Fast time-resolved X-ray diffraction for studying laser T-jump-induced phase transitions

Abstract

Phase transitions of phospholipid/water systems, triggered by a short 1–2 ms infrared laser heat pulse (Er-laser, wavelength: 1.5 μm, energy 1–2 J), were studied by recording their real time X-ray powder diffraction patterns at a time resolution down to 0.5 ms using synchrotron radiation. Theoretical calculations of the temperature ( T) profile show that the thermal gradient within the heated region of the aqueous sample is less than 2°C and that the influence of temporal heat diffusion can be neglected on the time scale of these experiments, i.e., ⩽ 5 s. With this technique, combining the fast heating source with a fast X-ray detection system, it is possible to study the molecular spatial rearrangements and to evaluate the kinetics of thermotropic phase transitions of phospholipids in the millisecond time range.