Emulsion colloid theory, applications

Kabalnov, A.S. Shchukin, E.D. Ostwald ripening theory applications to fluorocarbon emulsion stability. Adv. Colloid Interf. Sci. 1992, 38, 69-97. 

Classical theories of emulsion stability focus on the manner in which the adsorbed emulsifier film influences the processes of flocculation and coalescence by modifying the forces between dispersed emulsion droplets. They do not consider the possibility of Ostwald ripening or creaming nor the influence that the emulsifier may have on continuous phase rheology. As two droplets approach one another, they experience strong van der Waals forces of attraction, which tend to pull them even closer together. The adsorbed emulsifier stabilizes the system by the introduction of additional repulsive forces (e.g., electrostatic or steric) that counteract the attractive van der Waals forces and prevent the close approach of droplets. Electrostatic effects are particularly important with ionic emulsifiers whereas steric effects dominate with non-ionic polymers and surfactants, and in w/o emulsions. The applications of colloid theory to emulsions stabilized by ionic and non-ionic surfactants have been reviewed as have more general aspects of the polymeric stabilization of dispersions. ... 

Kabalnov, A. S. and Shchukin, E. D. 1992. Ostwald ripening theory Applications to fluorocarbon emulsion stabihty. Adv. Colloid Interface Sci. 38 69—97. 

Although the remainder of this contribution will discuss suspensions only, much of the theory and experimental approaches are applicable to emulsions as well (see [2] for a review). Some other colloidal systems are treated elsewhere in this volume. Polymer solutions are an important class—see section C2.1. For surfactant micelles, see section C2.3. The special properties of certain particles at the lower end of the colloidal size range are discussed in section C2.17. 

All of the petroleum emulsion applications or problems just discussed have in common the same basic principles of colloid science that govern the nature, stability, and properties of emulsions. The widespread importance of emulsions in general and scientific interest in their formation, stability, and properties have precipitated a wealth of published literature on the subject. This chapter provides an introduction and is intended to complement the other chapters in this book on petroleum emulsions. A good starting point for further basic information is one of the classic texts Becher s Emulsions Theory and Practice (4) or Sumner s Claytons Theory of Emulsions and... 

Application of DLVO Theory. Some of the concepts and expressions of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory of colloid stabihty have been described in Chapter 1, or can be found in many different textbooks 4, 5). The application of DLVO theory to oil-in-water colloids with special reference to the stability of bitumen-in-water emulsions will be discussed here. 

Some progress toward an understanding of these systems is also possible by considering the influence of the presence of water within the oil drops on the interaction between the oil drops and by consideration of the influence of the size of the internal water droplets on their internal stability and on the possibility of coalescence with the external aqueous phase. It is premature to consider all this in detail as the application of colloid stability theory to simpler emulsions has not been particularly successful (37). For type A w/o/w emulsions, the approach of Void (38) may perhaps be used if the oil layer is thought of as the homogeneous adsorbed layer. 

The use of emulsions and their range of practical application has been expanded enormously. As a result, the field of the theory of emulsions and technical emulsion science, as a part of classical colloid chemistry, can use a lot of theory developed there. 

Then mesoscopic aspects are treated. Chapter 9 gives a general introduction on disperse or particulate systems. It concerns properties that originate from the division of a material over different compartments, and from the presence of a large phase surface. Two chapters give basic theory. Chapter 10 is on surface phenomena, where the forces involved primarily act in the direction of the surface. Chapter 12 treats colloidal interactions, which primarily act in a direction perpendicular to the surface. Two chapters are concerned with application of these basic aspects in disperse systems Chapter 11 with emulsion and foam formation, Chapter 13 with the various instabilities encountered in the various dispersions foams, emulsions, and suspensions. 

The principles of colloid stability, particularly including DLVO theory and steric stabilization, can be applied to many food emulsions [80,81]. The applicability of DLVO theory is restricted, however, partly because the primary potential-energy minima are somewhat shallow and partly due to the tendency of adsorbed proteins extend outward from surfaces so far that steric stabilization becomes more important [34,126]. The presence of protein in an adsorption layer can also contribute a viscoelastic restriction to coalescence. Finally, the oils in food colloids are usually triglycerides (of either animal or vegetable origin). These oils may exist in liquid or crystalline states at room temperature frequently both simultaneously. The existence of the crystal form at interfaces contributes yet another stabilizing component [34]. 

For completeness we note that two other FFF subtechniques can be applied to certain polymeric materials, although applications are so far limited. Sedimentation FFF is the most notable example. For this system the driving force (centrifugally induced sedimentation) is directly proportional to molecular mass in a form that is calculable from first principles (see eqn 8.7). Accordingly, molecular mass distributions can in theory be obtained by calculation without empirical calibration. This principle has been successfully applied to the determination of the molecular mass and particle size distribution of numerous colloidal particles including viruses, latices, emulsions, liposomes, protein aggregates, and water-borne colloids [5,7,9]. However, as noted earlier, sedimentation FFF is not applicable to many polymers of interest because sedimentation forces (even in a powerful centrifuge) are not adequate to drive the components to the accumulation wall of the FFF channel. Thus molecular masses of less than 10 cannot be well... 

Patel VM, Sheth P, Kurz A, Ossenbeck M, Shah DO, Gower LB (2002) Synthesis of calcium carbonate-coated emulsion droplets for drug detoxification. In Markovic B, Somansundaran P (eds) Concentrated colloidal dispersions theory, experiments, and applications. ACS Symposium Series 878. American Chemical Society, Washington DC... 

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