|M.Sc Student||Kellarev Alexander|
|Department||Department of Physics||Supervisor||Professor Emeritus Stephen Lipson|
In the present research the application of the shadowgraph technique to thin film measurement is studied. The shadowgraph is a technique of optical measurement, which allows measurement of small gradients in the properties of the material under investigation. In the current application the shadowgraph is used to measure small surface gradients on a liquid surface.
The experimental system used to implement the shadowgraph is water-pentane-vapour system, in which pentane forms thin film on the water surface. This system has attracted much attention in recent years due to interesting wetting phenomena, which occur in the system. Pentane belongs to the group of medium length alkanes, which were found to have unusual wetting transitions behaviour. There were found two wetting transitions in the water-pentane system, the nature of which is not fully understood. The difficulty in investigation of the water-pentane system is that these two materials have similar refractive indices, which makes them almost undistinguishable when studied by means of usual optical methods. The shadowgraph method is believed to provide an adequate way for visualization and studying the formation of thin films and film patterns.
This report provides a theoretical background of the thin film of alkane formed on water surface, the current theory of the wetting transitions in water-alkane-vapour system, and the principle of the shadowgraph measurement. The experimental system is fully described, including the optical and the chemical parts of the system, and the considerations used for developing and building the measurement system. The results of two experiments are presented with experimental data analysis.