Name: novel techniques for observing structural dynamics of photoresponsive liquid crystals
Uploaded: 2018-05-29T14:00:00.000+00:00
Duration: 10 min 35 s
Description: Watch this Scientific Journal Video about Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals at JoVE.com

We thank Dr. S. Tanaka at Tokyo Institute of Technology for time-resolved IR vibrational spectroscopy measurements and Prof. M. Hara and Dr. K. Matsuo at Nagoya University for XRD measurements. We also thanks Prof. S. Yamaguchi at Nagoya University, Prof. R. Herges at Kiel University and Prof. R. J. D. Miller at the Max Planck Institute for the Structure and Dynamics of Matter for valuable discussion.
This work is supported by the Japanese Science Technology (JST), PRESTO, for funding the projects "Molecular technology and creation of new functions" (Grant Number of JPMJPR13KD, JPMJPR12K5, and JPMJPR16P6) and "Chemical conversion of light energy". This work is also partially supported by JSPS Grant Numbers JP15H02103, JP17K17893, JP15H05482, JP17H05258, JP26107004, and JP17H06375.

1.Time-Resolved Infrared Vibrational Spectroscopy
<ol>
	<li>Sample preparation
	<ol>
		<li>Solution: Dissolve the &#960;-extended cyclooctatetraene (&#960;-COT) molecules into dichloromethane with proper concentration (1 mmol/L).</li>
		<li>LC phase: Melt the &#960;-COT powder on a calcium fluoride (CaF2) substrate using hot plate at the temperature of 100 &#176;C. Cool the sample at a room temperature. 
		Note: We need to choose a material (CaF2 or barium fluoride (BaF2)) that is transparent in mid-IR range.</li>
	</ol>
	</li>
	<li>Apparatus setting-up
	<ol>
		<li>Switch on the titanium sapphire (Ti:sapphire) laser and the chirped pulse amplifier. Thermally stabilize them for several hours.</li>
		<li>Make sure the alignments are correct. Check the power and stability of the ultraviolet (UV) pump and the mid-IR probe and re-align the optical path if necessary. The optical setup of the time-resolved infrared spectroscopy is provided in Figure 5.</li>
		<li>Cool the HgCdTe IR detector array using liquid nitrogen. Make sure that the spectrometer is properly located so that reasonable amount of light is detected in the range of interest. Calibrate the spectrometer using absorption spectra of well-known materials such as polystyrene or polyethylene terephthalate.</li>
		<li>Mount a sample which shows large photo-induced transient response (Si wafer (1 mm) or Re(bpy)(CO)3Cl/CH3CN solution) on the sample holder. Locate the pump-probe delay to a positive value and optimize the amount of the transient signal by stirring the pump beam to ensure the pump-probe overlap.</li>
		<li>Find the time origin setting by taking long-range scan on the pump-probe delay using the home-built program (Figure 6). Check the position where the transient signal start to emerge.</li>
		<li>Check the dynamics of symmetric and anti-symmetric vibration of CO stretching in Re(bpy)(CO)3Cl whose dipole moments are orthogonal. Note that both should show exactly same dynamics when the magic angle condition is properly met.</li>
	</ol>
	</li>
	<li>Measurement and data acquisition
	<ol>
		<li>Solution: Mount the home-built flow cell. Setup the bubbling device with inert gas (nitrogen (N2) or Argon (Ar)) if necessary. LC phase: Mount the spin-coated &#960;-COT sample with the substrate on the motorized stage to continuously move the laser spots on the sample to minimize the laser-induced damage.</li>
		<li>Doublecheck the time zero position with the sample.</li>
		<li>Set the scan range of the pump-probe delay properly (start, end, and step).</li>
		<li>Choose a directory to save data.</li>
		<li>Start the data collection with the home-built program. 
		NOTE: The data are recorded automatically in the directory.</li>
	</ol>
	</li>
</ol>
2. Time-Resolved Electron Diffraction
<ol>
	<li>Fabrication of sample substrate
	<ol>
		<li>Purchase a silicon (001) wafer (200 &#181;m thick), both sides of which are pre-covered with 30-nm-thick silicon-rich silicon nitride (Si3N4, or simply SiN) film (Figure 11A). Cut the SiN/Si/SiN wafer in square (15 &#215; 15 mm2).</li>
		<li>Irradiate with Ar cluster ion beams41 at the fluence of 2.5 &#215; 1016 ions/cm2 onto one of the sides of the SiN/Si/SiN wafer though a metal mask (Figure 12), which is sufficient to remove the 30-nm-thick SiN film (Figure 11B,C). 
		NOTE: An alternative method to remove SiN film is plasma etching or ion beams etching.</li>
		<li>Prepare potassium hydroxide (KOH)aqueous solution at a concentration of 28%.</li>
		<li>Put the wafer into KOH solution at a temperature of 60-70 &#176;C for 1-2 days (Figure 11D), which perform further etching of the Si wafer via isotropic chemical etching42. 
		NOTE: The etching rate for Si by KOH solution is much faster than that for SiN, so the SiN thin film remains as self-supporting membranes (Figure 11E).</li>
		<li>Clean the wafer with SiN membranes in deionized water and dry it with nitrogen gas.</li>
	</ol>
	</li>
	<li>Sample preparation
	<ol>
		<li>Dissolve the &#960;-COT molecules in chloroform at a concentration of 10 mg/mL.</li>
		<li>Program the spin-coater: accelerate to 2000 rpm in 5 s, keep the rotation for 30 s, and stop the rotation. Spin-coat the &#960;-COT solution onto the SiN membrane substrate as shown in Figure 11F. 
		NOTE: A proper wafer size for spin-coating must be more than 10 &#215; 10 mm2, since the surface tension sometimes interferes with spin-coating of materials on smaller wafers, for example, a SiN membrane grid for transmission electron microscopy.</li>
		<li>Put the sample coated on the SiN membrane substrate on a hotplate at a temperature of 100 &#176;C, melt it, and cool it gradually to room temperature (Figure 11G).</li>
	</ol>
	</li>
	<li>Measurements
	<ol>
		<li>Mount the sample on the sample holder with a screw and put the sample holder in the vacuum chamber (sample chamber).</li>
		<li>Seal the vacuum chamber with a lid and switch on a rotary pump to evacuate the chamber until a vacuum level of less than 1000 Pa. Then, switch on the molecular turbo pumps until the electron-gun chamber is at the vacuum level of ~10-6 Pa (typically for more than 12 h).</li>
		<li>Switch on the Ti:sapphire laser and the chirp pulse amplifier, and thermally stabilize them for more than 1 h. The experimental setup of the time-resolved electron diffraction is provided in Figure 9. Set the repetition rate to 500 Hz.</li>
		<li>Switch on the thriller of the charge-coupled device (CCD) camera and cool it to 10 &#176;C.</li>
		<li>Switch on the electrical power supply and adjust the voltage to 75 kV. 
		NOTE: The leak current of the power supply should not fluctuate out of the 0.1 &#181;A range.</li>
		<li>Special overlap. Open the laboratory-coded automatic program (Figure 10A) and set the exposure time (50 ms). Find the electron beam position with a pinhole equipped in the sample holder using the program by setting Start type to Z_overlap for the overlap of Z-axis and Y_overlap and pressing Start button.</li>
		<li>Set the electron beam at the pinhole position and align the pump laser with the reflected pump light by the pinhole.</li>
		<li>Measure the time-zero position with an inorganic material (Bi2Te3) on the sample holder using a laboratory-coded automatic program (Figure 10B) by setting Start type to Time-resolved and pressing Start button. For this process, adjust the pump fluence to 2 mJ/cm2.</li>
		<li>Insert the Faraday cup to the pass of the electron beam and measure the fluence of the electron beam with a laboratory-built picoammeter and adjust it by rotating the adjustable ND filter on the probe line. Adjust thefluence of the pump pulse by rotating the waveplate on the pump line.</li>
		<li>Move to the sample position and set the exposure time of the CCD camera. Obtain the electron diffraction image using the laboratory-coded automatic program (Figure 10B) by setting Start type to Single and pressing Start button.</li>
		<li>Switch on the Peltier element of the CCD camera and cool it down to the temperature of -20 &#176;C.</li>
		<li>Set the time-step and number of steps for the time-resolved measurements. Obtain the time-resolved electron diffraction images using the laboratory-coded automatic program (Figure 10B) by setting Start type to Time-resolved and pressing Start button.</li>
		<li>Obtain the time-resolved background image with the electron acceleration power supply switching off using the laboratory-coded automatic program (Figure 10B) by setting Start type to Time-resolved and pressing Start button.</li>
	</ol>
	</li>
</ol>

The authors have nothing to disclose.

The crucial step of the process during the time-resolved electron diffraction measurements is maintaining the high voltage (75 keV) without current fluctuation since the distance between the photocathode and anode plate is only ~10 mm. If the current fluctuates above the range of 0.1 &#181;A before or during the experiments, increase the acceleration voltage up to 90 keV to discharge and set it again to 75 keV. This conditioning process has to be done until the current fluctuates in the range of 0.1 &#181;A. The proper d...

Liquid crystals (LCs) have a variety of functions and are widely used in scientific and technological applications1,2,3,4,5,6. The behavior of LCs can be attributed to their orientational ordering as well as to the high mobility of their molecules. A molecular structure of LC materials is typically characterized by a mesogen core and long flexible carbon chains that ensure high mobility of the LC molecules. Under external stimuli7,8,9,10,11,12,13,14,15, such as light, electric fields, temperature changes, or mechanical pressure, small intra- and intermolecular motions of the LC molecules cause drastic structural reordering in the system, leading to its functional behavior. To understand the functions of LC materials, it is important to determine the molecular scale structure in the LC phase and identify the key motions of the molecular conformations and packing deformations.
X-ray diffraction (XRD) is commonly employed as a powerful tool for determining structures of LC materials16,17,18. However, the diffraction pattern originating from a functional stimuli-responsive core is often concealed by a broad halo pattern from the long carbon chains. An effective solution to this problem is provided by time-resolved diffraction analysis, which enables direct observations of molecular dynamics using photoexcitation. This technique extracts structural information about the photoresponsive aromatic moiety using the differences between the diffraction patterns obtained before and after photoexcitation. These differences provide the means both to remove the background noise and to directly observe the structural changes of interest. Analyses of the differential diffraction patterns reveal the modulated signals from the photoactive moiety alone, thereby excluding the deleterious diffraction from the non-photoresponsive carbon chains. A description of this method of differential diffraction analysis is provided in Hada, M. et al19.
Time-resolved diffraction measurements can provide structural information about the atomic rearrangements that occur during the phase transition in materials20,21,22,23,24,25,26,27,28,29 and chemical reactions among molecules30,31,32,33,34. With these applications in mind, remarkable progress has been made in the development of ultrabright and ultrashort-pulsed X-ray35,36 and electron37,38,39,40 sources. However, time-resolved diffraction has only been applied to simple, isolated molecules or to single- or poly-crystals, in which highly ordered inorganic lattice or organic molecules produce well-resolved diffraction patterns providing structural information. In contrast, ultrafast structural analyses of more complex soft materials have been hampered because of their less ordered phases. In this study, we demonstrate the use of time-resolved electron diffraction as well as transient absorption spectroscopy and time-resolved infrared (IR) vibrational spectroscopy to characterize the structural dynamics of photoactive LC materials using this diffraction-extracted methodology19.

<table><tbody><tr><td>Chirped pulse amplifier</td><td>Spectra Physics Inc.</td><td>Spitfire ACE</td><td>For time-resolved IR vibration spectroscopy</td></tr><tr><td>Chirped pulse amplifier&amp;nbsp;</td><td>Spectra Physics Inc.</td><td>Spitfire XP</td><td>For time-resolved electron diffractometry</td></tr><tr><td>Femtosecond laser</td><td>Spectra Physics Inc.</td><td>Tsunami</td><td>For time-resolved IR vibration spectroscopy</td></tr><tr><td>Femtosecond laser</td><td>Spectra Physics Inc.</td><td>Tsunami</td><td>For time-resolved electron diffractometry</td></tr><tr><td>Optical parametric amplifier</td><td>Light Conversion Ltd.</td><td>TOPAS prime</td><td></td></tr><tr><td>64-channel mercury cadmium tellurium IR detector array</td><td>Infrared Systems Development Corporation</td><td>FPAS-6416-D</td><td></td></tr><tr><td>FT-IR spectrometer</td><td>Shimadzu Corporation</td><td>IR Prestige-21</td><td></td></tr><tr><td>High voltage supply</td><td>Matsusada precision</td><td>HER-100N0.1</td><td></td></tr><tr><td>Rotary pump</td><td>Edwards</td><td>RV12</td><td></td></tr><tr><td>Molecular turbo pumps</td><td>Agilent Technologies Japan, Ltd.</td><td>Twis Torr 304FS</td><td></td></tr><tr><td>Vacuum gauges</td><td>Pfeiffer vacuum systems gmbh</td><td>PKR251</td><td>For ICF70 flange</td></tr><tr><td>Vacuum monitors</td><td>Pfeiffer vacuum systems gmbh</td><td>TPG261</td><td></td></tr><tr><td>Fiber coupled CCD camera</td><td>Andor Technology Ltd.</td><td>iKon-L HF</td><td></td></tr><tr><td>BaF2 and CaF2 substrates</td><td>Pier optics</td><td></td><td>Thickness 3 mm</td></tr><tr><td>AgGaS2 crystal</td><td>Phototechnica Corporation</td><td></td><td>Custom-order</td></tr><tr><td>BBO crystals</td><td>Tokyo Instruments, Inc.</td><td></td><td>SHG &amp;theta;=29.2 deg&lt;br/&gt; THG &amp;theta;=44.3 deg</td></tr><tr><td>calcite crystals</td><td>Tokyo Instruments, Inc.</td><td></td><td>Thickness 1mm</td></tr><tr><td>Optical mirrors</td><td>Thorlabs</td><td>PF10-03-F01&lt;br/&gt; PF10-03-M01&lt;br/&gt; UM10-45A</td><td>Al coat mirrors&lt;br/&gt; Au coat mirrors&lt;br/&gt; Ultrafast mirrors</td></tr><tr><td>Optical mirrors</td><td>HIKARI,Inc.</td><td></td><td>Broadband mirrors</td></tr><tr><td>Dichroic mirrors</td><td>HIKARI,Inc.</td><td></td><td>Custom-order&lt;br/&gt; Reflection: 266 nm&lt;br/&gt; Transmission: 400, 800 nm</td></tr><tr><td>Optical chopper</td><td>Newport Corporation</td><td>3501 optical chopper</td><td></td></tr><tr><td>Optical shutters</td><td>Thorlabs Inc.</td><td>SH05/M&lt;br/&gt; SC10</td><td></td></tr><tr><td>Optical shutters</td><td>SURUGA SEIKI CO.,LTD.</td><td>F116-1</td><td></td></tr><tr><td>Beam splitters</td><td>Thorlabs Inc.</td><td>BSS11R</td><td></td></tr><tr><td>Fused-silica lenses</td><td>Thorlabs Inc.</td><td>LA4663&lt;br/&gt; LA4184</td><td></td></tr><tr><td>BaF2 lens</td><td>Thorlabs Inc.</td><td>LA0606-E</td><td></td></tr><tr><td>Polarized mirrors</td><td>Sigmakoki Co.,Ltd</td><td></td><td>Custom-order&lt;br/&gt; Designed for 800 nm&lt;br/&gt; Reflection: s-polarized light&lt;br/&gt; Transmission : p-polarized light</td></tr><tr><td>Half waveplate</td><td>Thorlabs Inc.</td><td>WPH05M-808</td><td></td></tr><tr><td>Mirror mounts</td><td>Thorlabs Inc.</td><td>POLARIS-K1&lt;br/&gt; KM100</td><td>Kinematic mirror mounts</td></tr><tr><td>Mirror mounts</td><td>Sigmakoki Co.,Ltd</td><td>MHAN-30M&lt;br/&gt; MHAN-30S</td><td>Gimbal mirror mounts</td></tr><tr><td>Mirror mounts</td><td>Newport Corporation</td><td>ACG-3K-NL</td><td>Gimbal mirror mounts</td></tr><tr><td>Variable ND filters</td><td>Thorlabs Inc.</td><td>NDC-25C-2M</td><td></td></tr><tr><td>Beam splitter mounts</td><td>Thorlabs Inc.</td><td>KM100S</td><td></td></tr><tr><td>Lens mounts</td><td>Thorlabs Inc.</td><td>LMR1/M</td><td></td></tr><tr><td>Rotational mounts</td><td>Thorlabs Inc.</td><td>RSP1/M</td><td></td></tr><tr><td>Retroreflector</td><td>Edmund Optics</td><td>63.5MM X 30&quot; EN-AL&amp;nbsp;</td><td></td></tr><tr><td>spectrometers</td><td>ocean photonics</td><td>USB-4000</td><td></td></tr><tr><td>Power meter</td><td>Ophir</td><td>30A-SH</td><td>Used for intensity monitor of CPA</td></tr><tr><td>Power meter</td><td>Thorlabs Inc.</td><td>S120VC&lt;br/&gt; PM100USB</td><td>Used for intensity measurements of pump pulse</td></tr><tr><td>Photodiodes</td><td>Thorlabs Inc.</td><td>DET36A/M&lt;br/&gt; DET25K/M</td><td></td></tr><tr><td>DC power supply</td><td>TEXIO</td><td>PW18-1.8AQ</td><td>Used for magnetic lens</td></tr><tr><td>Magnetic lens</td><td>Nissei ETC Co.,Ltd</td><td></td><td>Custom-order</td></tr><tr><td>Stages</td><td>Newport Corporation</td><td>M-MVN80V6&lt;br/&gt; LTAHLPPV6</td><td>Used for magnetic lens</td></tr><tr><td>Stage controller</td><td>Newport Corporation</td><td>SMC100</td><td></td></tr><tr><td>Stages&amp;nbsp;</td><td>Sigmakoki Co.,Ltd</td><td>SGSP20-35(X)&lt;br/&gt; SGSP20-85(X)</td><td>Used for sample position</td></tr><tr><td>Stages&amp;nbsp;</td><td>Sigmakoki Co.,Ltd</td><td>SGSP26-200(X)&lt;br/&gt; OSMS26-300(X)</td><td>Used for delay time generator</td></tr><tr><td>Stage controller</td><td>Sigmakoki Co.,Ltd</td><td>SHOT-304GS</td><td></td></tr><tr><td>Picoammeter</td><td></td><td></td><td>Laboratory built</td></tr><tr><td>spin coater</td><td>MIKASA Co.,Ltd</td><td>1H-D7</td><td></td></tr><tr><td>hot plate</td><td>IKA&amp;reg;&amp;nbsp;</td><td>C-MAG HP7</td><td></td></tr><tr><td>SiN wafer</td><td>Silson Ltd</td><td></td><td>Custom-order</td></tr><tr><td>KOH aqueous solution (50%)</td><td>Hiroshima Wako Co.,Ltd.</td><td>168-20455</td><td></td></tr><tr><td>Chloroform</td><td>Hiroshima Wako Co.,Ltd.</td><td>038-18495</td><td></td></tr><tr><td>Dichloromethane</td><td>Hiroshima Wako Co.,Ltd.</td><td>132-02456</td><td></td></tr><tr><td>Personal computers for the controlling programs</td><td>Epson Corporate</td><td>Endeavor MR7300E-L</td><td>32-bit operation system</td></tr><tr><td>Program for the control the equipment</td><td>National Instruments Corporation</td><td>Labview2016</td><td></td></tr><tr><td>Program for the data analysis</td><td>The MathWorks, Inc.</td><td>Matlab2015b</td><td></td></tr></tbody></table>

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.

We chose a saddle-shaped &#960;-COT skeleton43,44 as a photoactive core unit of the LC molecule, because it forms a well-defined columnar stacking structure and because the central eight-membered COT ring is expected to show a photoinduced conformational change into a flat form owing to the excited-state aromaticity19,45. Synthetic process of this material is provided in p...

Watch this Scientific Journal Video about Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals at JoVE.com

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

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 ...

novel-techniques-for-observing-structural-dynamics-photoresponsive

Research

JoVE Journal

Chemistry

8.7K Views.  Okayama University. 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.

Video: Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

Patterning via Optical Saturable Transitions - Fabrication and Characterization

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.

We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical ...

Engineering

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

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 ...

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The devices are patterned from epoxy glue using soft lithography and are suitable for in situ X-ray diffraction experiments at room temperature. The sample wells are lidded on both sides with polymeric polyimide foil windows that allow diffraction data collection with low X-ray background. This fabrication method is undemanding and inexpensive. After the sourcing of a SU-8 master wafer, all fabrication can be completed outside of a cleanroom in a typical research lab environment. The chip design and fabrication protocol utilize capillary valving to microfluidically split an aqueous reaction into defined nanoliter sized droplets. This loading mechanism avoids the sample loss from channel dead-volume and can easily be performed manually without using pumps or other equipment for fluid actuation. We describe how isolated nanoliter sized drops of protein solution can be monitored in situ by dynamic light scattering to control protein crystal nucleation and growth. After suitable crystals are grown, complete X-ray diffraction datasets can be collected using goniometer based in situ fixed target serial X-ray crystallography at room temperature. The protocol provides custom scripts to process diffraction datasets using a suite of software tools to solve and refine the protein crystal structure. This approach avoids the artefacts possibly induced during cryo-preservation or manual crystal handling in conventional crystallography experiments. We present and compare three protein structures that were solved using small crystals with dimensions of approximately 10-20 &#181;m grown in chip. By crystallizing and diffracting in situ, handling and hence mechanical disturbances of fragile crystals is minimized. The protocol details how to fabricate a custom X-ray transparent microfluidic chip suitable for in situ serial crystallography. As almost every crystal can be used for diffraction data collection, these microfluidic chips are a very efficient crystal delivery method.

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes in detail how to fabricate and operate microfluidic devices for X-ray diffraction data collection at room temperature. Additionally, it describes how to monitor protein crystallization by dynamic light scattering and how to process and analyze obtained diffraction data.

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

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 ...

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.

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 ...

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 ...

Bioengineering

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 ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

Summary

Explore More Videos

Chapters in this video

Patterning via Optical Saturable Transitions - Fabrication and Characterization

Free-form Light Actuators — Fabrication and Control of Actuation in Microscopic Scale

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

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

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

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

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

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