A. M. Biradar

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.

Enhanced photoluminescence in gold nanoparticles doped ferroelectric liquid crystals

We report the characterization and photoluminescence (PL) of newly synthesized deformed helix ferroelectric liquid crystal (DHFLC) material having short pitch and high spontaneous polarization. We observed ninefold enhancement in PL intensity in gold nanoparticles doped DHFLC material. This enhancement in the PL intensity has been attributed to the coupling of localized surface plasmon resonance from metal nanoparticles with DHFLC molecules, resulting in the increase in excitation and emission rate of the liquid crystal molecules in the localized electromagnetic field. These studies would provide a cutting edge tool in the realization of enhanced photoluminescent liquid crystal display devices.

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.

Nonvolatile memory effect based on gold nanoparticles doped ferroelectric liquid crystal

Nonvolatile memory effect based on gold nanoparticles (GNPs) doped deformed helix ferroelectric liquid crystal (DHFLC) has been observed. This observed memory effect has been attributed to electric field induced charge transfer from liquid crystal molecules to the GNPs and the stabilization of helix deformation of DHFLC material, which occurs on the application of electric field beyond a critical field. The memory effect has been analyzed by polarizing optical microscopy, high-resolution transmission electron microscopy, and dielectric spectroscopy. The observed memory effect combines two active research areas: nanotechnology and liquid crystal.

Memory effect in cadmium telluride quantum dots doped ferroelectric liquid crystals

A pronounced memory effect has been observed in cadmium telluride quantum dots (CdTe-QDs) doped ferroelectric liquid crystals (FLCs) by using dielectric and electro-optical methods. The memory effect has been attributed to the charge storage on the CdTe-QDs upon the application of dc bias across the sample cell. The FLC molecules remain in the switched state in vicinity of the charge stored on QDs even after removal of bias. It has been observed that the memory effect depends on doping concentrations of CdTe-QDs and the FLC material used.

A sub-hertz frequency dielectric relaxation process in a ferroelectric liquid crystal material

Dielectric studies of the first order phase transition of a ferroelectric liquid crystal material having the phase sequence chiral nematic to smectic C* have been performed using thin (2.5 mum) cells in the frequency range 0.01 Hz to 12 MHz. For planar alignment, one of the cell electrodes was covered with a polymer and rubbed. Optically well defined alignment was obtained by applying an a.c. field below the N*-SmC* transition. Charge accumulation was enhanced by depositing a thick polymer aligning layer for the alignment of the liquid crystal molecules. A sub-hertz frequency dielectric relaxation process is detected in smectic C*, in the chiral nematic and a few degrees into the isotropic phase, due to the charge accumulation between the polymer layer and the ferroelectric liquid crystal material. The effect of temperature and bias field dependences on the sub-hertz dielectric relaxation process are reported and discussed.

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.

Electrochemical impedance spectroscopy characterization of mercaptopropionic acid capped ZnS nanocrystal based bioelectrode for the detection of the cardiac biomarker--myoglobin.

3-Mercaptopropionic acid (MPA) capped ZnS nanocrystals (ZnS(MPA)) are covalently attached to a self assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APTES) on an indium-tin-oxide (ITO) coated glass plate. The protein antibody, anti-myoglobin (Ab-Mb), is covalently linked to free carboxyl groups present on ZnS(MPA) nanocrystals via carbodiimide coupling reaction to form a bioelectrode (Ab-Mb(BSA)/ZnS(MPA)/APTES/ITO-glass). This bioelectrode has been characterized using atomic force microscopy (AFM), contact angle measurements, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The optimal equivalent circuit model that matches the impedimetric responses of the bioelectrode describes three distinct regions: the electrolyte solution resistance (R(s)), the double layer capacitance (C(dl)) and the specific charge transfer resistance (R(et)). The EIS measurements revealed that the R(et) increases considerably with no significant change in C(dl) after immunoreaction with protein specific antigen myoglobin, Ag-Mb, so that the prepared bioelectrode can be used for the detection of Ag-Mb. The bioelectrode exhibits an electrochemical impedance response to Ag-Mb, in a linear range from 10ng to 1μgmL(-1) phosphate buffer solution (pH 7.4) with a R(et) sensitivity of 117.36Ωcm(2) per decade.

Soft mode behaviour in the smectic A* and smectic C* phases as studied by dielectric spectroscopy

Abstract The soft mode behaviour up to about 8 K below the smectic A*-smectic C* transition temperature has been studied by applying a D.C. bias field of ca. 10 V/25 μm to a planarly aligned sample of the ZLI-3654 ferroelectric liquid crystal mixture. The ϵ*⊥ complex electric permittivity component has been measured in the frequency range from 0.66 to 13000 kHz in the smectic C* phase and in the smectic A* phase up to about 3 K above the transition temperature. From the dielectric spectra obtained the dielectric increments and the critical frequencies have been computed for the soft mode. On both sides of the smectic C*-smectic A* transition the critical frequency of the soft mode obeys a linear temperature dependence with much different slopes and about the same intercepts. The smectic C*-smectic A* transition temperature agrees well with the value found in the absence of the bias field.

Tyrosinase conjugated reduced graphene oxide based biointerface for bisphenol A sensor

We have fabricated a nanocomposite of reduced graphene oxide (rGO) sheets and chitosan (Cn) polymer based highly sensitive electrochemical biosensor for detection of bisphenol A (BPA). The two-dimensional structure and chemical functionality of rGO and Cn provide an excellent electrode surface for loading of tyrosinase enzyme molecules. This rGO-Cn nanocomposite is capable of effectively utilizing their superior conductivity, larger effective surface area and superior electrochemical performance due to its synergistic effect between rGO and Cn. The structural, morphological and electrochemical characterizations of nanocomposite sheets have been performed by electron microscopy, X-ray diffraction, FTIR and Potentiostat/Galvanostat techniques. This fabricated biosensor is sensitive to nanomolar (0.74 nM) concentration of BPA and detection time is 10s compared to conventional BPA ELISA kit (0.3 µg/L and 2.5h). The rGO-Cn based biosensor exhibits a higher sensitivity (83.3 µA nM(-1) cm(-2)), wider linearity (0.01-50 µM) with good selectivity towards BPA. This biosensor is capable to quantify real sample of BPA using packaged drinking water bottles. This rGO-Cn nanocomposite sheets emerges as a potential electrode material for detection of other estrogenic substrate.