FAST TIME-RESOLVED X-RAY-DIFFRACTION FOR STUDYING LASER T-JUMP-INDUCED PHASE-TRANSITIONS

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. © 1990.