Theoretical Emulsification Flashcards Preview

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Flashcards in Theoretical Emulsification Deck (30)
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1
Q

What is an Emulsion?

A

2 or more parts that don’t mix well.

Metastable dispersion.

2
Q

Most emulsions have…

A

water as one of the phases

3
Q

Liquid droplets can either be..

Single Emulsion

A

Oil in Water emulsion

Water in Oil emulsion

4
Q

What is the double emulsion?

A

A 3 component system

W/O/W water in oil in water emulsion

O/W/ oil in water in oil emulsion

5
Q

What are colloids?

A

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

6
Q

How can colloids be used in medicine?

A

topical, parenteral, oral methods

7
Q

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

A

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

8
Q

What happens once you stop shaking the cup?

A

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

9
Q

How to make an emulsion last?

A

Make it stable.

10
Q

How to make droplets last? (2)

A

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

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

11
Q

Emulsion Instability

3 reversible ways an emulsion can be unstable:

A

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.

12
Q

Emulsion Instability

2 irreversible ways an emulsion can be unstable:

A

Cracking
- complete phase separation between oil and water phase.

Coalescence
- increase in size.

13
Q

How do droplets interact? (2)

A

DLVO theory

Van der Waals attraction

Electrical repulsion: electrical double layer

14
Q

Emulsions are..

A

metastable

15
Q

Droplets undergo…

A

brownian motion

16
Q

Attraction promotes..

Repulsion promotes..

A

Attraction - droplet consolidation which causes instability.

Repulsion - droplets separation which causes stability.

17
Q

How do the attractive and repulsive energies act?

A

They change at different rates with particle distance.

The sum of their energies explains particle dispersion oil flocculation.

18
Q

DLVO theory equation:

A

VT = VA + VR

VA = attractive energy
VR = repulsive energy
19
Q

Explain the 3 regions of a graph showing DLVO theory”

A

1 primary minimum
- net attractive, irreversible coagulation

2 primary maximum
- net repulsion, stable dispersion

3 secondary minimum
- net attraction, reversible flocculation

20
Q

Sedimentation depends on…

A

particle droplets sinking in continuous phases under opposing forces.

21
Q

The following promotes sedimentation: (3)

A

larger droplet size

greater density difference between droplet and continuous phase

lower fluid viscosity

22
Q

Sedimentation Equation

Stoke’s Law

A

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

v = sedimentation rate
r = particle radius
g = particle acceleration due to gravity
particle-fluid density difference
n = fluid viscosity
23
Q

How do we know the emulsion type?

A
  • disperse phase typically less than 70%

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

24
Q

A hydrophilic emulsifier would lead to…

A

O/W emulsion

25
Q

A lipophilic emulsifier would lead to…

A

W/O emulsion

26
Q

If the emulsifier more soluble in..

A

oil- it is lipophilic

water - hydrophilic

27
Q

What is the HLB?

A

Numerical scale indicating overall hydrophilicity/lipophilicity of an emulsifier.

28
Q

What if the HLB shows a value less than 10?

A

more soluble in oil

29
Q

What if the HLB shows a value more than 10?

A

emulsifier more soluble in water

30
Q

Where does the bulkier portion of the emulsifier face?

A

Outwards regardless of whether the portion is hydrophilic or hydrophobic.