Lab Final - Emulsions
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- thermodynamically unstable
- two phase system of at least two immiscible liquids and emulsifying agents
- one of the liquids is dispersed in the form of small droplets throughtout the other
two emulsion phases and their definitions
- internal/discontinuous phase: dispersed liquid
- external/continuous phase: dispersion medium
types of emulsion phases and their internal and external phases
- o/w - external is water and internal is oil
- w/o - external is oil and internal is water
emulsifier for o/w phase and the HLB
emulsifier for w/o phase and the HLB
what can act as an emulsifier
- surface actives
- wetting agents
advantages of emulsions
- stable mix of two immiscible liquids
- administration of unplatable oil
- increased absorption
- admin of irritant drugs to the skin
theories of emulsification
- surface tension
- oriented wedge
- plastic or interfacial film
Surface Tension theory
interfacial tension is lowered (tension between two different phases
orient wedge theory
when a single layer of emulsifying agent wraps around the dispersed/internal phase to form a micelle
film of emulsifying agent prevents contact and coalescing of the dispersed phase
what is the HLB? what is the usual range?
- hydrophil-lipophil balance
- indicates the polarity of the substance
- usual range - 1-20
a higher HLB means what?
a lower HLB means what?
- more hydrophilic
- more hydrophobic
types of instabilities
- phase inversion
what is creaming?
dispersed oil droplets merge and rise together (can be easily re-dispersed by shaking)
what is coalescence?
- breaking or cracking -
- complete fusion of the dispersed phase (irreversible)
what is phase inversion
changing from w/o to o/w or vice versa (irreversible)
what is the rate of separation related to?
- particle size
- density difference
determined by Stoke's law
methods of preparation
- bottle (Forbes) method
- syringe method
- stir bar method
- homogenizer method
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