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.     

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.     

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.     

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     

Ultrasound/radiation-responsive emulsions

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Solubilization in monodisperse emulsions

The kinetics of oil solubilization into micelles from nearly monodisperse alkane-in-water emulsion droplets was investigated. Emulsions containing either hexadecane or tetradecane oils were fractionated to be narrowly distributed, using a method developed by Bibette [J. Bibette, J. Colloid Interface Sci. 147 (1991) 474]. These monodisperse emulsions were mixed with SDS or Tween 20 aqueous micellar solutions of various concentrations. Time-dependent solubilization was monitored using light scattering and a decrease in average droplet size over time was observed, in contrast to what has been observed previously with polydisperse emulsions. The rate at which the droplet size decreased was found to be independent of the initial droplet size. Turbidity measurements were also used to track the solubilization kinetics, and a population balance analysis used on both types of measurements to extract effective mass transfer coefficients. The dependence of these transfer coefficients on droplet size, alkane type, surfactant type and concentration provide insights into plausible mechanisms of emulsion droplet solubilization within micellar solutions.     

固体粒子稳定的乳状液研究进展

综述了固体粒子对乳状液稳定性影响的有关研究进展。微细不溶的固体粒子构成重要的一类乳化剂,被水相和油相部分润湿的固体粒子能够有效地稳定乳状液。固体粒子稳定乳状液的效果取决于以下因素:粒子大小、粒子间相互作用和粒子的润湿性质。固体粒子存在的油-水界面表现出粘弹行为,这种粘弹界面膜可大大地提高空间位阻,减缓乳状液液珠间液膜变薄的速率,从而提高乳状液地稳定性。原油中的粘土、胶质、沥青质和石蜡等胶体粒子被证明对乳状液的稳定性起很大的作用。     

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.

     

Aggregation in Pickering emulsions

For the first time, the particle distribution and aggregation in Pickering emulsions were made visible by transmission X-ray microscopy. Oil/water emulsions were stabilized by heterocoagulates of a clay mineral and magnesium aluminum hydroxide. Stability is optimum when the particles surround the oil droplets and also assemble to form a network extending through the coherent phase. Received: 18 September 1998 Accepted: 28 September 1998     

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.     

Coalescence in double emulsions

Coalescence processes in double emulsions, water-in-oil-in-water, are studied by optical microscopy. The time evolution of such systems is determined by the interplay of two coalescence processes, namely, between inner water droplets and between the inner water droplets and the continuous external water phase. The predominance of one of those processes over the other, regulated by the relative amount of hydrophilic and lipophilic surfactants, leads to different evolutions of the system. We present here results for a class of systems whose evolution follows a master behavior. We also implemented a computer simulation where the system is modeled as a spherical cavity filled with smaller Brownian spheres. Collisions between spheres allow coalescence between them with probability P(i), whereas collisions between a sphere and the wall of the cavity allow coalescence with the external phase with probability P(e). The phenomenology observed in the experimental systems is well reproduced by the computer simulation for suitable values of the probability parameters.     

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.     

Protein nanocage-stabilized Pickering emulsions

The utilization of surface-active engineered protein nanocages as stabilizers for emulsions provides avenues for the design of new tailor-made functional materials in various fields including food, pharmaceutical, and biotechnology. They can be used to codeliver bioactive molecules of different polarities in a tailored manner to the body, act as a platform for screening cells or enzymes, or function as targeted drug delivery systems. Knowledge on the mechanisms that underlie the protein nanocage-driven stabilization of emulsions and their colloidal structure can have direct implications for the rational design of the new advanced functional colloids.This contribution summarizes the recent progress in protein nanocage-stabilized emulsions. It discusses the advances in the precision bioengineering of protein nanocages for emulsion design, highlights challenges in the characterization of structure and dynamics in these materials, and demonstrates selected applications in the field of functional food materials.