E2 L4 - Emulsion

Question 1

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

Answer 1

Emulsion

Question 2

Dispersed phase

Answer 2

“water in oil” (water is dispersed, oil is continuous)

Question 3

Continuous phase (=external phase)

Answer 3

Determines organoleptic properties (taste, smell, feel) of the emulsion

Question 4

Oral: Oil in water

Answer 4

to mask the tase of an oil
to enhance absorption of an oil

Question 5

External: Oil in water

Answer 5

water washable vanishing cream

Question 6

External water in oil

Answer 6

for cleansing skin – cold cream

Question 7

IV Lipid emulsion

Answer 7

Oil in water

Oil has to be very small so it does not block the blood vessel

Oil can provide more calories than solutions

Question 8

Emulsifying agents

Answer 8

Added to stabilize the emulsion

Question 9

Three types of emulsifiers

Answer 9

Surfactants
Polymers
Fine divided particles

Question 10

Three strategies of emulsifiers

Answer 10

Use surface activation (surfactants)
Use polymer (provide steric interest so they do not merge)
one purpose: Improve stability

Question 11

Surfactant

Answer 11

Empty vials
Hydrophilic and hydrophobic (amphipathic)
Align (hydrophilic - water; hydrophobic - oil)
Separate
Surface activation

Question 12

Hydrophilic colloid - polymer

Answer 12

Align with surface of the barrier
create barrier

Question 13

Fine particles

Answer 13

Smaller than polymer
Particles CANNOT MERGE because there is barrier created on the surface

Question 14

Which emulsifier is more different than the other two?

Answer 14

Surfactant
Surfactant - reduces interfacial tension
other two - do not reduce interfacial tension, just stop the things from merging

Question 15

Surface active agents - surfactants

Answer 15

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

Question 16

Log C

Answer 16

Concentration of surfactant

Question 17

Surfactants reduce surface tension to a certain extent why?

Answer 17

Over a certain concentration, it stops reducing tension
Forms micelles
Too much - they start to form their own assemblies, so they are not reducing surface tension anymore (since they are forming small vesicles themselves
When this happen: CMC - critical micelle count

Question 18

Know different types of surfactant chains, if they are anionic or cationic, and if they are a zwitterion or not

Answer 18

-

Question 19

Hydrophile-lipophile balance

Answer 19

A measure of the relative contributions of the hydrophilic and lipophilic regions of a surfactant

Calculated according to an empirical formula

Ranges 0-20 for non-ionic surfactants

Low HLBs indicate greater lipid solubility

In practice, a mix of emulsifying agents is used to get a desired HLB

Question 20

HLB equation

Answer 20

HLB = aX + (1-a)Y

X: HLB of surfactant 1

Y: HLB of surfactant 2

A: Fraction of surfactant 1 in the surfactant mix

Bigger than 10 - hydrophilic
Smaller than 10 - hydrophobic

HLB = X * a + y(1-a)

Question 21

Rule of Bancroft (1913)

Answer 21

A relative solubility of the surfactant determines they type of emulsion (i.e. the phase in which a surfactant is more soluble becomes the continuous phase)
E.g. a surfactant with a high HLB (>10, soluble in water) forms an o/w emulsion

Question 22

Micelles

Answer 22

As the concentration of a surfactant increases above a critical concentration, (the CMC) the surfactant molecules self-associate into small aggregates called MICELLES
The micelles formed in water have the hydrophobic groups of the surfactant oriented TOWARD the core of the micelle. The center of the micelle represents a lipid-like region that is capable of dissolving water-insoluble drugs

Question 23

Hydrophobic colloids

Answer 23

Hydrophilic polymers
Used for O/W emulsions – hydrophilic

Form a multimolecular film at the interface and increase the viscosity of water

Do NOT lower the interfacial tension

Ex: Acacia, tragacanth, gelatin

Natural polymers

Question 24

Finely divided solid particles

Answer 24

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

Question 25

Predicting type of emulsion

Answer 25

The phase in which the emulsifier is most soluble will be the external (=continuous) phase

Surface active agents

HLB < 10: W/O

HLB > 10: O/W

Hydrophilic colloids: Only O/W

Finely divided solids

Hydrophilic if contact angle < 90degrees O/W

Hydrophobic if contact angle >90 W/O

**Obtuse – hydrophobic

Acute – hydrophilic**

Question 26

Phase volume ratio

Answer 26

Phase volume ratio:

Volume of oil phase/Total volume of the emulsion

0-26%: O/W only

26-74%: either

74-100% W/O only

Question 27

T/F: emulsifier is a surfactant

Answer 27

FALSE - Correct to say surfactant is an emulsifier, NOT that emulsifier is surfactant (it is a subtype of emulsifier, but not the only one)

Question 28

Instability of emulsion - creaming

Answer 28

V = d2(pi-pe)980/18n (Stokes Law)

V = velocity of sedimentation

D: diameter of droplets

Pi: density of internal phase

Pe: density of external phase

980 cm/sec2: gravity constant

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

Droplets stay as droplets – shake before use

Natural process

Question 29

Instability of Emulsion - Coalescence

Answer 29

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 fic by shaking bottle

Must be reformulated

Molecules bump together and fuse – irreversible

Question 30

Instability of Emulsion - Phase inversion

Answer 30

Big problem in IN

Hard water

Due to phase volume ratio exceeding 74%

Rule of thumb: keep the phase volume ratio <50%

O/W emulsion stabilized w/sodium stearate can be inverted to W/O type using “hard” water (containing calcium)

Conversion of Na stearate to Ca stearate