High-pressure instrument for small- and wide-angle x-ray scattering. II. Time-resolved experiments

An instrument to facilitate small- and wide-angle x-ray scattering measurements of samples under elevated hydrostatic pressures or exposed to pressure jumps is described. Pressure from atmospheric up to 0.35 GPa is produced by a motor-driven, piston-type generator and transferred through a network containing pressurizing liquid to a sample cell. The cell, with the optical path length of 1.6 mm, has two Beryllium windows with a total transmission of 0.4 (for x rays of λ=0.154 nm) and low background scattering. Scattering can be observed at angles up to 30°. Samples can be solid or liquid with a minimal volume less than 30 μl and the irradiated volume up to 3 μl. Separation of the samples from the pressurizing medium is accomplished by Teflon pistons. The high-pressure network has two sections separated by a pneumatic valve. The inner section is connected permanently to the cell and the outer one to the pressure generator. For pressure jumps, the outer section is brought to a different pressure level than the inner one and the jumps are accomplished by opening fast the connection between both sections. At the same time a trigger signal is sent to the data acquisition electronics. All functions of the instrument are PC controlled. To illustrate the performance characteristics of the instrument, time-resolved small-angle x-ray scattering measurements of phase transitions in liquid crystalline phospholipid, dioleoylphosphatidylethanolamine are shown. Pressure-jump experiments with 5 ms time resolution as well as temperature scans at a constant elevated pressure are presented.