Anu Malik

Effect of graphene oxide nanomaterial in electroclinic liquid crystals

The collective dielectric relaxation studies have been carried out on the electroclinic liquid crystals (ELCs) doped with 0.1 to 0.2 wt % of graphene oxide (GO) in the frequency range of 20 Hz to 1 MHz. The GO favors for a good quality vertical alignment without any surface treatment of the substrates. The coupling of GO with indium tin oxide (ITO) substrate and ELC materials affects the molecular ordering and supports the ELC molecules to be aligned along the GO attached to the ITO surface in vertical direction. The vertical alignment can be changed to homogeneous by applying a high bias field to the sample and such converted homogeneous cell shows an additional dielectric relaxation peak in the low frequency side of Goldstone mode in SmC∗ phase due to presence of GO whereas in the pure material no such peak was observed. The frequency separation of both peaks (Goldstone mode and an additional peak) increases with temperature and low frequency peak vanishes near transition temperature.

Effect of ZnO nanoparticles on the SmC*-SmA* phase transition temperature in electroclinic liquid crystals

ZnO nanoparticles (NPs), synthesized in an alcoholic medium at room temperature, were added to electroclinic liquid crystal (ELC) materials. The addition of ZnO NPs in ELCs, caused a remarkable shift in SmC*-SmA* phase transition which was investigated from the dielectric and electro-optical measurements. The anchoring of ELC molecules around ZnO NPs creates orientational distortions near the surface, which may give additional ordering to the ELC molecular arrangement. After analyzing collective dielectric relaxation processes of ZnO NP doped ELCs, three distinct loss peaks were observed. The different behavior of ZnO NP doped ELC from pure ELC has been explained by determining the dielectric strength, the distribution parameter and the corresponding relaxation frequency, and so on, and then these results have been compared with the data calculated by using the theoretical model. The effect of ZnO NPs addition on physical parameters, such as spontaneous polarization (Ps) and rotational viscosity (η) has a...

Copper oxide decorated multi-walled carbon nanotubes/ferroelectric liquid crystal composites for faster display devices

We present faster display devices based on copper oxide decorated multi-walled carbon nanotubes (MWCNTs) doped ferroelectric liquid crystal (FLC) material. The fastening of the response has been attributed to decrease in rotational viscosity of the FLC material. The ionic impurities were also reduced by doping copper oxide decorated MWCNTs into the FLC material, and the reduction has been attributed to trapping of ions by the guest copper oxide decorated MWCNTs. The observations of fastening the response and reduction of ionic impurities have been verified by experimental data using dielectric and electro-optical studies. The underlying mechanism would certainly help to understand the basic mechanism of interaction of CNTs with FLC molecules and could be applied to fabricate ionic defects free faster display devices.

Dielectric and Polarization Properties of BaTio3 Nanoparticle/Ferroelectric Liquid Crystal Colloidal Suspension

We investigate the dielectric and polarization properties of a suspension of low concentration ferroelectric nanoparticles in ferroelectric liquid crystal (FLC) host. It is assumed that the particles do not disturb the liquid crystal alignment and the suspension macroscopically appears similar to the pure LC. It is found that the colloidal suspension exhibits dielectric memory and an enhancement in the spontaneous polarization values as compared to the pure LC. The effect is explained vis-à-vis the particles’ permanent polarization contribution that interacts with the LC molecules. We anticipate that these ferroelectric liquid crystalline (LC) nanocolloids can be used to improve the performance of liquid crystal displays and related optical communication applications.

Role of cell thickness in tailoring the dielectric and electro-optical parameters of ferroelectric liquid crystals

Here, we report thickness dependence of dielectric and electro-optical parameters in ferroelectric liquid crystals (FLCs) without surface stabilisation. The dependence of dielectric and electro-optical parameters on cell thickness is observed by dielectric spectroscopy and electro-optical measurements. The dielectric permittivity () measured by varying the cell thickness showed increase of with increase of cell thickness which is attributed to the presence of more ions and larger contributions of Goldstone mode in thick cells. The spontaneous polarisation also shows increment with increase of cell gap up to certain thickness range. The rotational viscosity decreases with increase in the cell thickness whereas the response time is more for thicker cells. The decrease in the rotational viscosity is attributed to lowering of elastic deformation with increase in cell thickness and the response time is directly proportional to cell gap. These studies would be utilised to understand the effect of cell thickness on dielectric and electro-optical properties of FLC materials and optimising the material parameters with cell thickness for better and efficient liquid-crystal-based devices.

Enhancement of ferro-para transition in ethanol doped ferroelectric liquid crystals

The influence of ethanol (C2H5OH) doping in the electroclinic liquid crystal has been investigated using dielectric spectroscopy. A giant shift in ferroelectric (SmC∗) to paraelectric (SmA) phase transition has been observed. After analyzing collective relaxation processes, it is confirmed that Curie–Weiss law is obeyed in the vicinity of SmC∗ to SmA phase transition after doping with ethanol. It has been predicted that the dipole-dipole interaction due to ethanol molecules creates the uniformity in the randomized liquid crystal molecules in paraelectric phase, resulting in the increase in the ferroelectric phase in de Vries electroclinic liquid crystal materials.

Memory effect near transition temperature in Sm C∗ phase in nonsurface stabilized ferroelectric liquid crystals

Memory behavior in the ferroelectric liquid crystal (FLC) material, Felix 17/100, has been investigated by electro-optical, dielectric, and hysteresis methods at different temperatures ranging from room temperature to near ferro-paraelectric phase transition. Memory effect has been observed in the studied material near the transition temperature in Sm C∗ phase in the cells having thickness greater than the pitch value of the material. This is in contrast to the memory effect observed in conventional FLCs where thickness of the cell has to be less than the pitch value of the material. Electrical conductivity measurements elucidate that the steep increase in the conductivity near the transition temperature in Sm C∗ phase enhances the motion of free ions and probably weakens the depolarization field in the material, thereby showing memory effect.

Anomalous Low Frequency Dielectric Relaxation in Nanoparticles/Isotropic Fluid Mixed Ferroelectric Liquid Crystals

The collective dielectric relaxation studies have been carried out on nanoparticles/isotropic fluid mixed ferroelectric liquid crystals (FLCs). It has been observed from the dielectric loss spectra that the mixing of nanoparticles (Graphene Oxide and ZnO) and isotropic fluid (Water) into FLCs possesses two dielectric relaxations in low frequency range (i.e. Goldstone and associated novel relaxation). The behavior of novel relaxation peak is found to be anomalous in terms of its strong dependence on type of nanoparticles/fluids, external electric field and temperature variation. The effective dipolar contribution of nanoparticles/fluids into FLC dipole moment could be the probable reason for such relaxation.

Field-induced transition from homeotropic to planar geometry in the SmC* phase of an electroclinic liquid crystal

The optical and electrical behavior was investigated of a symmetric liquid crystal (LC) cell: ITO–silane–LC–silane–ITO. The silane layer induces a perfect homeotropic alignment of the molecules of the studied electroclinic liquid crystal (ELC) material, BDH 764E. A field-induced transition from the perfect homeotropic to planar orientation in the chiral smectic C (SmC*) and smectic A (SmA) phases of the ELC was observed. Optical and dielectric studies were performed for both alignment (geometry) modes. The field-induced transition from the homeotropic to planar orientation was studied vis-à-vis the high negative dielectric anisotropy obtained in the studied material. Such an ELC with large negative dielectric anisotropy and perfect homeotropic alignment may have important implications for modern LC display technology.

Enhanced Memory Effect in Conducting Polymer Coated Surfaces of Ferroelectric Liquid Crystals

The influence of conducting polymer, poly(3-hexylthiophene) (P3HT), on the memory behavior of ferroelectric liquid crystal material has been investigated by textural, electro-optical, and dielectric spectroscopic methods. It has been observed that the memory effect decreases as concentration of P3HT is increased. The good memory effect has been observed when ∼0.2% (w/v) of P3HT in chloroform solution was used. We also observed that the memory effect in deep Sm C* is not much pronounced but it increases as one goes to near Sm C*–Sm A transition temperature. The observed memory effect has been attributed to minimization of depolarization field and ionic charges.