Lab 3: Formulation and evaluation of emulsions

Question 1

What is an emulsion?

Answer 1

A system consisting of 2 immiscible liquid phases

one phase is dispersed through the other phase to form droplets

Question 2

What are the 3 main types of emulsions?

Answer 2

oil in water
water in oil
multiple emulsions

Question 3

What is the HLB?

Answer 3

hydrophilic lipophilic balance.

This is a range of values FOR NON IONIC SURFACTANTS ONLY which describe its lipophilicity.

Question 4

What does an HLB value of 0 mean?

Answer 4

this corresponds to a lipophilic molecule

Question 5

What does an HLB value of 20 mean?

Answer 5

This corresponds to a hydrophilic molecule

Question 6

What is the formula for HLB?

Answer 6

HLB= 20 x (1 - (MW lipo/MWtotal)

Question 7

What is the required HLB?

Answer 7

This is a property of the oil and is the HLB value of the surfactant mixture which provides the lowest interfacial tension between the oil and water phase.

This is calculated individually for each oil

Question 8

What must the total HLB value of a surfactant mixture be if the rHLB of liquid paraffin required to make an o/w emulsion is 10?

Answer 8

the total HLB value of the surfactant must be 10 in order to formulate a stable o/w emulsion with low interfacial tension

Question 9

What is the formula for the rHLB of a mixture of 2 surfactants?

Answer 9

rHLB = HLB1X + HLB2Y

X is the amount of surfactant 1
Y is the amount of surfactant 2 (1-X)

substitute to find out X

Question 10

How can the rHLB be calculated experimentally?

Answer 10

by using a specific surfactant concentration which gives the lowest interfacial tension

Question 11

Does the rHLB vary for o/w and w/o emulsions?

Answer 11

yes.

Question 12

How is conductivity used to determine the type of emulsion?

Answer 12

A o/w emulsion will have high conductivity as the external phase is water and water conducts electricity.

A w/o emulsion will have low or no conductivity as the external phase is oil and this does not conduct electricity

Question 13

How is staining used to determine the type of emulsion?

Answer 13

methylene blue (water soluble) and Sudan III red (oil soluble)

A o/w emulsion will stain/mix with methylene blue as the external phase is water and will interact with the water soluble dye.

W w/o emulsion will stain/mix well with sudan III red as the external phase is oil and will interact with the oil soluble dye.
It will stain slow and patchy with the methylene blue.

Question 14

How is dilution used to determine the type of emulsion?

Answer 14

A o/w emulsion will be miscible with water

A w/o emulsion will be miscible with oil

Question 15

How is homogenisation used to stabilise an emulsion?

Answer 15

Homogenisation will help to stabilise an emulsion, by reducing the size of droplets of the internal phase.
This is one factor in slowing the aggregation of the internal phase thus increasing stability

Question 16

What is saponification?

Answer 16

The process of forming soap from fatty acid derivatives

Question 17

What is soap?

Answer 17

a salt of the fatty acid. It acts as an emulsifying agent

Question 18

How is viscosity used to determine the type of emulsion?

Answer 18

o/w emulsion has a lower viscosity than a w/o emulsion.

This is because oil has a higher viscosity

Question 19

How is creaming used to determine the stability of an emulsion?

Answer 19

If the emulsion is redispersible then it will not have coalesced

Question 20

What are the effects of saturation and metal ions on the surfactant’s formation of emulsions?

Answer 20

An unsaturated fatty acid has a double bond causing a kink in the structure, Resulting in a higher viscosity potential for a surfactant. When saponified with a monovalent ion such as potassium, it will form a o/w emulsion.
When saponified with a divalent ion such as Calcium it will form a w/o emulsion.

A saturated fatty acid has no kinks in the structure resulting in a lower viscosity potential for a surfactant. When saponified with a monovalent ion (K+) it forms an o/w emulsion
when saponified with a divalent ion (Ca2+) it forms an w/o emulsion

Question 21

What is the creaming ratio?

Answer 21

the creamed height divided by the total height.

This is an indication of the stability of an emulsion

Question 22

What does 1 unit of the microscope ruler equate to?

Answer 22

1um

10 units = 10 um

Question 23

What is span 80?

Answer 23

a sorbitan monoester

Question 24

What is tween 80?

Answer 24

a polyethoxylated monoester.

it is a PEG-lyated span.

Question 25

How are emulsifying agents classified?

Answer 25

surface active agents
hydrocolloids
solid particles

Question 26

What are surface active agents?

Answer 26

e.g. surfactants

they form a mononuclear film on the oil/water interface to reduce surface tension

Question 27

what are hydrocolloids?

Answer 27

e.g. …..
form a strong multilayer film at the interface to prevent the coalescence of droplets

Do not cause an appreciable reduction in the surface tension

Question 28

What are solid particles?

Answer 28

e.g. …..
These are wetted by both oil and water at the interface and forms a particulate film around the dispsersed droplets to prevent coalescence

Question 29

What are the 3 types of emulsifying agents?

Answer 29

surface active agents
natural containing materials and their derivatives
solid particles

Question 30

What are examples of surface active agents?

Answer 30

anionic, cationic, non ionic, amphoteric surfactants

Question 31

what are examples of nautral containing materials and their derivatives?

Answer 31

e.g. hydrocolloids, polysaccharides, sterol containing substances

Question 32

What are examples of solid particles?

Answer 32

bentonite, colloidal silicon dioxide

Question 33

In part 1 of hone experiment investigating the effect of phase ratio and surfactant HLB, what type of emulsion is formulation C?

Answer 33

O/w emulsion with excess water.

Span 80 was used

Question 34

How could formulation C be improved?

Answer 34

Its stability could be improved by

Adding a high HLB surfactant like tween 80 to form a o/w emulsion
Or changing the phase ratio so that liquid para film was the medium (15mL) and water was the suspending particle (4mL)

Question 35

What is the general trend of the dispersion medium, the HLB value of the surfactant and the nature of the emulsion ?

Answer 35

GENERALLY
If volume of water > oil, --> o/w emulsion
If volume of oil >, --> w/o emulsion
If surfactant HLB >10, --> o/w emulsion
If surfactant HLB < 10, --> w/o emulsion

Question 36

Will a divalent ion form a w/o emulsion?

Answer 36

Generally yes, because a divalent ion will bind to two fatty acid molecules to form a surfactant.
These surfactants will increase the viscosity of the medium more than a Monovalent ion formed surfactant.

Question 37

What is the main structural difference between oleic and stearic acid?

Answer 37

Oleic acid is unsaturated, contains a double bond and will form a kinked surfactant with a metal ion.
It has a low melting point

Stearic acid is saturated and does not contain a double bond.
It has a high melting point compared to oleic acid

Question 38

What sort of emulsions does potassium hydroxide form?

Answer 38

O/w emulsions as it is a Monovalent salt.
1 potassium ion will only bind to 1 fatty acid. This is not as lipophilic as divalent ions so will preferentially form a o/w emulsion.

Question 39

What sort of emulsion will calcium hydroxide form?

Answer 39

W/o emulsions. This is because calcium is a divalent ion and will bind to two fatty acid chains. This makes the surfactant more lipophilic and will preferentially form w/o emulsions

Question 40

What are the similarities between creams and emulsions?

Answer 40

A cream consists of water droplets dispersed in the oil phase or vice versa which is stabilised with a surfactant, similar to an emulsion

Question 41

What are the differences between creams and emulsions?

Answer 41

Creams are more structured than emulsions due to aggregation of excess surfactant molecules or polar lipid associates.

Consequently, creams consist of liquid crystalline or lamellar crystals
They have more force for shearing necessary
They have a higher viscosity

Question 42

So, is a cream an emulsion?

Answer 42

Sort of, a cream is a semi solid emulsion

Question 43

What are the optical differences between creams and emulsions?

Answer 43

A cream comprises of liquid crystals which explain birefrengence, an emulsion does not.
Consequently a cream will be seen under a polarised microscope while an emulsion will be not. (It will be darkened, the background will be black)

Question 44

What is stokes law?

Answer 44

A relationship encompassing the density, radius, visocsity, velocity, and the gravitational constant of an emulsion system.
It shows that the rate of sedimentation or settling velocity is inversely proportional to the viscosity of the medium

Question 45

What is creaming?

Answer 45

The separation of an emulsion into 2 distinct regions, one of which is richer in the get dispersed phase than the other.

This is not a serious stability problem as it is reversible upon shaking of the emulsion.

Question 46

How can creaming be prevented?

Answer 46

By producing emulsions with a smaller droplet size
By increasing the viscosity of the continuous phase
By reducing the density difference between the 2 phases

Question 47

What is flocculation?

Answer 47

This is the aggregation of the dispersed globules into loose clusters within the emulsion
This is also redispersable upon shaking

Question 48

What is coalescence?

Answer 48

This is when the surfactant layer at the interface is broken down
Resulting in cracking of the emulsion.

This is irreversible.

Question 49

How can coalescence be prevented?

Answer 49

By reducing the interfacial tension or using electrolytes or charged surfactants.

Question 50

What is the relationship between tween and span surfactants?

Answer 50

Although both spans and Tweens are from sorbitols, Tweens are essentially are a PEG-lyated span surfactant. It consists of a polyethoxylated monoester with more hydroxyl groups, making it more water loving, thus seeing tween in a emulsion formulation is a good indication that the emulsion is o/w.