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Using the concept of the Preisach model for a ferroelectric capacitor, we have analyzed the behavior of frequency (f)-dependent polarization reversal in surface-stabilized ferroelectric liquid crystals (SSFLCs) under an external field. At a fixed temperature, the peak height of the capacitance-voltage hysteresis loop is found to be decreasing with an increasing number of polarization cycles up to a certain typical value of frequency (e.g., fc) being different for different ferroelectric liquid crystals (FLCs). We also observed an inversion (a well instead of a peak) in the hysteresis loops appearing above a typical higher frequency denoted fi. The values of capacitance of the FLC capacitors became almost independent of the voltage for the frequencies between fc and fi. The frequency dependence of dielectric biaxiality in the SSFLCs is directly attributed to the appearance of such behavior. [ABSTRACT FROM AUTHOR]

Frequency (10 Hz-1 MHz) and temperature (22- 80 °C) dependent dielectric constant (both real and imaginary) of a ferroelectric liquid crystal ZLI-4851 film (21 μm thickness) showing a second order SmC*-SmA phase transition around 63.2 °C have been reported. The variation of dielectric constant as a function of temperature follows the generalized Landau theoretical model. Thermal variation of the complex dielectric constant has also been measured with different bias field strengths (0-20 V) for both the SmC* and the SmA phases. Interestingly, soft mode is observed in the SmC* phase only by applying a bias field perpendicular to the helix axis. Due to the application of the bias field, the SmC* phase loses stability of the helical structure, which is considered to be responsible for the appearance of soft mode in the present ferroelectric liquid crystal system. [ABSTRACT FROM AUTHOR]

Detail dielectric measurements were carried out on two different liquid crystalline (LC) samples formed by bent core (BC) molecules, showing B1 and B2 phases in the temperature range 100–150°C. The thermal variation of real part of dielectric permittivity (ϵ′) represents a tiny dip only in the saturated B1 phase which might arising from the dipole orientation disorder due to the inherent phase instability. The experimental data have been used to determine different relaxation parameters. Evidently only one relaxation mode has been detected in the dielectric relaxation spectrum for both phases, which is attributed to the long axis molecular rotation process. [ABSTRACT FROM AUTHOR]

The temperature- and electric field-dependent dielectric relaxation and polarisation of a new chiral swallow tailed antiferroelectric liquid crystal, i.e. 1-ethylpropyl (S)-2-{6-[4-(4'-decyloxyphenyl)benzoyloxy]-2-naphthyl}propionate (abbreviated as EP10PBNP), were investigated. The electric field-induced dielectric loss spectra of EP10PBNP revealed electroclinic and anomalous dielectric behaviour in the chiral smectic A (SmA*)-chiral antiferroelectric smectic C (SmCA*) pre-transitional regime. From an analysis of thermal hysteresis of the dielectric constant, electric field-induced polarisation and dielectric loss spectra, the appearance of a ferrielectric-like mesophase is observed followed by an unstable SmCA* phase in the SmA*-SmCA* pre-transitional regime. [ABSTRACT FROM AUTHOR]

We report the effects of the rotational motion of the director around the chiral smectic cone on the dielectric relaxation and polarization reversal process in a surface stabilized ferroelectric liquid crystal cell. Measurement was made at a fixed temperature (40°C), far below the SmA–SmC* transition temperature (62°C) of the ferroelectric liquid crystal material (CS‐1027). The amount of switchable polarization (ASP), during the polarization reversal, is found to decrease with increasing frequency of the applied signal until a typical value of frequency (fl) is reached. This behaviour is considered to be due to the time‐dependent rotational motion of the director. The ASP value was calculated by measuring polarization–voltage (P–V) and capacitance–voltage (C–V) hysteresis loops as a function of the applied signal frequency and then following the Preisach model for the ferroelectric capacitor. The peaks of the C–V hysteresis loop, which correspond to the reversal of polarization, are gradually converted into wells for frequencies greater than a critical value (fi). The hysteresis loops shows ‘frustrated’ behaviour for frequencies between fl and fi. The inversion of the C–V hysteresis loop at higher frequencies (>fi) is attributed to the inversion of the dielectric biaxiality and the corresponding ‘frustrated’ behaviour arising due to competition between the dielectric and ferroelectric torques. A suitable equivalent circuit can be designed to represent the frequency‐dependent C–V and magnitude of admittance (conductance) –voltage (G–V) hysteresis behavior. [ABSTRACT FROM AUTHOR]

The temperature (25–120°C) and frequency (10?Hz–1?MHz) dependent dielectric relaxation spectra of different ferroelectric liquid crystals are found to show interesting scaling behaviour. Considering relaxation frequency (?max) as the scaling frequency, the imaginary part of the dielectric constants (??) of the ferroelectric liquid crystals are found to follow the universal scaling formula, i.e. when (??/??max) is plotted as a function of (f/?max), the scaling behaviour of a ferroelectric liquid crystal can be represented by a single master curve irrespective of film thickness, bias field and temperature; ??max is the maximum value of ?? at the frequency ?max and m is a parameter ~1. [ABSTRACT FROM AUTHOR]

We report the dielectric relaxation behaviour in the antiferroelectric SmC A * and ferrielectric SmC γ * phases of the antiferroelectric liquid crystal 4-[5-(4-octloxyphenyl)-2-pyrimidinyl]phenyl 4,4,4-trifluoro-3-(methoxyphenyl)butanoate which shows an antiferroelectric transition at around 88±0.1°C. In the SmC A * phase, two dielectric relaxation modes have been found, namely the usual antiferroelectric Goldstone mode and another arising from molecular rotation around its short axis. In the SmC γ * phase, one dielectric relaxation mode has been observed due to the ferrielectric Goldstone mode. Dielectric increments and relaxation frequencies of the antiferroelectric and ferrielectric phases are estimated from the fits of the Cole-Cole function of the dielectric spectrum. The dependence of the bias field in the ferrielectric phase is also discussed. [ABSTRACT FROM AUTHOR]

Anomalous dielectric relaxation behaviour is observed in the ferroelectric liquid crystalline polymer (viz. ferroelectric copolysiloxane (R)-COPS 11-10) around the ferroelectric SmC* to paraelectric SmA phase transition. Measurements have been performed on sample of thickness ~10 mum in indium-tin-oxide coated cell in the frequency range 10 Hz to 13 MHz. With increase of temperature, a gradual shift of the soft mode frequency towards the higher frequency side was observed, while a decrease in the relaxation strength was seen with the corresponding increase in temperature. The shifts of the soft modes in the SmC* and SmA phase are considered to be due to change in the viscosity of the polymer, as an increase in viscosity increases fluctuations of the coupling between the dipoles in the network even far from the paraelectric-ferroelectric phase transition. Application of a bias field causes a shift of the critical frequency towards the higher frequency side, while the dielectric strength (Δε) decreases under the bias field. The Cole-Cole fitting parameters obtained from the best fit of the dielectric constant data are found to be consistent with other similar materials. Another relaxation mode (molecular mode) was also observed which comes into play in both the smectic phases (SmC* and SmA) and contributes to the dielectric permittivity. [ABSTRACT FROM AUTHOR]

The hysteresis areas for the saturated loops of a deformed helix ferroelectric liquid crystal, viz., (S)-4-(2-methyloctanoyl) 4′-biphenyl-4-octyloxybenzoate (MIP0806) have been studied. The scaling laws ∝f0.24E00.68 and ∝f0.28E00.70 connecting frequency (f) and amplitude (E0) of the applied signal are found to be valid close to and far away from the SmA-SmC* transition temperature (104 °C), respectively. The formation of ferroelectric monodomain in MIP0806 is weakly constrained by surface and dipolar interactions, which might be responsible for the observed small deviation obtained from theoretically predicted scaling laws. [ABSTRACT FROM AUTHOR]

Dielectric permittivity at different polarizing states during field driven ferroelectric-ferroelectric (F-F) transition and the dielectric relaxation spectra in the antiferroelectric liquid crystal (AFLC) phase have been studied to elucidate the interaction processes involved during the transition. The unwinding process of antiferroelectric helix has been found to be governed by the polar coupling between the applied field and the antiferroelectric polarization vector followed by nonpolar interaction with the dielectric anisotropy of the tilted molecules. Frequency dependence of the permittivity-voltage hysteresis behavior observed during the F-F transitions is concluded to be due to different relaxation processes involved in the AFLC phase. [ABSTRACT FROM AUTHOR]

Photosensitivity in ferroelectric liquid crystal (FLC) material has been developed by dispersing Cadmium Sulfide (CdS) nano-particles in FLC (CdS-FLC) host. The nematic (N*) – ferroelectric (SmC*) phase transition temperature for the CdS-FLC sample in absence and presence of white light excitation decreases by 6 and 14°C, respectively, compared to host material due to enhanced disorder. The anomalous behaviour in temperature dependent dielectric permittivity of CdS-FLC sample in presence of white light excitation in N* as well as SmC* phase has been explained on the basis of enhanced free charged density and self assembly of CdS-LC in the phases. [ABSTRACT FROM AUTHOR]

Dielectric permittivity at different polarizing states during field driven ferroelectric-ferroelectric (F-F) transition and the dielectric relaxation spectra in the antiferroelectric liquid crystal (AFLC) phase have been studied to elucidate the interaction processes involved during the transition. The unwinding process of antiferroelectric helix has been found to be governed by the polar coupling between the applied field and the antiferroelectric polarization vector followed by nonpolar interaction with the dielectric anisotropy of the tilted molecules. Frequency dependence of the permittivity-voltage hysteresis behavior observed during the F-F transitions is concluded to be due to different relaxation processes involved in the AFLC phase. [ABSTRACT FROM AUTHOR]

Dielectric relaxation spectra of a liquid crystalline (LC) material showing blue-phase-III (BPIII) for a considerably large temperature regime consisting of T-shaped molecules are investigated. A low frequency relaxation mode is observed in the isotropic phase (I) as well as in BPIII of the investigating material which is attributed to the short axis rotation of the T-shaped molecules. The outcome of the temperature and dc bias field variation of dielectric strength (Δe) and relaxation frequency (vc) in the vicinity of the I-BPIII transition is also discussed. The temperature dependence of vc in BPIII with a minor deviation from Arrhenius activities in the fluctuation-dominated nonlinear region (FDNLR) is found to follow the unusual thermal behavior of the activation energy (EA). The growth of pretransitionai fluctuations is found to be nonlinear in the vicinity of the /-BPIII transition. A moderate growth of transition fluctuation commences from the value of the exponent αef = 0.38/°C, which is obtained by an exponential variation of vc with respect to temperature in BPIII. Observed dynamic phenomenon in the vicinity of the I-BPIII transition regions is explained on the basis of the Landau-de Gennes and Maier-Saupe Theories. [ABSTRACT FROM AUTHOR]