Emulsions drop size

B.W. Brooks and H.N. Richmond Phase Inversion in Non-Ionic Surfactant-Oil-Water Systems, I. The Effect of Transitional Inversion on Emulsion Drop Size. Chem. Eng. Sci. 49, 1053 (1994). 

J.L. Salager, M. Perez-Sanchez, and Y. Garcia Physicochemical Parameters Influencing the Emulsion Drop Size. Colloid Polym. Sci. 274, 81 (1996). 

M. Perez, N. Zambrano, M. Ramirez, E. Tyrode, and J.L. Salager Surfactant-Oil-Water System near the Affinity Inversion. XII. Emulsion Drop Size Formulation and Composition. J. Dispersion Sci. Technol. 23, 55 (2002). 

Emulsion drop size analyses Since stability and other characteristics (such as viscosity and appearance) are known to be related to the drop size, they need to be measured. There are commercial instruments that can be used for such analyses. These are... 

Computer programs accounted for the presence of oil drops below- the detection limit of the Coulter Counter. The data processing procedure, which assumed that the oil-drop size distribution was lognormal, yielded accurate estimates of the true mean and standard deviation describing the emulsion drop size distribution. The data-analysis procedure did not affect the actual measured drop populations which were used in the kinetic studies. The computer programs are described in detail by Bycscda.8... 

The combination of reducing the flow and increasing the turbulence level has been shown by Brown and Pitt (4) to decrease emulsion drop size and, in systems as we have here with a fixed amount of dispersed phase, increase the emulsion surface area. 

Testing techniques for the evaluation of physical properties and other properties of finished margarine products as well as low-fat spreads have been stated to include (4, 91) appearance, oral melting characteristics, oil exudation, slump (collapse), penetrations, spreadability, emulsion viscosity at 35°C (95°F), emulsion drop size, and electrical conductivity. 

Phase inversion is a commonly observed phenomenon in which the continuous phase abruptly becomes the dispersed phase and vice versa (see Pacek et al. and Pacek, Nienow, and Moore Systematic studies on the effect of surfactant concentration and mixing on phase inversion and emulsion drop size have been carried out by Brooks and Richmond. Fig. 5 shows schematically the steps occurring during phase inversion. Although conflicting information exists on the subject, the following conclusions can be made ... 

Brooks, B.W. Richmond, H.N. Phase inversion in non-ionic surfactant-oil-water systems. I. The effect of transitional inversion on emulsion drop sizes. Chem. Eng. Sci. 1994, 49, 1053-1064. 

In the case of desorption the processes have the opposite direction.) Such interfacial expansions are typical for foam generation and emulsification. The rate of adsorption relaxation determines whether or not the formed bubbles/drops will coalesce upon collision and, in final reckoning how large the foam volume and the emulsion drop-size will be. - Below, we focus on the relaxation time of surface tension, X , which characterizes the interfacial dynamics. 

Perez, M., Zambrano, N., Ramirez, M., Tyrode, E. and Salager, J.L. (2002) Surfactant-oil-water systems near the affinity inversion. Part XII Emulsion drop size versus formulation and composition. /. Dispersion Sci. Technol., 23, 55-63. 

Effective compatibilization of binary polymer blends by addition of a copolymer reduces the dispersed particles size and Vj [Anastasiadis et al, 1987 Wu, 1987 Patterson et ai, 1971]. An illustration is shown on Figure 4.15. The effect of compatibilizer addition is similar to the emulsification of the classical emulsions. In the former systems, the compatibilizer effect on the drop size and Vj follows the same behavior as the emulsion drop size reduction upon addition of a surfactant. The latter behavior is usually described as the titration curve that characterizes the surfactant efficiency. The shape of the titration curve depends on the type of emulsifier and the emulsification process, e.g., mixing time and equipment. However, the amount of emulsifier to saturate the interface also depends on the affinity of emulsifier to the dispersed phase, the size of the dispersion, the orientation of the emulsifier at the interface and its ability to prevent flocculation and coalescence [Djakovic et al., 1987]. A similar behavior is to be expected for polymer blends upon addition of a compatibilizer. 

Figure 14 (right) indicates the variation of the emulsion drop size along a formulation scan, which here is a temperature scan with a non ionic surfactant. Optimum formulation, here optimum temperature T, essentially corresponds to Shinoda s phase inversion temperature (PIT) (80) where the surfactant affinity switches from hydrophilic to lipophilic. 

Figure 14 Typical variations of the imerfacial tension (left), emulsion stability tcenter). and emulsion drop size (right), along a formulation scan. Ca.se of nonionic system and temperature scan.

The emulsion drop size depend.s on such a high number of different variables that it is difficult to separate and impute ait effects. In what follows a standard emulsificalinn protocol is applied to a preequilibrated system, so that the change in drop size is only due to formulation or composition effects, or their direct con.sequences on other properties such as tension, stability, and vi.scosiiy. In fact, very few map.s have been experimentally determined and only lrend,s are available (81,92). 

JL Salager, M Perez-Sanchez, Y Garcia. Physicochemical parameters influencing the emulsion drop size. Colloid Polym Sci 274 81—84, 1996. 

The analytical methods and devices used are briefly described in the following. Selected analytical results refer to the main influencing material characteristics of the emulsion drop size distribution generation during emulsion preparation but in particular during emulsion spray processing. These material characteristics are... 

The extensional viscosity functions of emulsions were characterized using a Capillary Breakup Extensional Rheometry (CaBER). The apparent extensional viscosities ) of SE-la emulsions as a function of strain rate e are given in Fig. 23.5 for the different mean emulsion drop sizes of 2,4, and 10 pm. From this, an extensional viscosity characteristics for the emulsion with a drop size of 10 pm was derived close to constant and rather low (ca. 0.2 Pas, Newtonian-like). For emulsion drop sizes of 2 and 4 pm, pronounced extensional thinning was observed in the low elongation rate domain, whereas some pronounced extensional thickening behavior was monitored in the higher elongation rate domain. 

Particles that are small relative to emulsion drop size are also expected to have an effect on emulsion properties in systems stabilized by surfactants when present in only small amounts (say a sufficient number of particles to give 10% coverage of droplet surfaces). We reported elsewhere [40] on a preliminary smdy of the ways in which the stability to flocculation and coalescence of water-in-oil emulsions stabilized by the anionic surfactant Aerosol OT are modified by polystyrene latex particles. There is evidence that the particles bridge droplets to give weak floes, which slow down droplet coalescence. 

Emulsion drop size is the result of competing effects that take place during emulsification the drop breakup and the drop coalescence processes. Many properties and phenomena are likely to influence one or the other effect, sometimes in a complex way. As the formulation approaches HLD = 0 the interfacial tension decreases, thus facilitating the drop breakup and the formation of smaller drops. In a concomitant way, the emulsion stability becomes extremely low, allowing rapid coalescence, which favors the occurrence of larger drops. As a consequence of these opposite effects, the drop size exhibits a minimum for each type of emulsion, i.e., on each side of HLD = 0. For each system, the location of the minimmn depends not only on the formulation (HLD value) but also on the stirring energy and efficiency [40]. 

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