Nanosecond Dynamics of Photoexcited Lyotropic Liquid Crystal Structures

Abstract

Home-based soft X-ray time-resolved diffraction (TR-SXD) experiments with nanosecond time resolution (10 ns) and nanometer spatial resolution were carried out at a tabletop soft X-ray plasma source (2.7-5.9 nm). The investigated system was the lyotropic liquid crystal C(16)E(7)/paraffin/glycerol/formamide/IR 5. Usually, major changes in physical, chemical, and/or optical properties of the sample result from structural changes and shrinking morphology. Here, these effects occur as a consequence of the energy absorption in the sample upon optical laser excitation in the IR regime. The variations observed are integral intensity modulations and displacement in the Bragg diffraction angle. To follow the diffracted integral intensity changes, Patterson analysis was used, and the lattice parameter d variations have been followed by applying the Bragg diffraction law. The experimental intensity modulations occur on the nanosecond time scale, and they are assigned to photoinduced diffusion processes within the liquid crystalline phase. The structural response after photoexcitation is experimentally observed as an increase of the lattice constant by 0.5-1 A and is interpreted as a decrease of order in the liquid crystalline phase. This coincides with a reorientation to a photocreated liquid crystal lattice in the surface plane and with respect to the E-field vector of the laser light. The present studies emphasize the possibility of using TR-SXD techniques for studying the transient mechanical dynamics of nanosystems at the submicrosecond time scale.

Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer

“…[6][7][8][9] Too, the use of an optically pump/soft-x-ray probe setup of tabletop size has been demonstrated for nanosecond time-resolved x-ray diffraction experiments. [10][11][12] Time-resolved absorption spectroscopy, a powerful tool for investigations of the near-edge x-ray absorption fine structure (NEXAFS) for elemental and chemical analysis on the other hand, is so far almost exclusively performed at synchrotrons. Time-resolved NEXAFS spectroscopy can be used to obtain element specific information, as it probes intermolecular bonds and distances, giving rise to changes in oxidation states and the temporal evolution of these changes.…”

First steps towards probing chemical systems and dynamics with free-electron laser radiation-–case studies at the FLASH facility

“…The polymer matrix was photosensitized with a 10 −8 M rhodamine Rh101 dye solution leading to photosensitized polymethane metaacrylate (photo-PMMA). In these experiments, the FLASH pulse acts as a pump pulse and the femtosecond NIR pulse (800 nm) as a probe pulse whose reflectivity signal is enhanced by the photosensitization of the PMMA [20].…”

Development of Ultrafast X-ray Free Electron Laser Tools in (Bio)Chemical Research

“….12)[90,[94][95][96][97][98][99][100][101][102][103], X-ray scattering on macromolecules (Fig.17.13) and (Fig. 17.14) [90, 115, 116, 118, 121] and X-ray spectroscopy (Fig.…”