions

The more widespread application of ultrasonic and X-ray techniques have stimulated further examination of the phase transitions in the lipid phase of oil-in-water emulsions. The improved experimental data have supported the development of theories to describe the processes.     

High-internal-ionic liquid-phase emulsions

High-internal-ionic liquid-phase emulsions were formed for the first time. The novel emulsions are very stable and do not involve any volatile organic solvent. They have great potential of applications in different fields, such as material synthesis, extraction, encapsulation, and chemical reactions.     

Waterproofing latex-bitumen emulsions

Bitumen emulsions are developed based on new anionic emulsifiers, which are wastes of chemical industry. Optimal concentrations of emulsifiers in bitumen emulsions are established. The developed bitumen emulsions are not inferior in their process and service parameters to known domestic and foreign analogs. The obtained bitumen emulsions may be recommended for use as waterproofing and anticorrosion coatings.     

Rheology of double emulsions

New equations for the viscosity of concentrated double emulsions of core-shell droplets are developed using a differential scheme. The equations developed in the paper predict the relative viscosity (eta(r)) of double emulsions to be a function of five variables: a/b (ratio of core drop radius to shell outer radius), lambda(21) (ratio of shell liquid viscosity to external continuous phase viscosity), lambda(32) (ratio of core liquid viscosity to shell liquid viscosity), phi(DE) (volume fraction of core-shell droplets in double emulsion), and phi(m)(DE) (the maximum packing volume fraction of un-deformed core-shell droplets in double emulsion). Two sets of experimental data are obtained on the rheology of O/W/O (oil-in-water-in-oil) double emulsions. The data are compared with the predictions of the proposed equations. The proposed equations describe the experimental viscosity data of double emulsions reasonably well.