Amit Choudhary

Enhanced electro-optical properties in gold nanoparticles doped ferroelectric liquid crystals

Influential electro-optical and textural properties in the smectic C* phase have been observed using gold nanoparticles (Au NPs) in ferroelectric liquid crystals (FLCs). An application of mere 0.1V brings fivefold increase in optical tilt and doping creates a strong intrinsic field inside the sample generating high tilt and a reproducible observation of memory effect. The lowering of threshold voltage and the enhanced optical contrast is probably due to the interaction of electron wave oscillation in Au NPs with the incident light traversing through the FLC molecules.

Mechanism of homeotropic alignment of ferroelectric liquid crystals doped with ferro-fluid and applications

We report homeotropic (HT) alignment of ferroelectric liquid crystal (FLC) doped with various concentrations of ferro-fluid (FF) without using any type of alignment layer. The FF induced HT alignment of FLC was found to be dependent on the doping concentration as revealed by optical micrographs, contact angle, and dielectric spectroscopy studies. Higher water contact angle of FF doped FLC films with respect to pure FLC film suggests higher surface energy of FF doped FLC than the surface energy of substrate. The physico-chemical mechanism together with steric model successfully explains the HT alignment of the studied FLC on the ITO substrate.

Dielectric relaxation process of a partially unwound helical structure in ferroelectric liquid crystals

The fluctuations of unwound helical structure have been observed in deformed helix ferroelectric liquid crystal (DHFLC) and conventional FLC sample cells. The helix is partially unwound by strong anchoring on the substrates. In such sample cells, the helical decarlization lines are not observed in the texture under crossed polarized microscope. The dielectric spectroscopy is employed to observe the behavior of dielectric relaxation processes in these sample cells. A dielectric relaxation process is observed at a lower frequency than the Goldstone mode processes in DHFLC and FLC, which we call partially unwound helical mode (p-UHM). However, the p-UHM process is not observed in the sample cell in which the helical lines appear. The application of various amplitudes of probing ac voltages on this mode has shown the higher frequency shift, i.e., the larger the amplitude of ac voltage, the higher is the relaxation frequency of p-UHM. At sufficient amplitude of applied probing ac voltage, the p-UHM merges with the Goldstone mode process and is difficult to detect. However, the Goldstone mode relaxation frequency is almost independent of the cell geometry and sample configuration. The electro-optical behavior of the p-UHM has also been confirmed by electro-optical technique. The dielectric relaxation of UHM at a frequency lower than the Goldstone mode is interpreted as the fluctuation of partially unwound helix.

Reminiscence Shown by de Vries Electroclinic Liquid Crystal Material

De Vries as well as conventional ferroelectric liquid crystals have been studied using X-ray, electro-optical, and dielectric spectroscopy to outline the major distinct points of the two. We demonstrate that the second order transition as found in the studied de Vries material is one of the results of the randomization of the molecules pertaining into smectic A (Sm A) phase from Sm C* phase. Experiments show that the material exhibits a reminiscence behavior increasing with the every bias application.

Enormous Change in Tilt Angle and Transition Temperature of Smectic C*–Smectic A Phase in Electroclinic Liquid Crystal Material

Optical and textural studies have been carried out on special class of ferroelectric liquid crystals (FLCs) known as de Vries electroclinic liquid crystals (ELCs) in conjunction with ethanol (C2H5OH). Ethanol shifts the threshold voltage to a low value of 3 V and nearly doubles the optical tilt in the ELC under study. Addition of ethanol shifts the smectic C*–smectic A (Sm C*–Sm A) phase transition temperature remarkably thereby suggesting a strong interaction between ELC and ethanol. The typical randomized structure of de Vries ELCs probably paves way to a possible interaction with ethanol.

Dielectric and electro-optical properties of Mn12-acetate and ferroelectric liquid crystal composite

ABSTRACT The impact of single-molecule magnet (SMM), Mn12-acetate, on the dielectric properties of ferroelectric liquid crystal (FLC) has been investigated by dielectric spectroscopy and electro-optical techniques in a dual electrode sample cell (DESC). The temperature-dependent dielectric studies on Mn12-acetate/FLC composite have revealed the enhancement in the ferroelectric (smectic C*) to paraelectric (smectic A*) phase transition temperature by 3.5°C. The relaxation process corresponding to Goldstone mode in the ferroelectric phase of the composite is found to be slower compared to pure FLC sample. The electrical response for an input triangular wave shows the existence of one extra polarisation peak in Mn12-acetate/FLC composite which is ascribed to the induced dipole moment in Mn12-acetate molecule. The electro-optical texture of Mn12-acetate/FLC composite revealed that the incorporation of SMM in FLC significantly improve the memory effect. GRAPHICAL ABSTRACT

Polarisation-dependent dielectric processes in ferroelectric liquid crystals

ABSTRACT The behaviour of dielectric relaxation process has been investigated in four ferroelectric liquid crystal (FLC) materials having different spontaneous polarisation (Ps) values. Ps effect on the permittivity in four different FLCs has been carried out in highly anchored sample cells around ~8 μm thick. It has been found that the main contribution to the dielectric permittivity in chiral Smectic C (SmC*) phase is due to Goldstone mode (GM) and partially unwound helical mode (p-UHM). In higher PS value FLC materials, the p-UHM process is found to dominate the dielectric properties. It has also been observed that p-UHM process is highly dependent on the probing ac voltage and temperature, whereas GM is found to be weakly dependent of probing voltage and temperature in SmC* phase of all the studied FLC materials. The influential contribution of p-UHM has exhibited the dielectric properties in its intrinsic frequency range making the materials suitable for futuristic display and photonics devices. Graphical Abstract