Colloidal Dispersed Fomrulations 3 W2

Question 1

Dispersions can be maintained by controlling 2 aspects?

Answer 1

1. Particle motion and dynamics
   - control particle size and density
   - adjust viscosity of continuous phase
2. Particle-particle interactions
   - control interactions between particles
   - induce flocculation

Question 2

What happens when particles sediment

Answer 2

When sedimentation occurs, the particles will come closer together, so now they can interact.

Depending how they interact, they can form a dense sediment or ‘cake’ at the bottom of the container,

or they can form loose associations called ‘flocs’.

Question 3

If particles interact strongly……

Answer 3

They aggregate

Aggregations will sediment even quicker as they gain mass

Reach the bottom of container and compress even further due to their own mass and others sitting on top of them

This is till they are irreversibly aggregated and form a cake

Shaking will no longer resuspend the particles

Question 4

What happens when particles flocculate

Answer 4

If particles interact weakly the aggregates are loose and fluffy and remain suspended.

They sediment quickly but are easily redispersible by shaking

Question 5

Advantages and disadvantages of flocculated

Answer 5

+ Flocculation occurs rapidly;
+ Loose sediment occupies a high volume;
+ Easily resuspended.

• May appear unsightly to patient

Question 6

Advantages and disadvantages of de-flocculated

Answer 6

+ Suspended system looks uniform, not full of ‘bits’

• Sedimentation occurs more slowly
• Dense sediment occupies a low volume
• Irreversibly aggregated.

Question 7

Advantages and disadvantages of de-flocculated

Answer 7

+ Suspended system looks uniform, not full of ‘bits’

• Sedimentation occurs more slowly
• Dense sediment occupies a low volume
• Irreversibly aggregated.

Question 8

Sedimentation volume of sediments

Answer 8

Low

Question 9

Sedimentation volume of flocs

Answer 9

High