The microstructure of confined and thin polymer films

Polymers find wide application in biology and medical research. They can simulate the properties of some bio-composites, which are included into the cell structure of all living organisms. The application of polymers as building materials of membranes has pushed forward the investigation of polymer thin films and multilayers. Moreover, polymers are of big importance in microelectronic and coating industry. With the development of high-flux neutron and X-ray sources, surface and interface scattering methods became feasible techniques for structure studies. Due to the experimental difficulties a successful setup for scattering experiments on confined films with thicknesses of about a few hundreds of Angstroms is still not available. The development of an experimental setup that can confine liquid ultra thin films and simultaneously allows X-ray reflectivity and diffuse scattering measurements was attempted in the frame of this work. The thesis is organized as follows: After a short overview of previous literature data and results, the reflectivity theory is summarized. The experimental part is divided into two sections: The first deals with the time averaged dynamics of supported polymer thin films and the second with confined liquid and polymer films. In the first part the influence of thermally induced fluctuations on the polymer surface stucture depending on the film thickness, the molecular mass and the temperature is studied. The surface structure is probed by X-ray reflectivity and diffuse scattering measurements. In the second part a new setup for confined soft matter films is introduced. It was tested with liquid films of carbon tetrachloride (CCl4) and octamethylcyclotetrasiloxane (OMSTS). Additionaly, results of test experiments on confined polymers are presented. Polystyrene thin films have been studied depending on the molecular mass, film thickness, temperature and the hydrophobisites of the substrate. The diffuse scattering X-ray data have been refined using the Liquid model based on the capillary wave theory and the Fractal model describing the solid surfaces. The comparison of the two models shows that the surface structure of the polymer films is more similar to those of the solid surface then to the liquid one. The experimental data reveal that the observation of the cutoffs on the diffuse scattering curve depends on the molecular mass of the polymer and the film thickness. Differences in the structure of the polymer films deposited on the hydrophobic and hydrophillic were not found. This is probably due to the observed unstability of the hydrophobic substrates with the temperature and the storage time. In the frame of the experiments with liquids and polymers in confined geometry it was possible to build and test a special cell, which allows scattering measurements of confined fluids over areas in the square mm range and with gap sizes of some hundreds of Angstroms. The experiment with the liquids shows that impurities on the substrates strongly hinder the confinement process. They bend the wafer surfaces and destroy the interference fringes in the reflectivity curves. Moreover, from the polymer experiments it turned out that due to the small confinement area it is not possible to spin-coat a uniform film less than a few thousands of Angstrom, on the wafers. Thus, other techniques have to be developed. The behaviour of the confined polymer films, however, support the assumptions about the sluggishness of the dynamics in confined matter