Surface-stabilized State Research Articles

Influence of the Physical Properties of Ferroelectric Liquid-Crystal Mixtures on the Photorefractive Effect

The relationship between the thermal properties and the photorefractive effect of various ferroelectric liquid-crystal compositions was investigated. Mixtures of phenyl pirimidine derivatives were used as host liquid-crystal materials to which chiral dopants and photoconductive compounds were added. The photorefractive two-beam coupling gain coefficient was strongly dependent on the magnitude of spontaneous polarization and the uniformity of the surface-stabilized state.

Polymer-Stabilized Orthoconic Antiferroelectric Liquid Crystals

Horizontally surface-stabilized orthoconic antiferroelectric liquid crystals (OAFLCs) provide excellent contrast electrooptic switching. However, in very thin cells the bulk relaxation to the anticlinic state tends to be slow because the synclinic state is upheld by the surfaces. In cells thin enough to accomplish a surface-stabilized state of today's short-pitch OAFLC mixtures, the field-induced synclinic (ferroelectric) states often become metastable making the corresponding bright electrooptic state prevail for long times after the electric field is switched off. Fast relaxation is then achieved by specially designed waveforms. By introducing a polymer network formed by in-situ photopolymerization of a small concentration of a commercial reactive monomer dissolved in the OAFLC, we have succeded to drastically reduce the time for relaxation from the synclinic to the anticlinic state after switching off the field down to about 3 milliseconds at room temperature, without the use of any tailored electronic waveforms. The relaxation time of the polymer stabilized OAFLCs (PS-OAFLCs) is thus shorter than in todays nematic liquid crystal displays, which make PS-OAFLCs attractive for use in future high-contrast, blur-free displays.

Dynamical Behavior of a Ferroelectric Liquid Crystal with Monotropic Transition Temperatures during Electric-Field-Induced Switching Studied by Time-resolved Infrared Spectroscopy Combined with Singular Value Decomposition

The switching dynamics of a ferroelectric liquid crystal (FLC-154) with monotropic transition temperatures has been explored under the surface-stabilized states by polarized infrared (IR) absorption and time-resolved IR spectroscopy. The polarized IR and time-resolved IR studies have revealed that FLC-154 shows significantly different dynamics from FLCs with non-monotropic thermotropic transition temperatures. The analysis of the relative orientation of the transition moments of the CH2 symmetric and antisymmetric stretching modes has suggested that the alkyl chains of FLC-154 take a gauche-trans-gauche conformation. It has also been revealed from the same analysis that the alkyl chains take different alignment under dc applied voltages of 20 V of both polarities at 65°C. Time-resolved IR spectra of FLC-154 in a planar-aligned cell were measured as a function of the polarization angle ranging from 0° to 180° under a rectangular electric field of ±20 V with a 5 kHz repetition rate in the smectic-C* (Sm-C*) phase at 65°C. These spectra have enabled us to explore the reorientation processes of the alkyl chains, the core and the large C=O dipole moments of FLC-154 at all the delay times. The singular value decomposition (SVD) was applied to the time-resolved IR spectra in the 3020–1000 cm-1 region of FLC-154. The results of SVD have provided information about the profile of the principal component (PC) score versus the delay time, enhancing the ability of time-resolved IR in probing the switching dynamic. It has been found from the SVD analysis that the average orientation of a large C=Obiphenyl dipole moment (it arises from the C=O group adjoining the biphenyl ring) of FLC-154 is unchanged during the whole electric-field-induced switching. It seems likely that the core of FLC-154 straddles the polyimide molecules on the surface of the FLC layer. This configuration of FLC molecule forces the transverse C=Obiphenyl dipole moment to be parallel with the rubbing direction, and the molecules of FLC-154 revolve around the average orientation of the C=Obiphenyl dipole moment. These results have suggested that the FLC-154 molecules revolve around the large C=Obiphenyl dipole moment during the electric-induced-field switching. The dynamic SVD profile for the alkyl chains, a large C=Ochiral dipole moment (it arises from the C=O group in the chiral moiety) and the core moiety have shown that all the moieties require an induction period of 10 µs before responding to the electric field.

Influence of the Properties of Ferroelectric Liquid Crystals on the Spontaneous Polarization Reorientation Photorefractive Effect

The photorefractivity of 14 ferroelectric liquid crystals (FLCs) mixed with a photoconductive compound was investigated by two-beam coupling experiments. The influence of the properties of low-molecular-weight FLCs on the photorefractive effect was examined, and it was found that the photorefractive two-beam coupling gain coefficients and the refractive index grating formation time are strongly dependent on the properties of FLCs. The effects of the magnitude of the spontaneous polarization, the viscosity, and the homogeneity of the surface-stabilized state on the photorefractivities of FLCs are discussed based on these findings.

Time-resolved infrared spectroscopic study of the switching dynamics of a surface-stabilized ferroelectric liquid crystal.

The orientation dynamics of a ferroelectric liquid crystal with a naphthalene ring (FLC-3) during the electric-field-induced switching between two surface-stabilized states was investigated by means of time-resolved Fourier-transform infrared spectroscopy. Time-resolved infrared spectra of the planar-aligned cell of FLC-3 were measured as a function of the polarization angle ranging from 0 degree to 180 degrees under a rectangular electric field +/-40 V with a 5-kHz repetition rate in the smectic-C* (Sm-C*) phase at 137 degrees C. From these spectra details about the mutual arrangement of different molecular segments at all the delay times in the Sm-C* phase were derived. It was found that the C=O group in the core moiety exhibits a dynamical behavior different from that in the chiral moiety during the electric-field-induced switching between the two surface-stabilized states. The most important finding in the present study is that during the electric-field-induced switching the FLC molecule not only rotates around the layer normal, but also revolves around its own long axis. Furthermore, time-resolved infrared spectroscopy revealed that each group in the core moiety passes almost simultaneously through the projection of the layer normal in the cell window during the dynamic switching.

Effects of dielectric biaxiallity and surface pretilt on τ-V characteristics of SSFLCs

The surface pretilt angle in the surface-stabilized state and the dielectric biaxiallity of two kinds of ferroelectric liquid crystalline mixtures are evaluated based on the molecular orientational model. Using these values, the switching characteristics are calculated based on the elastic continuum theory of SmC* liquid crystals. These results are compared with the experimental ones, and the effects of the dielectric biaxiallity and the surface pretilt angle on τ—V characteristics are discussed.

Dynamics of electric-field-induced molecular reorientation and segmental mobility in the smectic-C^{*} phase of a ferroelectric liquid crystal: Faster reorientation of cores than the alkyl chains revealed by time-resolved infrared spectroscopy

We report a study of the dynamics of molecular reorientation and segmental mobility of a ferroelectric liquid crystal in the smectic-${C}^{*}$ (Sm-${C}^{*}$) phase having 2-hydroxy-benzilidenianiline as the mesogen core and $(S)\ensuremath{-}$ 2-chloro-3-methylbutanoyl as the chiral terminal group, at different temperatures during electric-field-induced switching between the two surface-stabilized states by use of a time-resolved Fourier-transform infrared technique. From polarized infrared spectra under static dc electric fields, details of mutual arrangement of different molecular segments in the Sm-${C}^{*}$ phase have been obtained. Contrary to the usual expectations, the average alkyl chain axis does not coincide with the mesogen axis and is less tilted with respect to the layer normal than the mesogen. On the other hand, motion of the carbonyl groups is found to be strongly hindered and the distribution function for the $\mathrm{C}\mathrm{=}\mathrm{=}\mathrm{O}$ bonds is not cylindrically symmetric with respect to the long molecular axis. Time-resolved infrared measurements at different temperatures and voltages have revealed that, on switching the polarity of the electric field, the hydrogen-bonded $\mathrm{C}\mathrm{=}\mathrm{=}\mathrm{O}$ group moves with the mesogen which reaches equilibrium orientations at a faster rate compared to the alkyl chain at the temperatures and voltages employed in this study.

Dynamical Behavior of Surface-Stabilized States of Ferroelectric Liquid Crystals in Electric Field Studied by Time-Resolved FT-IR Spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDynamical Behavior of Surface-Stabilized States of Ferroelectric Liquid Crystals in Electric Field Studied by Time-Resolved FT-IR SpectroscopyMiroslaw A. Czarnecki, Norihisa Katayama, Masahiro Satoh, Tetsuya Watanabe, and Yukihiro OzakiCite this: J. Phys. Chem. 1995, 99, 38, 14101–14107Publication Date (Print):September 1, 1995Publication History Published online1 May 2002Published inissue 1 September 1995https://doi.org/10.1021/j100038a049RIGHTS & PERMISSIONSArticle Views69Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (617 KB) Get e-Alerts

Vibrational Studies on the Dynamics of Switching between the Surface-Stabilized States of a Ferroelectric Liquid Crystal by Asynchronous Time-Resolved Fourier Transform Infrared Spectroscopy

Time-resolved polarized infrared spectra have been observed from a ferroelectric liquid crystal (chiral smectic C phase) consisting of a chiral dopant and a nonchiral smectic base during the course of switching between the surface-stabilized states. A primary fast process and the subsequent slow process have been observed for all infrared bands. The chiral dopant and smectic base molecules move simultaneously. The observed time behavior of the infrared bands can be mostly explained by the reorientation of a rigid molecule whose rotational motion around the molecular long axis is almost free. The static intensities and the time behavior of the ester and keto C=O stretching bands do not seem to be consistent with the simple view on the role of these groups.

Structures and responses of ferroelectric liquid crystals in the surface-stabilized geometry

We present experimental and theoretical studies of the structures and transitions of the molecular orientation field of a smectic C* liquid crystal in the surface-stabilized geometry. The experimental results show that structures having from two to six stable orientation configurations are possible. The optical properties of these states, electric-field-induced sequences of transitions between them, and defects which appear in them are analyzed to infer the states' structure. These studies show that in the surface-stabilized geometry: (1) the smectic layers can be tilted relative to the bounding plates; (2) the boundary conditions can stabilize molecular orientations tilted relative to the bounding plates. Evidence is also presented for the coupling of smectic layer deformation and the director field.The theoretical results show that the simplest models of the interactions of a ferroelectric liquid crystal with bounding surfaces and applied electric fields explain a variety of phenomena. First, a simple, low-order surface interaction preferring molecular orientations parallel to bounding surfaces produces an unwinding of the intrinsic helix when the bounding plates are spaced closely enough. The resulting unwound liquid crystal exhibits two states with the ferroelectric polarization uniformly perpendicular to the bounding plates. A third state with the polarization splayed across the sample thickness is also possible, and is stabilized either by interactions that favor a specific orientation of the polarization to the surface normal or by an intrinsic elastic distortion complementary to the one that produces the helix. The addition of the simplest coupling of the ferroelectric dipoles to an applied electric field predicts first-order transitions between the various surface-stabilized states. The transitions proceed by the motion of domain walls, whose structure may be calculated in the most simple instance. In the absence of predicted domain wall structures, dimensional arguments provide scaling behaviors for the dynamics of domain wall motion that agree with experiment.