This work was financially supported by the Netherlands Organization for Scientific Research (NWO - TOP PUNT Grant: 10018944) and the European Research Council (Vibrate ERC, Grant 669991). A. H. G. acknowledges the funding from the People Program (Marie Curie Actions) of the European Union&#39;s Seventh Framework Program FP7-2013, Grant No. 607602.

NOTE: The overall procedure is detailed in Figure 1.
1. Preparation of Cells
<ol>
	<li>Cleaning of glass plates
	<ol>
		<li>Carefully clean 3 cm x 3 cm glass plates using soap and hot water to remove contaminations (Figure 1A).</li>
		<li>Place the glass plates in a beaker and cover with ethanol 99.5% (Figure 1B).</li>
		<li>Place the beaker in an ultrasonic bath for about 10 min.</li>
		<li>Carefully dry the glass plates with a tissue and blown air.</li>
		<li>Make sure that there is no trace of solvent, dust, or any type of contamination left on the plates. 
		NOTE: The glass plates are now clean and should be manipulated with gloves.</li>
		<li>Place the glass plates in an UV-ozone photoreactor for 20 min in order to remove any organic residues. After the ozone treatment, the plates are ready for the coating step (Figure 1C).</li>
	</ol>
	</li>
	<li>Coating of glass plates 
	NOTE: Two sets of coated plates are prepared: one set with a planar alignment layer and the other with a homeotropic alignment. In a later stage, the cell will be composed of one planar glass plate and one homeotropic glass plate (Figure 1D).
	<ol>
		<li>Air blow a glass plate and place it on the spin coater.</li>
		<li>Deposit the polyimide solution onto the glass plate to cover the entire surface (about 0.5 mL of solution).</li>
		<li>Spin coat the alignment layer according to the following conditions: Program 1: 5 s at 17 x g and acceleration of 11 x g/s; Program 2: 40 s at 420 x g and acceleration of 17 x g/s.</li>
	</ol>
	</li>
	<li>Curing of the alignment layers
	<ol>
		<li>Place the coated glass plates on a hot plate at 110 &#176;C for 10 min in order to remove the majority of the solvent present in the alignment layer mixture (Figure 1E).</li>
		<li>Mark the glass plates (on the non-coated side) with distinctive signs to recognize the homeotropic and the planar alignment layers. A small arrow is usually helpful for the planar glass plate since it also indicates the rubbing direction described in a later stage (Figure 1F).</li>
		<li>Once all the glass plates are coated, and the solvent is removed, place the glass plates in an oven at 180 &#176;C for 1 h to cure the polyimide layer (Figure 1G). 
		CAUTION: This step involves extremely hot temperatures; wear gloves, eyeglasses and appropriate personal protection.</li>
		<li>After baking the glass plates, let them cool down to room temperature. 
		NOTE: To prevent any contamination between each step, it is recommended to place a protective foil over the glass plates.</li>
	</ol>
	</li>
	<li>Rubbing the planar alignment layer
	<ol>
		<li>Rub the glass plates coated with the planar alignment layer in order to create (sub) microchannels in the layer that will guide the LC in one direction. To do so, place the glass plates with the coated side downwards on a velvet cloth. Apply a uniform and soft pressure with two fingers. Carefully drag the glass plate along the surface of the velvet cloth in a straight direction. Lift the glass plate and repeat the same operation three times (Figure 1H). 
		NOTE: It is crucial to rub the plate in a single direction and only while going forward. Going back and forth in a straight direction will result in a poor alignment.</li>
	</ol>
	</li>
	<li>Gluing the cells
	<ol>
		<li>Air blow the glass plates using the air blower.</li>
		<li>Prepare the adhesive by mixing a UV-curing glue with spacers (glass beads) having a well-defined diameter of 20 &#181;m.</li>
		<li>Take a glass plate coated with a planar alignment layer and one glass plate coated with a homeotropic alignment layer. Place two tiny drops of glue at two adjacent corners of the planar glass. Then place two other drops of glue at about 5 mm from the two last corners (Figure 1I).</li>
		<li>Take the homeotropic glass plate and place it on top. Leave a gap of about 4 mm between the edges of the glass plates to provide enough space for the LC mixture. Make sure that the coated sides are facing each other.</li>
		<li>Cure the glue by placing the cell for 2 min under UV light. 
		CAUTION: UV light is hazardous; wear gloves, eyeglasses and appropriate personal protection.</li>
	</ol>
	</li>
</ol>
2. LC Mixture Preparation and Characterization
<ol>
	<li>Components
	<ol>
		<li>Weigh 97.5 mg of the LC diacrylate 1, 2.5 mg of photo-stabilizer and 1 mg of photoinitiator in a brown glass vial (Figure 2). Because of the sensitivity of the initiator, prevent UV light exposure to the mixture as best as possible.</li>
	</ol>
	</li>
	<li>Homogenous mixing of the powders 
	NOTE: This step is performed in a chemical hood.
	<ol>
		<li>Add 3 mL of dichloromethane (DCM) to the above components and shake until the solid is fully dissolved.</li>
		<li>Place the vial on a hot plate at 30 &#176;C for 30 min and add a flow of argon to promote the quick evaporation of the DCM. 
		NOTE: It is recommended to place the vial in vacuum to remove any residual trace of DCM.</li>
	</ol>
	</li>
	<li>Observation under Polarized Optical Microscope (POM) for phase transition determination
	<ol>
		<li>Once the mixture is fully dry, place a small amount (&#177; 10 mg) between two glass plates coated with the planar alignment layer. 
		NOTE: In order to characterize the phases properly, it is recommended to use unrubbed planar glass plates.</li>
		<li>Place the slides in a POM equipped with a hot stage. Heat up the cell until the image turns black (using crossed polarizers) indicating the isotropic phase.</li>
		<li>Slowly cool down the hot plate and note the transition temperatures. For the mixture described above, the isotropic to nematic transition is at 103 &#176;C and the nematic to smectic transition occurs at 86 &#176;C (Figure 3A).</li>
	</ol>
	</li>
</ol>
3. Film Preparation
<ol>
	<li>Filling of the cells (Figure 1J)
	<ol>
		<li>Place the cell on a hot plate with the homeotropic side upwards. Set the temperature to 110 &#176;C (isotropic phase) to facilitate the filling of the cell because the fluid is less viscous than in the nematic phase.</li>
		<li>Place part of the solid mixture on the edge of the cell.</li>
		<li>The solid melts and the liquid mixture flows by capillarity in the cell. Add more mixture at the edge until the cell is filled.</li>
	</ol>
	</li>
	<li>Cooling to the nematic phase and polymerization (Figure 1K)
	<ol>
		<li>Once the cell is filled, slowly cool it down (5 &#176;C/min) to 90 &#176;C to be in the nematic phase.</li>
		<li>As soon as the film is at the right temperature, polymerize the mixture by placing it under UV light at 90 &#176;C for 30 min. 
		CAUTION: UV light is hazardous, it is advised to perform the polymerization in a protected environment.</li>
		<li>A post-baking step is recommended to ensure the full polymerization of the network. Place the cell on a hot plate at 130 &#176;C for about 10 min and let it slowly cool down to room temperature.</li>
	</ol>
	</li>
	<li>Opening of the cell and cutting of the sample
	<ol>
		<li>To open the cell, put a razor blade at one edge and push it in between the two glass plates. The cell opens at once (Figure 1L).</li>
		<li>To peel off the film, lift a small corner with a razor blade. If needed, the glass plate can be placed in hot water to facilitate the removal of the film (Figure 1M).</li>
		<li>Remove the film from the water and gently peel it.</li>
		<li>Cut a stripe along the molecular director (rubbing direction of the planar side) of the film having the following dimensions: 4 mm x 2.5 cm (Figure 1N).</li>
	</ol>
	</li>
</ol>
4. Self-oscillation Observation
<ol>
	<li>Setup in the lab
	<ol>
		<li>Clamp the sample using a self-closing tweezer in such a way that 1.7 cm of the film is free to move.</li>
		<li>Hold the sample vertically and direct the light emitting diode (LED) beam (400 mW/cm2) perpendicular to the sample. Typically, the light is about 20 cm away from the sample. The light should reach the top of the film, below the tweezer (Figure 4). The oscillations obtained are recorded with a high-speed camera (150 frames/s) and analyzed with an image processing program.</li>
	</ol>
	</li>
	<li>Setup with direct sunlight
	<ol>
		<li>Proceed as described above in steps 4.1.1 but instead of using the LED light, focus the sunlight on top of the film with a lens.</li>
	</ol>
	</li>
	<li>Measurement of the thermal effect
	<ol>
		<li>Measure the temperature variation in the oscillating sample using a thermal camera15 (40 frames/s).</li>
	</ol>
	</li>
</ol>

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K., Run&#269;evski, T., Husain, A., Dinnebier, R. E., Naumov, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perpetually+Self-Propelling+Chiral+Single+Crystals.">Perpetually Self-Propelling Chiral Single Crystals.</a> J Am Chem Soc. 137 (5), 1895-1902 (2015).</li><li>Kumar, 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=A+chaotic+self-oscillating+sunlight-driven+polymer+actuator.">A chaotic self-oscillating sunlight-driven polymer actuator.</a> Nat. Commun. 7, 11975 (2016).</li><li>Camacho-Lopez, M., Finkelmann, H., Palffy-Muhoray, P., Shelley, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+liquid-crystal+elastomer+swims+into+the+dark.">Fast liquid-crystal elastomer swims into the dark.</a> Nat Mater. 3 (5), 307-310 (2004).</li><li>Kausar, A., Nagano, H., Ogata, T., Nonaka, T., Kurihara, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photocontrolled+translational+motion+of+a+microscale+solid+object+on+azobenzene-doped+liquid-crystalline+films.">Photocontrolled translational motion of a microscale solid object on azobenzene-doped liquid-crystalline films.</a> Angew Chem Int Ed. 48 (12), 2144-2147 (2009).</li><li>Yamada, 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=Photomobile+Polymer+Materials:+Towards+Light-Driven+Plastic+Motors.">Photomobile Polymer Materials: Towards Light-Driven Plastic Motors.</a> Angew Chem Int Ed. 47 (27), 4986-4988 (2008).</li><li>White, T. J., 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+high+frequency+photodriven+polymer+oscillator.">A high frequency photodriven polymer oscillator.</a> Soft Matter. 4 (9), 1796 (2008).</li><li>Lee, K. 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=Photodriven,+flexural-torsional+oscillation+of+glassy+azobenzene+liquid+crystal+polymer+networks.">Photodriven, flexural-torsional oscillation of glassy azobenzene liquid crystal polymer networks.</a> Adv Func Mater. 21 (15), 2913-2918 (2011).</li><li>Liu, D., Broer, D. 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N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anisotropic+thermal+expansion+of+densely+cross-linked+oriented+polymer+networks.">Anisotropic thermal expansion of densely cross-linked oriented polymer networks.</a> Polym Eng Sci. 31 (9), 625-631 (1991).</li><li>Mol, G. N., Harris, K. D., Bastiaansen, C. W. M., Broer, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermo-Mechanical+Responses+of+Liquid-Crystal+Networks+with+a+Splayed+Molecular+Organization.">Thermo-Mechanical Responses of Liquid-Crystal Networks with a Splayed Molecular Organization.</a> Adv Funct Mater. 15 (7), 1155-1159 (2005).</li><li>van Oosten, C. L., Harris, K. D., Bastiaansen, C. W. M., Broer, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glassy+photomechanical+liquid-crystal+network+actuators+for+microscale+devices.">Glassy photomechanical liquid-crystal network actuators for microscale devices.</a> Eur Phys J E Soft Matter. 23 (3), 329-336 (2007).</li><li>Yu, Y., Nakano, M., Ikeda, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photomechanics:+Directed+bending+of+a+polymer+film+by+light.">Photomechanics: Directed bending of a polymer film by light.</a> Nature. 425 (6954), 145 (2003).</li></ol>

The authors have no conflict of interest.

The results described here are comparable with the previous study15 on a LC diacrylate with a spacer of 6 carbons. It shows that the method to obtain oscillation can be applied to films with different mechanical properties16.
The preparation of a photo-thermal responsive LCN is reported. There are a few steps in the described protocol that are critical, such as the rubbing of the planar alignment layers and the preparation of the cell. Indeed, the success of the protocol relies on the high quality of the LC splay alignment, which also limits the application to thin films.
Previously, many examples of photo-actuators based on LCNs that contain a large quantity of photo-switches have been reported11,12,13,19. The main advantages of the method developed here are the limited quantity of dopants needed to observe the actuation (&#60; 5 wt%) and the broad choice of dopants available.15 These results expand the range of potential applications. Moreover, the power of this protocol is the ability to vary the frequency and the amplitude of the oscillation by changing the modulus of the film with a different matrix composition, the dimensions of the stripe and the light intensity.
This methodology can be readily extended to fabricate a broad range of LC materials for automated systems. The protocol described herein paves the way to the development of non-equilibrium systems for soft-robotics and automated materials.

The search towards sustainable energy is an area of growing interest in response to the depletion of fossil energy and climate change. Methods to convert light energy into mechanical work are currently being investigated, such as photovoltaics to generate electricity, biomass to produce fuels, solar water splitting to produce oxygen and hydrogen. However, all these processes fueled by light require multiple steps before their energy production can run machines that perform work. Although these approaches offer a large panel of applications, they require production, storage and transport of intermediates (e.g., electrical potential, chemical fuels). Hence, devices able to convert directly sunlight into macroscopic motion present advantages of simplification.
In the last decades, many examples of photo-actuators have been developed where polymers change shape upon irradiation1,2,3. However, in the large majority of these examples, continuous actuation requires turning the light on/off to switch from one state to the other. So far, only a limited number of photo-responsive materials working out-of-equilibrium has been described4,5,6,7. Systems based on liquid crystal networks (LCNs)8,9,10,11,12,13 are also investigated because of their intrinsic anisotropy that allows for preprogramming the deformation in a controlled fashion14. Recently, it was reported that the photo-thermal effect induced by excitation of photo-stabilizers incorporated in LCN can generate oscillatory motion15.
Here, the method to create LCN films that mechanically oscillate under continuous light irradiation is described. The conception of the films is detailed from the preparation of the cells to the characterization and the polymerization of the LC mixtures. The photo-actuation of the LCN films and the analysis of the motion are also reported. The LCNs are doped with molecules that can quickly dissipate light into heat within the network, which induces anisotropic thermal expansion and subsequent macroscopic deformation of the film. An interplay between self-shadowing, temperature variation and contraction/elongation of the material gives rise to the oscillatory motion15. The precise setup, including the orientation of the light and the sample to obtain this effect is highlighted in the protocol. The oscillation is characterized by its frequency and controlled by the properties of the LCN. To our knowledge, this is the first description of a method for the creation of LCN films that can self-oscillate, by a simple mechanism working with a broad range of dopants.

<table><tbody><tr><td>&lt;strong&gt;Material&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>LC diacrylate (compound &lt;strong&gt;1: Figure 2&lt;/strong&gt;)</td><td>Syncom</td><td>custom synthesis</td><td></td></tr><tr><td>photo-stabilizer</td><td>Ciba</td><td>tinuvin 328</td><td></td></tr><tr><td>photoinitiator</td><td>Ciba</td><td>Irgacure 819</td><td></td></tr><tr><td>Alignment layer planar</td><td>JSR micro</td><td>optimer Al1051</td><td></td></tr><tr><td>Alignment layer homeotropic</td><td>Nissan chemical industry</td><td>Sunever grade 5300</td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>UV-ozone photoreactor</td><td>Ultra Violet Products, PR-100</td><td>Not available</td><td></td></tr><tr><td>spin coater</td><td>Karl-SUSS</td><td>SUSS RC spin coater CT62 V098</td><td></td></tr><tr><td>UV light</td><td>Gentec</td><td>EXFO-Omnicure S2000</td><td></td></tr><tr><td>micropearl</td><td>Sekisui Chemicals</td><td>SP220-20um</td><td></td></tr><tr><td>Glue</td><td>Gentec</td><td>UVS91</td><td></td></tr><tr><td>LED 365 nm</td><td>Thorlabs</td><td>M365LP1</td><td></td></tr><tr><td>light collimator</td><td>Thorlabs</td><td>SM2F32-A</td><td></td></tr><tr><td>high speed camera</td><td>PCO.</td><td>PCO 5.5 sCMOS camera</td><td></td></tr><tr><td>thermal camera</td><td>Xenics Infrared solution</td><td>Gobi-640-GigE</td><td>used with Xeneth software</td></tr><tr><td>Differential Scanning Calorimeter</td><td>TA instruments</td><td>Q1000</td><td></td></tr><tr><td>Dynamic Mechanical Analyzer</td><td>TA instruments</td><td>Q800</td><td></td></tr><tr><td>Polarized Optical Microscope</td><td>Leica</td><td>DM6000M</td><td></td></tr></tbody></table>

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 success of the protocol is the observation of the oscillatory motion of the film under light irradiation. Oscillations are large and no misleading result can be seen. Moreover, the oscillations are stable over time (timescale of hours) and little fatigue was observed.
Among others, the quality of the splay alignment is of importance for the accomplishment of the self-sustained actuation (Figure 5A). The gradient in molecular orientation throughout the thickness of the film induces a contraction/expansion at the planar/homeotropic sides of the film upon actuation16,17,18. This asymmetric response enhances the macroscopic motion. The failure of the experiment (absence of bending, small deformation or odd bending) can be explained by a poor LC alignment. First, the film should be transparent. (Figure 5B).&#160; To verify the correct splay alignment in a simple step, the film attached to the glass substrate is observed between crossed polarizers above a diffused white light source(Figure 5C-E). By rotating the film between the cross polarizers from 0&#176; to 45&#176; in the xy plane, the film should sharply change brightness. By pivoting the film out of the plane around the molecular director, the film should change color from black (in plane) to white (out of plane) while viewing from the top. Similar verification steps can be done prior to polymerization by observing the cell through a polarizer on top of the hot plate covered with an aluminum foil. Moreover, when the film is cut in strips, it presents a natural curvature with the center of the curve in the homeotropic side. This is due to the residual stress originating from the polymerization at an elevated temperature, where the expansions of the two sides of the film have opposite signs (Figure 6A). In case the alignment is not successful, the method to prepare the polyimide layers should be reconsidered. The production of those cells is crucial to obtain well-aligned films. The most critical step is the rubbing: a too strong pressure on the plate will remove partially the polyimide layer and result in a very poor command layer for alignment. At room temperature the film is in the glass state (Figure 3B). If the film is soft and/or tacky, it means that the polymerization is not completed, most probably because the irradiation time is too short or the initiator is degraded. The mixture of LC mesogens should be homogeneous and dry before the filling of the cell, because the presence of solvent might influence the phase behavior of the LC mixture. The LC mixture should be aligned prior to polymerization. Precautions should be taken to avoid thermal polymerization during the process of alignment by going through the steps rapidly and not heating the sample above 130 &#176;C for a prolonged time. Filling the cell just above the clearing point is sufficient (110 &#176;C).
The mechanical and thermal oscillations registered by the high-speed camera confirm the success of the presented protocol (Figure 7; Video 1). When the film is clamped at one end, leaving 1.7 cm free to move and irradiated at the planar side with focused light, it unbends towards the flat state in the direction of the light (Figure 6B). The hinge is located at the position of the focus point of the light (Figure 4). The film should move smoothly, perpendicular to the clamp and not on the side. Then the film starts to move continuously with oscillations of frequency 7.6 Hz &#177; 5% and amplitude 30 &#176; &#177; 10% for a film of dimensions 1.7 cm x 0.4 cm x 20 &#181;m. The thermal oscillations measured with the thermal camera present the same frequency (7.4 Hz &#177; 5%), with a slight phase delay due to the inertia of the film. This frequency f is governed by the dimensions and the modulus of the film15. The amplitude of the oscillations varies with the light intensity and will be influenced by the setup, and in particular, the positioning of the focus point of the light on the sample. The mechanism of oscillation is as follows: 1) the curled film is irradiated with focused light, the dopant absorbs the light and converts it into heat, the film warms up at its hinge and unbends in the direction pre-defined by the LC alignment; 2) the tip shadows the hinge of the film, which induces a decrease of its temperature and its subsequent unbending by relaxation; 3) the hinge is again under irradiation, warms up and the film bends15. The repetition of these successive steps gives rise to the oscillations. The key factors in observing this phenomenon are the photo-thermal effect and the self-shadowing of the film, controlled by the intensity and the position of the focused light (Figure 4). For instance, a slightly tilted lamp will induce a complete curling of the sample. Moreover, too low of a light intensity does not give large bending because the temperature at the hinge is insufficient, while too high of a light intensity on the hinge will induce overshooting (Figure 6C, 180 &#176; bending of the film). Another requirement for the success of the experiment is to place the setup in an environment protected from wind to avoid perturbation.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56266/56266fig1.jpg" /> 
Figure 1. The Overall Procedure to Obtain the Splay Aligned LCN in 14 Steps (From A-N). Steps A-C: cleaning of the glass plates; steps D-G: coating of the glass plates to create planar or homeotropic alignment layers; step H: rubbing of the glass plates using a velvet cloth; step I: gluing the plates to form the cell; step J: filling the cell with the LC mixture and alignment in the nematic phase; step K: photo-polymerizing under UV light; steps L-N: opening of the cell and cutting of the film to obtain a strip. <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56266/56266fig2.jpg" /> 
Figure 2. Chemical Structures of the Components Used. <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56266/56266fig3.jpg" /> 
Figure 3. Thermal Characterization of the Monomer Mixture and Polymer Film. A) Differential scanning calorimetry (DSC) of the mixture prior to polymerization to determine the phase transitions. Insets: POM pictures, scale bars: 100 &#181;m. B) Dynamic mechanical thermal analysis (DMTA) measurement of the polymeric film. <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56266/56266fig4.jpg" /> 
Figure 4. Picture of the Setup Showing the LED on the Left Side, and the Oscillating Film Clamped to the Tweezer in Front of the Light. The inset shows the schematic representation of the bended film and the localized light illumination. The red area corresponds to the warm hinge mentioned in the text. <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56266/56266fig5.jpg" /> 
Figure 5. A) Schematic representation of the splay alignment. B) Picture of the glass cell in front of the TU/e logo showing the transparency and the absence of color of the film. The arrow indicates the rubbing direction of the planar glass plate. C-E) Pictures of the film taken between crossed polarizers showing the characteristics of the splay alignment (Picture D: rotation of 45 &#176; in the XY plane, Picture E: pivoting out of the xy plane). The molecular director of the alignment is indicated by the red arrow. Scale bar: 1 cm. <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56266/56266fig6.jpg" /> 
Figure 6. A) Picture of the film clamped with a tweezer showing a natural curvature with the center of the curve in the homeotropic side. B) Picture of the film going to a flat state upon photo-irradiation (365 nm, 0.52 W/cm2). C) Picture of a film irradiated with too high of a light intensity showing a bending at 180 &#176;. <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/56266/56266fig7.jpg" /> 
Figure 7. Mechanical Oscillations of the Tip of the Film Over Time During Irradiation with UV Light (LED 365 nm, 0.52 W/cm2). Insets: Screenshots of the moving film recorded with the high-speed camera. The film geometry is 1.7 cm (length) x 0.4 cm (width) x 20 &#181;m (thick). <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/56266/56266fig8.jpg" /> 
Figure 8. Thermal Oscillations of the Exposed Area (Hinge) Over Time During Irradiation with UV Light (LED 365 nm, 0.52 W/cm2). Insets: Screenshots of the oscillating film with the temperature profile registered with the thermal camera showing the changes of temperature at the hinge. The film geometry is 1.7 cm (length) x 0.4 cm (width) x 20 &#181;m (thick). <a href="https://cloudflare.jove.com/files/ftp_upload/56266/56266fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light at JoVE.com

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

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 ...

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11.5K Views.  Technical University of Eindhoven. Het doel van het protocol is het creëren van vloeibaar kristallijne polymeerlagen die mechanisch onder continu licht bestraling oscilleren kunnen. We beschrijven zeer gedetailleerd de Ontvangenis van vrijstaande films, van de vloeibare kristallen uitlijning methode om de foto-bediening. Het experimentele protocol toegepast ter voorbereiding van dit materiaal is breed toepasbare.

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

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

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 ...

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 ...

Chemistry

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 ...

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

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