A novel property caused by frustration between ferroelectricity and antiferroelectricity and its application to liquid crystal displays-frustoelectricity and V-shaped switching

Abstract

We have studied the frustration between ferro- and antiferro-electricity in chiral smectic C like liquid crystalline phases, which is not only fundamentally interesting but also very attractive from an application point of view. It causes temperature induced successive phase transitions as characterized by a devil's staircase and the thresholdless, hysteresis-free, V-shaped switching induced by an applied electric field. The devil's staircase indicates some type of interlayer ordering, while the V-shaped switching suggests considerably diminished tilting correlation. These two are apparently contradictory to each other, but result from the same cause, i.e. the frustration. We have first summarized experimental facts regarding subphases and successive phase transitions observed in many compounds and mixtures, which we believe are related to one another and result from the frustration. We have introduced several different theoretical explanations for these observed facts, and shown that only the axial next nearest neighbor Ising (ANNNI) model can explain almost all of the facts, provided that it is unified with the XY model appropriately. The unified model can make a comprehensive explanation in the most natural way based on the most probable molecular interactions. We have then emphasised that there are several modes regarding the V-shaped switching, because the system becomes so soft with respect to the tilting direction and sense that any additional external or internal force modifies the in-plane local director alignments. For the practically usable ones, we have emphasised the need for some type of randomization in the molecular alignment at the tip of the V and/or the switching process. In particular, the two dimensional (ideally, cylindrically symmetric) azimuthal angle distribution of local in-plane directors around the smectic layer normal is most attractive. Such a randomized state at the tip of the V is thermodynamically unique under a given condition imposed by interfaces. It stays stable even when the smectic layer structure, such as a chevron, changes with temperature. Finally, we have summarized the so-far reported compounds and mixtures for the V-shaped switching and introduced some prototypes of LCDs using them.

Optical rotatory power in tilted smectic phases

“…They can be classified in two kinds, the Ising-like [16,[28][29][30][31][32] and XY -like models [33][34][35][36][37][38][39][40][41]. In the first category, one assumes that the angle ϕ has only two values 0 or π regardless of the helical precession and that the sequence of values from layer to layer is given by a kind of devil's staircase which is temperature dependent.…”

Discrete Soliton with Variable Amplitude in Electric Field Induced SmCα*-SmC Transition

“…[177]/87 Chiral smectic C α phase (SmC α * ), appearing in some antiferroelectric smectic materials [8][9][10][11], is ferroelectric and a helical structure is unwound by the electric field like SmC * . Though the unwinding mechanism of SmC α * looks similar to SmC * , a pitch of helix at SmC α * is quite short, say, several layers [12][13][14].…”

Successive Phase Transitions in Antiferroelectric Liquid Crystal Systems—Axial Next-Nearest-Neighbor XY Model with Biquadratic Interaction

“…Several chiral liquid crystal (LC) compounds have found to exhibit intermediate subphases, SmC * FI1 (also called SmC * γ ), SmC * FI2 (also called AF), and other ferrielectric phases (FI H , FI L and FI) between ferroelectric SmC * and antiferroelectric SmC * A phases [1,2]. All these phases are tilted smectic phases and they have approximately the same tilt angle from the layer normal.…”

“…Each phase consists of a helical stack of unit-set-of-layers (unit cells); the helix pitch is typically on the order of several µm [3]. Structures of SmC * A , SmC * FI1 and SmC * FI2 among those are well-known [2,[4][5][6][7]: the unit cells characterizing SmC * , SmC * A , SmC * FI1 , and SmC * FI2 consist of 1, 2, and 3, 4 layers, respectively. The early experiments [1,2,8] have identified that the c-directors (the projection of a director onto layer-plane) of neighboring layers are parallel or antiparallel.…”