Summary
Summary Emulsions
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Pharmacy - physical pharmacy 2nd semester Bullet points, key notes, images and diagrams
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Colloids and FormulationsEmulsions
Two immiscible liquids finely subdivided from each other
2 phases continuous and dispersed (1-100mcm)
Humectants prevent water evaporation
Preservative required
Emulsifiers
Emulsions re highly unstable due to high interfacial tensions
Emulsifiers reduce the surface tension
Emulsion droplets aren’t uniform (micelles are)
Tests
Conductivity- water is a good conductor so O/W emulsion will conduct but W/O
won’t
Dye solubility- emulsion mixed with water-soluble dye (amaranth) and observed
under a microscope. If the continuous phase is red then it’s O/W and if the dye
gives scattered globules of red in the continuous phase then it’s W/O emulsion
Stability- based on interfacial tension which is the work to increase the area of
contact between 2 phases
ΔG= ΣNiπri2σ
Where Ni=number of droplets in population I of radius (r) and σ is the interfacial
tension
So reducing the interfacial tension increases the stability and this reaction isn’t
normally spontaneous
Energy input (ultrasound) causes dispersion but must be aware of interactions
between the interfaces
Types of Emulsifiers
Surfactants- reduce interfacial tension via adsorption onto droplet surface
Ionic surfactant in O/W-charged layer with counter-ions form and the repulsion
reduces coalescence
In non-ionic surfactants- repulsive effects in the continuous phase due to
interactions between hydrophobic chains
Can form a gaseous film on surface so droplets repel
Condensed film molecules remain in place
Spans- sorbitan esters with fatty acids are hydrophobic
Tweens are polyethylene glycol esters of sorbitan and are hydrophilic
Interfacial complexes- mixture of oil-soluble alcohols and ionic surfactants
that form complexes at the interface
The film has a high viscosity, high flexibility and lowers interfacial tension
Hydrophilic colloids-long chain hydrophilic polymers adsorb onto surface and
form multilayers which are strong and flexible
Some contain groups which ionise and provide electrostatic repulsion
Solid particles- solids at interface with a balance of hydrophilic and
hydrophobic groups. They form a film around the droplet of the dispersed phase
globules and prevent coalescence
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