Theoretical Emulsification Flashcards
What is an Emulsion?
2 or more parts that don’t mix well.
Metastable dispersion.
Most emulsions have…
water as one of the phases
Liquid droplets can either be..
Single Emulsion
Oil in Water emulsion
Water in Oil emulsion
What is the double emulsion?
A 3 component system
W/O/W water in oil in water emulsion
O/W/ oil in water in oil emulsion
What are colloids?
Colloids - multi component dispersed phase systems where the disperse phase is within the size range of 1-1000nm.
How can colloids be used in medicine?
topical, parenteral, oral methods
What happens when you shake a cup containing oil and water?
May temporarily form an emulsion but this is Transient - unstable dispersion and thermodynamically unfavourable.
What happens once you stop shaking the cup?
It changes back to the separate phases which is thermodynamically favourable and low energy associated.
How to make an emulsion last?
Make it stable.
How to make droplets last? (2)
Using an emulsifier to form an interfacial film around droplets - stabilises them by lowering interfacial energy.
Viscosity enhanced - inhibit droplet diffusion, prevent coalescence.(joining)
Emulsion Instability
3 reversible ways an emulsion can be unstable:
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.
Emulsion Instability
2 irreversible ways an emulsion can be unstable:
Cracking
- complete phase separation between oil and water phase.
Coalescence
- increase in size.
How do droplets interact? (2)
DLVO theory
Van der Waals attraction
Electrical repulsion: electrical double layer
Emulsions are..
metastable
Droplets undergo…
brownian motion
Attraction promotes..
Repulsion promotes..
Attraction - droplet consolidation which causes instability.
Repulsion - droplets separation which causes stability.
How do the attractive and repulsive energies act?
They change at different rates with particle distance.
The sum of their energies explains particle dispersion oil flocculation.
DLVO theory equation:
VT = VA + VR
VA = attractive energy VR = repulsive energy
Explain the 3 regions of a graph showing DLVO theory”
1 primary minimum
- net attractive, irreversible coagulation
2 primary maximum
- net repulsion, stable dispersion
3 secondary minimum
- net attraction, reversible flocculation
Sedimentation depends on…
particle droplets sinking in continuous phases under opposing forces.
The following promotes sedimentation: (3)
larger droplet size
greater density difference between droplet and continuous phase
lower fluid viscosity
Sedimentation Equation
Stoke’s Law
v = 2r2g (Pparticle-Pfluid) / 9n
v = sedimentation rate r = particle radius g = particle acceleration due to gravity particle-fluid density difference n = fluid viscosity
How do we know the emulsion type?
- disperse phase typically less than 70%
- Bancroft rule: the phase in which the emulsifier is more soluble is the continuous phase.
A hydrophilic emulsifier would lead to…
O/W emulsion
A lipophilic emulsifier would lead to…
W/O emulsion
If the emulsifier more soluble in..
oil- it is lipophilic
water - hydrophilic
What is the HLB?
Numerical scale indicating overall hydrophilicity/lipophilicity of an emulsifier.
What if the HLB shows a value less than 10?
more soluble in oil
What if the HLB shows a value more than 10?
emulsifier more soluble in water
Where does the bulkier portion of the emulsifier face?
Outwards regardless of whether the portion is hydrophilic or hydrophobic.
