T. Pal Majumder

Bias dependent dielectric relaxation dynamics of electrically tuned large-scale aligned zinc oxide nanorods in nematic liquid crystal host

It was observed that mixed ZnO nanorods and twisted nematic liquid crystals (LCs) show highly ordered molecular system. The observed molecular relaxation arose due to a reorientation of long molecular axis of the order of 400 kHz for pure ZLI-1636, while such relaxation was shifted to a lower frequency for mixture. By using the proposed equations, f=fDB−α exp[−EV/(B−BC)] and σ=σDB−sα exp[−sEV/(B−BC)], the obtained equivalent activation energy was increased remarkably by the introduction of ZnO nanorods in pure LC. A strong long-range interaction is established in 0.01% ZnO nanorods mixed LC system.

Electro-optical properties of an orthoconic liquid crystal mixture (W-182) and its molecular dynamics

We observed that the perfect dark state problem could be solved by using orthoconic antiferroelectric liquid crystal (OAFLC) instead of normal AFLC by comparing the properties of isocontrast and dispersion chromaticity of W-182 OAFLC and normal AFLC CS-4001. We electro-optically observed that several subphases such as SmCγ*, SmC*β, SmC*α and antiferroelectric SmI*A phases exist in W-182 OAFLC. We dielectrically observed in 4μm thin cell that during heating, several new phases appeared. In the high temperature antiferroelectric region, a higher order than SmC* phase could be detected dielectrically, in the temperature range of 91–98°C, behaving similar to SmCγ* and also, another phase below SmC* region could be dielectrically detected in the temperature range of 103–1100°C, behaving similar to SmCα*, and an antiferroelectric, similar to SmIA* phase, was observed in the lower temperature region of the antiferroelectric phase; those are definitely arising due to surface force and interfacial charges interact...

Theory of nanoparticles doped in ferroelectric liquid crystals

We developed a theory for the statistical mechanics of nanoparticles doped in ferroelectric liquid crystals (FLC). The presence of nanoparticles in FLC medium creates strong local fields that produce large alignment effects over the distribution of the nanosuspensions. Considering these local field effects, we presented a modified Landau free energy to calculate the electro-optic properties of the system. Then, we investigated the response of the nanoparticles doped FLC to an applied electric field. The variations in the polarization and the tilt angle show marked differences with the pure FLC medium. The rotational viscosity of the system is also calculated with its possible variation in temperature and applied field. Then, we conjectured on the possibility of shift in transition temperature, which is supposed to be induced by an electrostatic interaction between the nanoparticles and the liquid crystal molecules. Finally, strong experimental evidence is presented in favor of our results emerged from thi...

Theory of ion-chirality relation in ferroelectric liquid crystals

The presence of impurity ions in ferroelectric liquid crystals (FLC) could produce a significant impact on the chirality of the medium with a possible modification in the polarization profile of the system. We theoretically observed these possibilities by considering an in-plane and bulk free energy density for the sample. Based on a suitable chirality transfer formalism, we explained the role of impurity ions in altering the chiral nature of a FLC medium. A continuous transition from modulated phases to uniform phases is also predicted within the framework of this theory. Then, we investigated the possible modification in the polarization profile driven by ionic impurities.

Theoretical approach to study the effect of free volumes on the physical behavior of polymer stabilized ferroelectric liquid crystal molecules

It was clearly indicative that the polymer chains make a tremendous interaction with the tilt angle in case of a polymer stabilized ferroelectric liquid crystal (PSFLC). After suitable consideration of such interaction, we expanded the Landau free energy for a PSFLC system. We theoretically demonstrated the effect of free volumes, which expected to create bulk self-energy, on the physical functionalities of a PSFLC system. Then we obtained spontaneous polarization, tilt angle, rotational viscosity and dielectric constant strongly correlated with the assumed interactions. We also observed a shift of transition temperature highly influenced by this interaction between polymer network and liquid crystal molecules. A microscopical picture of this polymer-liquid crystal interaction is provided in view of the free volume charge density present in the composite system.

Double-peak polarization current response in the unusual SmA* phase of a fluorinated high-tilt antiferroelectric liquid crystal

A detailed investigation of the dielectric, electro-optical properties and X-ray studies have been made in the vicinity of the transition from Smectic-A* to Smectic-C* as well as in the Smectic-A* phase of a newly synthesized partially fluorinated high-tilt antiferroelectric liquid crystal (AFLC) material. The Smectic-A* phase of this material exhibits high optical tilt, minimum layer shrinkage from paraelectric-to-ferroelectric phase transition and unusual dielectric behavior, which are the complementary evidences that the Smectic-A* phase is of de Vries type. Double-peak polarization current response and tristable-optical-switching studies have revealed an antiferroelectric molecular ordering in the de Vries SmA* phase of this material. Two distinct dielectric relaxation peaks in the SmA* phase also complement the antiferroelectric-like ordering of the molecule in the SmA* phase. The material undergoes a first-order SmA*-SmC* transition which is confirmed by a high enthalpy change and the discontinuity of the dielectric parameters at the phase transition.