Theoretical Emulsification

Question 1

What is an Emulsion?

Answer 1

2 or more parts that don’t mix well.

Metastable dispersion.

Question 2

Most emulsions have…

Answer 2

water as one of the phases

Question 3

Liquid droplets can either be..

Single Emulsion

Answer 3

Oil in Water emulsion

Water in Oil emulsion

Question 4

What is the double emulsion?

Answer 4

A 3 component system

W/O/W water in oil in water emulsion

O/W/ oil in water in oil emulsion

Question 5

What are colloids?

Answer 5

Colloids - multi component dispersed phase systems where the disperse phase is within the size range of 1-1000nm.

Question 6

How can colloids be used in medicine?

Answer 6

topical, parenteral, oral methods

Question 7

What happens when you shake a cup containing oil and water?

Answer 7

May temporarily form an emulsion but this is Transient - unstable dispersion and thermodynamically unfavourable.

Question 8

What happens once you stop shaking the cup?

Answer 8

It changes back to the separate phases which is thermodynamically favourable and low energy associated.

Question 9

How to make an emulsion last?

Answer 9

Make it stable.

Question 10

How to make droplets last? (2)

Answer 10

Using an emulsifier to form an interfacial film around droplets - stabilises them by lowering interfacial energy.

Viscosity enhanced - inhibit droplet diffusion, prevent coalescence.(joining)

Question 11

Emulsion Instability

3 reversible ways an emulsion can be unstable:

Answer 11

flocculation
- the droplets are close together and becomes like groups of tablets but don’t fuse.

creaming
- floccules come together as one layer at the top.

sedimentation
- like creaming but at the bottom.

Question 12

Emulsion Instability

2 irreversible ways an emulsion can be unstable:

Answer 12

Cracking
- complete phase separation between oil and water phase.

Coalescence
- increase in size.

Question 13

How do droplets interact? (2)

Answer 13

DLVO theory

Van der Waals attraction

Electrical repulsion: electrical double layer

Question 14

Emulsions are..

Answer 14

metastable

Question 15

Droplets undergo…

Answer 15

brownian motion

Question 16

Attraction promotes..

Repulsion promotes..

Answer 16

Attraction - droplet consolidation which causes instability.

Repulsion - droplets separation which causes stability.

Question 17

How do the attractive and repulsive energies act?

Answer 17

They change at different rates with particle distance.

The sum of their energies explains particle dispersion oil flocculation.

Question 18

DLVO theory equation:

Answer 18

VT = VA + VR

VA = attractive energy
VR = repulsive energy

Question 19

Explain the 3 regions of a graph showing DLVO theory”

Answer 19

1 primary minimum
- net attractive, irreversible coagulation

2 primary maximum
- net repulsion, stable dispersion

3 secondary minimum
- net attraction, reversible flocculation

Question 20

Sedimentation depends on…

Answer 20

particle droplets sinking in continuous phases under opposing forces.

Question 21

The following promotes sedimentation: (3)

Answer 21

larger droplet size

greater density difference between droplet and continuous phase

lower fluid viscosity

Question 22

Sedimentation Equation

Stoke’s Law

Answer 22

v = 2r2g (Pparticle-Pfluid) / 9n

v = sedimentation rate
r = particle radius
g = particle acceleration due to gravity
particle-fluid density difference
n = fluid viscosity

Question 23

How do we know the emulsion type?

Answer 23

• disperse phase typically less than 70%

- Bancroft rule: the phase in which the emulsifier is more soluble is the continuous phase.

Question 24

A hydrophilic emulsifier would lead to…

Answer 24

O/W emulsion

Question 25

A lipophilic emulsifier would lead to…

Answer 25

W/O emulsion

Question 26

If the emulsifier more soluble in..

Answer 26

oil- it is lipophilic

water - hydrophilic

Question 27

What is the HLB?

Answer 27

Numerical scale indicating overall hydrophilicity/lipophilicity of an emulsifier.

Question 28

What if the HLB shows a value less than 10?

Answer 28

more soluble in oil

Question 29

What if the HLB shows a value more than 10?

Answer 29

emulsifier more soluble in water

Question 30

Where does the bulkier portion of the emulsifier face?

Answer 30

Outwards regardless of whether the portion is hydrophilic or hydrophobic.