Part Four
Questions
(1) SANS
Explain what is meant by 'contrast variation' in small angle neutron scattering and show how it can be used to give direct structural and compositional information about sterically stabilised particulate colloids.
Where in colloid science might you find a ‘core-shell’ structure? How does neutron scattering contrast variation help in a structural analysis of these objects?
(2) Neutron scattering lengths
Calculate the scattering length densities for heavy and light water.
(you may assume that the density of H20 is 1g/cc)
Density of dodecane (c12 alkane) 0.750 g/cm3
Heptane (c7) is 0.684g/cm3
The scattering lengths of C, H and D are 0.665, -0.374 and 0.667 x10-12 cm
What are the scattering length densities of protonated and deuterated 'tail' of SDS (sodium dodecylsulphate)?
What combination of light and heavy water will most closely match this?
(3) Nucleation and growth
Outline how nucleation and growth is important in preparation of colloidal particles, phase separation of polymer blends and cloud chambers.
(4) Entropy
Outline how entropy effects are important in:
Steric stability of colloids
Depletion flocculation of colloids
Mixing of polymer blends
Elasticity of elastic bands and phase separated block co-polymers
Collidal crystallistaion
(5) Emulsions and Phase Behaviour
What factors govern the shape of emulsions droplets?
How does variation in the salt concentration and temperature effect the shape of emulsion drops.
Hence outline the concept of spontaneous interfacial curvature and indicate wherelse in colloid science such ideas are useful.
(6) What experimental techniques would you use to determine the phase diagram of the surfactant C12E4 in water?
Past Papers:
June 2000 Q2(a)
1999 (2) 45(b)
1999 20(b)
2000(2) 24(a)
2000 Paper 1 2(a)