Assignment:
1. Explain with the use of a diagram what physical mechanism gives rise to the surface tension in a liquid. Explain also which of the following two liquids has a higher surface tension and why: water and hexane. Describe with the use of diagrams two proceedures to measure the surface tension of a liquid together with the physical principles and equations involved. The surface tension at the mercury/water interface has the high value of 415 mN m-1 compared to that of the water/air interface of 73 mN m-1.
What is the physical reason in molecular terms for the high value of the mercury/water interfacial (surface) tension? One way to decrease this surface tension is to apply an electrical potential to the mercury. Why does charging of the mercury surface cause its surface tension in water to decrease? Can you explain another way to decrease the surface tension at the mercury/water interface.
2. Derive expressions of (a) the work of adhesion (Dupre equation) between two immiscible liquids and (b) the work of cohesion for a single liquid in terms of the surface tensions of the respective liquids. What is the expression for the free energy (ΔG) of the spreading of an insoluble liquid on water expressed in terms of the surface tension values of the respective interfaces. Define the Spreading Coefficient for the spreading of one imiscible liquid on another. What is the condition for spreading of the Spreading Coefficient value? Express the Spreading Coefficient in terms of the work of adhesion and the work of cohesion for two immiscible liquids.
3. What is a liposome? Draw the structure of a unilamellar liposome. Describe two applications of liposomes? Describe one method for preparing unilamellar liposomes. Finally detail the forces which hold the liposome together in its organised structure.