DESIGN OF A COMPACT HIGH-PRESSURE X-RAY DIFFRACTION CELL M.Kriechbaum, M.Steinhart, K.Pressl, P.Laggner, Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences, A-8010 Graz, Austria.

A compact X-ray sample cell capable of measuring diffraction patterns within a maximal angular range of 30 at hydrostatic pressures of up to 3 kbar - using water as the pressure transmitting liquid - has been developed. The sample thickness can be 1.5 mm with a volume of approximately 1 mm3 completely irradiated by pin-hole collimated (1.0 mm diameter) X-rays. Additionally, the temperature in the pressure cell can be regulated by external Peltier devices in the range from -10C to 80C. The large accessible angular range in the reciprocal space 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 diagrams can be studied. Results of these measurements obtained with laboratory X-ray sources as well as at the synchrotron source DESY in Hamburg, Germany, will be presented.

Currently, this system is being adapted for the use of time-resolved measurements of dynamic processes (pressure-jump relaxation experiments) with a targeted time resolution of diffraction patterns in the millisecond range and integrated into the sample stage environment of the SAXS beamline at the synchrotron source ELETTRA, Trieste, Italy.