Surface Stabilized Liquid Crystal Cell Research Articles

Influence of applied electric fields on the positive magneto-LC effects observed in the ferroelectric liquid crystalline phase of a chiral nitroxide radical compound

By measuring the electric field dependence of EPR spectra of the ferroelectric liquid crystalline (FLC) phase of (2S,5S)-1 confined in a surface-stabilized liquid-crystal cell, two magnetic bistable states were observed. These states occur because of the anisotropy in spin–spin dipole interactions responsible for positive ‘magneto-LC effects’, which refer to the generation of a sort of spin glass-like ferromagnetic interactions (average spin–spin exchange interaction constant > 0) induced by weak magnetic fields in the various liquid crystalline (LC) phases of nitroxide radical compound 1.

EPR Investigations on Molecular Orientation of Paramagnetic Liquid Crystals in a Surface-Stabilized Liquid Crystal Cell: Studies on a Smectic C or Chiral Smectic C Phase

By electron paramagnetic resonance spectroscopy we investigated the molecular orientation in a surface-stabilized liquid crystal (LC) cell, which includes a racemic (±) or an enantiomerically enriched (S,S) paramagnetic LC, (2S,5S)-2,5-dimethyl-2-tridecyloxyphenyl-5-[4-(4-tridecyloxy-benzenecarbonyloxy)phenyl]pyrrolidine-1-oxy (2), whose spin source is fixed inside the rigid core. For both the smectic C (SmC) phase of (±)-2 and the chiral smectic C (SmC*) phase of (S,S)-2 in a surface-stabilized LC cell (antiparallel configuration, thickness of 4 µm), the profile of the observed g-value as a function of the angle between the applied magnetic field and the cell plane could be explained by the orientation model, where, with some disordering, the molecules align uniformly with the direction which tilts from the normal line of the smectic layer being orthogonal to the rubbing direction on the cell surface. We divided the effect from the disordering into two parts, one of which is concerning the direction of the molecular long axis and the other is concerning the rotation around the molecular long axis. As a result of the analysis, the SmC* phase gave quite lower ordering concerning the direction of the molecular long axis and a little lower ordering concerning the rotation around the molecular long axis than the SmC phase at the same temperature (80 °C). The obtained lower ordering in the SmC* phase is probably due to the chirality that would result in the formation of a helical superstructure in a bulky state.

EPR Studies on Molecular Orientation in a Surface-Stabilized Paramagnetic Liquid Crystal Cell

By EPR spectroscopy, we have developed a new method for determining the molecular orientation in a surface-stabilized liquid crystal (LC) cell, which includes a paramagnetic LC, (2S,5S)-2,5-dimethyl-2-heptyloxyphenyl-5-[4-(4-octyloxybenzenecarbonyloxy)phenyl]pyrrolidine-1-oxy (1), whose spin source is fixed in the rigid core. For each phase of racemic [(+/-)] and enantiomerically enriched [(S,S)] 1 in a surface-stabilized LC cell (4 microm thickness), the observed g-value profiles depending on the angle between the applied magnetic field and the cell plane were successfully simulated by the orientation models: (i) the LC molecule in the nematic (N) phase of (+/-)-1 freely rotates around the long axis, which is always parallel to the rubbing direction; (ii) the long axis of the freely rotating LC molecule in the chiral nematic (N*) phase of (S,S)-1 is always parallel to the cell plane but rotates in the plane to form a helical superstructure; and (iii) in the crystalline phase of (S,S)-1, the molecular long axis forms a helical superstructure similar to that of the N* phase, but the molecule is fixed around the long axis so that the NO bond lies in the cell plane. Fitting the temperature profile of the g-value in the N phase of (+/-)-1 by use of the Haller equation, we determined the molecular g-values along the molecular long axis (g(parallelM)) and short axis (g(perpendicularM)), which were successfully reproduced by the use of the set of principal g-values of a similar nitroxide with consideration of the structure of the LC molecule optimized by Molecular Mechanics 3 (MM3).

An Integrated 2 × 2 SSFLC Optical Switch with Channel Ion-Exchanged Glass Waveguides

A novel compact structure suitable for the realization of a 2 × 2 bistable integrated optical switch using ferroelectric liquid crystal is reported. The switch consists of a vertical coupler formed by two Ag+-Na+ ion-exchanged single-mode channel waveguides diffused in two BK7 glass substrates of a surface stabilized liquid crystal cell. The coupling properties, and thus the switching state (bar or cross), of this structure can be controlled by electrically reorienting the director of the aligned liquid crystal layer. The device was simulated and optimized at λ = 1550 nm by using a beam propagation method algorithm. The simulation of the TE 00 mode propagating along the designed device showed crosstalk attenuation and losses of 42.5 dB and 0.49 dB respectively with a coupling length of 141 μ m.