Emulsion Overbeek theory

From the survey of the above literature, it is concluded that only a limited work is done on such type of problems. In the present study, the stability of emulsion has been discussed in the light of Derjaguin, Landau, Vervey and Overbeek theory (8) using Deoxyribonucleic acid and ribonucleic acid as flocculants for the emulsion stabilized by the drug sulphapyridine. 

Abstract. The stability of suspensions/emulsions is under consideration. Traditionally consideration of colloidal systems is based on inclusion only Van-der-Waals (or dispersion) and electrostatic components, which is refereed to as DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. It is shown that not only DLVO components but also other types of the inter-particle forces may play an important role in the stability and colloidal systems. Those contributions are due to hydrodynamic interactions, hydration and hydrophobic forces, steric and depletion forced, oscillatory structural forces. The hydrodynamic and colloidal interactions between drops and bubbles emulsions and foams are even more complex (as compared to that of suspensions of solid particles) due to the fluidity and deformability of those colloidal objects. The latter two features and thin film formation between the colliding particles have a great impact on the hydrodynamic interactions, the magnitude of the disjoining pressure and on the dynamic and thermodynamic stability of such colloidal systems. 

Two kinds of barriers are important for two-phase emulsions the electric double layer and steric repulsion from adsorbed polymers. An ionic surfactant adsorbed at the interface of an oil droplet in water orients the polar group toward the water. The counterions of the surfactant form a diffuse cloud reaching out into the continuous phase, the electric double layer. When the counterions start overlapping at the approach of two droplets, a repulsion force is experienced. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stabiUty that is called DLVO, after its originators Derjaguin, Landau, Vervey, and Overbeek (14,15). The theory provided substantial progress in the understanding of colloidal stabihty, and its treatment dominated the colloid science Hterature for several decades. 

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. 

The DLVO theory, which was developed independently by Derjaguin and Landau and by Verwey and Overbeek to analyze quantitatively the influence of electrostatic forces on the stability of lyophobic colloidal particles, has been adapted to describe the influence of similar forces on the flocculation and stability of simple model emulsions stabilized by ionic emulsifiers. The charge on the surface of emulsion droplets arises from ionization of the hydrophilic part of the adsorbed surfactant and gives rise to electrical double layers. Theoretical equations, which were originally developed to deal with monodispersed inorganic solids of diameters less than 1 pm, have to be extensively modified when applied to even the simplest of emulsions, because the adsorbed emulsifier is of finite thickness and droplets, unlike solids, can deform and coalesce. Washington has pointed out that in lipid emulsions, an additional repulsive force not considered by the theory due to the solvent at close distances is also important. 

From the brief sketch of the Deijaguin, Landau, Verwey, Overbeek (DLVO)-theory the following three important practical conclusions, suitable for foams and emulsions, can be drawn ... 

Two approaching emulsion droplets may be resisted by electrostatic forces. Electrostatic forces consist of Coulombic repulsion between two like charged objects and attractive van der Waals forces. These two forces are accounted for by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. A third force. Born repulsion, occurs at very small separation distances when electron clouds overlap [1,6,20,21], In emulsion systems an electrical double-layer may form around the disperse phase droplets. While electrical double-layer repulsion is certainly important in o/w emulsions, it does not play a large role in the stabilization of w/o emulsions due to the low dielectric constant of oil [55,56],... 

Surface forces are well known and are important in colloid science. They determine the stability and behavior of colloidal suspensions and emulsions [2]. In the case of emulsions/suspen-sions, their properties and behavior (stability, instability, rheology, interactions, and so oti) are governed by surface forces acting between colloidal particles or droplets [2]. The corresponding theory is widely referred to as DLVO flieory [1] according to the names of four scientists who substantially contributed to the area Deijaguin, Landau, Vervey, and Overbeek. 

Because of the drastic energy increase involved in the emulsification process, the resulting emulsion is not thermodynamically stable and the deemulsification process must be either slowed down to get stable goods or accelerated in separation operations. This chapter will focus on stabilizing emulsions. This stabilization can be explained using two different concepts the interfadai film using the hydrophilic-lipophilic balance (HLB) method and the Deijaguin, Landau, Verwey, and Overbeek (DLVO) theory. 

Now, if we think that the increase of the interfacial area involved in the emulsification process is of a 10 order of magnitude and that even the most efficient surface-active agent can reduce the interfacial tension by a factor of 5-10, we cannot understand why emulsifiers can stabilize the emulsions on the base of surface-tension calculations. In order to answer this question, the modem theory of Deijaguin, Landau, Verwey, and Overbeek (DLVO) will be used, but from a qualitative point of view because this chapter is devoted to the formulation job. 

Emulsions and microemulsions are dispersions of liquid in liquid. Therefore, an important feature is their interfacial fluidity and deformability, which distinguishes them from suspensions of solid particles. The stability of the latter is usually treated in the framework of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, " which accounts for the electrostatic and van der Waals interactions between solid particles. During recent years it was shown that other types of interparticle forces may often play an important role for the stability of dispersions—hydrodynamic interactions, hydration and hydrophobic forces, oscillatory structure forces, etc. - It was proven both experimentally and theoretically that steric and depletion " interactions may sometimes be a decisive factor for the dispersion stability. 

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