Time-Resolved X-ray Diffraction Experiments up to 3000 bar with a New Developed Compact High-Pressure X-Ray Cell. M. Kriechbaum, M. Steinhart, K. Pressl, P. Laggner, Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences, Graz, Austria

A compact X-ray sample cell capable of measuring diffraction patterns at hydrostatic pressures up to 3 kbar has been developed. The exit- and the removable entrance-window for the X-rays are made of 1.5 mm thick Be-discs (3.5 mm diameter), coated with 5###m polyimide with a total transmission of 55% for X-rays at a wavelength of 1.54 Å. The sample thickness can be 1.5 mm with a volume of approximately 1mm³ completely irradiated by pin-hole collimated (1.0 mm diameter) X-rays. The cone-shaped exit window allows detection of scattered X-rays from the sample within a maximal angular range of 30deg.. The cell can currently be operated in a temperature range from 5 to 80 deg.C. Temperature/pressure scans and data collection during scattering experiments are completely computer controlled.

The large accessible angular range of the scattered radiation makes the cell well suited for scattering/diffraction measurements in the small- and wide-angle region of samples like solid polymers, liquid-crystalline probes and biological model-membrane systems. Thus, information on the short and long range order can be obtained simultaneously, i.e lattice and chain packing parameters in lipid bilayers. Particularly, barotropic and thermotropic phase transitions of liquid crystalline systems at constant temperature or pressure, respectively, and their p-T phase diagram can be studied.

Results of these measurements obtained with laboratory X-ray sources as well as at the SAX beamline at ELETTRA (Trieste, Italy) will be presented. Static measurements of phospholipid samples at different pressures showed an excellent signal/noise ratio of the diffraction patterns at exposure times of 10s, whereas in pressure-jump relaxation experiments (jump amplitude of 2 kbar/10ms) time-sliced diffraction patterns with 5ms time resolution could be recorded.