Time-resolved x-ray studies of the dynamics of smectic-Alayer realignment by magnetic fields

Abstract

While the rotation of smectic layers under an applied field may at first appear to be a relatively simple problem, the dynamic processes involved are rather complex. An applied field produces a torque on the liquid crystal director, but has no direct influence on the smectic layers. If the director is reoriented significantly, however, the layers must also reorient in order to accommodate this (the layered structure is produced by short-range molecular interactions). Indeed, if the liquid crystalline order is not maintained during the realignment then matters become even more complex. In this paper we use time-resolved x-ray scattering to investigate the realignment of smectic- A layers in thin-film devices using a magnetic field. No evidence is found for continuous rotation of the smectic layers under any circumstances in such devices, a result that is not found when using bulk samples. No evidence indicating the formation of the nematic phase is observed during realignment. A molecular-dynamics technique is used to model the system which indicates that the sample becomes significantly disorganized during the realignment process when large angular rotations are induced.

Order-Disorder Transition and Alignment Dynamics of a Block Copolymer Under High Magnetic Fields byIn SituX-Ray Scattering

“…3(a). This continuous microdomain rotation in a bulk nematic state stands in contrast with the noncontinuous nature of director reorientation observed by time resolved studies in smectic A thin films as recently reported [26] and the overall complexity of reorientation in the smectic state [27]. The intensity variations of the microdomain scattering, integrated azimuthally AE15 around ¼ 90 and ¼ 180 are shown in Fig.…”

Soft Matter Sample Environments for Time-Resolved Small Angle Neutron Scattering Experiments: A Review

“…The requirement to use superconducting magnets is a severe complication. Some static on-line X-ray experiments are published [95,96] and even some dynamic studies, where the sample was rotated inside the magnetic field and observed whilst rotating back [97,98]. For neutron experiments, occasionally an off-line magnet was used to produce aligned samples from fibrous biological macromolecules [99,100] and more recently the use of an on-line 8 T magnet to measure alignment by SANS of bicelles complexed with lanthanides was reported [101].…”

Second-harmonic generation and the influence of flexoelectricity in the nematic phases of bent-core oxadiazoles

“…The hot stage was mounted on a custom-built rotation stage described previously. [25,26] The rotation stage allows the sample to be tilted relative to the direction of propagation of the beam, in order to change the angle of incidence on the sample, and rotated about the direction of propagation of the beam, in order to orient the nematic director relative to the direction of polarisation of the fundamental beam. A pulsed, Q-switched Nd:YAG laser (Spectron Lasers, SL804 1615) was used to provide a linearly polarised, near infrared (NIR) fundamental beam of wavelength 1064 nm and diameter 1.8 mm.…”