Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Open AccessCCS ChemistryCOMMUNICATION1 Mar 2022Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators Bin Ni, Gaoyu Liu, Mengxue Zhang, Patrick Keller, Michael Tatoulian Min-Hui Li Ni Chimie ParisTech, Université Paris Sciences & Lettres, CNRS, Institut de Recherche Paris, UMR8247, 75005 Google Scholar More articles by this author , Liu Zhang Keller *Corresponding authors: E-mail Address: [email protected] Curie, Sorbonne Université, Laboratoire Physico-Chimie UMR168, https://doi.org/10.31635/ccschem.021.202100818 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Nature is providing inspiration for researchers mimic its functions or existing structures, which could remarkably promote the development of new materials. Here, a large-size honeycomb-shaped liquid crystal elastomer (LCE) actuator with LC orientation along height honeycomb shape built combining magnetic field alignment soft lithography technology. This homeotropic allowed contraction pore size expansion hexagons in reversible manner upon temperature variation. Therefore, LCE can be used as structure temperature-gated separation particles. Another example an iris-like actuator, has capability adjusting aperture Our approach provides simple way design customizable sophisticated actuators various potential applications. Download figure PowerPoint Introduction Many biological systems exhibit either ingenious structures like dynamic functionalities iris. New materials mimicking nature’s are becoming attractive research domain aimed make strong impact technological advances. For example, smart polymers ability sense multiple environmental variations convert them into detectable active responses,1–5 have attracted considerable interest. elastomers (LCEs), initially discussed De Gennes 1975,6 later on other investigators,7–9 one class these Oriented LCEs outstanding anisotropic deformations external stimuli such temperature,10 light,11 pH change,12 solvents,13 so forth. These excellent properties polymeric choice biomimetic applications robots,14–17 self-cleaning surfaces,18–20 iris regulation,21,22 flowers,23 on. Nevertheless, complexity brings many difficulties further their motions, especially some three-dimensional (3D) large sizes. To obtain LCEs, prerequisites molecules sample. Taking nematic average macromolecular polymer coupled orientational order therefore elongated phase. Upon nematic–isotropic (N–I) phase transition, change produced from spherical because chain recovers random coil isotropic In oriented LCE, where all mesogens uniformly whole sample (monodomain), individual translated macroscopic at N–I transition.7 3D main challenge resides two somehow contradictory constraints, viz, making molecularly crystalline complex volume. Frequently approaches preparation severely limit possibilities producing structures. The mechanical stretch method proposed Küpfer Finkelmann24 monodomain suitable samples, but mainly form films fibers.25 popular surface method26–30 allows small areas thickness only ≤200 μm, intrinsically limited anchor force. extrusion shows promising results, printing LCEs; however, direction restricted printer direction.31 we revisited another method, alignment, beneficial aromatic due exceptionally high diamagnetism. rings tended align planes parallel minimize energy. A polydomain without any treatment contains tiny monodomains optical axis (director n ¯ ) different directions, just powder crystallites. field, readily director (typically, ring plane) coupling energy was larger than thermal agitation (kBT).32 Consequently, obtained under 0.1–1 T. As volume been proved useful fabricating pillars micrometer size33,34 centimeter size.35,36 Also, there were few reports (up 10 mm) tunable aperture18 freeforms voxelated molecular patterning.37 However, last examples, setups used, multitude pairs magnets complicated configuration,21 reorientable (with mounted rotation stage) combined digital micromirror device.37 Herein, effective fabricate sizes using lithography. long time, most replicate scales.38 Keller’s group19,33,39 first prepared micropillars work, developed protocol prepare stimuli-responsive actuation (see Figure 1). Soft employed customize comparable actual (cell side ∼3 human (inner outer diameters ∼4 ∼10 mm). pair chosen monomers filled mold get orientation, that is, hexagonal cylindrical walls, finally photopolymerization. Notably, applied here produce desired function. best our knowledge, until now, little attention paid LCEs. At point, it necessary recall important property LCEs: When transits phase, remains constant following reasons.40 First, volumetric coefficient 10−4 (K−1), negligible. Second, shear moduli those classical elastomers, times compression (a liquid-like behavior); therefore, essentially deform during thermally actuated contraction. implies contracts expands directions.7,41 taking advantage often-overlooked fundamental property, fabricated separate selectively glass beads change, work temperature-controlled diaphragm. Moreover, beyond provided 1 | (a) polymerization process schematic organization shown. (b) Chemical components mixture. Results Discussion presented (that similar). template made polylactic acid (PLA) printing. Then PLA polydimethylsiloxane (PDMS) negative called mold. Each hexagon 2 mm (side) × (height) 0.5 (wall thickness) 3 ( Supporting Information S1). thin hollow disk had diameter 6 mm, inner thickness. monomer mixture PDMS comprised 2-methyl-1,4-phenylene bis(4-(4-(allyloxy)butoxy)benzoate) (C4), chain-extender (2,2′-(ethylenedioxy)diethanethiol) (EDDET), cross-linker (2-methyl-1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate)) (RM82), photoinitiator (2-benzyl-2-dimethylamino-1-(4-morpholinophenyl) butanone-1) (Irgacure 369) (Figure 1b). Their molar ratio kept C4∶EDDET∶RM82 = 1∶1∶0.4 experiments concentration Irgacure 369 wt %. maintained mesophase characteristic room least 4 days [see Figures S2a–S2c differential scanning calorimetry (DSC) curves].42 possibility perform photopolymerization conveniently previously aligned Two permanent adhesion strength ∼60 kg (∼588 N) remanence 1.29–1.32 T set facing cm-distancing each other, offered homogeneous orientate S3). simulation flux density (B) finite element commercial software COMSOL® https://www.comsol.com/comsol-multiphysics) confirmed good homogeneity central area value B ∼ S3b detail). achieved heating (110 °C) naturally cooling (∼0.5 °C/min). Finally, locked down “monodomain” state thiol-ene/acrylate photopolymerization.43–45 2a 2b S4a S4b show final fused lattices lattice peeled off dimensions slightly smaller initial [e.g., 1.8 instead thickness)] (Figures 2b). might stress process. irregular caused pulling force when peeling mold, became more regular relaxation, shown 2d S4b. deformation stimulation. b) Side views. (c d) Top directions reversibly cooling. Scale bar 5 mm. also closely examined. film ∼160 μm beside wall same block 1a) prepared. mixtures before after observed polarizing microscopy (POM), S5. maximal birefringence apparent both angle 45° relative polarizer. characterized two-dimensional (2D) wide-angle X-ray scattering (WAXS), 3a 3b. crescent-like signals Y-axis showed clearly mesognes B. From crescents, parameter (S) estimated S (according described previously46), lateral distance between 0.44 nm. X-axis gave 2.3 nm, corresponding mesogen length. Thus, inferred us effectively orientation. illustration 2D WAXD experiment. pattern film. red arrow indicates director. (parallel B) allow measuring give nm frame then heated 130 °C (above transition TN–I 125 °C; S2d). expansions 2c Video S1), agreement fact that, essentially, deformed length ultimately changed ∼2.55 4a), increased 11 21 mm2 4b). temperature, regained original S6 variation, resulting changes conformation transition. variation one-hexagonal-lattice S7. function temperature. cell. Pore Such significant suggested application passage 5a–5c S2 7 ball hole up °C. investigate particle special structure, balls diameters, D 5.2 4.2 positioned two-hexagonal-lattice frame. Due stand 5d). started expand increase, led sinking through 5e). Ultimately, passed successfully reached Meanwhile, remained top 5f addition, Three 5.2, 4.2, 3.9 respectively, frame, able pass one-by-one successively increase S8 S4). changing capacity particles size. results extended varying and/or shapes. Honeycomb-shaped (a–c) particles’ (d–f). 25 °C, (b e) f) (a–c), around 2.5 (e–f), respectively; color (d–f) reflection transparent balls. supported (for transparency) submerged low viscosity silicone oil reduce friction beads. homeotropically designed 6). mimicked aperture. 6a 6b, diameter) 4.7 heating–cooling stimulation cycle 6b 6c, Videos S5 S6). 6c demonstrates modified continuously Schematic (nematic perpendicular disc surface). (c) (inner-diameter) adjustable stimulation, demonstrating controllability states. Conclusion Inspired natural real scales via combination exhibited behaviors stimulated. Thin controlled variations. present complex, deformations, greatly benefit manufacture robots future better control drive currently, photothermally dopants gold nanoparticles carefully dyes introduced easily.23,47 progress help explore possible sophisticated, even exotic shapes method. available includes experimental procedures characterization data (PDF), (Videos S1, S5, S6), S2, S3, Conflict Interest There no conflicts declare. Funding study received support French National Research Agency (ANR-16-CE29-0028) “Institut Pierre-Gilles Gennes” (IPGG, laboratoire d’excellence, “Investissements d’avenir” programs ANR-10-IDEX-0001-02 PSL, ANR10-LABX-31 ANR-10-EQPX-34). Acknowledgments B.N. 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