|internt fagligt projekt, 3. modul, 2001, id:171|
|Findes på RUb:||ja|
This report is a master thsis in physics, handed in by Kim Bruno Andersen in January 2001. The work presented in this thesis has been conducted at the Department of Mathematics and Physics and the Department og life Sciences and Chemistry, at the University of Roskilde. The main focus of this thesis is the thermodynamical and structual properties of phospholipid membranes, and in particular the anomalous swelling phenomenon, which is observed in multi lamella vesicles, on the high temperature side of the main phase transition. These subjects have been studied in fully hydrated and semi-dry systems, by means of partial water vapour pressure measurements (IPPM) and small angle x-ray scattering measurements (SAXS). Of the experimental work, the dominant part has consisted in finding ways of preparing lipid samples, with a well defined lipid to water ratio, for the SAXS experiments in particular. And preparation methods that ensures an isotropic sample, in general. One of the key features in this subject, is a large number of frees-thaw circles. In reference to anomalous swelling, it is found that the lipid membrane it self, is responsible for some of the awelling, and there is found indications of that the rest of the swelling, is due to an increase in the membrane separation. Swelling in the membrane separation is supported by work of Korremann et al.(B). It have also been observed that reducing the hydration level, greatly reduces undulations of the soft thermal fluctuating membrane. Finally it is shown that hydration of the phospholipid membrane, close to full hydration and at room temperature, is enthalpic unfavourable and entropicaly favoured.