Emulsion droplet formation

Kobayashi, S. Mukataka, M. Nakajima, CFD simulations and analysis of emulsion droplet formation from straight-through microchannels, Langmuir, 2004, 20, 9868-9877. 

Kobayashi I, Yasuno M, Iwamoto S, Shono A, Satoh K, Nakajima M. 2002b. Microscopic observation of emulsion droplet formation from a polycarbonate membrane. Colloids Surf A 207 185-196. 

Fig. 2. Aerosol emulsion droplets containing propellant (a) in the internal phase with subsequent formation of aerosol foam and (b) in the external phase...

Figure 5.16 Formation of emulsion droplets, (a) Aqueous MPS solution after acid-catalysed hydrolysis and condensation, (b) Micrometre-sized emulsion droplets are rapidly formed upon addition of the base catalyst triethanolamine. (Reproduced from ref. 28, with permission.)... 

Rgure 2.31. Two adhesive emulsion droplets of few tens of microns. The adhesion induces the formation of a large contact angle of about 40°. (Reproduced from [113], with permission.)... 

The stability of any emulsion is dependent on needs and the application area. In some cases, the emulsion need to be stable for longer time than in other cases. As in the case of hair cream, the emulsion should destabilize as soon as it is applied to the hair, as otherwise, the hair will be white with emulsion droplets. On the other hand, any emulsion used in spraying on plants needs to be stable for longer time. Further, if one needs to clean oil spills on oceans, the emulsion formation then needs to be destabilized. 

It seems that increasing the surfactant concentration causes thinning of the films between adjacent droplets of dispersed phase. Above a certain level, the films become so thin that on polymerisation, holes appear in the material at the points of closest droplet contact. A satisfactory explanation for this phenomenon has not yet been postulated [132], It is evident, however, that the films must be intact until polymerisation has occurred to such an extent as to lend some structural stability to the monomer phase if not, large-scale coalescence of emulsion droplets would occur yielding a poor quality foam. In general, vinyl monomers undergo a volume contraction on polymerisation (i.e. the bulk density increases) and in the limits of a thin film, this effect may play a role in hole formation, especially at higher conversions in the polymerisation process. 

FIGURE 7.4 Intuitive explanation of the spontaneous formation of emulsion droplets from a SEDDS. 

Tsapkina, E., Semenova, M., Pavlovskaya, G., Leontiev, A., Tolstoguzov, V. (1992). The influence of incompatibility on the formation of adsorbing layers and dispersion of n-decane emulsion droplets in aqueous solution containing a mixture of 11S globulin from Viciafaba and dextran. Food Hydrocolloids, 6, 237-251. 

When a biopolymer mixture is either close to phase separation or lies in the composition space of liquid-liquid coexistence (see Figure 7.6a), the effect of thermodynamically unfavourable interactions is to induce biopolymer multilayer formation at the oil-water interface, as observed for the case of legumin + dextran (Dickinson and Semenova, 1992 Tsapkina et al, 1992). Figure 7.6b shows that there are three concentration regions describing the protein adsorption onto the emulsion droplets. The first one (Cprotein< 0.6 wt%) corresponds to incomplete saturation of the protein adsorption layer. The second concentration region (0.6 wt% < 6 proiem < 6 wt%) represents protein monolayer adsorption (T 2 mg m 2). And the third region (Cprotein > 6 wt%) relates to formation of adsorbed protein multilayers on the emulsion droplets. 

It seems that there is probably greater availability of positively charged residues on the adsorbed protein for electrostatic interaction with sulfate groups of the anionic polysaccharide. This could lead to a greater extent of neutralization of dextran sulfate as a result of complex formation, and consequently to a lower thermodynamic affinity of the complexes for the aqueous medium and a lower value of the ( -potential for emulsion droplets in bilayer emulsions. 

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