Physical aspects - Prior knowledge - Interactions - Effect of pH and salt on electrostatic repulsion
3 important questions on Physical aspects - Prior knowledge - Interactions - Effect of pH and salt on electrostatic repulsion
The formula for the electrostatic repulsive force consist of 2 parts:
- First part related to the wall potential --> charge density of particles --> depends on pH
- close to pI --> low charge, weak repulsion
- far from pI --> high charge, strong repulsion
- Second part related to kappa --> double layer --> depends on salt concentration
- when the salt concentration increases, kappa increases and electrostatic repulsive force decreases
How does the salt concentration influence the electrostatic repulsion?
Salt concentration increases --> charges are screened --> double layer gets smaller --> interaction potential decreases, decrease in electrostatic repulsion
When are particles close to each other and when is there a large distance?
Close:
Large distance:
- Low charge (pH = pI)
- High salt content (small Double layer)
- Low repulsion
- Decrease interaction potential
Large distance:
- High charge (pH >/< pI)
- Low salt content
- High repulsion
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