Colloid chemistry chapter 10

COLLOID CHEMISTRY Chapter 10 – Emulsion Dr Ngo Thanh An Email: ngothanhan@gmail.com 1 Introduction Emulsion – Suspension of liquid droplets (dispersed phase) of certain size within a second immiscible liquid (continuous phase) Introduction Classification of emulsions - Based on dispersed phase Oil in Water (O/W): Oil droplets dispersed in water Water in Oil (W/O): Water droplets dispersed in oil Beside these two mayor groups of emulsions also more complex emulsion systems are possible (W/O/W and O/W/O) - Based on size of liquid droplets 0.2 – 50 mm Macroemulsions (Kinetically Stable) 0.01 – 0.2 mm Microemulsions (Thermodynamically Stable) Introduction Introduction Introduction Pesticide Metal cutting oils Asphalt Skin cream Margarine Ice cream Stability of emulsions may be engineered to vary from seconds to years depending on application Emulsion agent Reduction of the surface tension is the key to avoid the coagulation of the emulsion Substances which reduce the surface tension are called surfactants In O/W and W/O, surfactants play a role of emulsifying agent Surfactants must exhibit the following characteristics to be effective as emulsifiers - Good surface activity - Should be able to form a condensed interfacial film - Diffusion rates to interface comparable to emulsion forming time Emulsion agent Emulsion agent Emulsion agent Surfactants Anionic – Sodium stearate, Potassium laurate, Sodium dodecyl sulfate, Sodium sulfosuccinate Nonionic – Polyglycol, Fatty acid esters, Lecithin Cationic – Quaternary ammonium salts, Amine hydrochlorides Solids Finely divided solids with amphiphilic properties such as soot, silica and clay, may also act as emulsifying agents (Pickering Emulsions: Attribute of high stability)