Principle of Emulsification

Liquid fabric softeners are formulated by dispersing the melted raw material in well-stirred hot water. Although DHTDMAC aqueous dispersions are not emulsions in the strict sense, chemical and mechanical principles of emulsification apply to control the viscosity and phase stability [10]. 

Pressure applied on the dispersed phase Figure 1.1. Schematic principle of membrane emulsification. 

Figure 1.2. Schematic principle of microchannel emulsification, (a) Top view (b) side view.

Figure 1.3. Schematic principle of flow focusing emulsification.

E.S. Rajagopai, Principles of Emulsion Formation Sonic and Ultrasonic Emulsification, Emuision Science, Academic Press, London, 1968. 

Although capsule membrane PTC is not suitable for direct scale-up to industrial level due to the inconveniences of working with capsules, the principles can be exploited in membrane reactors, with the PT catalyst immobilized on the membrane surface. This would not only enable easy recovery of both aqueous and organic phases after reaction without any problems of emulsification, but also ensure that the PT catalyst does not contaminate the product in the organic phase. Using a membrane reactor will also ensure high mass-transfer rates due to high interfacial areas per unit volume of reactor. More importantly, it will open up possibilities for continuous operation. 

Bancroft summarized the results of emulsification experiments carried out from the late I9th until the early 20th century by a rule of thumb which stated that in order to have a kinetically stable emulsion the emulsifying agent must be soluble in the continuous phase (23). In principle, this rule finds its expression in the empirical system of the HLB values (hydrophilic-lipophilic balance) which was developed in the middle of the 20th century to allow the... 

The emulsification process in principle consists of the break-up of large droplets into smaller ones due to shear forces (10). The simplest form of shear is experienced in lamellar flow, and the droplet break-up may be visualized according to Figure 4. The phenomenon is governed by two forces, ie, the Laplace pressure, which preserves the droplet, and the stress from the velocity gradient, which causes the deformation. The ratio between the two is called the Weber number. We, where Tj is the viscosity of the continuous phase, G the velocity gradient, r the droplet radius, and y the interfacial tension. 

These tests established that detection of the chloroform emulsification was the principle underlying action of the autotitrator. However, while there is agreement in the qualitative dependence on the salt level there are differences in the apparent rates of change in signal with aliquot addition. These can be attributed mainly to non-equilibrium effects. 

The physico-chemical theory of surface activity is a vast field and no more than broad principles can be touched on here major reference sources exist for those who require more detail of the relationship between chemical structure and the various surfactant properties such as wetting, detergency and emulsification-solubilisation [32-36]. 

No generalities seem justified regarding the relationship between concentration of emulsifier and oil deposit obtained. An increase in the concentration of certain emulsifiers has been found to increase the oil deposit, while in other cases the reverse has been true. It is clear that both the individual characteristics of the emulsifier and the concentration used affect deposit, but, in spite of the extensive literature on the role of emulsifiers in emulsification and deposition, no satisfactory method of evaluating emulsifiers for spray oils other than by actual trial imder field conditions has been found. A rather complete discussion of emulsifiers and the principles involved in emulsification is given in the work of Sutheim (21),... 

This phenomenon of self-emulsification was first observed by Johannes Gad in 1878 when he gently layered a solution of lauric acid on top of an aqueous alkaline solution, thereby making a soap in situ but also forming an emulsion without the aid of external agitation. A laboratory curiosity for the next 50 or so years, the principle became recognized as being valuable for the formulation of herbicides and insecticides such as DDT. The concentrate could be reconstituted with ditch water and sprayed without the need to carry water to the site. 

As described later, liquid-liquid reactors are mechanically agitated in order to achieve a good dispersion and large interfacial area between two immiscible liquids. The increase in interfacial area due to stirring enhances the reaction rate (e.g., saponification, bead polymerization, etc.). It should be noted that the interfacial area is also increased by the addition of surfactants. This process is called emulsification and is governed by completely different principles than the ones described here. 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

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