Colloidal dispersions

Question 1

What are colloidal dispersions?

Answer 1

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

Question 2

What is the size of colloids?

Answer 2

Often polydisperse

Question 3

What shapes are colloids?

Answer 3

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

Question 4

Colloids are often monodisperse. True or false?

Answer 4

False - often polydisperse - rarely monodisperse

Question 5

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

Answer 5

False - they are bigger

Question 6

Colloidal dispersions are stable. True or false?

Answer 6

False - they are very unstable

Question 7

What forces contribute to the stability/destabilisation of colloids?

Answer 7

Repulsion
Attraction
Steric forces
Solvation forces

Question 8

What is the DLVO theory?

Answer 8

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

Question 9

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

Answer 9

False

Question 10

Which forces are responsible for repulsion?

Answer 10

Electrostatic and Born (short range)

Question 11

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

Answer 11

overlapping

Question 12

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

Answer 12

True

Question 13

Which force is responsible for attraction?

Answer 13

Van der Waals

Question 14

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

Answer 14

False - it is inversely proportional

Question 15

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

Answer 15

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

Question 16

What determines the height of the primary maxiumum?

Answer 16

The colloids’ surface charge and the range of repulsive forces

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

True

Question 20

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

Answer 20

The particles always repel each other therefore no close contact

Question 21

What happens when the secondary minimum is moderately deep?

Answer 21

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

Question 22

What happens to the double layer when electrolytes are added?

Answer 22

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

Question 23

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

Answer 23

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