Shape switching

Matsumoto, T., Fukuda, A., Johno, M., Motoyama, Y., Yui, T., Setnnun, A.-S., Yamashita, M. A novel pnrpcrty caused by frustration between ferroelectricity and antiferroelectricity and its application to liquid crystal displays Ferroelectricity and V-shape switching. J. Mater. Chem. 9, 2051-2080 (1999)... 

O Callaghan, M. J. Wand, M. D. Walker, C. M. Michi, N. Charge controlled, fixed optic axis analog ( v-shaped ) switching of a bent-core ferroelectric liquid crystal. Appl. Phys. Lett. 2004, 85, 6344-6346. 

This system represents a compromise among competing goals of flexibility and simplicity, between general purpose and specialized application. The inboard microprocessors create a powerful instrument which will accept instruction, but which also has a mind of its own. The star-shaped switch of Kemula could be understood by a child even the designers of the model 273 cannot know fully how it operates. Thus critical scientific evaluation of results becomes the only acceptable foundation for using these instruments. 

A molecular machine, a machine at the molecular level, is defined as a discrete number of molecular components that perform mechanical-like movements (output) in response to specific stimuli (input). Molecular machines include both naturally occurring devices found in biological systems and artificial molecular machines. There are many molecular machines in biological systems. Among the most prominent examples of molecular machines in living organisms are the muscle linear and ATPase rotary motors. In order to develop artificial machinery, scientists have constructed a variety of molecular and supramolecular systems with differences in shape, switching processes, or movements... 

In Fig. 6.3.9, the relationship between applied voltage and transmittance in the case of SSFLCs, AFLCs and modes (l)-(6) and (9) are shown. Theses modes (l)-(6) and (9) show the V-shaped switching property which is appropriate for TFT-driving. Mode (8) shows a unique switching property and requires a special driving scheme. 

Frustration Between Ferroelectricity and Antiferroelectricity—V-Shaped Switching... 

For the V-shaped switching, Inui et al. [85] and Fukuda et al. [86] have suggested a phase with randomly oriented C-directors due to the reduction of the interlayer tilting correlation, without any piece of experimental evidence. The dynamic switching behaviors seemed to be explained by the random model based on the two-dimensional Langevin function [85]. However, the phase with randomly oriented C-directors has never yet been confirmed. 

Figure 9.26. Materials showing V-shaped switching, two mixtures/five compounds.

Figure 9.27. Transmittance versus electric field on applying a triangular waveform of 0.1 Hz and 0.5 Hz at 23 C, 26 C, and 29 C in a homogeneously aligned cell of the compound 3 of Figure 9.26. Note that evolution is observed from tristable to V-shaped switching by changing the frequency and temperature.

Figure 9.28 illustrates the electro-optic responses observed at two 0 s 0° and 30°, where 0 is the angle between the layer normal and one of the crossed polarizer directions. As shown in Figure 9.28 [92], the electric field dependence of transmittance at 0 = 0° shows the typical thresholdless, hysteresis free, V-shaped switching. From the electro-optic measurements at every 5° of 0, the transmittance T versus 0 was obtained at given electric fields. Figure 9.29(a) shows three examples of T versus 0 curves at applied fields of 0, +6, and 6 V/pm [92]. The transmittance T is described by... 

Simulation of 0app and Awefr was made for the two extreme models, i.e., the random and collective models. The results are shown by solid (collective) and broken (random) curves in Figure 9.29(c). It is clear that the calculated A eff for the collective model with a layer tilt angle of 8° is the same as the experimental result, while the random model gives serious disagreement. From these results, it is clear that the collective behavior of liquid crystal molecules is more reasonable than the random distribution for the V-shaped switching. 

C) using the same cell shows small anisotropy at zero field, as shown in Figure 9.30(d), because of the antiferroelectric molecular ordering. These results clearly show that the SmX phase exhibiting V-shaped switching definitely has a different molecular orientation from that in the antiferroelectric phase and the random orientation but has rather uniform orientation. 

Figure 9.33. Illustration of the collective switching model for the V-shaped switching.

The next question is why molecules switch collectively. The V-shaped switching occurs in the system where ferroelectric and antiferroelectric interactions compete and frustration between these structures takes place [99], [100]. Since such a frustrated system is very soft and the relaxation time becomes long, molecules change their steady-state orientation continuously under the surface constraint and varying field, resulting in the collective motion. 

Questions still exist the SmX phase exhibiting V-shaped switching is a new phase or there are some conventional phases such as ferroelectric, antiferroelectric, and ferrielectric phases. One of the most important experiments remaining is the quantitative measurement of the tilting correlation between adjacent layers. This is a future problem. 

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