Depletion interactions

Question 1

When a depletion interaction occurs?

Answer 1

Occurs in mixtures of small and large objects. Two large objects that are present between small objects.
*High concentration, the distance between the large particles will become small, maybe become so small that is malles than the diameter of the smaller particles. So the smaller particles cannot enter between the large ones.

Question 2

The amount of particles present determine the osmotic pressure of the system

Answer 2

The osmotic pressure is going to be higher in area B ( outside) and because there is no particles between the big ones, the osmotic pressure is much lower in are A. This differences leads to a transport of water from A to B, to lower the concentration of small particles there. So the big particles will pushed further together. So there is an attractive interaction which leads to aggregation and phase separation ( one phase with small particles and the other with large particles).

Question 3

Depletion interactions can occur in a wide range of systems: EXAMPLES

Answer 3

a) oil droplets with flexible polysaccharides
b) polysaccharides with smaller particles or proteins
c) between different polymers or polysaccharides
Stiff polysaccharide is xanthan, forms helices that limit their flexibility

Question 4

When a depletion interaction occurs, which part is going to be up and which down ?

1. Casein micelles or protein aggregates + polysaccharides.
2. Oil + polysaccharides

Answer 4

1. Particles lower phase and polysaccharides in the upper phase.
2. Polysaccharides down and oil droplets move up.