Interactions - Steric repulsion and bridging flocculation

Question 1

Which two components has to be present in STERIC REPULSION?

Answer 1

• Large particles: oil droplet, casein micelles, protein aggregates.
• Other ingredients are present: polysaccharides or polymers, much smaller than the particles.

Question 2

STERIC REPULSION: attractive interactions

Answer 2

When the are attractive interactions present between the particle and the polysaccharides, the polysaccharides move to the particle. This could be due to electrostatic interactions (negative poly and positive protein),
This could also be due to hydrophobic interactions if both the particle and the polymer in the aqueous phase have hydrophobic groups.

Question 3

STERIC REPULSION: we assume that the particle is completely cover. What happen?

Answer 3

At high surface loading: particle become larger due to an additional layer of poly ( hairy layer–stabilizes the particle). Two particles –>repulsive, based on excluded volume interactions (additional layer):
*Steric repulsion (Born or hard sphere repulsion)
When particles approach to a point where polymer layers start to overlap, the chains will hinder each other. This results in a repulsive interaction.

Question 4

BRIDGING INTERACTION:

Answer 4

At low surface loading: attractive, based on sharing of polymer
between two particles: bridging interaction.
Particles can be
- oil droplets (1 µm)
- casein micelles (200 nm)
- protein aggregates