Post on 21-Apr-2015
Embed Size (px)
Colloid chemistryLecture 13: Emulsions
food cosmetics pharmaceutics biological systems bituminous carpet (asphalt) etc.
Emulsion suitable for intravenous injection.
Balm: Water in oil emulsion
Sodas: Oil in Water emulsion Milk: Oil in Water emulsion
Dodecane droplets in a continuous phase of water/glycerol mixture.
Mayonnaise: Oil in Water emulsion
Emulsions encountered in everyday life!
metal cutting oils
Stability of emulsions may be engineered to vary from seconds to years depending on application
IntroductionEmulsion Suspension of liquid droplets (dispersed phase) of certain size within a second immiscible liquid (continuous phase). 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 - Based on size of liquid droplets 0.2 50 mm Macroemulsions (Kinetically Stable) 0.01 0.2 mm Microemulsions (Thermodynamically Stable)
Emulsifying agentsStable suspensions of liquids constituting the dispersed phase, in an immiscible liquid constituting the continuous phase is brought about using emulsifying agents such as surfactants 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
Common Emulsifying AgentsSurfactants Anionic Nonionic Cationic Sodium stearate, Potassium laurate Sodium dodecyl sulfate, Sodium sulfosuccinate Polyglycol, Fatty acid esters, Lecithin 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)
surfactant oil droplet in water (unstable)po lym
oil droplet in water (stabilized)er
oil droplet in water (stabilized)
G = H A >> 0 emulgeation requires large energy input
G = H A