exam 1 lecture 2

Question 1

emulsion

Answer 1

two liquids, where one is dispersed as droplets
a water phase + an oil phase

Question 2

two phases

Answer 2

dispersed phase + continuous phase (external phase)

Question 3

oil in water O/W

Answer 3

dispersed: oil
continous: water

Question 4

water in oil W/O

Answer 4

dispersed: water
continuous: oil

Question 5

application of emulsion

Answer 5

oral: O/W to mask taste of oil or enhance absorption of oil (Vit A/D)
external: O/W water-washable –> vanishing cream. W/O for cleansing –> cold cream
intravenous lipid emulsion (O/W): parenteral nutrition

Question 6

interfacial phenomena

Answer 6

in bulk portion of each phase, molecules are attracted to each other equally in all directions
at boundary between phases, molecules are acted on by unequal forces
thus, molecules at interface experience different forces to molecules at bulk phase
in liquid systems, imbalance results in spontaneous movement of molecules interface to bulk phase
water: h-bond
mineral oil: LDF

Question 7

interfacial tension

Answer 7

force of tension per unit length due to reversing spontaneous movement of molecules
liquid-liquid interface: oleic acid - water

Question 8

surface tension

Answer 8

liquid-air interface
water - air
oleic acid - air
ex - ethanol spreads faster when dropped on surface, water has higher surface tension so it won’t spread as much

Question 9

things effecting interfacial surface tension

Answer 9

stronger intramolecular force in bulk phase –> higher interfacial tension
greater tendency to interact –> less interfacial tension
higher temp –> lower interfacial tension bc intramolecular forces reduce at higher temps

Question 10

emulsifying agent

Answer 10

stabilize emulsion
types:
surface active agents (surfactants)
hydrophilic colloids (polymers)
finely divided solid particles

Question 11

surfactant (surface active agents)

Answer 11

containing both hydrophilic + hydrophobic regions
orient at liquid-liquid or liquid-air interface to lower interfacial or surface tension

Question 12

hydrophile-lipophile balance (HLB)

Answer 12

measures relative contributions of hydrophilic + lipophilic regions of surfactant
lower HLB = greater lipid solubility

Question 13

micelles

Answer 13

as concentration of surfactant increases above critical concentration, surfactant molecules aggregate into micelles
hydrophilic heads, hydrophobic tails

Question 14

hydrophilic colloids (polymers)

Answer 14

used in O/W emulsions
forms a multimolecular film at interface to increase viscosity of water
does not lower interfacial tension

Question 15

finely divided solid particles

Answer 15

particles less than micron absorb at interface and form a film of fine particles

Question 16

predicting type of emulsion

Answer 16

surfactant: HLB < 10: W/O HLB > 10: O/W
hydrophilic colloids: only O/W
finely divided solids:
hydrophilic - contact angle < 90: O/W
hydrophobic - contact angle > 90: W/O

Question 17

phase volume ratio

Answer 17

volume of oil phase/ volume of emulsion
0-26%: O/W
26-74%: either
74-100%: W/O

Question 18

creaming

Answer 18

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

Question 19

coalescence

Answer 19

droplet size increases because the interfacial film is unable to maintain the integrity of individual droplets –> so they combine

irreversible and will lead to layer of oil + layer of water
cannot fix by shaking

Question 20

phase inversion

Answer 20

phase volume ratio exceeding 74%
O/W emulsion stabilized with sodium stearate can be inverted to W/O using hard water(containing calcium)

Question 21

prepping emulsion

Answer 21

dissolve all water soluble ingredients in water
mix all oil soluble ingredients in oil. heat if necessary to melt
heat aqueous solution to same temp as oil
mix oil + water solution w/ mixing
cool slowly
pass through colloid mill or homogenizer