S. S. Bhattacharyya

Devices and materials for high-performance mobile liquid crystal displays

Mobile liquid crystal displays (LCDs), often playing a role in hand-held computers, have become indispensable electronic tools to human beings in modern society. Innovative technological developments in the devices and materials have paved a successful road toward the development of mobile LCDs. Herein, after reviewing the trends and performance requirements of mobile LCDs, organic–inorganic materials as the key components of high performance mobile LCDs are addressed. Additionally, the developing trends in mobile LCDs are discussed with respect to these materials.

Dynamic electro-optic response of graphene/graphitic flakes in nematic liquid crystals

Electric field induced dynamic reorientation phenomenon of graphene/graphitic flakes in homogeneously aligned nematic liquid crystal (NLC) medium has been demonstrated by optical microscopy. The flakes reorient from parallel to perpendicular configuration with respect to boundary plates of confining cells for an applied field strength of as low as tens of millivolt per micrometer. After field removal the reoriented flakes recover to their initial state with the help of relaxation of NLC. Considering flake reorientation phenomenon both in positive and negative dielectric anisotropy NLCs, the reorientation process depends on interfacial Maxwell-Wagner polarization and NLC director reorientation. We propose a phenomenological model based on electric field induced potential energy of graphitic flakes and coupling contribution of positive NLC to generate the rotational kinetic energy for flake reorientation. The model successfully explains the dependence of flake reorientation time over flake shape anisotropy, electric-field strength, and flake area. Using present operating scheme it is possible to generate dark field-off state and bright field-on state, having application potential for electro-optic light modulation devices.

Effects of carbon nanotubes on electro-optic characteristics in vertically aligned liquid crystal display

Size- and aggregation-controlled dispersion of thin multiwalled carbon nanotube (t-MWCNT) in negative dielectric anisotropic liquid crystal (LC) material exhibits remarkable improvement in electro-optic response time in vertically aligned LC cells. The physical properties such as birefringence, dielectric anisotropy and clearing temperature of nanotube dispersed LC material appear to be almost invariant to that of pristine LC. Nevertheless, the response time shows noticeable improvement, especially in decaying time associated with transition from maximum to minimum transmission, hence important for faster switching LC devices. The effect is attributed to that vertically aligned t-MWCNTs along the field direction play role of vertical alignment layer between LCs, consequently resulting in increased bend elastic constant of LCs.

Multiphoton dissociation dynamics of SF6 via a completely rotationally resolved model

The infrared multiphoton absorption (IRMPA) and dissociation (IRMPD) Of SF6 have been studied incorporating specific dissociation rate constants K(E,J) obtained from a simplified statistical adiabatic channel model (SACM) in an excitation model investigated by the authors recently. This model includes a rotationally resolved coherent-incoherent interface and rotationally selective excitation in the quasicontinuum. The J specific dissociation rates have been adjusted to match the results at intermediate J with RRKM rates. Use of the SACM rates K(E,J) show changes in the intensity, temperature and pressure dependence of the dissociation yields and rovibrational energy distribution of the molecules dissociating during the laser pulse from that obtained using the simple RRKM rates. The vibrational energy distribution of the molecules below and above the dissociation threshold and the average number of photons absorbed, however, remain unaffected. The differences between the results predicted by the two models decrease with increasing rotational temperature. The collisional quenching of the dissociation after the laser pulse in an argon buffer has also been studied. The nature of ground and excited state rotational distributions of molecules at different pulse times and fluences over wide ranges of experimental parameters are investigated. The various predictions of the model obtained using both linear and non-linear down transition rates in the low energy region of QC are discussed in the light of experimental results on SF6 and CF3I.

Viewing angle controllable liquid crystal display with high transmittance

All conventional viewing angle switchable liquid crystal displays with pixel division have drawback in light efficiency because the sub-pixel that controls viewing angle does not transmit the incident light at normal direction. In this paper, we propose new viewing angle controllable homogeneously aligned liquid crystal display in which the pixel is composed of red, green, blue, and white pixels. The colored pixels are driven by fringe-field switching and the white pixel is driven by complex field. In wide-viewing angle mode, the liquid crystal (LC) directors in all pixels rotate in plane, contributing to high transmittance. In narrow-viewing angle mode, the LC directors in color pixels rotate in plane for light transmission while the LC directors in white pixel can rotate or tilt upward by simultaneous fringe and vertical electric field. The high tilted LC directors generate light leakage in oblique directions which can be utilized for viewing angle control and also transmission at normal direction for image expression. The proposed device overcomes the long standing problem of transmittance sacrifice in the conventional devices.

Variational calculation for the doubly excited state (2p2)3Pe of BeIII

Nonrelativistic energy of the (2p(2))(3)P(e) state of Be(2+) has been calculated using Ritz-variational method. The trial wave function is of Hylleraas type. The upper-bound energy E=-3.382 712 420 77 a.u. calculated by us is the lowest yet obtained.

Above-threshold multiphoton dissociation of and in intense laser fields

We have studied multiphoton above-threshold dissociation (ATD) of and by a time-independent close-coupling (CC) method over a wide range of intensities for three initial bound states (v = 0, 1, 2 and J = 0) at a laser frequency of . Molecular rotation is taken into account by including 30 channels with J = 0 - 5 for and 20 channels with J = 0 - 7 for and number of absorbed photons n = 1 - 4. All the radiative couplings (including those due to the permanent dipole moment of ) have been considered in a truncated length-gauge form of interaction. At lower intensities the total dissociative decay is exponential, but at high intensity several dressed states with different linewidths contribute to the decay and no single decay rate can be defined. Use of the proper potential surfaces for , including intramolecular nonadiabatic coupling, enables us to obtain the branching ratios between the production of and fragments. The branching ratios for different numbers of photon absorption (n = 1, 2, 3) change dramatically with intensity. For , branching to channels, forbidden in by symmetry, may become dominant over a certain range of intensity. We have tried to interpret these intensity dependences in terms of the motion of the nuclei on the adiabatic field + molecule potential surfaces.

Anomalous behaviour in the SmA*–SmCA* pre‐transitional regime of a chiral swallow‐tailed antiferroelectric liquid crystal

The temperature‐ and electric field‐dependent dielectric relaxation and polarisation of a new chiral swallow tailed antiferroelectric liquid crystal, i.e. 1‐ethylpropyl (S)‐2‐{6‐[4‐(4′‐decyloxyphenyl)benzoyloxy]‐2‐naphthyl}propionate (abbreviated as EP10PBNP), were investigated. The electric field‐induced dielectric loss spectra of EP10PBNP revealed electroclinic and anomalous dielectric behaviour in the chiral smectic A (SmA*)–chiral antiferroelectric smectic C (SmCA*) pre‐transitional regime. From an analysis of thermal hysteresis of the dielectric constant, electric field‐induced polarisation and dielectric loss spectra, the appearance of a ferrielectric‐like mesophase is observed followed by an unstable SmCA* phase in the SmA*–SmCA* pre‐transitional regime.

Scaling behavior of dynamic hysteresis of a deformed helix ferroelectric liquid crystal

The hysteresis areas ⟨A⟩ for the saturated loops of a deformed helix ferroelectric liquid crystal, viz., (S)-4-(2-methyloctanoyl) 4′-biphenyl-4-octyloxybenzoate (MIP0806) have been studied. The scaling laws ⟨A⟩∝f0.24E00.68 and ⟨A⟩∝f0.28E00.70 connecting frequency (f) and amplitude (E0) of the applied signal are found to be valid close to and far away from the SmA-SmC* transition temperature (104°C), respectively. The formation of ferroelectric monodomain in MIP0806 is weakly constrained by surface and dipolar interactions, which might be responsible for the observed small deviation obtained from theoretically predicted scaling laws.

High performance transflective liquid crystal display associated with fringe-field switching device

The outdoor readability of the most popular portable liquid crystal display (LCDs) viz. fringe field switching has been addressed both in single and dual cell gap transflective devices. The devices use dual orientation, such as, homogeneous alignment in transmissive (T) part and 64° twisted alignment in reflective (R) part. The dark states of the proposed devices are achieved by controlling phase retardation in T part and polarization rotation in R part and the white state is realized by rotating optic axis of liquid crystal and removing phase retardation in T and R parts, respectively. The devices show high light efficiency without requiring any optical compensation films, exhibiting strong potential for portable display applications.