DS - Colloids

Question 1

Define colloidal dispersions and list their main characteristics

Wk4

Answer 1

a

Question 2

Explain the Tyndall effect and the basis of DLVO theory

Answer 2

What is light diffraction/scattering?
This is a phenomenon you have all observed either in presence of fog or by just looking at a glass of milk. The Figure below shows different views of milk the most well-known emulsion.
When looking at a glass of milk with your eye, it appears to be uniformly white or opaque; this result is due to the scattering of light. A closer look using an optical microscope reveals the presence of transparent particles/droplets. This is further confirmed using an electron microscope which has a far better resolution and reveals that milk is made of droplets/particles many of them being fat.
To conclude here, milk is not white as microscopes images have shown; however diffraction/scattering of light in the milk sample make it appear white. This effect is called the Tyndall effect.

Question 3

Discuss colloids stabilisation

Answer 3

Coagulation: permanent contact between particles; soluble aggregates  Aggregates: next step after coagulation; insoluble aggregates
 Flocculated particles: temporary contact
 Dispersed particles: rebound and remain free as single particles.
There are different forces that will contribute to the formation of these objects:
 For lyophilic systems (e.g. monoclonal antibodies in aqueous solutions) three types of forces are considered: electrical forces of repulsions (between particles), forces of attraction (between particles) and solvation forces (for
each particle).
 For lyophobic systems (e.g. emulsions or suspensions), only two types of
forces are considered: electrical forces of repulsions (between particles), forces of attraction (between particles).