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Two soluble polyimides containing chalcone derivatives in the main chains were successfully prepared using the Mitsunobu reaction at room temperature, reacting diols with diimides. With this reaction procedure the high temperature imidization step normally needed for the synthesis of polyimides is avoided and the polymers can be used for temperature sensitive applications. The main chain polyimides were characterized with FT-IR, NMR and DSC and the extent of the photoreaction was measured with FT-IR and UV-vis spectroscopy. Isobestic points were observed in the absorption spectral changes at the early stage of UV irradiation as a result of a single photochemical process. Further photoirradiation is accompanied by deviation from the isobestic points, implying that another photochemical process has started. With FT-IR investigations it was concluded that photodimerization is the process occurring at low UV exposure doses and that trans-cis isomerization is starting simultaneously at higher doses. The optical anisotropic properties were investigated upon exposure of the polymers as thin films to linearly polarized UV (LPUV) light of different doses. Selected crosslinking in the parallel direction relative to the direction of the LPUV light and subsequent optical anisotropy in the film were achieved.

A series of novel bifunctionalized photochromic monomers were synthesized, focusing on those with polymerizable acrylic/methacrylic groups attached to both ends of an azobenzene core via flexible spacers. The phase behaviour of the monomers was investigated using DSC, polarizing optical microscopy and X‐ray diffraction. The change in UV‐vis absorbance of the monomers under illumination with non‐polarized/polarized UV light was studied for both solutions and thin films; also studied was its relaxation in the dark. On illumination with LPUV light, in‐plane reorientation of the molecules normal to the polarization of the exciting UV light, and aggregation of the molecules in the films, were found.

The kinetics of phase transformations in a chiral siloxane polymer has been studied with an Avrami analysis of the differential scanning calorimetry data. Ferroelectric switching has been measured as a function of the driving voltage and temperature. The evolution of the switching at a constant temperature has been studied within the temperature range of the kinetically governed smectic C*/smectic B phase transition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1779–1784, 2005

In this work, we have used photoelectron spectroscopy and time of flight secondary ion mass spectroscopy to study the conversion process of dichroic self organized molecule films formed from a lyotropic liquid crystal solution with BaCl2. This conversion process changes the material from water soluble to water insoluble by a cross linking polymerization. Our results show that the conversion is complete and that the remaining ammonium and chloride ions are completely removed after the conversion. The ToF-SIMS measurements show a constant amount of barium through the crystal film indicating a complete conversation through the film.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Lev M. Blinov, Mikhail V. Kozlovsky, Masanori Ozaki, Kent Skarp, andKatsumi Yoshino, Journal of Applied Physics 84, 3860 (1998) and may be found at https://doi.org/10.1063/1.368565., Photochromism has been studied for two comb-like liquid-crystalline copolymers (I) and (II) containing azobenzene chromophores in their side chains. In a smectic glass phase of both copolymers, upon short-time irradiation by UV light, long-living cis isomers are observed. Both copolymers manifest the photoinduced anisotropy, the physical mechanisms of which seem to be quite different. In spin-coated films of polymer (II), the origin of the anisotropy is a strong stable dichroism, which is due to an enrichment and depletion of the chosen angular direction, correspondingly, with trans and cis isomers of the azobenzene chromophores. Polymer (I) manifests no dichroism at all, and its induced optical anisotropy may be accounted for by a rather slow chromophore reorientation. In copolymer (II) a considerable reorientation of the mesogenic groups also occurs as a secondary phenomenon at the stage of the cis isomer formation only. This observation shed more light on the general process of the light-induced molecular reorientation in polymers, liquid crystals, and Langmuir–Blodgett films, which is of great importance for holographic information recording.

The syntheses of chiral liquid crystalline side chain polysiloxanes with lateral nitro substituents in the mesogenic core are described. The influence of the substituents and substituent positions on phase behaviour and electro-optical properties are investigated and compared. The lateral nitro groups strongly affect the phase behaviour of the side chain precursors as well as the liquid crystalline polymers. Properties in smectic A and C* phases are discussed with respect to substituent position. One side chain precursor exhibits very large spontaneous polarization of ∼700 nC cm–2 .

The synthesis of a series of side-chain liquid crystalline siloxane copolymers is reported, and comparative studies of physical properties of members of the series with different side-chain length have been attempted. All the five members show smectic C∗ and smectic A phases. Measurements of ferroelectricity, relaxation times and electroclinic properties have been carried out, aiming at finding structure-property relationships for the longer side-chain members. A relationship between electroclinic coefficient and side-chain length was also found.

Well-aligned thin films of polymeric ferroelectric liquid crystal have been prepared by means of a spin-coating method. Several types of electro-optical effects and the optical second-harmonic generation in these films have been measured. The characteristics of spin-coated polymeric ferroelectric liquid crystal film with a free surface have been discussed in comparison with those of conventional sandwich cells. The influences of the glass plates on the PFLC are also discussed.

The synthesis of a series of side-chain liquid crystalline siloxane copolymers is reported, and comparative studies of physical properties of members with different side-chain length have been attempted. Measurements of ferroelectricity and relaxation times aimed at studying structure-property relationships for the longer side-chain members. It was found that the stability of the chiral smectic C phase decreases with decreasing length of the terminal alkyl ester.

The synthetic route to a chiral side chain copolymer exhibiting broad smectic phases is described. The copolymer shows a smectic C∗ phase from below room temperature up to 105°C. Ferroelectric properties of this copolymer are reported as well as results showing electroclinic switching. The pyroelectric effect and the dielectric behaviour of the copolymer are also demonstrated.

The second-order nonlinear optical properties of ferroelectric liquid crystalline polymer have been studied. Angular phase-matched Second-Harmonic Generation (SHG) is observed in the chiral smectic C (SmC*) phase of siloxane copolymer with chiral mesogen in the side chain. The effective nonlinear optical coefficient deff under the phase-matching condition is determined. The intense SHG is observed even in the crystalline phase by cooling down from the SmC* phase under the electric field. The effective coefficient of SHG in the crystalline phase is more than ten times larger than that of the phase-matched SHG in the SmC* phase. The enhancement of SHG in the crystalline phase is observed only in a homeotropically aligned cell and maintained even in the non-biased state for at least several days. The angular dependence of the SHG in the crystalline phase is confirmed.

By using dielectric relaxation spectroscopy it has been observed that while the molecular reorientation around the long axis in the smectic B-crystal phase is active, the rotation around the short axis is frozen. Thus we show that the molecular dynamics of the liquid crystal phase designated as smectic B-crystal is intermediate between that of crystals and that of conventional smectic phases (like smectic A, B, C etc.). The temperature dependence of the complex dielectric permittivity e* (e* = e′ - je″) has been studied in the frequency regime 10Hz to 1 GHz on a binary mixture of a chiral epoxy compound and a non-chiral compound. The measurements were carried out on the isotropic phase (110–102°C), the narrow range cholesteric phase, the chiral smectic A phase (98–59°C), a chiral smectic B phase, so far classified as smectic B-crystal (59–33°C), and a crystal phase (below 33°C). The dielectric measurements were made for planar and homeotropic orientations. From the analysis of the dielectric abso...

A fluorinated chiral side-chain polysiloxane with very large tilt angles in the ferroelectric phase was studied. The optical response on an applied square wave could be analyzed in detail by an optical/electrical model for the cell, only assuming book-shelf geometry and negligible dielectric director torques. The model yields molecular tilt angles to a high accuracy by a curve-fitting procedure. Comparisons to other mesogenic substituents were also made, and indications were found that small (monatomic) substituents favor large tilt angles.

A new chiral side-chain polymer was prepared by hydrosilylation of a dimethylsilane-methyl-hydrosilane copolymer. The chiral group of the mesogenic side-chain was (+)2-chloro-3-(3-nitro-4-hydroxyphenyl)propionic acid butyl ester while the main part of the aromatic nucleus consisted of 4′-hydroxybiphenyl-4-carboxylic acid. Phase behaviour was studied by DSC and polarizing microscopy, and correlated with dielectric measurements. Alignment properties and ferroelectricity were studied in cells with surface-induced alignment and in shear cells. The polymer exhibits chiral C-and A-phases. The spontaneous polarization is 130 nC/cm2 at 60°C and the polymer shows ferroelectric switching at room temperature.

Switching behaviors of ferroelectric polymer liquid crystal (FPLC), poly(2-methylbutyl 4′-(10-acryloyloxydecyloxy) biphenyl-4-carboxylate), were successfully modulated reversibly by photochemical reaction of photochromic guests (azobenzene derivatives) doped in the FPLC. Chiral azobenzene (ABchi) possessing the same structure as the host FPLC at the chiral part was found to enhance the transmitted light intensity through a pair of crossed polarizers on the trans to cis photoisomerization, while the other achiral azobenzene derivatives reduced the transmitted light intensity on photoisomerization. This difference in photoresponsiveness has been attributed to the different effect of the trans-cis photoisomerization on the host mesogens, the change in molecular shape for the achiral azobenzenes and the change in dipole moment for ABchi.

Electro-optic and polarization reversal measurements were performed on a side-chain polymer exhibiting a chiral smectic phase. Based on the observed electro-optic and current responses, we discuss the possibility of an antiferroelectric structure in the polymer. In order to establish a model for the observed behavior, a detailed comparison with the properties of the low molar mass antiferroelectric substance MHPOBC was made. The birefringence modulation in the chiral smectic polymer, originating from the field-induced antiferroelectric-to-ferroelectric transition, is analyzed for the case of a randomly oriented sample. The result shows that the coincidence of birefringence modulation and polarization current peaks is strong evidence for the existence of antiferroelectric order in the smectic layers. Such coincidence was observed both for MHPOBC and the chiral side-chain polyacrylate.

Electric field induced mechanical vibrations are investigated in an SSFLC cell using a piezoelectric accelerometer. It is shown that vibrations exist both normal and parallel to the confining substrates. Typical waveforms and frequency spectra of the acceleration signal are presented. Dependences of the vibration amplitude on the frequency and amplitude of the applied voltage as well as on the temperature are analysed.

The electro-optic response in the C* phase of a side-chain polyacrylate and its monomer has been found to exhibit an anomalous dependence on temperature. The apparent tilt angle undergoes a sign re...

The electroclinic effect in the chiral smectic A phase has been investigated in side-chain polysiloxane liquid crystals. The amplitude of the electro-optical response in the smectic C* phase was studied, and the tilt angle determined by studying the response at very low frequency. The electroclinic effect shows the same general behaviour as in low-molecular weight systems, with a divergent electroclinic coefficient near Tc and a field-independent response time of about 10 microseconds a few degrees from Tc

The complex dielectric permittivity of the soft mode in the A * phase and the Goldstone mode in the C* phase has been studied as a function of temperature and frequency. Using simple evaluation models, the soft mode and the Goldstone mode rotational viscosities have been determined in the A * and C* phases respectively. The models enabled us to calculate values of the elastic constant of the Goldstone mode. A correction of the usually measured dielectric anisotropy in the C* phase is also presented.

A side-chain polymer exhibiting a chiral smectic phase was investigated. Due to its anomalous current and electrooptic responses, we discuss the possibility of antiferroelectric order in the polymer, and compare its behaviour with a low-molar mass antiferroelectric substance. In particular, we study the birefringence modulation resulting from the field induced antiferroelectric-to-ferroelectric transition, and determine the induced polarization by the field reversal method.

In the SmC* phase, 22.5° tilt materials are optimum for cells operating in the birefringent mode (under idealized bookshelf conditions), while for SmA 11.25° at present is of special interest, since it makes it possible to induce a full 90° rotation of incoming plane-polarized light using a double-cell, or even a single cell in reflective mode. We present one of the first practical A mixtures yielding 11.25° tilt at room temperature and at moderate field strengths, at the same time being easily aligned and stable. The mixtures presented are ideally suited for use in continuous grey-scale double cells, in reflective single cells and, eventually in combination with semiconductive elements, in applications such as SLM:s (Spatial Light Modulators).

Electro-optic modulators can be used as choppers, function generators or optical power controllers. The materials dealt with are PLZT ceramics and nematic LC compared with smectic A and C LCs. PLZT is fast in the scatter mode, but its contrast is poor. The NCAP nematic LC structure has a high contrast, but is slow. Both PLZT ceramics and smectic phases can achieve microsecond switching times in the polarization mode. The achieved contrast is high with PLZT, while with LCs it depends on the switching speed. A modulator based on polarization has a complicated structure when non-polarized light is used.

Different contributions to the dielectric permittivity in ferroelectric liquid crystals are discussed, with emphasis on the soft mode and the Goldstone mode and their location in the dielectric spectrum. Experimentally, the complex dielectric permittivity has been studied as a function of temperature and frequency in the range 5 Hz - 13 MHz for three different ferroelectric liquid crystal materials. The main problems encountered in dielectric measurements at low and high frequency are discussed in some detail. The soft mode dielectric behaviour has been studied as a function of temperature, frequency and bias electric field. The applicability of the Curie-Weiss law for the soft mode dielectric contribution in the A* phase was analyzed. In the C* phase the temperature dependence of the dielectric contribution of the Goldstone mode has been measured. By applying a bias electric field, we have been able to study the soft mode dielectric behaviour also deep into the C* phase. In the A* and C* phases ...

In a chiral smectic material having an N* to C* transition, the smectic state can be induced by an applied electric field several degrees in the cholesteric state above TC. At a certain critical field strength the smectic layers grow out along one of two directions determined by the tilt angle of the C* material and of the sign of its ferroelectric response and thus selected by the sign of the applied field.

Measurements of the relevant anisotropic part of the dielectric constant for ferroelectric liquid crystals allows a calculation of the dielectric torque acting upon the director during addressing conditions in a matrix‐multiplexed device. The frequency dependence of the dielectric anisotropy is presented for different commercially available ferroelectric liquid‐crystal materials in the range 103–106 Hz. The field dependence of the switching time has been measured for one of the materials in order to determine the field at the minimum value. The ratio between this field and the field at which switching ceases has been determined and found to be in good agreement with the theoretically calculated value. The results enable us to consider the torque balance as a function of field and frequency, and thereby identify appropriate driving conditions.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Shoji Okazaki, Sadahito Uto, Masanori Ozaki, Katsumi Yoshino, Kent Skarp, and Bertil Helgee, Appl. Phys. Lett. 71, 3373 (1997) and may be found at https://doi.org/10.1063/1.120399., We have proposed an electro-optic effect in dichroic-dye-doped polymer ferroelectric liquid crystal thin films prepared by a spin-coating technique. A high-quality homeotropically aligned film has been realized. Guest-host type electro-optic switching is confirmed in the dye-doped film, and basic properties such as electric field dependence of the response time are studied.

Application of both the conservative rapid scan and a novel step-scan Fourier-transform spectroscopy enables us to follow the intra- and intermolecular motion of ferroelectric liquid crystalline polymers and elastomers during electro- optical switching on a time scale from seconds down to microseconds. It has been detected that although all molecular parts move synchronously in course of the switching, the amplitude of such motions is different. The obtained results are discussed in terms of the role played by the molecular segments during the process of reorientation.

A method is presented allowing the determination of the three principal values (∈ 1 ,∈ 2 ,∈ 3 ) of the dielectric tensor for a chiral smectic-C liquid crystal in the case that the material has an uncompensated helix. Hence it is applicable for essentially all single substances and therefore suitable for developing correlations between molecular structure and dielectric properties of the smectic-C, materials. The method requires two samples and uses three different measurement geometries

The static dielectric permittivity of the smectic-${\mathit{B}}^{\mathrm{*}}$ phase is studied as a function of temperature. The field-induced tilt angle, which is due to the electroclinic response, is measured as a function of temperature. The investigated phase precedes the chiral smectic-${\mathit{A}}^{\mathrm{*}}$ phase upon heating. In the ${\mathit{A}}^{\mathrm{*}}$ phase, the soft-mode dielectric contribution increases with decreasing temperature but does not diverge at the transition, a behavior similar to that of a first-order phase transition. Below the ${\mathit{A}}^{\mathrm{*}\mathrm{\ensuremath{-}}}$${\mathit{B}}^{\mathrm{*}}$ transition temperature ${\mathit{T}}_{\mathit{C}}$, the dielectric permittivity shows a sharp drop to a value considerably lower than that of the adjacent ${\mathit{A}}^{\mathrm{*}}$ phase. On further cooling one would expect a monotonic decrease of the soft-mode contribution. However, in this compound, at a certain temperature ${\mathit{T}}_{\mathrm{rev}}$, in the ${\mathit{B}}^{\mathrm{*}}$ phase, the dielectric permittivity starts to increase again with decreasing temperature. This anomaly in the soft-mode dielectric response is attributed to a change of sign in the electroclinic coefficient, which has been observed by an electro-optic experiment. An attempt to fit the measured dielectric permittivity to a modified expression for the dielectric function that contains a temperature-dependent coupling coefficient is presented.

We introduce a method for determination of the optical retardation, its wavelength dispersion, the cell twist angle, and the orientation of the input director in a reflective liquid crystal (LC) ce ...

In this paper we have studied inkjet printing as an alternative for coating of photo-polymerizable polymer (LPP) as alignment layers in LCD's. Film properties such as boundary condition, film thickness and surface topography are investigated, and compared with those of spin-coated LPP films. In addition, inkjet printing parameters are studied and optimized.

We present the system MePaLC for characterization of empty and filled transmissive and reflective LC cells in a production line. Cell gap and twist angle are determined from spectroscopic measurements in real time. The measurements do not require knowledge of an alignment direction.

We study optical properties of bistable reflective and transflective direct view ferroelectric liquid crystal displays (FLCDs). Single and double polarizer FLCDs with and without a retardation film are considered. Maximal contrast ratio versus optical retardation of liquid crystal layer for different configurations of FLCDs is calculated. Advantages and disadvantages of each configuration are discussed.

We propose several new methods for measuring cell gap of filled reflective LC cells on plastic substrates. Cases when plastic is anisotropic, and the LC cell consists of either one or two internal polarizers are considered. Proposed methods are well suited for both reflective and transmissive LC cells.

In this work we have studied the stabilization process with BaCl2 of Optiva Inc.'s Thin Crystal Film polarizers with photoelectron spectroscopy and time of flight secondary ion mass spectroscopy. Our results show that the conversion is complete and that the remaining ions are almost completely removed after the cleaning.

Anchoring Energy Control and Bistable Surface Switching Based on Photo-Alignment Technology

Using a twisted nematic liquid crystal as an example, this paper discusses the use of the Jones matrix to find the parameters of a light wave propagating in an inhomogeneous anisotropic medium, which is represented for the numerical calculations by a sequence of thin homogeneous layers. The accuracy of the result is analyzed as a function of the parameters of the medium and the number of layers into which it is broken up. A criterion is proposed for finding the optimum number of layers.

Optical modes for the surface-controlled direct-view single-polarizer reflective BTN (bistable twisted nematic) LCD (liquid-crystal display) are derived with the Jones matrix method. The modes show excellent brightness and high contrast ratio. By use of a quarter-wave retardation film in the optical configuration, the contrast can be increased.

Optical modes for the direct view single-polarizer reflective bistable nematic display are derived using Jones matrix method. Both theoretical and experimental results show that these modes possess excellent brightness, high contrast ratio and wide viewing angles. Bistable switching realized by anchor breaking on a photosensitive polymer is demonstrated.

Second-harmonic generation (SHG) of ferroelectric liquid crystal (FLC) has been studied in the smectic A (Sm A) phase in 4'-(1-butoxycarbonyl-1-ethoxy)-3'-nitrophenyl 4-[4-(ω-alkenyloxy)phenyl]benzoate (1BC1ENPAPB) with large electroclinic (EC) effect and a large spontaneous polarization. Type I phase-matching has been observed in the angular dependence of SHG intensity in the Sm A phase. SHG intensity caused by the EC effect is proportional to the square of applied electric field, and it has been found that the effective optical coefficient is proportional to electric field.

Using dielectric relaxation spectroscopy, the soft mode rotational viscosity has been determined in the smectic A* phase of a ferroelectric liquid crystal polymer. The dielectric strength and relaxation frequency of the soft mode have been measured in the smectic A* and C* phases in the presence of a bias electric field. The experimental results have been discussed in terms of the Landau free energy expansion of the smectic A* to C* phase transition. The main problems encountered in dielectric measurements in the frequency range 10 Hz to 10 MHz are explained in some detail. It is found that a bias electric field enhances the measurements resolution especially in polymeric system where the conductivity, in this case, is higher than in the low molecular weight compounds.

Well-aligned thin films of polymeric ferroelectric liquid crystal have been prepared by means of a spin-coating method. Several types of electrooptical effects and the optical second-harmonic generation in these films have been measured. The characteristics of their effects in spin-coated polymeric ferroelectric liquid crystal film with a free surface have been discussed in comparison with those of conventional sandwich cells.

The second-order nonlinear optical properties of ferroelectric liquid crystalline polymer have been studied. Angular phase-matched second-harmonic generation (SHG) is observed in the chiral smectic C phase of siloxane copolymer with chiral mesogen in the side chain. The effective nonlinear optical coefficient d eff under the phase-matching condition is determined.

Measurements of the soft-mode and electroclinic behavior in the smectic A*-phase of a compound with very high spontaneous polarization (about 5 mC/m2 (0.5 µC/cm2) in the smectic C*-phase) are presented. It is found that for large induced tilt angles, one observes a strip texture giving rise to a strong characteristic light scattering. Once created this periodic stripe pattern remains even when the field is turned off. Furthermore, the electric field-induced modulation of the pattern allows scattering intensity modulation, resulting in anomalous electroclinic behavior.

The SmCα * phase which was discovered between SmA and SmC* in 4-(1-metylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) has been studied by means of electric-field-induced tilt angle measurements and conoscopic observation. The induced tilt angle increases not smoothly but stepwise in SmCα * and its neighboring SmA temperature ranges, suggesting successive structural changes, namely, Devil's staircase. According to the conoscopic figures, the existence of the ferrielectric orientation was confirmed. Devil's staircase observed as a result of changing field strength was discussed in comparison with that induced by changing temperature.

A nematic liquid crystal, pentyl-cyano-biphenyl (5CB) is studied in two different flow situations: Poiseuille flow and torsional shear flow, in both cases with and without the simultaneous application of an electric field. The Poiseuille flow set-up gives an accurate determination of the Miesowicz viscosity ηc and a less precise estimation of ηb. With ηc known it is possible to separately determine the elastic constants K 11 and K 33 and the viscous coefficients α2, α3, and thereby γ1, γ2 from the torsional shear flow experiment. Using the data we have also been able to calculate the actual director profile in the liquid crystal as a function of applied shear and electric field. Curves are given of K 11, K 33, K 11/K 33, α2, α3, γ1, γ2, γ1/γ2, ηb and ηc for 5CB as a function of temperature through the whole nematic range from 22.0 °C to 35.1 °C. After the completion of our manuscript we have noticed the recent article by J. Wahl, Z. Natur-forsch. 34a, 818 (1979). Wahl discusses shear flow in the ...

The last decade has seen a tremendous growth in the research and development activities in the area of ferroelectric liquid crystals. The field was opened up by the work of Meyer in 1974, and has now grown rapidly into one of the major research areas in liquid crystal science. The emphasis of the earlier work was on basic material characterization and phenomenology. Only very few liquid crystalline compounds exhibiting a ferroelectric phase were known at that time, and furthermore these Schiff-base organic compounds were chemically and thermally unstable and presented their ferroelectricity only at elevated temperatures. After the work by Clark and Lagerwall in 1980 on a fast electro-optic effect in a surface-stabilized ferroelectric liquid crystal (SSFLC) structure, both basic and applied research have accelerated, and today a great number of papers deal with development and characterization of ferroelectric compounds and mixtures and various aspects of device physics and manufacturing. It is of...