Nanosecond Dynamics of Photoexcited Lyotropic Liquid Crystal Structures

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 C16E7/paraffin/glycerol/formami...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2010-07, Vol.114 (26), p.8593-8599
Main Authors: Quevedo, Wilson, Peth, Christian, Busse, Gerhard, Mann, Klaus, Techert, Simone
Format: Article
Language:English
Subjects:
B: Macromolecules, Soft Matter
Kinetics
Lasers
Liquid Crystals - chemistry
Optical Phenomena
Photochemical Processes
Scattering, Small Angle
X-Ray Diffraction
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Summary: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 C16E7/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 Å 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.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp101609q