Multiple emulsions classification

Figure 9.16. Multiple emulsion classification based on droplet characteristics in the primary emulsion.

This kind of classification is not always appropriate. For example, O/W/O denotes a multiple emulsion containing oil droplets dispersed in aqueous droplets that are in turn dispersed in a continuous oil phase. The type of emulsion that is formed depends upon a number of factors. If the ratio of phase volumes is very large or very small, then the phase having the smaller volume is frequently the dispersed phase. If the ratio is closer to 1, then... 

The initial step in the fabrication of a multiple emulsion (W/OAV) is to prepare a primary emulsion (W/0). It is generally agreed that the surfactant for the primary emulsion should have an HLB value of 3-6 (in the hydrophilic-lipophilic balance system of surfactant classification). Surfactants that have successfully been utilized include Span 80 (sorbitan oleate Nianxi et al, 1992 Zheng et al, 1993 Omotosho et al, 1990), E644 (polyamine Nianxieia/., 1992),N205 (polyamine Nianxi eta/., 1992), TX-4 (polyoxyethylene aUcylphenol ether Nianxi et al, 1992), MO A3 (polyoxyethylene aliphatic alcohol ether Nianxi et al, 1992), Brij 93 (Nianxi et al, 1992), polyoxamers [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer Law et al, 19861, and egg lecithin. The surfactant or combination of surfactants is then dissolved in the oil... 

Three types of multiple emulsions may be distinguished [16] (Figure 12.11). This classification is based on the predominance of the multiple emulsion droplet type. Using isopropyl myristate as the oil phase, 5% Span 80 to prepare the primary W/O emulsion, and various surfactants to prepare the secondary emulsion, three main types of multiple emulsions were observed [16] Type A droplets contained on a large internal droplet, similar to that observed by Matsumoto et al. [17]. This type was produced when polyoxyethylene oxide (4) lauryl ether (Brij 30) was used as secondary emulsifier at 2%. Type B droplets contained several small internal droplets. These were prepared using 2% polyoxyethylene (16.5) nonylphenyl ether (Triton X-165). Type C drops entrapped a large number of small internal droplets. These were prepared using a 3 1 Span 80-Tween 80 mixture. 

This chapter will start with a short account of the general classification and description of polymeric surfactants. This is followed by a summary on then-solutions properties. The adsorption and conformation of polymeric surfactants at the solid-liquid interface will be discussed at a fundamental level and some experimental results will be presented to illustrate the prediction of the theories. The interaction energies between particles or droplets containing adsorbed polymeric surfactants will be briefly described. The final section will give some applications of polymeric surfactants in suspensions, emulsions, and multiple emulsions. 

Figure 1 Droplet classification in multiple emulsions. Type A is a single-compartment double emulsion type B is a double emulsion with a few compartments type C is a multicompartment double emulsion.

The nature of the droplets in a multiple emulsion will depend on the size and stability of the primary emulsion. A system of classification has been proposed dividing W/OAV multiple emulsions into three classes according to the nature of the oil-phase droplets (Figure 9.16). Type A systems are characterized as having one large internal drop essentially encapsulated by the oil phase. Type B systems contain several small, well-separated internal drops, and systems of type C contain many small internal drops in close proximity. It is understood that any given system will in all probability contain all three classes of drops, but one will be found to dominate, depending primarily on the surfactant system employed. 

M De Luca. C Vaution. A Rabarron. M Seiller. Classification et ohtention dcs emulsions multiples. STP Pharma 4 679-687, 1988. 

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