nan Khushboo

Electro-optic, dielectric and optical studies of NiFe2O4-ferroelectric liquid crystal: a soft magnetoelectric material

ABSTRACT In the present study, magnetic nanoparticles (NP, nickel ferrite) in different concentrations into ferroelectric liquid crystal (FLC) mixture have been prepared and studied. The effect of nickel ferrite concentration on the electro-optic, dielectric and optical properties of FLC mixture has been studied and discussed. An improvement in spontaneous polarization, response time in nickel ferrite-FLC-doped samples compared to FLC is observed and explained on the basis of dipole moment and anchoring phenomena. The Goldstone mode (GM) is detected in all samples and follows a Debye-type relaxation behaviour. A twofold increase in relaxation frequency for the doped sample rather than the pure sample has been observed. The band gap was found more or less independent of doping concentration. The activation energy (Ea) also decreases on increasing the doping amount. GRAPHICAL ABSTRACT

Dielectric and electro-optical studies of a nickel-ferrite-nanoparticle- doped ferroelectric liquid crystal mixture

Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ∼200 and ∼500 Hz in an undoped and a doped sample, respectively.

Textural, thermal, optical and electrical properties of Iron nanoparticles dispersed 4′-(Hexyloxy)-4-biphenylcarbonitrile liquid crystal mixture

ABSTRACT In this work, the effect of Iron nanoparticles (Fe NPs) dispersion in 4′-(Hexyloxy)-4-biphenylcarbonitrile (6OCB) nematic liquid crystal properties has been studied. Inclusion of Fe NPs (0.25 wt. %) in 6OCB liquid crystal (LC) on textures, isotropic–nematic transition temperature (TI–N), electro-optical and dielectric properties have been investigated in planar aligned cell. The threshold voltage (Vth) and TI–N decrease after dispersion of Fe NPs. Dielectric spectroscopy in nematic phase show that relaxation frequency (fr) also decreases after dispersion of Fe NPs in 6OCB. The observed relaxation mode is due to the flip-flop motion of LC molecules about their short axis. The band gap and AC conductivity in case of 6OCB-Fe sample increase over pure 6OCB sample. A decrease in activation energy is also noticed. GRAPHICAL ABSTRACT

Effect of polymer concentration on morphology, dielectric and optical properties in a polymer-dispersed ferroelectric liquid crystal

ABSTRACT Photocurable polymer-dispersed ferroelectric liquid crystal were prepared by polymerisation-induced phase separation (PIPS). Morphological behaviour was analysed by polarising optical microscopy (POM) and scanning electron microscopy (SEM). FLC droplet size was found in the range of ~ 2–70 µm and decreases with an increase in polymer content. Relaxation frequency, dielectric strength and ac conductivity were evaluated as a function of polymer concentration and it was concluded that the polymer concentration has a significant effect on these parameters. The energy band gap () increases with polymer concentration and was found in the range of ~ 3.3 eV at higher concentration of polymer. Graphical Abstract

Properties of Ferroelectric Liquid Crystal/Multiwall Carbon Nanotube Doped Composite

Carbon nanotubes-ferroelectric liquid crystal composites have been prepared and studied. Doping of carbon nanotubes into ferroelectric liquid crystal in varying concentration has been investigated in thin cells in the frequency range of 50 Hz–1 MHz. Decrease in the dielectric permittivity and dielectric strength is found with the doping of carbon nanotubes, however ∼32% increase in the relaxation frequency has been observed in higher concentration carbon nanotubes doped ferroelectric liquid crystal composite than pure ferroelectric liquid crystal sample. A decrease in conductivity has also been noticed after doping.

Textural and optical studies of magneto-mesogen material for display applications

ABSTRACT In this work, a magneto-mesogen material has been prepared by nematic liquid crystal (6OCB) and magnetic nanoparticles (Fe). The effect of small amount of Fe doping on textural behaviour and optical responses has been investigated in a planar aligned cell in the nematic phase. The doped sample shows relatively higher transmission intensity than pure 6OCB and decreases a threshold voltage from 1.4 V to 1.0 V. The UV-Vis spectra show that after dispersion the absorbance peak shift from 319 nm to 315 nm. The measured band gap in 6OCB and Fe-6OCB composite was found 3.71 eV and 3.72 eV respectively.

Size-dependent studies in ferromagnetic nanoparticles dispersed ferroelectric liquid crystal mixtures

ABSTRACT In the present study, ferromagnetic nickel nanoparticles (NiNPs) of size (~20 nm, 40 nm) into ferroelectric liquid crystal (FLC) mixture has been dispersed and investigated. Effect of size of NiNPs on the electro-optic, dielectric and optical properties of FLC mixture have been studied and discussed. A minor improvement in spontaneous polarisation, rotational viscosity and faster response time in NiNPs-FLC samples than pure FLC is noticed. Goldstone mode of relaxation frequency ~100 Hz is detected in all samples and follow a Debye type relaxation behaviour. In addition, it is observed that size of NiNPs does not have any remarkable effect on relaxation frequency and dielectric strength. A single absorption peak at 363, 362 Hz is also noticed in pure FLC and NiNPs-FLC samples. GRAPHICAL ABSTRACT

Dielectric and polarization switching studies in nickel nanoparticles dispersed ferroelectric liquid crystal mixtures

ABSTRACT We have investigated the effect of nickel nanoparticles (NiNPs) in a pure ferroelectric liquid crystal (FLC) mixture. Dielectric spectroscopy was done in the frequency range of 20 Hz–10 MHz. Switching time, spontaneous polarisation, rotational viscosity has been measured using field reversal technique in SmC* phase. The spontaneous polarisation increases for NiNPs-FLC sample which may be due to the induced dipole moments around FLC molecules. Response time decreases with temperature and NiNPs dispersion. The relaxation frequency and dielectric strength of observed mode in SmC* phase is also discussed in pure FLC and NiNPs-FLC samples. The relaxation frequency in NiNPs-FLC sample decreases than pure FLC sample and found ∼120 Hz.

Electro-optics of polymer-stabilised blue phase liquid crystal in in-plane switching mode

ABSTRACT In the present work, polymer-stabilised blue phase liquid crystal ***(PS-BPLC) that exhibit the blue phase (BP) in a temperature range of 312.15 K to 298.15 K has been prepared. The textural and electro-optic studies were performed in the BP range using an in-plane switching (IPS) cell. Platelet-type textures of cubic BP having an average domain size of ~12 µm were observed. The on-state voltage increased with increasing the temperature due to reduced value of the Kerr constant. Further, the hysteresis was found to be reduced from 19.2% to 5.1% by operating the PS-BPLC sample cell at an elevated temperature. GRAPHICAL ABSTRACT

Dielectric studies of iron nanoparticles-ferroelectric liquid crystal mixture

Iron nanoparticles doped ferroelectric liquid crystal mixtures have been prepared and studied in thin planar cell. The effect of temperature and frequency on permittivity behavior in SmC* phase has been studied. Permittivity increases with increasing the temperature in SmC* phase and show a reduction near the SmC*-SmA transition temperature. A Goldstone mode is clearly observed at ~100 Hz.