Exam 1 - emulsions

Question 1

List the types of emulsions

Answer 1

oil in water (O/W)
water in oil (W/O)

Question 1

Describe O/W emulsions

Answer 1

Dispersed: oil

Continuous (external phase – taste, smell, feel): water

Question 2

Describe W/O emulsions

Answer 2

Dispersed: water

Continuous (external phase – taste, smell, feel): oil

Question 3

Describe the clinical application for O/W emulsions for oral dosage forms

Answer 3

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

Question 4

Describe the clinical application for O/W emulsions for external dosage forms

Answer 4

O/W: water-washable → vanishing cream

Question 5

Describe the clinical application for W/O emulsions for external dosage forms

Answer 5

W/O: for cleansing skin → cold cream like PONDS makeup remover

Question 6

Describe the clinical application for O/W IV lipid emulsions

Answer 6

• 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 um

Question 7

Explain the importance of droplet size in intravenous lipid emulsions (O/W)

Answer 7

It is critical that the droplet size is less than 1 um to avoid embolisms - traveling clots

Question 8

Describe interfacial tension at the boundary between phases

Answer 8

At the boundary between phases, molecules are acted upon unequally because they are in contact with other molecules exhibiting different forces of attraction

Water: hydrogen bond
Mineral oil: london dispersion forces

Question 9

Describe the effects of molecules being acted upon unequally at the boundary between phases in a liquid system

Answer 9

In liquid system such imbalance leads to spontaneous movement of molecules from the interface into the bulk phase leaving fewer molecules per unit area at the interface

Question 10

Describe the interface orientation of surfactants and the effect on interfacial / surface tension

Answer 10

Surfactants orient at the liquid-liquid or liquid-air interface & lower interfacial or surface tension

(bc they contain both hydrophilic/water part and hydrophobic/oil part regions)

Question 11

Define “HLB”

Answer 11

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

Question 12

Describe what a low HLB indicates about a surfactant

Answer 12

greater lipid solubility, more oil-like, hydrophobic

Question 13

Define a “low” HLB

Answer 13

ranges 0-20 for non-ionic surfactants

Question 14

Which interface is interfacial tension based on?

Answer 14

liquid-liquid interface

Question 15

Describe the effect of intermolecular forces in the bulk phase on interfacial tension

Answer 15

The stronger the intermolecular force in a bulk phase, the higher the interfacial tension

Question 16

Describe how a surfactant’s tendency to interact affects interfacial tension

Answer 16

The greater the tendency to interact, the less the interfacial tension

Question 17

Describe the effect of temperature on interfacial tension

Answer 17

The higher the temperature, the lower interfacial tension

Question 18

What type of excipient is used to stabilize emulsions?

Answer 18

Emulsifying agents

Question 19

List types of emulsifying agents that can be used to stabilize emulsions

Answer 19

Surfactants (surface active agents)
Polymers (hydrophilic colloids)
Finely divided solid particles

Question 20

Explain what happens when the concentration of a surfactant increases above a critical concentration

Answer 20

the surfactant molecules self-associate into small aggregates called micelles

Question 21

Describe the cause of surfactant molecules self-associating into small aggregates called micelles

Answer 21

the concentration of a surfactant increasing above a critical concentration

Question 22

LO 5 !!

Answer 22

need to phrase into question

Question 23

Describe how hydrophilic colloids act as emulsifying agents

Answer 23

• Forms a multimolecular film at the interface and increase the viscosity (thickness) of water
• DOES NOT lower interfacial tension
• stabilizes the surface, forms barriers around droplets

used on O/W emulsions

Question 24

List examples of hydrophilic colloids used as emulsifying agents

Answer 24

acacia, tragacanth, gelatin

Question 25

Describe how finely divided solid particles act as emulsifying agents

Answer 25

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

Question 26

List examples of finely divided solid particles used on O/W emulsions

Answer 26

hydrophilic: bentonite, magnesium aluminum silicate, aluminum hydroxide

Question 27

List examples of finely divided solid particles used on W/O emulsions

Answer 27

hydrophobic: charcoal

Question 28

Describe how surfactants act as emulsifying agents

Answer 28

Orient at the liquid-liquid or liquid-air interface and lower interfacial or surface tension

Question 29

What type of emulsion does a surfactant with a high HLB (> 10) form?

Answer 29

O/W emulsions

Question 30

Define "creaming"

Answer 30

the process where dispersed droplets move up or down due to gravity, leading to phase separation. However, **it does not break the emulsion**

Question 31

Describe Stoke's Law

Answer 31

if there are two liquids, the velocity is based on the density difference. positive = settle negative = float

Question 32

Define "V" in Stoke's Law

Answer 32

velocity of sedimentation

Question 33

Define "d" in Stoke's Law

Answer 33

diameter of droplets **larger droplets = moves faster**

Question 34

Define "p1" in Stoke's Law

Answer 34

density of internal phase **if suspended droplet has a lower density than the surrounding aqueous phase, it causes an overall negative value → oil will float**

Question 35

Define "pe" in Stoke's Law

Answer 35

density of external phase **if suspended droplet has a lower density than the surrounding aqueous phase, it causes an overall negative value → oil will float**

Question 36

Define "n" in Stoke's Law

Answer 36

viscosity of external phase **higher viscosity slows down the movement**

Question 37

convert 1 centipoise -> __ poise

Answer 37

1 centipoise = 0.01 poise

Question 38

convert 0.01 poise -> __ centipoise

Answer 38

0.01 poise = 1 centipoise

Question 39

Is creaming reversible?

Answer 39

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

Question 40

What is the key reason that creaming is reversible?

Answer 40

The droplets remain intact and do not coalesce. the interfacial film prevents them from fusing together **if the emulsion is shaken or stirred, the droplets can redistribute back into the liquid, restoring uniformity**

Question 41

Describe coalescence

Answer 41

Droplet size increases because the interfacial film is unable to maintain the integrity of individual droplets

Question 42

Is coalescence reversible?

Answer 42

Coalescence is irreversible and will lead to a layer of oil and a layer of water = broken emulsion **Can NOT fix by shaking the bottle and MUST be reformulated**

Question 43

Describe the cause of phase inversion?

Answer 43

Due to phase volume ratio exceeding 74% **usually want to keep it <50%**

Question 44

Give an example of phase inversion

Answer 44

O/W emulsion stabilized with sodium stearate can be inverted to W/O using hard water (contains calcium)

Question 45

If the HLB of a surfactant is < 10, what is the type of emulsion?

Answer 45

W/O

Question 46

If the HLB of a surfactant is > 10, what is the type of emulsion?

Answer 46

O/W

Question 47

Give examples of common surfactants

Answer 47

- sodium lauryl sulfate - anionic: alkyl sulfate, alkylbenzene sulfonate - cationic: alkyltrimethylammonium bromide, alkylpyridinium chloride - zwitterionic: alkyl betaine, alkyldimethylamine oxide - nonionic: alcohol ethoxylate

Question 48

If the emulsion contains hydrophilic colloids, what is the type of emulsion?

Answer 48

O/W only

Question 49

If the contact angle of finely divided solids in an emulsion is < 90, what is the type of emulsion?

Answer 49

the solids are hydrophilic, so the emulsion is O/W

Question 50

If the contact angle of finely divided solids in an emulsion is > 90, what is the type of emulsion?

Answer 50

the solids are hydrophobic, so the emulsion is W/O

Question 51

List the steps required to manufacture an emulsion

Answer 51

- Dissolve all water soluble ingredients in water - Mix all oil soluble ingredients in oil - Heat the aqueous solution to the same temperature as the oil solution - Mix oil solution and water solution - Cool slowly - Pass through a colloid mill or homogenizer