Ferroelectric Liquid Crystalline Polymers Research Articles

The switching process in a ferroelectric liquid crystalline side-chain polymer by time-resolved step-scan FT-IR spectroscopy and 2D correlation analysis

Time-resolved Fourier-transform infrared (FT-IR) spectroscopy and two-dimensional (2D) correlation analysis were used to study the segmental mobility of a ferroelectric liquid-crystalline polymer (FLCP) in the S c * phase. It has been shown that, under the influence of an electric field, only the mesogen reorients together with the terminal group attached to it and a fragment of the spacer. The remaining part of the spacer and the main chain of the FLCP do not participate in the reorientation. The estimated relaxation times for selected bands revealed that, according to the theoretical predictions, the reorientation rate increases with temperature. This effect is due to the decrease of the reorientational viscosity with temperature. However, the temperature does not effect the mechanism of the reorientation on a molecular level. Although the experiment was performed at different voltages we did not observe a field-dependence of the relaxation times.

Dielectric relaxation study of ferroelectric liquid crystalline polymer (LCP1) in the smectic C* and isotropic phases

Dielectric dispersion of a ferroelectric liquid crystalline polymer (LCP1) has been investigated to study the dynamical behavior of the side-chain mesogenic groups. Frequency and temperature dependences of the dielectric constants have been analyzed by fitting the data to a formula with three Debye-type relaxation processes. Temperature dependences of the dielectric strength, relaxation frequency and index β for each of the processes were determined.

Pyroelectric investigations of polarization and charge distributions in sandwich cells containing a ferroelectric liquid crystalline polymer

With the laser intensity modulation method (LIMM), polarization and charge profiles in sandwich cells containing the ferroelectric liquid crystal side group polymer LCP1 have been investigated. In a sample with a thickness larger than the helical pitch, contributions to the polarization profile due to surface anchoring were found. Additional contributions inside the cell occurred. The validity of the results, concerning numerical deviations in the deconvolution process of the pyrospectra, has been tested by simulations. The influence of space charges for measurements with a static external electrical field is discussed, giving contributions to the profile in addition to those arising from polarization.

In Situ Photopolymerization Behavior of a Chiral Liquid-Crystalline Monomer Showing a Ferroelectric Phase

The in situ photopolymerization behavior of a ferroelectric liquid-crystalline (FLC) monomer possessing a chiral moiety is discussed on the basis of molecular alignment in the liquid-crystalline phase. In an early stage of polymerization, the polymerizability of the FLC monomers was highest in the ferroelectric chiral smectic C (SmC*) phase in the absence of an external electric field. The polymerization behavior was found to depend mainly on the molecular alignment in the initial state of polymerization. In contrast, in the late stage of polymerization, the polymerization behavior of the FLC monomers was governed by their diffusion rather than their alignment. This may be due to the change in the phase structure during in situ polymerization. In addition, the alignment of the photopolymerized FLC was evaluated by optical polarizing microscopy. It was found that the application of an electric field to the FLC monomer resulted in the appearance of the immobilized SmC * phase, in which all mesogens of the resulting FLC polymer were aligned in one direction, leading to the formation of a monodomain of LC phase.

Optical Characterization of a Ferroelectric Liquid Crystalline Polymer Studied by Time-Resolved Optical Waveguide Spectroscopy

Te static structures and switching dynamics of side chain ferroelectric liquid crystalline polymer (PSiOFLC) [Si(Me)(R)O] n (R= (CH 2 ) 10 OPhCO 2 PhCO 2 CH 2 CH(Me)(Et)) were investigated by using time-resolved optical waveguide spectroscopy (TROWS). A good alignment of the mesogenic side chains was obtained by a shearing procedure. The liquid crystalline phases of PSiOFLC were characterized by determining the dielectric tensor diagonals of PSiOFLC, in which the contribution of the main chain to the optical anisotropy could be neglected. The PSiOFLC layer in the S A phase could be treated as a uniaxial refractive index ellipsoid which aligned parallel to the substrate plane with bookshelf structure. The PSiOFLC layer in the S C* phase under the large electric field was also considered as a uniaxial ellipsoid model. The transient waveguide mode patterns of PSiOFLC were successfully obtained with a millisecond time resolution. During the reorientation, the smectic layer structure changed from bookshelf to chevron and then back to the bookshelf structure. The slowness of the switching time was attributed to a polymer effect in which the polymer backbones lying in the smectic layer plane act as a hook to restrict the motion of side chains due to the binding of the mesogenic moieties to the polymer backbone, resulting in the increase of viscosity.

Temperature Dependent AFM on Ferroelectric Liquid Crystalline Polymer and Elastomer Films

Ferroelectric liquid crystalline (LC) polymers are studied by temperature dependent atomic force microscopy (AFM). The samples, thin films of homeotropic orientation prepared as freestanding films,...

Synthesis and Characterization of Novel Combined Type Ferroelectric Liquid Crystalline Polymers Having Polyester Main Chains

A novel synthetic route for the preparation of a new class of side chain liquid crystal (LC) polymers with an aromatic polyester main chain utilizing a diacid chloride/diol solution polycodensation is detailed in this report. Mesogenic α,β-diols, (S)-(−)-4-(((methylbutyl)oxy)carbonyl)phenyl 4‘-(((bis(6-hydroxyhexyl)methylsilyl)alkyl)oxy)biphenyl-4-carboxylate, which are composed of a long methylene spacer with a carbon−silicon−carbon linkage at the center and a side chain mesogen connected via the silicon atom, exhibited smectic A (SA) and chiral smectic C (S-C) mesophases. Molecular weights of the LC polymers of the above diols with terephthaloyl chloride and biphenyl-4,4‘-dicarbonyl chloride were found to be in the range 7000−20 000. The polymer having a terephthalic ester moiety and a hexyl spacer was found to be isotropic at room temperature. When the side chain hexyl spacer was replaced by an octyl spacer, the polymer exhibited an enantiotropic room-temperature S*C phase. When a biphenyl moiety was introduced to the main chain, instead of a phenyl group, the polymer isotropization temperature increased, suggesting a strong LC character. In this series, when the side chain spacer was hexyl and octyl, the polymers exhibited LC phases with a fine grain texture, while the polymer with a decyl spacer exhibiting a fan textured S*C phase. The latter polymer was switchable by an external electric field.

Aggregation states and bistable light switching effects in a side chain ferroelectric liquid crystalline polysiloxane

AbstractAggregation states and transient light scattering in the chiral smectic C phase of a ferroelectric liquid crystalline polymer (FLCP) were studied. The smectic phase shows an interlayer spacing of 38–39.5 Å, which is about 1.41 times the length of the side chain mesogenic group. The transient scattering mode obtained by repeated voltage polarity reversal. A reversible transparent‐opaque (light scattering) change was observed in the chiral smectic C state upon application of electric fields with low and high frequencies, respectiely. Both transparent and opaque states were maintained stably even when the electric field was turned off (bistable light swiching). A novel type of electro‐optical effect based on light scattering was obtained for the FLCP in the chiral smectic C state.

Ferroelectric block copolymers

AbstractA block copolymer consisting of polystyrene and a side chain ferroelectric liquid crystalline polymer was synthesized using polymer analogous chemistry on a monodisperse poly(styrene‐b‐isoprene). Composition was adjusted to give lamellar microstructure after addition of the mesogenic side groups. If placed in an LC cell without orientation of domains, no ferroelectric response was observed. After shearing the thin film, presumably due to alignment of lamellae, a bistable ferroelectric switching could be detected.

Segmental orientation and mobility of ferroelectric liquid crystal polymers

IR spectroscopy was used to study the orientation and mobility of different molecular segments in a side chain ferroelectric liquid crystalline polymer (FLCP) in the book-shelf geometry. It was directly shown that the tilt angles for the mesogenic units and the spacers are different. The data obtained allowed us to construct a detailed model of segmental orientation in the SC phase for this FLCP. This model is consistent with the ‘zigzag’ model for tilted smectic phases. The rotational bias of carbonyl bonds is also confirmed and a possible orientation function for the carbonyl group is discussed. Time-resolved step-scan FTIR spectroscopy enabled us to follow the intra- and inter-molecular response of the FLCP to an external electric field with a time resolution of 5 mus. It was detected that mesogenic moiety, spacer and backbone take part in the reorientation process. The time responses of different molecular segments are similar on the time scale of a few hundred microseconds.

Dielectric study of a ferroelectric side-chain liquid crystalline polysiloxane with a broad temperature range of the chiral smectic C phase: 2. Doping effect of a non-linear optically active dye

Dielectric relaxation behaviour of the guest-host mixture of a ferroelectric side chain liquid crystalline polymer (FLCP) and a nonlinear optical (NLO) dye has been investigated with broadband dielectric relaxation spectroscopy. The liquid crystal (LC) phases of these guest-host materials were characterized with the differential scanning calorimeter, optical polarizing microscopy, and X-ray diffractometer. No phase separation is observed when the doping level of the NLO dye is below 10 wt%. The doping of the NLO dye into the FLCP results in the significant increase of the relaxation intensity and frequency of the Goldstone mode in the chiral smectic C phase ( S C ∗ ). Moreover, the NLO dye has high relaxation intensity in the LC phase for such guest-host material. On the other hand, the occurrence of phase separation is observed when the doping level of the NLO dye is 30% by weight. The phase separation results in the reduction of the relaxation intensity for both the Goldstone mode of the FLCP and molecular motion of the NLO dye. The relationship between the thermal dynamic behaviour and the environment around molecules for such NLO active guest-host material was discussed in great detail.

Bistable light scattering effects in a (side chain liquid crystalline polymer)/(low molecular weight liquid crystal) composite and in a ferroelectric liquid crystalline polymer

The electro-optical effects and aggregation states of liquid crystalline polymer (LCP)/ low molecular weight liquid crystal (LC) composite and ferroelectric liquid crystalline copolymer (FLCP) have been investigated. The nematic LCP was observed to be miscible with the nematic LC over wide ranges of concentration and temperature. The binary mixture showed an induced smectic phase in the range of 80/20-20/80 mol%. The electro-optical effects of the LCP/LC composite in an induced smectic phase could be classified into the turbid (light- scattering) and the transparent states upon application of AC and DC electric fields, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal in the chiral smectic C phase of FLCP. The reversible transparent-opaque (light scattering) change was observed in the chiral smectic C state upon application of DC and AC electric fields, respectively. Both transparent and light-scattering states of the LCP/LC composite and the FLCP could be maintained, even after the electric field had been turned off (memory effect). The bistable effects of LCP/LC composite and FLCP are opposite under the same conditions. A novel type of electro-optical effect on light scattering was obtained for liquid crystalline polymer in the smectic states.

Device Applications of Side-Chain Ferroelectric Liquid Crystalline Polymer Films

Side-chain ferroelectric liquid crystalline polymers are currently used in a number of applications, including displays and electrical sensors. Comparisons with existing technologies and materials indicate that relative to ceramics, such polymers have lower figures of merit but offer greater durability in sensor applications.

Dielectric and electro-optical properties of ferroelectric side-chain liquid-crystalline polysiloxanes containing 4′-(2-chloro-3-methylpentanoyloxy)-4-alkanyloxybiphenyl side groups

Abstract A series of ferroelectric liquid-crystalline polymers (FLCPs) with siloxane backbone were synthesized in this study. The dynamics of these polymers was studied by broad-band dielectric spectroscopy (10 −1 to 10 7 Hz). The collective (Goldstone and soft mode) and molecular (α, β, γ, δ relaxation) relaxation processes were observed. These FLCPs exhibited large values of spontaneous polarization (larger than 190 nC cm −2 ), fast switching time (less than 1 ms) and reversible bistable effects in the chiral smectic C (SmC∗) phase.

Synthesis of Ferroelectric Liquid Crystalline Polymers by Ring Opening Polymerization

AbstractThe synthesis of two series of side-chain liquid crystalline polyoxetanes and polyoxiranes containing 4-alkanyloxybiphenyl-4′ -yl (2S,3S)-2-chloro-3-methylvalerate side groups is presented. Differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry reveal smectic mesomorphism for all obtained polymers. Most of the prepared polyoxetanes present smectic A and chiral smectic C phases. The polyoxetane containing tweleve methylene units in the spacer is the only one showing two enantiotropic smectic A and B phases. All of the obtained polyoxiranes display two enantiotropic smectic A and B phases. Although the polyoxetane and polyoxirane backbones are more flexible than the polymethacrylate backbone, side-chain crystallization do not occur in any of the synthesized polymers.

Ferroelectric liquid crystalline side group polymers derived from mesogenic vinyl ether monomers

Abstract Two classes of ferroelectric polymers, polysiloxanes and polyvinyl ethers, have been synthesized, starting from the same mesogenic vinyl ether as precursor. The polysiloxane materials obtained by polymer analogous reaction of vinyl ethers with H-siloxanes exhibit larger ranges of ferroelectric S*C phases than the corresponding polyvinyl ethers. The effect of changing the nature of the link of the terminal chiral end group on the phase behaviour and ferroelectric properties of the new side chain polymers is reported.

Synthesis and electro‐optical properties of some ferroelectric liquid crystalline polymers

AbstractThe synthesis and characterization of several series of ferroelectric side‐chain polymers were presented. Differential scanning calorimetry, optical polarizing microscopy and X‐ray diffraction measurement were used to determine their thermal transitions and analyze their anisotropic textures. The influence of polymer backbones, flexible spacers, mesogenic cores as well as chiral end groups on the mesomorphic properties of the polymers was discussed. Furthermore, the dielectric relaxation properties of the obtained polymers were also evaluated.

The first high polarization ferroelectric main chain liquid crystalline polymers

Abstract The first high polarization ferroelectric main chain liquid crystalline polymers have been synthesized via hydrosilation polyaddition using α, ω-dihydro(tetramethyldisiloxane) and chiral, low molar mass mesogenic compounds bearing at each end an olefinic group. They exhibit broad, chiral smectic C and smectic A mesophases. Aligned samples have been obtained using a combination of surface and mechanical effects, giving opportunities for fully characterizing the electro-optical properties of the polymers. Very high polarizations have been measured: 600 nC cm−2 at room temperature.

Fourier‐transform infrared study of the switching process in a ferroelectric liquid crystalline polymer

AbstractThe implementation of the step‐scan technique on our FT‐IR spectrometer enabled us to follow the electric‐field induced reorientation dynamics of different molecular segments of a ferroelectric liquid crystalline polymer on a sub‐millisecond time scale. It was detected that not only the mesogen but also the spacer and at least part of the backbone take part in the reorientation process.

Dielectric and electro-optical studies of a ferroelectric copolysiloxane.

This paper reports an extensive study of the static (spontaneous polarization, ${\mathit{P}}_{\mathit{s}}$, tilt angle \ensuremath{\theta}, and pitch) and dynamic properties of a ferroelectric liquid-crystalline polymer. It is shown that a ferroelectric liquid-crystalline polymer (diluted polysiloxane) exhibits physical behavior similar to that of a low-molar-mass liquid crystal in terms of contrast ratio, pitch of the helix, and relationship between ${\mathit{P}}_{\mathit{s}}$ and \ensuremath{\theta}. The degenerated collective modes for the director rotation are shown to split into two modes at the Sm-A--Sm-${\mathit{C}}^{\mathrm{*}}$ phase transition temperature using dielectric spectroscopy. Both frequency and the inverse dielectric strength show critical slowing down behavior in the vicinity of the Sm-A--Sm-${\mathit{C}}^{\mathrm{*}}$ phase transition temperature. The dynamical behavior and the relative dependence of the dielectric strength on temperature for the soft mode in Sm-${\mathit{C}}^{\mathrm{*}}$ and Sm-A phase is consistent with the influence of a significant biquadratic coupling compared to its linear coupling between ${\mathit{P}}_{\mathit{s}}$ and \ensuremath{\theta}. The material parameters of the generalized Landau model for the diluted polysiloxane liquid-crystalline polymer have been found by fitting the experimental data to the mean-field theory.