This work was supported by the HAS-JSPS bilateral joint research project. Financial support from grants NKFIH PD 121019 and FK 125134 is acknowledged.

1. Preparation of rubbed surfaces for aligning LC molecules planarly
<ol>
	<li>Prepare clean glass substrates.
	<ol>
		<li>Cut glass substrates using a diamond-based glass cutter (Table of Materials) into small square pieces with averages sizes of 1 cm x 1 cm. Wash them by sonication at 38 kHz or 42 kHz in an alkaline detergent (Table of Materials, diluted in water at a detergent:water volume ratio of 1:3) and rinse with distilled water repeatedly (typically, more than 10x with 5 min o...

<ol>
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Reversible Solution Viscosity Change of Polymamides Having Azobenzene Residues in the Main Chain.</a> Macromolecules. 14, 262-267 (1981).</li><li>Ito, S., Akiyama, H., Sekizawa, R., Mori, M., Yoshida, M., Kihara, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-Induced+Reworkable+Adhesives+Based+on+ABA-type+Triblock+Copolymers+with+Azopolymer+Termini.">Light-Induced Reworkable Adhesives Based on ABA-type Triblock Copolymers with Azopolymer Termini.</a> ACS Applied Materials and Interfaces. 10, 32649-32658 (2018).</li><li>Yamamoto, T., Norikane, Y., Akiyama, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photochemical+liquefaction+and+softening+in+molecular+materials,+polymers,+and+related+compounds.">Photochemical liquefaction and softening in molecular materials, polymers, and related compounds.</a> Polymer Journal. 50, 551-562 (2018).</li><li>Petr, M., Helgeson, M. 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Y., Lee, S. A., Kim, H., Kim, S. M., Kim, N., Jeong, K. U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+azobenzene-based+photochromic+liquid+crystalline+amphiphile+for+a+remote-controllable+light+shutter.">An azobenzene-based photochromic liquid crystalline amphiphile for a remote-controllable light shutter.</a> Chemical Communications. 51, 11080 (2015).</li><li>Saito, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-melt+adhesive+based+on+dynamic+carbon+frameworks+in+a+columnar+liquid-crystal+phase.">Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase.</a> Nature Communications. 7, 1-7 (2016).</li><li>Peng, S., Guo, Q., Hughes, T. C., Hartley, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversible+Photorheological+Lyotropic+Liquid+Crystals.">Reversible Photorheological Lyotropic Liquid Crystals.</a> Langmuir. 30, 866-872 (2014).</li><li>Ito, S., Yamashita, A., Akiyama, H., Kihara, H., Yoshida, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Azobenzene-Based+(Meth)acrylates:+Controlled+Radical+Polymerization,+Photoresponsive+Solid&#8211;Liquid+Phase+Transition+Behavior,+and+Application+to+Reworkable+Adhesives.">Azobenzene-Based (Meth)acrylates: Controlled Radical Polymerization, Photoresponsive Solid&#8211;Liquid Phase Transition Behavior, and Application to Reworkable Adhesives.</a> Macromolecules. 51, 3243-3253 (2018).</li><li>Yue, Y., Norikane, Y., Azumi, R., Koyama, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-induced+mechanical+response+in+crosslinked+liquid-crystalline+polymers+with+photoswitchable+glass+transition+temperatures.">Light-induced mechanical response in crosslinked liquid-crystalline polymers with photoswitchable glass transition temperatures.</a> Nature Communications. 9, 1-8 (2018).</li><li>Lee, H. Y., Diehn, K. K., Sun, K., Chen, T., Raghavan, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversible+Photorheological+Fluids+Based+on+Spiropyran-Doped+Reverse+Micelles.">Reversible Photorheological Fluids Based on Spiropyran-Doped Reverse Micelles.</a> Journal of the American Chemical Society. 133, 8461-8463 (2011).</li><li>Su, X., Cunningham, M. F., Jessop, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Switchable+viscosity+triggered+by+CO2+using+smart+worm-like+micelles.">Switchable viscosity triggered by CO2 using smart worm-like micelles.</a> Chemical Communications. 49, 2655-2657 (2013).</li><li>Cho, M. Y., Kim, J. S., Choi, H. J., Choi, S. B., Kim, G. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultraviolet+light-responsive+photorheological+fluids:+as+a+new+class+of+smart+fluids.">Ultraviolet light-responsive photorheological fluids: as a new class of smart fluids.</a> Smart Materials and Structures. 26, 1-8 (2017).</li><li>Oh, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+route+to+fluids+with+photo-switchable+viscosities+based+on+a+reversible+transition+between+vesicles+and+wormlike+micelles.">A simple route to fluids with photo-switchable viscosities based on a reversible transition between vesicles and wormlike micelles.</a> Soft Matter. 9, 5025-5033 (2013).</li><li>Akamatsu, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoinduced+viscosity+control+of+lecithin-based+reverse+wormlike+micellar+systems+using+azobenzene+derivatives.">Photoinduced viscosity control of lecithin-based reverse wormlike micellar systems using azobenzene derivatives.</a> RSC Advances. 8, 23742-23747 (2018).</li><li>Song, B., Hu, Y., Zhao, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single-component+photo-responsive+fluid+based+on+a+gemini+surfactant+with+an+azobenzene+spacer.">A single-component photo-responsive fluid based on a gemini surfactant with an azobenzene spacer.</a> Journal of Colloid and Interface Science. 333, 820-822 (2009).</li><li>Borshch, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nematic+twist-bend+phase+with+nanoscale+modulation+of+molecular+orientation.">Nematic twist-bend phase with nanoscale modulation of molecular orientation.</a> Nature Communications. 4, 2635-2643 (2013).</li><li>Panov, V. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+Periodic+Deformations+in+Nonchiral+Planar-Aligned+Bimesogens+with+a+Nematic-Nematic+Transition+and+a+Negative+Elastic+Constant.">Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic Constant.</a> Physical Review Letters. 105, 1-4 (2010).</li><li>Aya, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast-and-Giant+Photorheological+Effect+in+a+Liquid+Crystal+Dimer.">Fast-and-Giant Photorheological Effect in a Liquid Crystal Dimer.</a> Advanced Materials Interfaces. 6, 1-7 (2019).</li><li>Ishiba, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoliquefiable+ionic+crystals:+A+phase+crossover+approach+for+photon+energy+storage+materials+with+functional+multiplicity.">Photoliquefiable ionic crystals: A phase crossover approach for photon energy storage materials with functional multiplicity.</a> Angewandte Chemie International Edition. 54, 1532-1536 (2015).</li><li>Zhou, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoswitching+of+glass+transition+temperatures+of+azobenzene-containing+polymers+induces+reversible+solid-to-liquid+transitions.">Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions.</a> Nature Chemistry. 9, 145-151 (2017).</li></ol>

The authors have nothing to disclose.

As revealed in Figure 1, CB6OABOBu is a photo-responsive material with I, N, TB, and Cry phase sequences upon cooling. Since local ordering of these phases differs significantly, the photo-driven switching of rheological properties is expected to exhibit good viscoelastic contrast. To quantitatively investigate this, photo-rheology measurements were performed.
First, we consider the rheological data measured in the dark (Figure 2<stro...

Smart mechanical materials with the capability to change their viscoelastic properties in response to environmental variation have generated tremendous interest among researchers. Switchability is considered to be the most important material factor, which offers robustness of repetitive mechanical response in living organisms. To date, artificial switchable materials with versatile functions have been designed by utilizing soft matter (i.e., photoresponsive hydrogels1,2,3, polymers4,5,6,7,8,9,10,11, liquid crystals [LCs]9,10,11,12,13,14,15,16,17, pH-responsive micelles18,19,20,21,22, and surfactants23). However, these materials suffer from more than one of the following problems: lack of reversibility, low switching contrast ratio of viscoelasticity, low adaptivity, and slow switching speed. In conventional materials, a tradeoff exists between the switching contrast ratio of viscoelasticity and switching speed; thus, designing materials covering all of these criteria with high performance is challenging. To realize materials with the aforementioned omnicapability, selecting or designing molecules that carry emergent natures of both high fluidity (viscous property) and rigidity (elastic property) is essential.
Liquid crystals are ideal systems with a potentially large number of liquid crystalline and solid phases that can be tuned by molecular design. This allows for self-assembled structures at different length scales in particular LC phases. For example, while high-symmetry nematic LCs (NLCs) exhibit low viscosity and elasticity because of their short-range spatial order, low-symmetry columnar or smectic LCs show high viscosity and elasticity due to one- and two-dimensional long-range periodicities. It is expected that if LC materials can be switched between two phases with large differences in their viscoelastic properties, then a viscoelastic smart material with high performance can be achieved. A few examples have been reported9,10,11,12,13,14,15.
This article demonstrates the preparation of a photorheological LC material with a phase sequence of isotropic (I)-nematic (N)-twist-bend nematic (TB)24-crystal (Cry) upon cooling (and vice versa upon heating), which exhibits fast and reversible viscoelastic switching in response to light. Presented here are the methods for measuring viscoelasticity and an illustration of the microscopic structure-viscoelasticity relationship. Details are described in the representative results and discussion sections.

<table>
	<tbody>
		<tr>
			<td>21-401-10</td>
			<td>AS ONE</td>
			<td></td>
			<td>Microspatula</td>
		</tr>
		<tr>
			<td>AL1254</td>
			<td>JSR</td>
			<td></td>
			<td>Planar alignment agent for liquid crystals</td>
		</tr>
		<tr>
			<td>BX53P</td>
			<td>Olympus</td>
			<td></td>
			<td>Polarising microscope with transmission/epi-illumination units</td>
		</tr>
		<tr>
			<td>Discovery DSC 25P</td>
			<td>TI instruments</td>
			<td></td>
			<td>Photo-DSC equipment</td>
		</tr>
		<tr>
			<td>Glass cutter PRO-1A</td>
			<td>Sankyo</td>
			<td></td>
			<td>A diamond-based glass cutter</td>
		</tr>
		<tr>
			<td>HS82</td>
			<td>Mettler Toledo</td>
			<td></td>
			<td>hot stage</td>
		</tr>
		<tr>
			<td>MCR502</td>
			<td>Anton Paar</td>
			<td></td>
			<td>A commercial rheometer</td>
		</tr>
		<tr>
			<td>MRJ-100S</td>
			<td>EHC</td>
			<td></td>
			<td>Rubbing machine</td>
		</tr>
		<tr>
			<td>Norland Optical Adhesive 65, 81</td>
			<td>Norland Products</td>
			<td></td>
			<td>Photoreactive adhesions</td>
		</tr>
		<tr>
			<td>OmniCure S2000</td>
			<td>Excelitas Technologies</td>
			<td></td>
			<td>A commericial high-pressure mercury vapor short arc lamp. Maximum 70 mW/cm^2.</td>
		</tr>
		<tr>
			<td>PILATUS 6M</td>
			<td>Dectris</td>
			<td></td>
			<td>Hybrid photon counting detector for X-ray diffraction dectection</td>
		</tr>
		<tr>
			<td>S1126</td>
			<td>Matsunami Glass</td>
			<td></td>
			<td>Glass substrate</td>
		</tr>
		<tr>
			<td>SC-158H</td>
			<td>EHC</td>
			<td></td>
			<td>Spin coater</td>
		</tr>
		<tr>
			<td>SCAT-20X</td>
			<td>DKS</td>
			<td></td>
			<td>Alkaline detergent</td>
		</tr>
		<tr>
			<td>SLUV-4</td>
			<td>AS ONE</td>
			<td></td>
			<td>Low-pressure mercury vapor short arc lamp</td>
		</tr>
		<tr>
			<td>UV-208</td>
			<td>Technovision</td>
			<td></td>
			<td>Ultraviolet-ozone (UV-O3) cleaner</td>
		</tr>
	</tbody>
</table>

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.

POM images, photorheometric data, photo-DSC data, and XRD intensity profiles were collected in darkness during temperature variation and while shining UV light. Figure 1a,b represents the structure of CB6OABOBu, with its phase sequence and possible conformations optimized by the MM2 forcefield in the modeling program (e.g., ChemBio3D).
When CB6OABOBu is in the trans-state, two energy-plausible conformational states appear, and the twisted conforma...

Watch this Scientific Journal Video about High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal at JoVE.com

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

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 ...

This protocol explains how to characterize the viscoelastic stretching properties of liquid crystals, and it helps to answer key questions about how to develop new photorheological materials. The main advantage of this method is that the rheological properties and relevant structural properties can measured under light stimuli in real time, allowing recording of the photorheological switching behavior. Before beginning the procedure, use a diamond-based glass cutter to cut glass substrates with average sizes of one-by-one centimeter, and wash the pieces at 38 or 42 kilohertz in an alkaline detergent.Next rinse the substrates with 10 five-minute washes with sonication in fresh distilled water per wash, and subject the substrates to UV-ozone for at least 10 minutes. To add a planar alignment layer, use a pipette to dispense one milliliter of a polyamide planar alignment solution in 20-microliter droplets onto each cleaned glass substrate. Immediately use a spin coater to spin coat an approximately 20-nanometer thick alignment layer onto the substrates.At the end of the spin, bake the coated glass substrates at 80 degrees Celsius for 60 minutes to remove the solvent, followed by curing for at least 60 minutes at 180 degrees Celsius. Then use a rayon cloth rubbing machine to rub the substrates at the appropriate parameters. Add 100 microliters of a photoreactive adhesive and 0.1 milligram of five-micrometer diameter glass particles onto a new glass substrate, and use the tip of a paperclip to mix the materials.Transfer the mixed material to four corners of the glass substrate cell to adjust the cell gap, and use a low-pressure mercury vapor short arc lamp or a UV led to illuminate the cell with a 365-nanometer wavelength. After the illumination, place the cell onto a hot stage, and set the target temperature of the stage to heat the cell to a temperature above the isotropic liquid nematic phase transition. At the end of the phase transition, transfer the entire 0.2 to 10-microliter liquid crystal material onto one open surface of the cell.Use a microspatula to push the materials towards the cell entrance to obtain contact between the liquid crystal material and the entrance of the cell. Then wait for the liquid crystal material to fill in the cell by capillary force. For texture characterization of the liquid crystal cells, place the samples onto the hot stage to control the sample temperature with a plus or minus 0.1 kelvin accuracy under a polarizing light microscope.Use a digital color camera and a UV epi-illuminator to sequentially record the textures during cooling and heating with and without UV irradiation. For rheological measurement of the samples, first perform geometry inertia and zero gap calibrations within the software according to the manufacturer's instructions. Then weigh out 250 milligrams of the powdered CB6OABOBu sample.Next load the sample onto the base quartz plate of the rheometer, and set the temperature of the sample chamber to a value above the isotropic-nematic phase transition point. Then set a gap value for approaching the measuring plate to the base quartz plate to sandwich the sample. Use paper lab wipes to trim any excess sample that is outside of the gap when the measuring plate stops at the trimming position.To perform the measurement, irradiate the sample at 365 nanometers, measuring the photorheological switching of CB6OABOBu using the high-pressure mercury vapor short arc lamp. In the nematic phase, a uniaxial alignment of the molecules is realized. When decreasing the temperature to the twist-bend in darkness, a striped pattern forms, in which the stripes run parallel to the rubbing direction of the liquid crystal cell.Further decreasing of the temperature leads to crystallization. Irradiation with UV light alters the conformation from a trans to a cis state, resulting in phase variation and thus texture variation, with the UV light transforming the striped texture to the uniaxial aligned state of the nematic phase when starting from the twist-bend phase. Turning off the UV light allows the molecules to relax and reenter the trans state, resulting in reformation of the striped texture of the twist-bend phase.Measurement of the effective viscosity of the CB6OABOBu under various conditions reveals the temperature dependence of the effective shear viscosity. Here the shear stress dependence of the effective shear viscosity at different temperatures during the first and second runs can be observed. In this graph, the variation among the effective shear viscosity triggered by UV irradiation at different temperatures is shown.And these graphs illustrate the switching curves of the effective shear viscosity in a log scale at two different temperatures. To obtain reliable data, it is crucial to calibrate the rheometer right before acquiring measurements. One idea for future studies on photosensitive dimers is to check a broadband dielectric spectra that could give insight into the molecular dynamics on the different phases and illumination conditions.

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JoVE Journal

Chemistry

6.3K 조회수.  RIKEN Center for Emergent Matter Science (CEMS). 이 프로토콜은 액정의 점탄성 스트레칭 특성을 특성화하는 방법을 설명하고 새로운 광원 물질을 개발하는 방법에 대한 주요 질문에 답하는 데 도움이됩니다. 이 방법의 주요 장점은 유변학적 특성및 관련 구조 적 특성이 실시간으로 빛 자극하에서 측정할 수 있어 광변 스위칭 동작을 기록할 수 있다는 것입니다. 절차를 시작하기 전에 다이아몬드 기반 유리 커터를 사용하여 ...