Splay State Research Articles

P-155: A Novel Liquid Crystal Display Device Applicable to Memory and Dynamic Modes with a Single Panel

The monostable and bistable LCD modes have separately been researched and developed until now. We propose a novel liquid crystal display device that can be operated as memory mode as well as dynamic mode, namely dual mode. The feature of this dual mode exhibits switching among the splay, π twist, and bend states. We demonstrate switching characteristics of the novel LCD. This novel LCD device has not only a long term memory time as memory mode but also a fast response time as dynamic mode.

P-135: Fast Bend Transition of the Pi-Cell at Low Temperature

We have developed fast bend transition method of pi-cell in low temperature. This cell requires a transition of the liquid crystals (LC) from an initial splay state to bend transition before normal driving operation. This study analyzed the conditions under which this transition is generated in low temperature. Consequently, a method of fast bend transition by applying waveform that make the most of LC's dynamic response, using structure of top-gate electrode and surface alignment in Low Temperature Poly-Silicon (LTPS) Thin Film Transistor (TFT) cell was established.

Model for line defects in complex-oscillatory spiral waves

Spiral waves in period-doubled and other complex-oscillatory media possess line defects across which the phase of the oscillation changes by multiples of 2pi. For such systems, the concept of a splay state, introduced for coupled oscillator systems, is generalized to an Archimedean spiral splay field. In this splay field a spiral wave in a two dimensional space is considered to be a special splay state where spatial points having identical phase space orbits take phases determined by the Archimedean spiral on which they lie. Using the Archimedean spiral splay field, an equation that determines the shape of the line defect is derived.

The influence of flow on symmetric and asymmetric splay state relaxations

We present a detailed discussion of the relaxation of splayed states in untwisted devices — the asymmetric H state (Ha), and the recently observed symmetric H state (Hs). Experimental evidence suggests that the Hs does not experience the optical bounce due to induced backflow usually associated with splay state relaxation. A dynamic model using Leslie–Eriksen–Parodi theory has been developed, and is used to model the flow within the device during switching. We show that there is no backflow during Hs relaxation, and that the flow profile is similar to that present during relaxation of the V state (the state used for pi‐cell operation). This flow enhances the switching of the Hs, leading to a faster relaxation than might be expected. The influence of the different viscosity parameters is examined in detail, and a comparison between the experimental and simulated results is given.

Electro-Optical Characteristics and Morphology of a Bend Nematic Liquid Crystal Device Having Templated Polymer Fibrils

We demonstrated a fast-switching liquid crystal display with bent polymer fibrils templated from a nematic host with a bend structure. The morphology of the bent polymer fibrils, formed by photopolymerizing a small amount of reactive monomer in a liquid crystal host, depends on monomer concentration, condition of photopolymerization, and applied electric field during UV exposure. At low monomer concentration and low curing voltage, the liquid crystal can be oriented into the twist or splay state at zero applied field. In contrast, high monomer concentration conveys dominance of the polymer network on the liquid crystal and damps the electro-optical properties of the liquid crystal. With the current nematic host, the condition for obtaining a stabilized bend state is using 3 wt% monomer concentration and 5 V curing voltage. The SEM images of polymer network morphology show a templating effect, where highly ordered fibers mimic the bend state of the liquid crystal (originally having a splay structure) under a small bias field. The device shows fairly fast optical response to the applied electric field because the templated polymer fibrils stabilize the bend state.

Novel technique for splay to bend transition in a π cell

A π cell is initially in splay state. Before driving a π cell, transition from splay to bend state is always necessary which originates from nucleation. We propose a novel technique to make bend transition fast and effectively by forming transition cores around the pixels with the technique of multi‐domain alignment, where domain boundaries play a crucial role in splay to bend transition. This noble technique enables the splay to bend transition to occur within less than 2 seconds with a low applied voltage.

The Transition from the Splay to Bend State in the OCB Cell

Optically compensated bend mode (OCB-mode) [1,2] LCD is promising for next generation displays, because it offers the fast response times and a wide viewing angle. However, this mode requires a transition of the liquid crystals from an initial splay state to bend state before operation. This study analyzed the conditions under which this transition is generated. Consequently, a method of creating a transition nucleus for splay to bend state by controlling the boundary of right and left twist state and that of asymmetrical up and down state was established.

Anisotropy of domain growth in nematic liquid crystals

We have studied domain growth in nematic liquid crystals using a lattice Boltzmann algorithm to solve the full, three-dimensional equations of hydrodynamics. An initially cylindrical V (bend) domain in an H (splay) state grows or shrinks anisotropically in agreement with experiment. A disclination loop forms at the mid-point of the wall surrounding the domain. We argue that different director configurations at different points on the loop lead to velocity anisotropy and show that both elastic effects and backflow are relevant. We discuss the dependence of the domain wall velocity on surface tilt and on the magnitude of an applied electric field.

Analytical approach to V-shaped characteristics in antiferroelectric liquid crystal displays

Not only in ferroelectric liquid crystal displays (LCDs), but also in antiferroelectric LCDs, grey levels are possible by actively addressing the ‘continuous director rotation mode’. For ferroelectric LCDs this was shown qualitatively and quantitatively in previous articles. In this article it is shown that an exact analytical approach is also possible for antiferroelectric LCDs. In two consecutive layers the director orientations are symmetric, and at zero voltage they are in a splayed state. The conditions on alignment layer thickness and interaction coefficients are related to those of ferroelectric liquid crystal but are easier to fulfill.

Splay-splay transition in bistable nematic liquid crystals

The bistability of a nematic liquid crystal layer with the asymmetric directions of easy orientation and weak orientational anchoring is considered within the framework of the continuum theory. The feasibility of passive storage applications based on two differing states of lateral bending is demonstrated. Switching between these splay states does not require the motion of the domain walls and can be accomplished by the two-frequency control of the low electric field applied to the crystal.

Stability Criterion for V-Shaped Characteristics in FLC and AFLC

The V-shaped characteristics in FLC are explained through the existence of a splayed state caused by a strong polar interaction with the alignment layers. In this paper the relation is described between the non-polar interaction coefficient n 1, the polar interaction coefficient n 2, the permanent polarization density P and the thickness of the alignment layer d a that guarantees stability of the V-shaped characteristics. For AFLC there is no agreement that V-shaped characteristics are possible. In this article we show that the condition for stability, expressed in function of a fictitious negative non-polar interaction coefficient, is formally the same as for FLC, but no exact analytical expression for this coefficient can be found. Simulation results however show that stability is possible under conditions that are approximately the same as for FLC.

Generalized splay state in coupled chaotic oscillators induced by weak mutual resonant interactions.

Dynamic behavior of coupled chaotic oscillators is investigated. A transition from high-dimensional hyperchaos to a generalized periodic splay state is found for extremely weak coupling. Chaotic nature of a single oscillator and mutual resonant interactions are regarded to be responsible for this self-organized ordering. The functional phase distribution of the generalized splay state, which is essentially different from the equal-phase-separation distribution of the conventional splay states, can be well predicted by analyzing a single periodically forced oscillator.

Bend Transition in Pi-cell

Despite lack of knowledge on the nucleation process, the bend domain growth is observed as a motion of disclinations, whose velocity can be determined from the energy difference between two states by applying the boundary-layer model and a damping factor. The disclination velocity is proportional to the electric field across the cell. Upon application of a bias, a transient splay state having a fast bend spreading velocity emerges, which then changes into the asymmetric splay state very quickly, leaving the average bend spreading velocity very low. When the bias voltage drops down to zero, the asymmetric splay state relaxes back to a homogenous state, which, applying the bias voltage again, returns to the transient splay. The repetition of turning on and off the bias voltage enhances the average bend advancing velocity, and therefore is useful for fast bend transitions in an active-matrix liquid crystal display.

Synchronization transitions in Josephson arrays: a puzzle and its resolution

AbstractWe resolve a long standing puzzle concerning synchronization in Josephson junction series arrays. We introduce a modified averaging technique to recover a crucial piece of the collective dynamics. The predicted transition between inphase and splay states is fundamentally changed, introducing the hysteresis long known to be observed in these systems. The analogous problem arises in a general class of globally coupled oscillators.

Mean-field theory of globally coupled integrate-and-fire neural oscillators with dynamic synapses.

We analyze the effects of synaptic depression or facilitation on the existence and stability of the splay or asynchronous state in a population of all-to-all, pulse-coupled neural oscillators. We use mean-field techniques to derive conditions for the local stability of the splay state and determine how stability depends on the degree of synaptic depression or facilitation. We also consider the effects of noise. Extensions of the mean-field results to finite networks are developed in terms of the nonlinear firing time map.

Stability of Periodic Solutions in Series Arrays of Josephson Junctions with Internal Capacitance

A mystery surrounds the stability properties of the splay-phase periodic solutions to a series array of NJosephson junction oscillators. Contrary to what one would expect from dynamical systems theory, the splay state appears to be neutrally stable for a wide range of system parameters. It has been explained why the splay state must be neutrally stable when the Stewart-McCumber parameter β(a measure of the junction internal capacitance) is zero. In this paper we complete the explanation of the apparent neutral stability; we show that the splay state is typically hyperbolic-either asymptotically stable or unstable-when β > 0. We conclude that there is only a single unit Floquet multiplier, based on accurate and systematic computations of the Floquet multipliers for β ranging from 0 to 10. However,N-2 multipliers are extremely close to 1 for β larger than about 1. In addition, two more Floquet multipliers approach 1 as β becomes large.We visualize the global dynamics responsible for these nearly degenerate multipliers, and then estimate them accurately by a multiple time-scale analysis. For N=4 junctions the analysis also predicts that the system converges toward either the in-phase state, the splay state, or two clusters of two oscillators, depending on the parameters.

Director configuration of a ferroelectric liquid crystal in a cell with antiparallel surface tilt

Abstract Using the half-leaky guided wave technique we have characterized the optical director profile of a ferroelectric liquid crystal in a homogeneously aligned cell with rubbed nylon surfaces. At high temperatures the N phase is in the expected splayed state, with opposite surface tilts of the order 3°. On cooling into the SA phase, the director corresponds to that of an almost uniform slab with a tilt of 5°. Further cooling into the SC phase does not produce the expected chevron structure; rather a tilted-bookshelf structure is recorded with an initially, at high temperatures, increased tilt of 8°. As the sample is further cooled, this tilt diminishes and eventually at room temperature changes sign to -2°. In addition, the room temperature SC phase has a uniform twist of about 1.4° away from the initial alignment direction. This accords well with the polarization microscopy measurement of an extinction angle of about 1.5° for this cell.

Averaged equations for Josephson junction series arrays.

We derive the averaged equations describing a series array of Josephson junctions shunted by a parallel inductor-resistor-capacitor load. We assume that the junctions have negligible capacitance (\ensuremath{\beta}=0), and derive averaged equations that turn out to be completely tractable: in particular, the stability of both in-phase and splay states depends on a single parameter, \ensuremath{\delta}. We find an explicit expression for \ensuremath{\delta} in terms of the load parameters and the bias current. We recover (and refine) a common claim found in the technical literature, that the in-phase state is stable for inductive loads and unstable for capacitive loads.

Dielectric properties of a surface stabilized ferroelectric liquid crystal in cells of various thickness

Abstract Measurements of the complex dielectric permittivity have been performed in the frequency range of the collective director modes (101–106 Hz) in the vicinity of the S*C↔S*A phase transition of the compound 4-[(R)(-)-(2-chloro-3-methylbutanoyloxy)]-phenyl-[4n-decyloxy]benzoate and revealed that a dielectric relaxation process due to collective director fluctuations is active in the helically unwound S*C as well in the S*A phase, if the formation of the S*c helix is suppressed. A twisted and bent director configuration (splayed state) occurs in thin, planar oriented samples with various cell gaps (2–27 μm). The observed mode of Debye type was characterized as a function of temperature and cell thickness. By a decrease of the cell thickness the dielectric increment is lowered in the S*C phase but enhanced in the S*A phase. This Debye mode is only in part suppressed by the application of a bias electric field. With decreasing cell thickness its relaxation frequency decreases in the S*A phase, but incr...

Non-neutral dynamics of splay states in Josephson-junction arrays.

We study the effect of the phase dependent conductance on the splay state dynamics of series Josephson arrays. In most cases, the splay states are destabilized, and the array evolves into a more coherent state, e.g., the in-phase state. A smaller parameter range exists where the splay state becomes attracting.