Name: An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation (Video) | JoVE Journal
Uploaded: 2019-02-27T14:30:00.000+00:00
Duration: 10 min 33 s
Description: Discover how to create an electrochemical cholesteric liquid crystal device for rapid color modulation using FcD dopant. This protocol achieves the fastest reported switching with low-voltage operation for advanced reflective displays.

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5 minutes

We&#160;thank Dr. Keisuke Tajima from RIKEN Center for Emergent Matter Science for valuable discussions. A part of this work was conducted at the Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This work was financially supported by a JSPS Grant-in-Aid for Scientific Research (S) (18H05260) on &#34;Innovative Functional Materials based on Multi-Scale Interfacial Molecular Science&#34; for T.A. Y.I. is grateful for a JSPS Grant-in-Aid for Challenging Exploratory Research (16K14062). S.T. thanks the JSPS Young Scientist Fellowship.

1. Preparation of the cholesteric LC mixture
<ol>
	<li>Add 84.6 mg of 5OCB and 5.922 mg of FcD19&#160;(3.1 mol% to 5OCB) into a clean 10 mL glass vial.</li>
	<li>Add 12.9&#160;mg of EMIm-OTf and 10 mL of dichloromethane (CH2Cl2) into a new clean 10 mL glass vial and mix well. Transfer 2.1&#160;mL of the EMIm-OTf solution into the 5OCB- and FcD-containing glass vial. Gently shake the vial to let all the components mix well.</li>
	<li>Cover the glass vial with an aluminum foil and make several holes at the top.</li>
	<li>Heat the above CH2Cl2&#160;solution containing 5OCB, FcD (3.1 mol% to 5OCB) and EMIm-OTf (3.0 mol% to 5OCB) at 80 &#176;C in a well-ventilated hood. After 60 min, most of the CH2Cl2&#160;is evaporated. This procedure is important to ensure homogeneous mixing of the components.</li>
	<li>Evaporate the remaining CH2Cl2&#160;under reduced pressure (~5.0 Pa) by oil rotary vacuum pump at 80 &#176;C for 60 min in the well-ventilated hood to obtain a clear orange LC mixture.</li>
</ol>
2. Preparation of the sandwich-type ITO glass cell
<ol>
	<li>Cleaning procedure of the ITO coated glass
	<ol>
		<li>Cut an ITO patterned glass (10 cm x 10 cm, resistance: ~30 &#937;), which contains 100 pieces of a designated electrode to a smaller size (10 mm x 10 mm) by a diamond tipped glass cutter so that one piece includes one pattern of the electrode. Always check the resistance of the surface of the glass to know which side is patterned with ITO using, for example, digital multi-meter (ITO patterned side has low resistance).</li>
		<li>Cut a fully ITO coated glass (10 cm &#215; 10 cm, resistance: ~30 &#937;) to a smaller size (10 mm x 12 mm) by a diamond tipped glass cutter. Again, check the resistance of the surface of the glass to know which side is coated with ITO.</li>
		<li>Prepare a washing solution by mixing 60 mL of Extran MA01 and 240 mL of ultrapure water in a glass vessel (~500 mL). Soak the above prepared ITO glass plates into the solution thoroughly in such a way that the surface of each glass plate does not touch with one another. In case of washing many ITO glass plates, it is recommended to use some support (e.g., shampoo brush).</li>
		<li>Put the vessel containing ITO glass plates in an ultrasonic bath and sonicate it for 30 min. After decanting off the washing solution, rinse the vessel containing ITO glass plates by 200 mL of ultrapure water for three times.</li>
		<li>Add 300 mL of ultrapure water and sonicate the vessel for 20 min. Then, remove the water by decantation. Repeat this washing cycle using ultrapure water for three times. For each washing cycle, check the arrangement of the ITO glass plates in the vessel so that the surfaces of the plates are not attached to one another.</li>
		<li>After finishing the washing cycles, dry the ITO glass plates one by one through the nitrogen gas flow. When putting the ITO glass plates on the clean place, keep the ITO surface upward in order to avoid any damage or contamination of the surface.</li>
	</ol>
	</li>
	<li>Fabrication of the PEDOT+ coated ITO glass plate
	<ol>
		<li>Put the glass vial containing a nitromethane solution of poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+, 0.7 wt%) into an ultrasonic bath and sonicate it for 60 min to obtain a well dispersed solution.</li>
		<li>Place the fully ITO coated glass plate on the rotator of the spin coater with the ITO surface facing upright. Blow off dust from the ITO surface by using a nitrogen blow gun. Carefully transfer 50 &#181;L of freshly sonicated PEDOT+ solution by pipette.</li>
		<li>Fabricate the PEDOT+ film by spinning the plate at a rate of 1000 rpm for 60 s at ambient conditions (~25 &#176;C, humidity: ~45%). Keep the PEDOT+ coated ITO glass plates under the ambient conditions for 1 h without baking.</li>
	</ol>
	</li>
	<li>Fabrication of the ITO glass cell
	<ol>
		<li>Blow off dust from ITO patterned glass plates by using a nitrogen blow gun.</li>
		<li>Rub the ITO face of the glass plates (10 mm x 10 mm) with rayon cloth thoroughly using a rubbing machine. During the whole process, use a nitrogen blow gun to avoid the contamination of dusts.</li>
		<li>Carry out the following procedures in a place that can avoid the contamination of dusts, ideally in a clean room.</li>
		<li>Mix a drop of an optical adhesive and a rice-sized amount of glass beads thoroughly.</li>
		<li>Lay down the PEDOT+ coated ITO glass plate on the table with the PEDOT+ surface facing upright. Put a very small amount of the adhesive mixture onto the PEDOT+ coated ITO glass plate where the four corners of the ITO patterned glass plate come.</li>
		<li>Put the ITO patterned glass plate onto the PEDOT+ coated ITO glass plate in such a way that the ITO surfaces of the two glass plates are facing to each other to fabricate a cell. Gently push the four corners of the cell. Confirm a uniform cell gap by the disappearance of a fringe pattern observed at the surface of the cell.</li>
		<li>Irradiate the above ITO glass cell with a 365 nm UV lamp for 20 s to strengthen the adhesion.</li>
		<li>Heat the above cell on a hot stage at 100 &#176;C for 3 h to continue strengthening the adhesion.</li>
		<li>Connect two conducting wires to each of the ITO area of the glass plates in the cell by ultrasonic soldering.</li>
	</ol>
	</li>
</ol>
3. Color modulation experiments
<ol>
	<li>Introduction of the cholesteric LC mixture into the ITO glass cell for the fabrication of the LC device
	<ol>
		<li>For easily handling, fix the wires of the above prepared glass cell to a microscope slide with an insulating tape.</li>
		<li>Heat the glass vial containing the cholesteric LC mixture at 80 &#176;C for 10 to 15 min on a hot stage. Also heat the ITO glass cell and a spatula, which is used for transferring the sample, at the same temperature.</li>
		<li>Transfer a small amount of the hot cholesteric LC mixture by using the heated spatula quickly to the gap of two ITO glass plates of the cell. Fill up the gap between the two glass plates by capillary action, which takes ~60 s.</li>
		<li>Lower the temperature of the hot stage so that the temperature of the cell reaches 37 &#176;C.</li>
		<li>Push the center of the device to exhibit bright reflection color.</li>
	</ol>
	</li>
	<li>Color modulation experiments by using a digital optical microscope.
	<ol>
		<li>Apply +1.5 and 0 V alternately to the LC device for 4 s and 8 s, respectively, by using a potentiostat at 37 &#176;C. The voltage values are defined for non-PEDOT+-coated ITO electrode in reference to that for PEDOT+-coated ITO electrode in the device. Observe and record the color change of the LC device by digital optical microscope.</li>
	</ol>
	</li>
	<li>Spectrometric color modulation experiments
	<ol>
		<li>Use the following UV-vis spectrophotometer setup parameters: photometric mode: %T, response: fast, bandwidth: 1.0 nm, scan speed: 2,000 nm/min, scan range: 800 to 300 nm</li>
		<li>For the baseline measurement, place the hot stage into the spectrophotometer without the LC device. Ensure that the observation hole is properly placed in the optical path of the spectrophotometer and the angle of incidence is 0&#176;. Monitor the transmittance value in real-time at a certain wavelength whose value is maximized by adjusting the placement of the hot stage. Then start for the baseline measurement.</li>
		<li>Place the LC device into this hot stage, and then, place the hot stage to the appropriate position in a same way as described in section 3.3.2. Start the measurement and record the spectrum.</li>
		<li>Apply +1.5 V for 4 s and start the measurement. After the measurement, apply 0 V for 8 s and, again, start the measurement.</li>
		<li>Apply +1.5 and 0 V alternately for 100 times to the LC device for 4 s and 8 s, respectively, by using a potentiostat. Record transmittance at a designated wavelength (510 nm) during the voltage application cycles.</li>
	</ol>
	</li>
</ol>

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We have nothing to disclose.

Upon application of +1.5 V to the top ITO electrode (Figure 1C), FcD undergoes an oxidation reaction to generate FcD+. As the helical twisting power of FcD+ (101 &#181;m-1, Figure 1B) is lower than that ...

Cholesteric liquid crystals (LCs) are known to exhibit bright reflection colors due to their internal helical molecular arrangements1,2,3,4. The reflection wavelength &#955; is determined by the helical pitch P and the average refractive index n of the LC (&#955; = nP). Such LCs can be generated by doping chiral compounds (chiral dopants) to nematic LCs and its helical pitch is defined by the equation P = 1/&#946;MC, where &#946;M is the helical twisting power (HTP) and C is the molar fraction of the chiral dopant. Based on this notion, various chiral dopants that can respond to a variety of stimuli such as light5,6,7,8, heat9, magnetic field10, and gas11&#160;has been developed. Such properties are potentially useful for various applications such as sensors12&#160;and lasers13,14,15&#160;among others16,17,18.
Recently, we developed the first redox-responsive chiral dopant FcD (Figure 1A)19&#160;that can change its HTP value in response to redox reactions. FcD is composed of a ferrocene unit, which can undergo reversible redox reactions20,21,22, and a binaphthyl unit, which is known to exhibit high HTP value23. The cholesteric LC doped with FcD, in the presence of a supporting electrolyte, can change its reflection color within 0.4 s and recover its original color in 2.7 s upon voltage application of +1.5 and 0 V, respectively. The high response speed and low operating voltage observed for the device is unprecedented among any other cholesteric LC device so far reported.
One of the important applications of the cholesteric LCs is in reflective displays, whose energy consumption rate is much lower than the conventional LC displays. For this purpose, cholesteric LCs should change its reflection color with electrical stimuli. However, most of the previous methodologies utilize an electrical coupling between the applied electrical stimuli and the host LC molecules, which requires high voltage over 40 V24,25,26,27,28. For the use of the electrically responsive chiral dopant, there are only few examples29,30&#160;including our previous work31, which also requires high voltage with low response speed. Considering these previous works, the performance of our FcD-doped cholesteric LC device, especially for the fast color modulation speed (0.4 s) and low operating voltage (1.5 V), is a groundbreaking achievement that can greatly contribute to the development of next generation reflective displays. In this detailed protocol, we demonstrate the fabrication processes and the operating procedures of the prototype cholesteric LC display devices.

<table><tbody><tr><td>1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate, 98%</td><td>TCI</td><td>E0494</td><td></td></tr><tr><td>4-Cyano-4&#039;-pentyloxybiphenyl, 98%</td><td>TCI</td><td>C1551</td><td></td></tr><tr><td>Diamond tipped glass cutter</td><td>AS ONE</td><td>6-539-05</td><td></td></tr><tr><td>Dichloromethane, 99.5%</td><td>KANTO CHEMICAL</td><td>10158-2B</td><td>HPLC grade</td></tr><tr><td>Differential Scanning Calorimeter</td><td>METTLER TOLEDO</td><td>DSC 1</td><td></td></tr><tr><td>Digital microscope&amp;nbsp;</td><td>KEYENCE</td><td>VHX-5000</td><td></td></tr><tr><td>Extran MA01</td><td>Merck</td><td>107555</td><td></td></tr><tr><td>Fully ITO-coated glass plate</td><td></td><td></td><td>Costum order, Resistance: ~30&amp;Omega;</td></tr><tr><td>Glass beads</td><td>Thermo Fisher Scientific</td><td>9005</td><td>5 &amp;plusmn; 0.3 &amp;mu;m in diameter</td></tr><tr><td>Hot stage</td><td>INSTEC</td><td>mK1000</td><td></td></tr><tr><td>ITO-patterned glass plate</td><td></td><td></td><td>Costum order, Resistance: ~30&amp;Omega;</td></tr><tr><td>Oil rotary vacuum pump</td><td>SATO VAC</td><td>TSW-150</td><td>Pressure: ~5 Pa</td></tr><tr><td>Optical adhesive</td><td>Noland</td><td>NOA81</td><td></td></tr><tr><td>Poly(3,4-ethylenedioxythiophene), bis-poly(ethyleneglycol), lauryl terminated</td><td>Sigma Aldrich</td><td>687316</td><td>0.7 wt% (dispersion in nitromethane)</td></tr><tr><td>Potentiostat</td><td>TOHO TECHNICAL RESEARCH</td><td>PS-08</td><td></td></tr><tr><td>Rubbing machine</td><td>EHC</td><td>MRJ-100S</td><td></td></tr><tr><td>Spectrophotometer</td><td>JASCO</td><td>V-670 UV/VIS/NIR</td><td></td></tr><tr><td>Spin coater</td><td>MIKASA</td><td>1H-D7</td><td></td></tr><tr><td>Ultrapure water</td><td>Merck&amp;nbsp;</td><td>Milli-Q Integral 3</td><td></td></tr><tr><td>Ultrasonic bath</td><td>AS ONE</td><td>ASU-2</td><td>Power: 40 W</td></tr><tr><td>Ultrasonic soldering</td><td>KURODA TECHNO</td><td>SUNBONDER USM-IV</td><td></td></tr><tr><td>UV lamp</td><td>AS ONE</td><td>SLUV-4</td><td>Power: 4 W</td></tr></tbody></table>

an electrochemical cholesteric liquid crystalline device for quick and low-voltage color modulation

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The cholesteric LC is composed of a nematic LC 4&#39;-pentyloxy-4-cyanobiphenyl (5OCB), redox-responsive chiral dopant (FcD), and a supporting electrolyte 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-OTf). The most important component is FcD. This molecule changes its helical twisting power (HTP) value in response to redox reactions. Therefore, in situ electrochemical redox reactions in the LC mixture allow for the device to change its reflection color in response to electrical stimuli. The LC mixture was introduced, by a capillary action, into a sandwich-type ITO glass cell comprising two glass slides with patterned indium tin oxide (ITO) electrodes, one of which was coated with poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+). Upon application of +1.5 V, the reflection color of the device changed from blue (467 nm) to green (485 nm) in 0.4 s. Subsequent application of 0 V made the device recover the original blue color in 2.7 s. This device is characterized by its fastest electrical response and lowest operating voltage among any previously reported cholesteric LC device. This device could pave the way for the development of next generation reflective displays with low energy consumption rates.

Photographs, transmittance spectra, and time dependent transmittance change profiles at 510 nm are collected for the LC device containing FcD-doped (3.1 mol%) cholesteric LC in the presence of EMIm-OTf (3.0 mol%) during the voltage application cycles between 0 and +1.5 V at 37 °C.
The LC mixture containing FcD (3.1 mol%), ...

A protocol for the fabrication of a reflective cholesteric liquid crystalline display device containing a redox-responsive chiral dopant allowing quick and low-voltage operation is presented.

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

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Discover how to create an electrochemical cholesteric liquid crystal device for rapid color modulation using FcD dopant. This protocol achieves the fastest reported switching with low-voltage operation for advanced reflective displays.

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

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