JP5211599B2 - Liquid crystal property evaluation system - Google Patents

Description

  The present invention relates to a liquid crystal material property evaluation apparatus and measurement method.

  At present, liquid crystal displays are widely used in flat-screen TVs and personal computer monitors. In particular, improving the responsiveness of a liquid crystal device used in a television is an important issue.

In developing a liquid crystal element material, it is important to design a member constituting the material. To improve the response, it is necessary to analyze the arrangement of liquid crystal material molecules in the liquid crystal element. Conventionally, a viscosity coefficient measuring device (see Patent Literatures 1 and 2), a dielectric constant measuring device (see Patent Literatures 3 and 4), an elastic constant measuring device (see Patent Literature 5), a refractive index measuring device (see Patent Literature 6), etc. A physical property measuring apparatus has been proposed. Among them, Patent Documents 3, 4 and 5 describe the relationship between the voltage applied to the liquid crystal and the change in the dielectric constant caused thereby.
JP 2006-243638 A JP2004-20255 JP-A-5-66376 JP 7-35797 A JP 2004-286485 A JP 2000-98314 A

  As described above, methods for independently measuring dielectric constant, viscosity coefficient, elastic modulus, etc. have been conventionally known, but admittance measurement, in particular, easy estimation of changes in the arrangement of molecules including viscosity, elastic modulus, etc. An evaluation method and an evaluation apparatus are not provided.

  In view of these problems, an object of the present invention is to provide an apparatus for simply measuring a change in the arrangement of molecules due to an applied voltage.

  The present invention relates to the following matters.

1. A liquid crystal cell having two opposing electrodes and sandwiching a liquid crystal therebetween,
As a voltage to be applied between the two opposing electrodes, a sweep voltage component Vs that changes at a controllable sweep speed Rs (V / sec), and a frequency f and a peak-peak amplitude Vpp superimposed on the sweep voltage component. A signal generating means capable of applying a signal voltage obtained by synthesizing a high-frequency AC component having
Admittance measurement means capable of measuring an admittance corresponding to the sweep voltage component of the signal voltage;
A liquid crystal physical property evaluation apparatus comprising:

  2. 2. The liquid crystal physical property evaluation apparatus according to 1 above, further comprising display means capable of displaying the absolute value of the admittance with respect to the sweep voltage component Vs.

  3. 3. The liquid crystal property evaluation apparatus according to claim 1 or 2, wherein the sweep voltage component Vs is repeatedly swept at least once in the positive direction and the negative direction between a predetermined voltage -Vmax and + Vmax.

4). The absolute value of admittance when the sweep voltage component Vs = 0 is Y0,
The absolute value of the sweep voltage component Vs when the absolute value of the admittance rises from Y0 when V2 is swept in the direction in which the absolute value of the sweep voltage component Vs increases,
The absolute value of the sweep voltage component Vs when the absolute value of the admittance returns to Y0 when V1 is swept in the direction in which the absolute value of the sweep voltage component Vs decreases,
ΔV, ΔV = V2−V1
Are defined as
4. The liquid crystal physical property evaluation apparatus according to 3 above, wherein V2, V1 and ΔV are measured or determined.

  5. 5. The liquid crystal physical property evaluation apparatus according to claim 4, wherein a sweep speed v0 at which ΔV = 0 is measured or determined by changing a sweep speed Rs of the sweep voltage component Vs.

  6). The liquid crystal physical property evaluation apparatus according to any one of the above 1 to 5, further comprising display means capable of displaying the phase of the admittance with respect to the sweep voltage component Vs.

  7). 7. The liquid crystal according to claim 6, wherein a frequency f and a peak-peak amplitude Vpp of the high-frequency component can be changed, and the frequency f is set so that the phase change of the admittance is most sensitively observed. Physical property evaluation device.

  8). 8. The liquid crystal physical property evaluation apparatus according to any one of 1 to 7 above, wherein the two electrodes have alignment means for determining an alignment direction of liquid crystal sandwiched therebetween.

  ADVANTAGE OF THE INVENTION According to this invention, the apparatus which can measure easily the change of the arrangement | sequence of the molecule | numerator by the applied voltage can be provided. In the apparatus of the present invention, it is possible to measure changes in admittance associated with changes in applied voltage, and in a preferred embodiment, changes in the orientation of liquid crystal molecules including viscosity and elastic modulus can be easily measured.

  The measurement of admittance potential dependence as in the present invention has not been known so far. In particular, V2, V1 and ΔV described later are new parameters which have not been proposed so far. It is expected to be used as an indicator of behavior. In addition, the performance of the alignment film can be easily evaluated.

  The liquid crystal cell used in the measuring apparatus of the present invention has a known structure as schematically shown in FIG. 1 and has a structure in which two opposing electrodes 2 are provided and a liquid crystal layer 4 can be sandwiched therebetween. Have. In general, the two electrodes are formed on opposite inner surfaces of the two substrates 1.

  Although it will not specifically limit if it is a board | substrate conventionally used as a board | substrate for liquid crystal elements, A glass substrate is preferable. An electrode layer will not be specifically limited if it is conventionally used as an electrode for liquid crystal elements, For example, ITO etc. can be mentioned.

  The liquid crystal cell includes an alignment film 3 as necessary as means for controlling the alignment of molecules of the liquid crystal to be measured (practically given by a mixture of plural kinds of compounds). The alignment film / alignment method can be appropriately selected from those conventionally used as alignment films / alignment methods for liquid crystal elements. Examples of the horizontal alignment film include a polyimide film, a nylon film, and a polyvinyl alcohol film. These are generally used after being rubbed. Examples of the vertical alignment film include surfactants, silane compounds and the like (treatment of the electrode surface), and specific examples include trimethylcetylammonium bromide and octadecyltriethoxysilane.

  The orientations of the two upper and lower electrode surfaces facing each other need not be the same. For example, one can be horizontal and one can be vertical. Further, a structure without using an alignment film is also possible. Furthermore, when both the upper and lower alignment directions are horizontal alignment, the twist angle can be changed as appropriate. The pretilt angle can also be set as appropriate. In addition, by changing the angle of vertical alignment, it can be expected to be applied to the evaluation of the liquid crystal material's turning ability (helical twisting power).

  The structure of the liquid crystal cell is set, and a liquid crystal material (both a single compound and a mixture of a plurality of compounds) is sandwiched between the electrodes to be measured. In this case, it is preferable to set the liquid crystal cell to be used for measurement so that the characteristics of the physical properties that affect the liquid crystal device in which the use of the liquid crystal material is scheduled to appear well. For example, for evaluation of a liquid crystal material having negative dielectric anisotropy, for example, for evaluation of a liquid crystal material usable in a VA mode liquid crystal device, a liquid crystal cell having a vertical alignment can be used. For example, a liquid crystal cell having a horizontal alignment can be used for evaluating a liquid crystal material having positive dielectric anisotropy, for example, a material usable in a TN mode, an IPS mode, or the like.

  In the present invention, not only the liquid crystal material can be evaluated, but also the alignment film / alignment method can be evaluated by setting the liquid crystal material sandwiched between the electrodes and changing the alignment film or the alignment method. It is.

  The measuring apparatus of the present invention includes signal generating means capable of applying a signal voltage to the liquid crystal cell, and admittance measuring means for measuring admittance in cooperation with the signal generating means.

  The signal voltage applied to the liquid crystal cell for measurement is a sweep voltage component Vs whose voltage changes linearly at a predetermined changeable sweep speed Rs (V / sec), and a high-frequency AC component as a probe signal for admittance measurement. Has a superimposed waveform. The sweep voltage component Vs is generally set to include a voltage range or an applied electric field range in which the liquid crystal material to be measured can be used (or is of interest).

  The sweep voltage component Vs preferably changes at a constant sweep speed Rs (V / s), and in particular, + | Rs | and − | Rs | (where | Rs | indicates an absolute value) having the same absolute value. It is preferable to change so as to repeatedly sweep between the maximum voltage + Vmax and the minimum voltage −Vmax.

  Specifically, the voltage sweep is preferably performed at least once in one cycle of, for example, 0 (volt) → + Vmax → −Vmax → 0 (volt). In general, the initial 0 (volt) → Vmax may behave differently from the subsequent cycles. Therefore, the hysteresis is observed by performing at least one cycle sweep except the initial 0 (volt) → Vmax. It is preferable. Furthermore, it is preferable to observe the hysteresis by performing multiple sweeps.

  In this sweep voltage cycle, it is preferable that the positive sweep speed and the negative sweep speed be the same. Further, although the voltage may be held at Vmax and −Vmax, it is usually preferable to immediately reverse the sweep speed Rs from + | Rs | to − | Rs |, that is, a so-called triangular wave AC signal.

  The absolute value of the sweep speed is not particularly limited, but is, for example, in the range up to 50 V / s, and preferably in the range of 10 mV / s to 5 V / s. A typical range includes a range of 10 mV / s to 1 V / s.

  The high-frequency AC component superimposed on the sweep voltage component Vs is a probe signal for admittance measurement. Therefore, it is preferable to use a sine wave as the high-frequency AC component, and the frequency needs to have a frequency sufficiently higher than the cycle frequency of the sweep voltage component, preferably 10 times or more, more preferably 50 times or more. Have a frequency of Measurements in the low frequency range are inaccurate with the sweep voltage. Specifically, it is preferably 10 Hz to 10 kHz, and more preferably 10 Hz to 1 kHz.

  Moreover, it is preferable to employ a small voltage amplitude so that the amplitude of the high-frequency signal component does not affect the alignment of the liquid crystal molecules. The peak-peak amplitude Vpp is, for example, 1 mV to 1 V, preferably 0.5 V or less, more preferably 0.1 V or less, and 0.05 V in a typical example.

Furthermore, in the measuring apparatus of the present invention,
The absolute value of admittance when the sweep voltage component Vs = 0 is Y0,
The absolute value of the sweep voltage component Vs when the absolute value of the admittance rises from Y0 when V2 is swept in the direction in which the absolute value of the sweep voltage component Vs increases,
The absolute value of the sweep voltage component Vs when the absolute value of the admittance returns to Y0 when V1 is swept in the direction in which the absolute value of the sweep voltage component Vs decreases,
ΔV, ΔV = V2−V1
Are defined as
It is preferable that measurement of V2, V1 and ΔV is possible.

  In the admittance measurement of the liquid crystal material by applying the measurement signal voltage described above, a curve having hysteresis as shown in FIG. 2 (vertical axis: absolute value of admittance, horizontal axis: sweep voltage) is obtained as an example.

  In the vicinity of the sweep voltage component Vs = 0 volts, the admittance absolute value Y0 is shown. However, as the sweep voltage is increased, the liquid crystal molecules change their orientation in a stable direction (direction in which the dielectric constant increases). The absolute value of admittance rises. This voltage is V2. Further, the voltage at which the absolute value of admittance drops to Y0 when the voltage is lowered is defined as V1. The difference between V2 and V1 is ΔV (= V2−V1).

  In the apparatus of the present invention, the sweep speed Rs can be changed. When the sweep speed Rs is changed to be larger or smaller, a sweep speed Rs that matches V2 and V1 and satisfies ΔV = 0 is found. Rs at this time is defined as v0.

  These values of V1, V2, ΔV, and v0 are expected to be applied as indices for evaluating physical properties that represent voltage responsiveness of liquid crystal materials. In relation to conventional parameters, it is understood that Δε, elastic constant, viscosity coefficient and the like are combined.

  Further, the apparatus of the present invention is preferably capable of measuring the phase of admittance, and in particular, the frequency f of the high frequency component is preferably adjustable so that the phase change appears most sensitively with respect to the sweep voltage. The deviation of admittance from 90 ° means that a conductivity component exists, and the long-term stability of the liquid crystal material or the alignment film becomes a problem.

  The liquid crystal property evaluation apparatus of the present invention as described above can have software that causes hardware to function together with hardware. Therefore, the signal generation means and the admittance measurement means may each be configured by a single hardware, or may be configured by a plurality of hardware, or both may be configured by a single hardware. Furthermore, software or a logical configuration combined with hardware may be included as a part thereof.

  FIG. 3 is a block diagram showing an example of the configuration of the liquid crystal physical property evaluation apparatus. In this example, a sweep voltage component Vs is generated by the constant potential holding device 13 and the potential sweep device 12, a high-frequency AC component is generated by the AC oscillator 14, and a signal voltage is generated by combining the sweep voltage component and the high-frequency AC component to generate a liquid crystal cell. 11 is applied. The AC amplitude measuring device 15 can measure the amplitude and phase of the AC current and compare the signal voltages to obtain an admittance (absolute value and phase of admittance). Furthermore, by providing the XY recorder 16, it is possible to plot the absolute value or phase of the admittance on the vertical axis with the sweep voltage as the horizontal axis.

  Next, examples in which liquid crystal materials were evaluated are shown. In the experiment, the following apparatus was used corresponding to the configuration of FIG.

  Potentiostat and galvanostat model 2020 manufactured by Toho Giken Co., Ltd. (maximum set voltage ± 10 V was used. Current range ± 1 μA to ± 1 A, 7 ranges, minimum current ± 1 nA or less) was used as the constant potential holding device. .

  As the AC oscillator, a 1941/1945 multifunction synthesizer (amplitude 0 mVp-p to 20,000 Vp-p, frequency 0.01 μHz to 15 MHz) manufactured by NF Circuit Design Block Co., Ltd. was used.

  As a potential sweeping device, a simple function generator HB-111 (set potential range −5.000 V to 0 to +5.000 V, sweep speed 0.1 mV / s to 5 kV / min) manufactured by Hokuto Denko Co., Ltd. was used.

  The AC amplitude measuring device includes a synchro track lock-in amplifier LI-575 (sensitivity range 100 nV to 500 mV / FS, frequency range 0.5 Hz to 200 kHz, input voltage range 0.3 V to 30 Vp, manufactured by NF Circuit Design Block Co., Ltd. -P) was used.

  As the XY recorder, XY Recorder WX1200-UM-101 (pen run width 0.5 to 5000 mV / cm, maximum pen speed 800 mm / s) manufactured by Graphic Co., Ltd. was used.

(Experimental example 1)
A VA device having a cell gap of 5 μm was assembled from two glass substrates prepared by adjusting alignment films of cetyltrimethylammonium bromide. As a liquid crystal material, MLC-6608 (Merck) was injected into the obtained VA element, and an AC signal of Vpp = 0.05V and 1 kHz was applied at a sweep rate of 200 mV / s between cell electrodes of -5V to 5V. A voltage sweep was performed. The obtained admittance potential dependence is shown in FIG.

  In addition, the potential dependence of the phase shift was measured simultaneously with the admittance potential dependence. The results are shown in FIG.

(Experimental example 2)
The admittance potential dependence was measured in the same manner as in Experimental Example 1 except that the sweep rate was changed to 50 mV / s. The results are shown in FIG.

(Experimental example 3)
The admittance potential dependence was measured in the same manner as in Experimental Example 1 except that the sweep rate was changed to 1 V / s. The results are shown in FIG.

  Table 1 shows values of ΔV in the VA elements of Experimental Examples 1, 2, and 3.

この結果から、掃引速度を大きくしていくにつれて、ΔＶの値が大きくなり、この液晶材料およびセル構成の場合では、表の速度範囲ではΔＶが−から＋へ変化し、ΔＶ＝０は０．２Ｖ／ｓより大きく１Ｖ／ｓより小さい掃引速度で現れる。

From this result, as the sweep speed is increased, the value of ΔV increases, and in the case of this liquid crystal material and cell configuration, ΔV changes from − to + in the speed range shown in the table, and ΔV = 0 is 0. Appears at a sweep rate greater than 2 V / s and less than 1 V / s.

  V2 means a voltage that is oriented by the electric field energy and starts to change the dielectric constant, and V1 means a voltage that is released from the electric field energy and is restored by the anchoring force of the alignment film. Therefore, ΔV indicates the magnitude of the influence of the electric field related to the viscosity and the influence of the alignment film related to the elasticity, and the sweep speed v0 at which ΔV = 0 is balanced between the influence of the electric field related to the viscosity and the influence of the alignment film related to the elasticity. It means that there is a point.

(Experimental example 4)
Admittance potential dependence was measured in the same manner as in Experimental Example 1 except that the AC signal was changed to Vpp = 0.05 V and 500 Hz. The results are shown in FIG.

(Experimental example 5)
The admittance potential dependence was measured in the same manner as in Experimental Example 1 except that the AC signal was changed to Vpp 0.05 V and 200 Hz. The results are shown in FIG.

  From the results of Experimental Examples 1, 4 and 5, it is observed that the potentials of V1 and V2 do not change when the frequency of the AC signal is changed as a measurement condition. That is, V1 and V2 mean that a constant measurement can be performed regardless of the leakage current.

(Experimental example 6)
A TN device having a twist angle of 90 degrees to the right and a cell gap of 5 μm was assembled from two glass substrates prepared by adjusting polyimide alignment films. MLC-6601 (Merck) was injected as a liquid crystal into the obtained TN device, and an AC signal of Vpp = 0.05V and 1 kHz was applied at a sweep rate of 200 mV / s, and the voltage between the cell electrodes was −10 V to 10 V. A sweep was performed. The obtained admittance potential dependence is shown in FIG.

(Experimental example 7)
Admittance potential dependence was measured in the same manner as in Experimental Example 6 except that the twist angle was changed to 180 degrees (anti-parallel). The results are shown in FIG.

(Experimental example 8)
The admittance potential dependence was measured in the same manner as in Experimental Example 6 except that the twist angle was changed to 90 degrees to the left. The results are shown in FIG.

(Experimental example 9)
Admittance potential dependence was measured in the same manner as in Experimental Example 6 except that the twist angle was changed to 360 degrees (parallel). The results are shown in FIG. 13 and Table 5.

(Experimental example 10)
Admittance potential dependence was measured in the same manner as in Experimental Example 6 except that the liquid crystal was changed to MLC-6601 (Merck) to which 0.5% of chiral dopant ZLI-4571 (Merck) was added. The results are shown in FIG.

(Experimental Examples 11 to 13)
Except for changing the chiral dopant ZLI-4571 (Merck) to MLC-6601 (Merck) to which 0.1%, 0.2% and 1% were added, respectively, the same as in Experimental Example 6, It was measured. The results are shown in Table 2.

(Experimental Examples 14-17)
Except that the liquid crystal was changed to MLC-6601 (Merck) to which the chiral dopant ZLI-4571 (Merck) was added 0.1%, 0.2%, 0.5%, and 1%, respectively, the same as Experimental Example 7 The admittance potential dependence was measured. The results are shown in Table 3.

(Experimental Examples 18 to 21)
The same as Experimental Example 8 except that the liquid crystal was changed to MLC-6601 (Merck) to which 0.1%, 0.2%, 0.5% and 1% of the chiral dopant ZLI-4571 (Merck) was added, respectively. The admittance potential dependence was measured. The results are shown in Table 4.

(Experimental Examples 22 to 20)
The same as Experimental Example 9 except that the liquid crystal was changed to MLC-6601 (Merck) to which 0.1%, 0.2%, 0.5% and 1% of the chiral dopant ZLI-4571 (Merck) was added, respectively. The admittance potential dependence was measured. The results are shown in Table 5.

  From the results of Experimental Examples 6 to 25, FIG. 15 shows the relationship between the addition amount of the chiral dopant and ΔV for each twist angle. It can be seen that as the amount of the chiral dopant is increased, the hysteresis is increased and the influence on the orientation is increased, and the influence on the orientation is saturated at a certain concentration or more. On the other hand, when the addition amount is too small, the influence on the orientation becomes small. Therefore, ΔV means that it becomes an index for determining the optimum addition amount of the chiral dopant.

(Experimental example 26)
The admittance potential dependence was measured in the same manner as in Experimental Example 6 except that the sweep rate was changed to 50 mV / s. The results are shown in FIG.

(Experiment 27)
The admittance potential dependence was measured in the same manner as in Experimental Example 6 except that the sweep rate was changed to 1 V / s. The results are shown in FIG.

  Table 6 shows values of ΔV in the TN elements of Experimental Examples 6, 26, and 27.

この結果から、掃引速度を大きくしていくにつれて、表の速度範囲ではΔＶが＋の範囲で大きくなった。この液晶材料およびセル構成の場合では、外挿すると、ΔＶ＝０は０．０５Ｖ／ｓより小さな掃引速度で現れる。

From this result, as the sweep speed was increased, ΔV increased in the + range in the speed range shown in the table. In the case of this liquid crystal material and cell configuration, when extrapolated, ΔV = 0 appears at a sweep rate less than 0.05 V / s.

  In addition, when a liquid crystal material (liquid crystal material used in Experimental Example 1) having a negative dielectric anisotropy is injected into a TN cell (the cell used in Experimental Example 6), a VA element (Experimental Example 1) is measured. When the liquid crystal material having a positive dielectric anisotropy (the liquid crystal material used in Experimental Example 6) was injected into the cell used in the above, the admittance potential dependence was not observed.

It is a figure which shows typically the structure of the liquid crystal cell used for this invention. It is a graph which shows typically an example of the dependence of the absolute value of admittance with respect to a sweep voltage. It is a block diagram which shows one example of the liquid-crystal physical-property evaluation apparatus of this invention. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 1. FIG. It is a figure which shows the voltage dependence of the phase of the admittance measured in Experimental example 1. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 2. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 3. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 4. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 5. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 6. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 7. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 8. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 9. FIG. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 10. FIG. It is a graph which shows the addition amount of a chiral dopant, and the relationship of (DELTA) V. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 26. It is a figure which shows the voltage dependence of the absolute value of the admittance measured in Experimental example 27.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Electrode 3 Alignment film 4 Liquid crystal layer 11 Liquid crystal cell 12 Potential sweep device 13 Constant potential holding device 14 AC oscillator 15 AC amplitude measurement device 16 XY recorder

Claims (6)

A liquid crystal cell having two opposing electrodes and sandwiching a liquid crystal therebetween,
As a voltage to be applied between the two opposing electrodes, a sweep voltage component Vs that changes at a controllable sweep speed Rs (V / sec), and a frequency f and a peak-peak amplitude Vpp superimposed on the sweep voltage component. A signal generating means capable of applying a signal voltage obtained by synthesizing a high-frequency AC component having
Admittance measurement means capable of measuring an admittance corresponding to the sweep voltage component of the signal voltage;
I have a,
The sweep voltage component Vs is repeatedly swept between a predetermined voltage −Vmax to + Vmax at least once in the positive direction and the negative direction,
The absolute value of admittance when the sweep voltage component Vs = 0 is Y0,
The absolute value of the sweep voltage component Vs when the absolute value of the admittance rises from Y0 when V2 is swept in the direction in which the absolute value of the sweep voltage component Vs increases,
The absolute value of the sweep voltage component Vs when the absolute value of the admittance returns to Y0 when V1 is swept in the direction in which the absolute value of the sweep voltage component Vs decreases,
ΔV, ΔV = V2−V1
Are defined as
A liquid crystal physical property evaluation apparatus , wherein V2, V1, and ΔV are measured or determined .   The liquid crystal physical property evaluation apparatus according to claim 1, further comprising display means capable of displaying the absolute value of the admittance with respect to the sweep voltage component Vs. 3. The liquid crystal physical property evaluation apparatus according to claim 1, wherein the sweep speed Rs of the sweep voltage component Vs is changed, and the sweep speed v <b> 0 at which ΔV = 0 is measured or determined. Liquid crystal physical property evaluation apparatus according to any one of claims 1 to 3, characterized in that a display means capable of displaying the phase of the admittance with respect to the sweeping voltage component Vs. 5. The frequency f and peak-peak amplitude Vpp of the high-frequency AC component can be changed, and the frequency f is set so that the phase change of the admittance is observed most sensitively. Liquid crystal physical property evaluation device. The two electrodes, the liquid crystal physical property evaluation apparatus according to any one of claims 1 to 5, characterized in that it comprises an orientation means for determining the orientation of the liquid crystal to be sandwiched therebetween.

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