Dynamic bending rigidity of surfactant layers in swollen lyotropic lamellar liquid-crystal phases

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 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 soft X-ray diffraction reveals transient structural distortions of ternary liquid crystals

Home-based soft X-ray time-resolved scattering experiments with nanosecond time resolution (10 ns) and nanometer spatial resolution were carried out at a table top soft X-ray plasma source (2.2-5.2 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 occur as a result of 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 liquid crystal shows changes in the structural response within few hundred nanoseconds showing a time decay of 182 ns. A decrease of the Bragg peak diffracted intensity of 30% and a coherent macroscopic movement of the Bragg reflection are found as a response to the optical pump. The Bragg reflection movement is established to be isotropic and diffusion controlled (1 micros). Structural processes are analyzed in the Patterson analysis framework of the time-varying diffraction peaks revealing that the inter-lamellar distance increases by 2.7 A resulting in an elongation of the coherently expanding lamella crystallite. The present studies emphasize the possibility of applying TR-SXRD techniques for studying the mechanical dynamics of nanosystems.