CHEE2945 – Lecture 8
Colloid stability:
- A key property of the colloidal dispersions is the tendency for the particles to
aggregate.
- The principal cause of aggregation is the van der Waals attractive force.
- The main force providing stability is the electrical double layer (EDL) force.
- The van der Waals dispersion force cannot be ‘turned off’.
DLVO theory:
- This is a quantitative theory describing colloidal stability. It was developed by:
o Deryagin and Landau in Russia (1939),
o Verwey and Overbeek in the Netherlands (1948).
- It explains the stability of hydrophilic suspensions, especially in terms of
added electrolyte.
- It involves estimating the energy changes when particles approach one
another from the vdW, and EDL overlap energies.
V T =V EDL+ V vdW where V is interaction energy.
Van der Waals forces:
- This is an attraction force between neutral, chemically saturated molecules,
postulated by van der Walls to explain non-ideal gas behaviour.
- Three possible intermolecular interactions are recognised:
o Two dipolar molecules,
o A dipolar molecule and non-polar molecule,
Dipolar molecules induce dipoles in surrounding non-polar
molecules.
o Two non-polar molecules.
Polarisation still occurs due to fluctuation in electron density,
resulting in attraction. These are called dispersion forces (or
London forces).
- Dispersion forces account for near all vdW attractive forces in operation.
- Dispersion forces are very short range (varies with 6 th power of distance).
- vdW interaction energy may be calculated by summing the attractions
between all inter-particle molecule pairs.
- For two particles in a vacuum where:
o Particles are of equal radius.
Colloid stability:
- A key property of the colloidal dispersions is the tendency for the particles to
aggregate.
- The principal cause of aggregation is the van der Waals attractive force.
- The main force providing stability is the electrical double layer (EDL) force.
- The van der Waals dispersion force cannot be ‘turned off’.
DLVO theory:
- This is a quantitative theory describing colloidal stability. It was developed by:
o Deryagin and Landau in Russia (1939),
o Verwey and Overbeek in the Netherlands (1948).
- It explains the stability of hydrophilic suspensions, especially in terms of
added electrolyte.
- It involves estimating the energy changes when particles approach one
another from the vdW, and EDL overlap energies.
V T =V EDL+ V vdW where V is interaction energy.
Van der Waals forces:
- This is an attraction force between neutral, chemically saturated molecules,
postulated by van der Walls to explain non-ideal gas behaviour.
- Three possible intermolecular interactions are recognised:
o Two dipolar molecules,
o A dipolar molecule and non-polar molecule,
Dipolar molecules induce dipoles in surrounding non-polar
molecules.
o Two non-polar molecules.
Polarisation still occurs due to fluctuation in electron density,
resulting in attraction. These are called dispersion forces (or
London forces).
- Dispersion forces account for near all vdW attractive forces in operation.
- Dispersion forces are very short range (varies with 6 th power of distance).
- vdW interaction energy may be calculated by summing the attractions
between all inter-particle molecule pairs.
- For two particles in a vacuum where:
o Particles are of equal radius.
