Colloidal dispersions Flashcards Preview

Pharmacy (year one) > Colloidal dispersions > Flashcards

Flashcards in Colloidal dispersions Deck (23)
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1
Q

What are colloidal dispersions?

A

Most common ones are suspensions, emulsions, micelles, liposomes and inhalation aerosols

2
Q

What is the size of colloids?

A

Often polydisperse

3
Q

What shapes are colloids?

A
Spherical (emulsion globules)
Ellipsoid (proteins)
Discs (clays - bentonite)
Rods (large micelles)
Coils (large macromolecules e.g DNA)
4
Q

Colloids are often monodisperse. True or false?

A

False - often polydisperse - rarely monodisperse

5
Q

Colloids are smaller than the size of a drug. True or false?

A

False - they are bigger

6
Q

Colloidal dispersions are stable. True or false?

A

False - they are very unstable

7
Q

What forces contribute to the stability/destabilisation of colloids?

A

Repulsion
Attraction
Steric forces
Solvation forces

8
Q

What is the DLVO theory?

A

It considers forces of attraction, repulsion and accounts for stability of hydrophobic colloids

9
Q

DLVO is not useful for predicting the stability of colloids. True or false?

A

False

10
Q

Which forces are responsible for repulsion?

A

Electrostatic and Born (short range)

11
Q

Electrostatic repulsion forces arise from _______ of the diffuse parts of the double layers around two particles

A

overlapping

12
Q

The electrostatic repulsive force decays as an exponentail force with distance. True or false?

A

True

13
Q

Which force is responsible for attraction?

A

Van der Waals

14
Q

The potential of attraction between colloids is proportional to the distance between the colloids. True or false?

A

False - it is inversely proportional

15
Q

How is the total potential energy of attraction between two colloids calculated?

A

It is the sum of the attractive forces and the repulsive forces

16
Q

What determines the height of the primary maxiumum?

A

The colloids’ surface charge and the range of repulsive forces

17
Q

Is the system stable or unstable when the primary maximum is greater than the thermal energy?

A

Stable - particles don’t have sufficient energy to overcome the maximum so do not enter in close contact

18
Q

Is the system stable or unstable with the primary maximum is smaller than the thermal energy?

A

Unstable - interacting particles can overcome the primary maximum and reach the primary minimum but cannot escape

19
Q

One factor influencing the primary maximum and the secondary minimum is the amount of added electrolyte. True or false?

A

True

20
Q

What happens when the secondary minimum is lower than the thermal energy?

A

The particles always repel each other therefore no close contact

21
Q

What happens when the secondary minimum is moderately deep?

A

The system gives rise to loose, easily reversible form of flocculation - important for emulsions and suspensions (for them to be stable)

22
Q

What happens to the double layer when electrolytes are added?

A

The double layer becomes compressed, reducing the repulsion forces therefore reducing the primary maximum - which may cause instability

23
Q

What happens when there is a low amount of salt in solution?

A

There are strong repulsive forces therefore a high primary maximum and no secondary minimum

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