lecture 2

Question 1

emulsions

Answer 1

A system of two immiscible liquids
in which one is dispersed as droplets. (e.g., water phase + oil phase

Question 2

o/w

Answer 2

oil in water
dispensed: oil
continuous: water

Question 3

w/o

Answer 3

water in oil
dispersed: water
continuous: oil

Question 3

oral applications of emulsion

Answer 3

• O/W to mask the taste of an oil (e.g., mineral oil emulsion as a laxative)
  – O/W to enhance absorption of an oil (Vitamin A and D, cod liver oil)

Question 3

external applications of emulsion

Answer 3

– O/W: Water-washable; Vanishing cream
– W/O: For cleansing skin; Cold cream

Question 3

instability of emulsions: creaming

Answer 3

-strokes law
-reversible as long as the interfacial film is effective in maintaining the integrity of individual droplets

Question 4

intravenous lipid emulsion (O/W) applications of emulsion

Answer 4

– For parenteral nutrition
– 100 mL of 20% lipid emulsion provides 200 kcal, while 100 mL of 5% dextrose only provides 20 kcal.
– Smallest capillaries are 5 μm. It is critical that the droplet size is less than 1 μm to avoid embolisms.

Question 4

emulsifying agents

Answer 4

-Emulsifying agents are added to stabilize the emulsion.
-Types of emulsifying agents
◦ Surface active agents (= surfactants)
◦ Hydrophilic colloids (polymers)
◦ Finely divided solid particles

Question 4

surface active agents

Answer 4

• Molecules that contain both a hydrophilic region and a hydrophobic region
• Orient at the liquid-liquid or liquid-air interface and lower interfacial or surface tension

Question 4

finely divided solid particles

Answer 4

• Particles less than a micron can adsorb at the
  interface and form a film of fine particles.
• Examples:
  – Bentonite, magnesium aluminum silicate, aluminum hydroxide: Hydrophilic, for O/W emulsion.
  – Charcoal: Hydrophobic, for W/O emulsion

Question 4

instability of emulsions: coalescene

Answer 4

◦ Droplet size increases because the interfacial film is unable to maintain the integrity of individual droplets.
◦ Irreversible and will ultimately lead to a layer of oil and a layer of water (broken emulsion)
◦ Cannot fix by shaking the bottle.
◦ Must be reformulated.

Question 4

hydrophilic colloids

Answer 4

• Hydrophilic polymers
• Used in O/W emulsions.
• Form a multimolecular film at the interface and increase the viscosity of water.
• Do not lower the interfacial tension.
• Examples: Acacia, tragacanth, gelatin

Question 5

instability of emulsions: phase inversion

Answer 5

◦ Due to Phase volume ratio exceeding 74%
* Rule of thumb: Keep the phase volume ratio <50%
◦ O/W emulsion stabilized with sodium stearate can be inverted to W/O type using “hard” water (containing calcium)
* Conversion of Na stearate to Ca stearate