colloid chemistry

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Colloid chemistryLecture 13: Emulsions

Emulsions

food cosmetics pharmaceutics biological systems bituminous carpet (asphalt) etc.

Emulsion suitable for intravenous injection.

Balm: Water in oil emulsion

Emulsions

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!

pesticide

asphalt

skin cream

metal cutting oils

margarine

ice cream

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)

Making emulsions

surfactant oil droplet in water (unstable)po lym

oil droplet in water (stabilized)er

solid particles

oil droplet in water (stabilized)

G = H A >> 0 emulgeation requires large energy input

G = H A

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