On the other hand heavy metal soaps (eg., Ca, Al oleate/palmitate etc) which are more soluble hydrocarbons then water yield water in oil type emulsion. For example, alkali metal soaps gelatin etc which are insoluble in hydrocarbons but soluble in water give rise to oil in water type emulsion. According to Bancroft rule the phase in which the emulsifier (or stabilizer) is more soluble becomes the outer phase. Other emulsifying agents used are gums, proteins, agar−agar etc., The nature of emulsifying agent determines the type of the emulsion formed. Soaps and detergents are the most commonly employed emulsifiers.
The emulsifiers decrease the surface tension of the two liquids thereby the tendency of the tiny droplets to coalesce and form aggregates is reduced. In milk and cod liver oil emulsifiers are albumin + casein and egg yolk + casein + gums respectively. The emulsifying agent forms a film around every drop of the dispersed phase thereby preventing these drops from coalescence and consequent separation into two layers. To stabilize an emulsion a third substance like gelatin, soap, gum arabic etc (called emulsifying agents or emulsifier) has to be added. For example milk belongs to oil in water type emulsion while butter is an example of water in oil type emulsion.Īn emulsion formed by mere shaking of an oil with excess of water or vice versa is not stable and soon separates into two distinct layers when allow to stand. On the other hand if a little water is shaken with an excess of oil, an emulsion of water in oil (W−O) type is formed. When a little oil is shaken with excess of water, an emulsion of oil in water (O−W) type is formed. (i) Water in oil type and (ii) Oil in water type The emulsion can be classified into two classes. The familiar examples of emulsion are milk (liquid fat) liver oils etc.
An emulsion is a colloidal system consisting of two immiscible liquid phases, one of which is dispersed as globules in another.
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