Emulsifier phase behaviour

Phase Behaviour. The differences in the self-emulsifying behaviour of Tagat TO - Miglyol 812 binary mixtures can, in part, be explained from considerations of their phase behaviour. Figures 4a-4d show the representative equilibrium phase diagrams obtained when binary mixtures containing 10,25,30 and 40J surfactant were sequentially diluted with water. The phase notation used is based on that of Mitchell et ai (li). 

In the preceding sections, the phase behaviour of rather simple ternary and quaternary non-ionic microemulsions have been discussed. However, the first microemulsion found by Schulman more than 50 years ago was made of water, benzene, hexanol and the ionic-surfactant potassium oleate [1, 3]. Winsor also used the ionic-surfactant sodium decylsulphate and the co-surfactant octanol to micro-emulsify water/sodium sulphate and petrol ether [2], In the last 30 years, in-depth studies on ionic microemulsions have been carried out [7, 8, 65, 66]. It toned out that nearly all ionic surfactants which contain one single hydrocarbon chain are too hydrophilic to build up microemulsions. Such systems can only be driven through the phase inversion if an electrolyte and a co-surfactant is added to the mixture (see below and Fig. 1.11). 

The influence of emulsifiers on the powder production and encapsulation efficiency will also be craisidered at a later stage in this project, so the phase behaviour between two nOTi-iraiic surfactants and carbon dioxide was also investigated as no literature data was available. The results are presented in Fig. 15.11 for Span 80 and in Fig. 15.12 for Tween 80. 

The self-emulsifying behaviour of a binary nonlonlc surfactant vegetable oil mixture has been shown to be dependant on both temperature and surfactant concentration. The quality of the resulting emulsions as assessed by particle size analysis showed that manipulation of these parameters can result In emulsion formulations of controlled droplet size and hence surface area. Such considerations are Important when the partition of lipophilic drugs Into aqueous phases and drug release rates are considered. 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

In particular, the full potential to control colloids is not presently realized. There are several types of complex, mixed colloid that are only poorly understood. For example, the properties of colloids in which more than one type of colloidal species is dispersed may be dominated by the behaviour of the minor dispersed-phase component. The nature and properties of colloids within colloids, such as suspended solids in the dispersed phase of an emulsion, or emulsified oil within the aqueous lamellae of a foam, are only beginning to be understood [2-4]. 

The anionic and cationic emulsion polymerization of dimethylcyclosiloxanes in aqueous phase, has received little study to date. The acid-catalysed emulsion polymerization of a series of cyclic dimethylsiloxane monomers, with varying emulsifiers, has recently been studied. Whilst qualitatively the mechanism appears consistent with the Harkins model, quantitatively the system, as might be expected, shows wide deviations from Smith-Ewart predicted behaviour. This emulsion polymerization system is interesting in that initiation, propagation, and termination proceed by ionic pathways. 

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