Physical aspects - Instability mechanisms
8 important questions on Physical aspects - Instability mechanisms
Which 4 processes affect the emulsion stability?
- Flocculation (aggregation)
- Coalescence
- Creaming and sedimentation
- Ostwald ripening (disproportionation)
What happens when flocculation occurs in emulsions?
- Low volume fraction of dispersed droplets --> aggregation leads to formation of large clusters/aggregates/flocs --> faster creaming
- High fraction dispersed oil droplets --> lead to formation 3D space filling network, system will act as a gel
What happens when coalescence occurs in emulsions?
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What happens when creaming occurs in emulsions?
- Oil droplets are lighter than continuous phase --> oil droplets cream
- Heavier dispersed particles --> particles will move down --> sedimentation
What happens when Ostwald ripening occurs in emulsions?
How is Ostwald ripening in emulsions caused?
Ostwald ripening can only take place in emulsions when?
- Emulsions with water soluble oils --> oil not soluble, cannot diffuse, no Ostwald ripening. More soluble the oil --> larger degree of Ostwald ripening, faster process
- Emulsion need wide size distribution --> when droplets re same size, no difference in pressure, no diffusion of oil. Bigger difference in size, larger difference in pressure, larger effect on Ostwald ripening.
What is the disproportionation in foams influenced by?
- Solubility of air in water --> air is more soluble in water compared to oil in water --> rate faster
- Gas with different solubility --> less soluble gas, less soluble in water than air, e.g. Nitrogen, less fast disproportionation
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