Name: an electrochemical cholesteric liquid crystalline device for quick and low-voltage color modulation
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Description: Watch this Scientific Journal Video about An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation at JoVE.com

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

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 &#176;C.
The LC mixture containing FcD (3.1 mo...

Watch this Scientific Journal Video about An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation at JoVE.com

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

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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Research

JoVE Journal

Chemistry

8.4K Views.  The University of Tokyo. 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.

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

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

Engineering

Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active layer which consists of blue-fluorescent poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and &#960;-conjugated triphenylamine molecules. This white light emission originates from exciplexes formed between PFD and amines in electronically excited states. A device containing PFD, 4,4&#39;,4&#39;&#39;-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), Poly(ethylene oxide) and K2CF3SO3 showed white light emission with Commission internationale de l&#39;&#233;clairage (CIE) coordinates of (0.33, 0.43) and a Color Rendering Index (CRI) of Ra = 73 at an applied voltage of 3.5 V. Constant voltage measurements showed that the CIE coordinates of (0.27, 0.37), Ra of 67, and the emission color observed immediately after application of a voltage of 5 V were nearly unchanged and stable after 300 sec.

The authors present a method for fabricating stable white-light-emitting electrochemical cells utilizing emission from exciplexes formed between a blue-emitting fluorene polymer and aromatic amines.

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active ...

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Optical Control of Living Cells Electrical Activity by Conjugated Polymers

Hybrid interfaces between organic semiconductors and living tissues represent a new tool for in-vitro and in-vivo applications. In particular, conjugated polymers display several optimal properties as substrates for biological systems, such as good biocompatibility, excellent mechanical properties, cheap and easy processing technology, and possibility of deposition on light, thin and flexible substrates. These materials have been employed for cellular interfaces like neural probes, transistors for excitation and recording of neural activity, biosensors and actuators for drug release. Recent experiments have also demonstrated the possibility to use conjugated polymers for all-optical modulation of the electrical activity of cells. Several in-vitro study cases have been reported, including primary neuronal networks, astrocytes and secondary line cells. Moreover, signal photo-transduction mediated by organic polymers has been shown to restore light sensitivity in degenerated retinas, suggesting that these devices may be used for artificial retinal prosthesis in the future. All in all, light sensitive conjugated polymers represent a new approach for optical modulation of cellular activity.
In this work, all the steps required to fabricate a bio-polymer interface for optical excitation of living cells are described. The function of the active interface is to transduce the light stimulus into a modulation of the cell membrane potential. As a study case, useful for in-vitro studies, a polythiophene thin film is used as the functional, light absorbing layer, and Human Embryonic Kidney (HEK-293) cells are employed as the biological component of the interface. Practical examples of successful control of the cell membrane potential upon stimulation with light pulses of different duration are provided. In particular, it is shown that both depolarizing and hyperpolarizing effects on the cell membrane can be achieved depending on the duration of the light stimulus. The reported protocol is of general validity and can be straightforwardly extended to other biological preparations.

A method for stimulation of in-vitro cell cultures electrical activity with visible light, based on the use of organic semiconducting polymers is described.

Hybrid interfaces between organic semiconductors and living tissues represent a new tool for in-vitro and in-vivo applications. In particular, conjugated ...

Bioengineering

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...