Lecture 12

Question 1

emulsion

Answer 1

a system of two immiscible liquids in which one is dispersed as droplets
example - water phase + oil phase

Question 2

two phases of emulsions

Answer 2

dispersed phase
continuous phase (external) – determines organoleptic properties

Question 3

applications of emulsions

Answer 3

oral, external, intravenous lipid (O/W)

Question 4

O/W oral

Answer 4

used to mask the taste of an oil (mineral oil emulsion as a laxative)
used to enhance absorption of an oil (vitamin a/d, cod liver oil)

Question 5

o/w external

Answer 5

water-washable
vanishing cream

Question 6

w/o external

Answer 6

for cleansing skin
cold cream

Question 7

intravenous lipid emulsion

Answer 7

o/w only
for parenteral nutrition
100mL of 20% lipid emulsion provides 200kcal, while 100mL of 5% dextrose only provides 20kcal
smallest capillaries are 5 mcm (critical that the droplet size is less 1 mcm to avoid embolisms)

Question 8

emulsifying agents

Answer 8

emulsifiers
added to stabilize the emulsion

Question 9

types of emulsifying agents

Answer 9

surface active agents (surfactants, monomolecular film)
hydrophilic colloids (polymers, multimolecular film)
finely divided solid particles (solid particle film)

Question 10

surfactants

Answer 10

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
act as clamp to bind oil and water together

Question 11

types of surfactants

Answer 11

anionic - alkyl sulfate, alkylbenzene sulfonate
cationic - alkyltrimethylammonium bromide, alkylpyridinium chloride
zwitterionic - alkyl betaine, alkyldimethylamine oxide
nonionic - alcohol ethoxylate, poly-poly-poly block copolymer

Question 12

hydrophile-lipophile balance (HLB)

Answer 12

a measure of the relative contributions of the hydrophilic and lipophilic regions of a surfactant
calculated according to an empirical formula
ranges from 0 to 20 for non-ionic surfactants

Question 13

low HLBs

Answer 13

indicate greater lipid solubility

Question 14

HLB of a mixture equation

Answer 14

aX + (1-a)Y
X – HLB of surfactant 1
Y – HLB of surfactant 2
a – fraction of surfactant 1 in the surfactant mixture

Question 15

rule of bancroft (1913)

Answer 15

a relative solubility of the surfactant determines the type of emulsion (= the phase in which the surfactant is more soluble becomes the continuous phase)

Question 16

surfactant with high HLB

Answer 16

soluble in water
forms an o/w emulsion

Question 17

micelles

Answer 17

small aggregates that form as surfactant molecules self-associate, occurs as the concentration of a surfactant increases above a critical concentration (CMC)
have hydrophobic groups of the surfactants oriented toward the center/core

Question 18

core of the micelle

Answer 18

represents a lipid-like region that is capable of dissolving water-insoluble drugs

Question 19

hydrophilic colloids

Answer 19

hydrophilic polymers
used in O/W emulsion
form a multimolecular film at the interface and increase the viscosity of water
does not lower the interfacial tension
examples - acacia, tragacanth, gelatiun

Question 20

finely divided solid particles

Answer 20

particles less than a micron can adsorb at the interface and form a film of fine particle

Question 21

hydrophilic finely divided solid particles

Answer 21

bentonite
magnesium aluminum silicate
aluminum hydroxide
used for O/W emulsion

Question 22

hydrophobic finely divided solid particles

Answer 22

charcoal
used for W/O emulsions

Question 23

predicting type of emulsion

Answer 23

based on surface active agents, hydrophilic colloids, or finely divided solid

Question 24

surfactant predicts emulsion type

Answer 24

HLB less than 10, W/O
HLB greater than 10, O/W

Question 25

hydrophilic colloids predicts emulsion type

Answer 25

only O/W

Question 26

finely divided solids predict emulsion type

Answer 26

hydrophilic if contact angle is less than 90, O/W
hydrophobic if contact angle is greater than 90, W/O

Question 27

phase volume ratio

Answer 27

volume of oil phase / total volume of the emulsion
0-26 –> O/W only
26-74 –> either O/W or W/O
74-100 –> W/O only

Question 28

creaming

Answer 28

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

Question 29

Stokes Law

Answer 29

velocity of sedimentation

(squared diameter of droplets)(density of internal phase - density of external phase)980
/
18(viscosity of external phase)

Question 30

coalescence

Answer 30

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 be fixed by shaking
must be reformulated

Question 31

phase inversion

Answer 31

due to phase volume ratio exceeding 74% (should keep the ratio below 50%)
O/W emulsion stabilized with sodium stearate can be inverted to W/O type using hard water – containing calcium (high HLB to low HLB)

Question 32

instability of emulsion factors

Answer 32

creaming
coalescence
phase inversion