The aim of this paper is to present a short overview of the main mechanisms operative in the formation and stabilization of emulsions by solid particles and, on this basis, to make comparisons between solid particles, surfactants and globular proteins as emulsifiers. When available, simple quantitative relations are presented, with the respective numerical estimates and discussion of the applicability of these relations to particle-stabilized systems. Non-obvious similarities between the different types of emulsifiers are outlined in several cases in which the description of the system can be performed at a phenomenological level. Examples are presented for the process of emulsification, where we show that several simple theoretical expressions, derived originally in the studies of surfactants and protein emulsifiers, can be successfully applied to particle-stabilized emulsions. In contrast, for the phenomena in which the detailed mechanisms of particle adsorption and film stabilization are important, the differences between the various emulsifiers prevail, thus making it impossible to use the same theoretical description. The most important specific characteristics of the solid particles which strongly affect their behavior are the high barrier to particle adsorption, high desorption energy and strong capillary forces between particles trapped in liquid films, which all originate in the relatively large particle size (as compared to the size of surfactant and protein molecules). The capillary mechanism of stabilization of liquid films by solid particles is reviewed in some detail, to emphasize its specific features and to demonstrate the applicability of several simple expressions for approximate estimates. Interestingly, we found that the hypothesis for some exceptionally high coalescence stability of the particle-stabilized emulsions is not supported by the experimental data available in literature. On the other hand, the particles are able to completely arrest the process of Ostwald ripening in foams and emulsions, and this effect can be easily explained with the high desorption energy of the particles and the resulting capillary effects.

Comparison of solid particles, globular proteins and surfactants as emulsifiers

High internal phase emulsions (HIPEs) are concentrated systems possessing a large volume of internal, or dispersed phase. The volume fraction is above 0.74, resulting in deformation of the dispersed phase droplets into polyhedra, which are separated by thin films of continuous phase. Their structure, which is analogous to a conventional gas-liquid foam of low liquid content, gives rise to a number of peculiar and fascinating properties including high viscosities and viscoelastic rheological behaviour. Like dilute emulsions, HIPEs are both kinetically and thermodynamically unstable; nevertheless, it is possible to prepare metastable systems which show no change in properties or appearance over long periods of time.

High internal phase emulsions (HIPEs) — Structure, properties and use in polymer preparation

A new experimental method is presented using fluorescein dye to determine the spatial and temporal variations of the liquid volume fraction in aqueous foams This method is used for quantitative studies of liquid redistribution (drainage) in three types of experiments: forced, free, and pulsed drainage Characteristic quantities, such as the drainage velocity, show power-law dependences on experimental parameters that are inconsistent with traditional foam drainage models based on Poiseuille-type flow in the liquid-carrying channels (Plateau borders) of the foam To obtain a theoretical description, the foam drainage equation is generalized using an energy argument which accounts for viscous dissipation in both the channels and the nodes (or vertices, which are the junctions of four channels) of the liquid network Good agreement with results for all three types of drainage experiments is found when using this new model in the limit where the dissipation is dominated by the nodes

https://www.princeton.edu/%7Estonelab/Publications/pdfs/From%20Howard/Langmuir/KoehlerLangmuir00.pdf

A Generalized View of Foam Drainage: Experiment and Theory

Rheology of foams and highly concentrated emulsions: IV. An experimental study of the shear viscosity and yield stress of concentrated emulsions

https://www.lcpe.uni-sofia.bg/publications/2006/pdf/2006-27-SC-ND-IBI-BC-Protein-Stabilized-Emulsions.pdf

Coalescence stability of emulsions containing globular milk proteins.

Osmotic pressure of foams and highly concentrated emulsions. 2. Determination from the variation in volume fraction with height in an equilibrated column

A. D. Kiss

Papers

Osmotic pressure of foams and highly concentrated emulsions. 2. Determination from the variation in volume fraction with height in an equilibrated column