Tilak Joshi

Low power operation of ferroelectric liquid crystal system dispersed with zinc oxide nanoparticles

We present the results based on electro-optical properties of zinc oxide nanoparticles (ZnO-NPs) doped ferroelectric liquid crystal (FLC). It is observed that ZnO-NPs-FLC system has low operating voltage and improved optical contrast. The lowering in operating voltage and improvement in optical contrast has been attributed to larger dipole moment of ZnO-NPs that enhances the anchoring of FLC molecules around ZnO-NPs. The effect of ZnO-NPs on the material parameters of FLC has also been observed. These studies will certainly provide a tool to understand the interaction of ZnO-NPs with FLC molecules that can be utilized to fabricate low threshold electro-optic devices.

Low frequency dielectric relaxations of gold nanoparticles/ferroelectric liquid crystal composites

We present the characterisation and dielectric relaxation spectroscopy of a ferroelectric liquid crystal (FLC), namely KCFLC 7S. It was observed that the studied FLC material possesses the tendency of homeotropic alignment on glass substrates coated with indium tin oxide. A low frequency dielectric mode, along with the Goldstone mode, was observed in the SmC* phase of the FLC material. The low frequency mode became more dominant on doping gold nanoparticles into the FLC material. The occurrence of the low frequency mode was attributed to the ionisation–recombination-assisted diffusion of slow ions present in the FLC material. The behaviour of the relaxation frequency of the low frequency mode with applied dc bias and temperature was also demonstrated.

Alumina nanoparticles find an application to reduce the ionic effects of ferroelectric liquid crystal

We observed that the doping of alumina nanoparticles (AL-NPs) has suppressed the undesired ionic effect in ferroelectric liquid crystals (FLCs). The pure and AL-NPs doped FLC cells were analysed by means of dielectric spectroscopy and electrical resistivity/conductivity measurements. Dielectric loss spectra confirmed the disappearance of the low-frequency relaxation peak, which appears due to the presence of ionic impurities in the FLC materials. The reduction of ionic effects has been attributed to the strong adsorption of ionic impurities on the surface of AL-NPs. The adsorption capability of AL-NPs has been studied with both the size and their concentration in FLC material. This study would be helpful to minimize the undesired ionic effects of LC-based display devices.

Self assembled monolayer based liquid crystal biosensor for free cholesterol detection

A unique cholesterol oxidase (ChOx) liquid crystal (LC) biosensor, based on the disruption of orientation in LCs, is developed for cholesterol detection. A self-assembled monolayer (SAM) of Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP) and (3-Aminopropyl)trimethoxy-silane (APTMS) is prepared on a glass plate by adsorption. The enzyme (ChOx) is immobilized on SAM surface for 12 h before utilizing the film for biosensing purpose. LC based biosensing study is conducted on SAM/ChOx/LC (5CB) cells for cholesterol concentrations ranging from 10 mg/dl to 250 mg/dl. The sensing mechanism has been verified through polarizing optical microscopy, scanning electron microscopy, and spectrometric techniques.

Enhanced dielectric and electro-optical properties of a newly synthesised ferroelectric liquid crystal material by doping gold nanoparticle-decorated multiwalled carbon nanotubes

In this article, a newly synthesised ferroelectric liquid crystal (FLC) material, namely LAHS 22, has been characterised. The characterisation of the FLC material has been performed using dielectric relaxation spectroscopy, differential scanning calorimetry and polarisation optical microscopy. We observed an enhancement in the dielectric and electro-optical properties of the FLC material by incorporating gold nanoparticles (GNPs)-decorated multiwalled carbon nanotubes (MWCNTs). The GNPs-decorated MWCNTs cause an increment in dielectric dispersion (up to kHz), absorption, spontaneous polarisation and rotational viscosity of the FLC material. The pure and GNPs-decorated MWCNTs doped FLC cells were analysed by means of various dielectric spectroscopic and optical measurements. The observed enhancement in the dielectric and electro-optical properties of the FLC material has also been studied with concentration of GNPs-decorated MWCNTs in FLC material. The GNPs-decorated MWCNTs/FLC composites are not only of fundamental importance, but also useful materials for device applications such as liquid crystal displays and memory devices.

Tailoring of electro-optical properties of ferroelectric liquid crystals by doping Pd nanoparticles

We demonstrate here the tailoring of electro-optical properties of ferroelectric liquid crystals (FLCs) by doping different concentrations of Selenium Docosane (SD) capped palladium nanoparticles (PdNPs). The operating voltage is lowered by ∼50% in doped FLC as compared to undoped one. The remarkable increment in optical tilt angle of doped FLC is monitored, which is concentration-dependent. The steric interactions among alkyl chains of SD capped PdNPs and FLC molecules could be the probable reason for enhanced optical tilt angle. More importantly, present investigations on doped FLCs are indicative of their indispensible impact on next generation FLCs-based electro-optical devices.

Low-voltage electro-optical memory device based on NiO nanorods dispersed in a ferroelectric liquid crystal

We present a low voltage driven electro-optical memory device fabricated by dispersing nano-sized nickel oxide (nNiO) composed of short length nanorods into a ferroelectric liquid crystal (FLC) host material. The nNiO/FLC composite showed a tremendous decrease in saturation voltage compared to the pristine FLC material along with non-volatile memory behavior which is confirmed through dielectric spectroscopy, polarized optical microscopy and electro-optical response methods. This drop off in saturation voltage is due to the fast alignment of dipolar nNiO and mesogens in the nNiO/FLC composite along the direction of the applied electric field and reduced screening effect. The non-volatile memory behavior of the composite is attributed to the reduction in the depolarization field by adsorption of impurity ions onto the surface of nNiO, which is verified through dielectric spectroscopy and electrical conductivity measurements. These studies pave the way for fabricating non-volatile, low power electro-optical memory devices for advanced information storage applications.

Spontaneous Polarization in Smectic A Phase of Carbon Nanotubes Doped Deformed Helix Ferroelectric Liquid Crystal

Observation of non-zero spontaneous polarization in paraelectric phase in multiwalled carbon nanotubes doped deformed helix ferroelectric LC is reported. Electro-optical response, spontaneous polarization, rotational viscosity, dielectric permittivity, dielectric loss factor, and electrical resistance of pure and multiwalled carbon nanotubes doped deformed helix ferroelectric LC have been measured. Non-zero spontaneous polarization in paraelectric phase has been attributed to the possible short range orientational order of deformed helix ferroelectric LC surrounding the multiwalled carbon nanotubes through surface anchoring and ionic impurities. The results presented will help to understand the basic mechanism of interaction of multiwalled carbon nanotubes with deformed helix ferroelectric LC.

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.

Electrically modulated photoluminescence in ferroelectric liquid crystal

Electrical modulation and switching of photoluminescence (PL) have been demonstrated in pure deformed helix ferroelectric liquid crystal (DHFLC) material. The PL intensity increases and peak position shifts towards lower wavelength above a threshold voltage which continues up to a saturation voltage. This is attributed to the helix unwinding phenomenon in the DHFLC on the application of an electric field. Moreover, the PL intensity could be switched between high intensity (field-on) and low intensity (field-off) positions. These studies would add a new dimension to ferroelectric liquid crystals application in the area of optical devices.