Emulsions Flashcards
Definition of emulsion
Thermodynamically unstable system consisting of at least two immiscible liquid phases, one of which is dispersed as globules in the other liquid phase stabilised by a third substance called emulsifying agent
What does an emulsifier do
Stabilises two immiscible liquids
Hydrophile Lipophile Balance
Higher HLB value= more hydrophilic
Lower HLB value= more Lipophilic (able to dissolve)
How to form oil in water emulsion
Hydrophilic surfactants
High HLB value
How to form water in oil emulsion
Lipophilic surfactants
Low HLB value
How do emulsifiers stabilise emulsions
Forms a rigid film on the oil/water interface
Prevents separation
Cold emulsion: wet gum method
Emulsifier placed in mortar
Water is added to emulsifier and mixed
Oil is added
Mix
Add continuous phase slowly
Mix in 1 direction to not break the interfacial film
Cold emulsion: dry gum method
Emulgent placed in mortal
Oil is added
Dispersed to form mucilage
Water is added
Continuous titration
Emulsification by heat
Oil soluble components dissolved in oil (evaporating basin)
Water soluble components in water
Oil phase is heated to melt components
Heated to 70° separately
Internal phase added to external at the same temp
Initially mix slowly to avoid air bubbles
High speed mixing with decrease in temp
Identification of emulsion type: dilution test
Add oil to emulsion
Oil mixes well= water in oil emulsion
Oil appears as droplets= oil in water emulsion
Add water to emulsion
Water mixes well= oil in water emulsion
Water as droplets= water in oil emulsion
Identification of emulsion type: dye solubility test
Add few drops of red dye
Emulsion becomes red- oil in water type
Identification of emulsion type: conductivity test
Two electrodes placed in emulsion
Electrodes connected to low voltage lamp
Electric current
Positive= oil in water emulsion
Identification of emulsion type: fluoresecene test
Microscope
Fluorescence of oils on exposure to uv lights
Oil in water emulsions= spotty pattern
Water in oil= fluoresce throughout the field
Types of physical stability/ instability
Gravitational (reversible)such as creaming and sedimentation
Coalescence - droplets merge to form single droplet upon contact
Flocculations- aggregates
Cracking/breaking (irreversible)
Factors affecting creaming/ sedimentation
Increase globule size= increase creaming
Densities of continuous phase and disperse phase
Gravity
Decrease velocity= increase creaming
