Surfactant concentration effects emulsion viscosity

In this process, one starts with the phase that should become the dispersed phase. We call this phase A. One then slowly adds the other phase (B) to phase A while the system is agitated (or rapidly flowing, or homogenized in a suitable machine). Initially, droplets of phase B are formed, which are broken up into small droplets by the agitation. In time, more and more of these droplets are formed However, one ultimately wants to have an emulsion of in 5 therefore, the surfactant system is dissolved in phase B and not in phase A. Thus, at a certain time, the emulsion becomes so concentrated and the viscosity becomes so high, that the droplets of B are sheared apart droplets of B then start to coalesce. As soon as this coalescence sets in, all droplets start to coalesce, as a snowball effect. So, suddenly the droplets of B combine and start to form a continuous phase, taking up droplets of phase A, which starts to be the dispersed phase. 

Effect of Surfactant Concentration Emulsion stabdity generally increases with increasing surfactant concentration [92,93]. As discussed in Section 25.4.2.3, an increase in surfactant concentration leads to the lowering of leakage due to an increase in the mechanical resistance of the membrane. An increase in this parameter also increases the membrane phase viscosity as well as its resistance to mass transfer including water mass transfer, thus reducing osmosis [89,94]. 

This exclusion of polymers from the interior of the vesicles results in an osmotic compression of the water layers and a decrease in the water layer thickness and lamellar phase volume. This effect allows the control of bulk properties such as viscosity and also provides a probe of water layer dimensions in lamellar dispersions. The lamellar surfactant system used in this study is the sodium dodecyl sulfate (SDS)/dodecanol (Ci20H)/water system that has been used to prepare submicron diameter emulsions (miniemulsions) from monomers for emulsion polymerization (5) and for the preparation of artificial latexes by direct emulsification of polymer solutions such as ethyl cellulose (4). This surfactant system forms lamellar dispersions (vesicles) in water at very low surfactant concentrations (< 13 mM). 

For surfactant concentrations close to or above the CMC, the Gibbs elasticity and the interfacial viscosity are large enough to immobilize the interface, = 0 (see Refs. 5, 58, 267, and 420). A similar effect is observed when the droplet dynamic viscosity is much larger than the dynamic viscosity of the continuous phase (e.g., in the bitumen emulsions, T d, is about 150,000 p at room temperature). For the case of fllm with inunobile surfaces, from Eq. (251) one can deduce the well-known Reynolds formula [466], in which the disjoining pressure, II, can be also included ... 

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