Specular Reflection of Neutrons and X-Rays from Interfaces.

Available from UMI in association with The British Library. Requires signed TDF. The two new techniques of X-ray and neutron specular reflection have been applied to the study of adsorption at the liquid-vapour interface for the first time. Since the possibilities of using these techniques had hardly been considered at the start of the work, the potential of the techniques has also been extensively investigated by simulation. Experimental results have been obtained from three different interfacial systems. The thickness of the wetting layer in the methanol/cyclohexane system has been investigated, although it was found that it was difficult to achieve equilibrium with this system. The neutron reflectivity from a Newton black soap film has been analysed to give the first direct measurement of the thickness of the aqueous core (20 A). The neutron reflectivity from a butyl arachidate monolayer, spread on water, has been measured over a range of surface pressures. The presence of an adsorbed layer was readily detected on the gravity mirror and the reflectivity was enhanced as the density of the monolayer was increased. However, at such low values of momentum transfer, it was not possible to determine the film thickness. The thickness of the monolayer was determined from X-ray reflectivity measurements over a wide range of scattering vectors. The overall thickness of 30 A is consistent with the molecules being orientated close to perpendicular to the surface, with the butyl chain penetrating the subphase. The complexities of methods hitherto used to calculate reflectivity profiles have made it difficult to assess the best way of utilizing reflection most effectively. A simpler, approximate, model has been used in a range of simulations to show how contrast variation is best used and as a means of assessing suitable graphical methods for analysing experimental data.