Emulsions

Question 1

What are the three types of emulsifying agents?

Answer 1

-surface active agents (surfactants)
-hydrophilic colloids (polymers)
-finely divided solid particles

Question 2

Characteristics of surfactants

Answer 2

-molecules that contain a hydrophilic region and hydrophilic regions
-designed to decrease surface tension (by binding oil and water together)

Question 3

Classification of surfactants

Answer 3

-anionic
-cationic
-zwitterionic
-nonionic

Question 4

Characteristics of anionic surfactants

Answer 4

-has a NEGATIVE charge on the hydrophilic head
-will not have a covalent bond leaving a counter ion

Question 5

Characteristics of cationic surfactants

Answer 5

-has a POSITIVE charge on the hydrophilic head
-will not have a covalent bond leaving a counter ion

Question 6

Characteristics of zwitterionic surfactants

Answer 6

-has BOTH positive and negative charges on the hydrophilic head
-will have a covalent bond

Question 7

Characteristics of nonionic surfactants

Answer 7

-NO charges at all

Question 8

Hydrophile-lipophile balance (HLB)

Answer 8

a measure of the contribution of the hydrophilic and lipophilic regions of a surfactant

Question 9

What is the range of HLB

Answer 9

0-20
LOW HLB is hydrophobic
HIGH HLB is hydrophilic

Question 10

Rule of Brancroft

Answer 10

-if you are designing a W/O emulsion use a surfactant with LOW HLB
-if you are designing a O/W emulsion use a surfactant with HIGH HLB

Question 11

Critical micelle concentration (CMC)

Answer 11

this is the concentration where surfactant molecules turn into micelles

Question 12

Micelles

Answer 12

have hydrophobic groups pointed inward acting as a lipid like region and dissolving water-insoluble drugs

Question 13

Characteristics of hydrophilic colloids/polymers

Answer 13

-used in O/W emulsions
-creates a steric barrier that doesn’t allow for molecules to merge
-has nothing to do with interfacial tension

Question 14

Examples of hydrophilic colloids/polymers

Answer 14

Acacia
Tragacanth
Gelatin

Question 15

Characteristics of finely divided solid particles

Answer 15

-particles are less than a micron
-absorb into the membrane and forms a film of fine particles
-creates a steric barrier that doesn’t allow for the droplets to merge

Question 16

Examples of finely divided solid particles

Answer 16

Hydrophilic: bentonite, magnesium aluminum silicate, aluminum hydroxide
Hydrophobic: charcoal

Question 17

Hydrophobic emulsions

Answer 17

-HLB < 10
-greater than 90 degree contact angle
-has oil content greater than 74%

Question 18

Hydrophilic emulsions

Answer 18

-HLB > 10
-less than a 90 degree contact angle
-oil content less than 26%

Question 19

What are the 3 instabilities of emulsion?

Answer 19

-creaming
-coalescence
-phase inversion

Question 20

Creaming

Answer 20

-happens when the emulsified droplets start to float
-REVERSIBLE as long as the individual droplets maintain their integrity

Question 21

Coalescence

Answer 21

-happens when the emulsifying droplets float, then bump into each other a lot to form a layer of oil and water
-IRREVERSIBLE (can’t be fixed by shaking) must be reformulated

Question 22

Phase Inversion

Answer 22

-if an O/W emulsion can be inverted to W/O if treated with “hard” water
-conversion of Na stearate to Ca stearate