Multiresponse Shape-Memory Nanocomposite with a Reversible Cycle for Powerful Artificial Muscles

Abstract

In the field of bionic soft robots and microrobots, artificial muscle materials have exhibited unique potential for cutting-edge applications. However, current mainstream thermal-responsive artificial muscles based on semicrystalline polymers (SCPs), despite their excellent physical properties, suffer from the limitation of environmental stimuli in practice, while their photodriven counterparts adopting liquid crystal elastomers (LCEs) lack ductility. Herein, a novel multifunctional programmable artificial muscle with a unique patch-sewing structure formed by π−π stacking between azobenzene groups was designed, which combined the advantages of SCPs and LCEs. The nanocomposite demonstrated a unique combination between artificial muscle performance (46.5 times the energy density and 26.6 times the power density of human skeletal muscles) and programmability (274.84% strain and 100% shape-memory recovery rate within 1 s). Meanwhile, coupling the photoisomerization of azobenzene and the photothermal conversion of gold nanorods, the cycle of deformation triggered by ultraviolet light and restoring by infrared light could be accomplished rapidly within 30 s. A COMSOL Multiphysics model was established and the corresponding finite element analysis verified the photoactuation and captured the general principle of light initiation in elastomers. These demonstrate that the multifunctional programmable elastomer is promising for artificial muscle applications, especially for photoinduced actuation.

Reversible Writing/Re‐Writing Polymeric Paper in Multiple Environments

“…As shown in Figure a, the structure of the composites hybridized from polyurethane (PU), liquid crystalline phase (AZO11), and submicron Fe‐based oxide (smFe), abbreviated as PU‐AZO11‐smFe, could be exhibited in detail as the patch‐sewing structure between polymeric linear chain and the regular liquid crystal network based on the impact of hydrogen bonding and the π–π stacking effect as we have proposed. [ 14 ] Simply put, p ‐aminobenzyl carbinol and 4 ‐ethoxyaniline were chosen as the nitrogen source of the azobenzene monomers AZO‐diOH and AZO11 while the synthesis relied on the combinations among diazotization reaction, alkylation reaction, recrystallization, and silica gel column chromatography. As for polymerization, the composites were fabricated by the one‐pot method based on AZO‐diOH, hexamethylene diisocyanate (HDI), hydroxy terminated polycaprolactone (PCL‐diOH), AZO11, and smFe, functioning in the system as the hard segment, chain extender, soft segment, liquid crystal element, and photothermal particles, respectively.…”

“…[ 23 ] On the other hand, as Figure 3b detailed, the double peaks appeared from 2869 to 2934 cm −1 connected to the CH 2  symmetric and asymmetric vibrations while the azobenzene group of AZO11 occurred at the orange zone from 1470 to 1600 cm −1 , which was corresponding to the previous work. [ 14 ] As the content of smFe augmented, there was no distinguished change of the PU. In contrast, when the substrate switched to PU‐5.0%AZO11, the characteristic peaks of amide (I) split, which implied the change of the chemical environment of the electron cloud from hydrogen bonding interaction.…”

“…Furthermore, thanks to the magnetism of Fe 3 O 4 (Figure S21, Supporting Information), the paper could be easily attached to the metal surface by a magnet like a refrigerator sticker serving as a memo (Figure 5a2, Supporting Information). Given the considerable ductility of the composite (ε B = 546.06% in Figure 3d), it could be kneaded into various shapes without difficulty, and the nearly 100% shape fixation rate [ 14 ] was conducive to keep the shape unchanged (Figure 5a3–5a4). For the last stage, NIR initiated the shape recovery process through the photothermal effect and finally made the paper restore to its original situation on shape, fold, and surface.…”

“…For the last stage, NIR initiated the shape recovery process through the photothermal effect and finally made the paper restore to its original situation on shape, fold, and surface. [ 14 ] It was worth mentioning that such reversible behavior could be repeated for at least ten cycles with outstanding stability. To explore the potential and exhibit the performance, several samples were designed in various shapes, such as the postcard with words and a right angle (Movie S1 and S2, Supporting Information), blooming flower (Movie S3, Supporting Information), and unexpanded panel (Movie S4, Supporting Information).…”

“…Some reaction steps were similar to the previous work. [ 14 ] 4 ‐ethoxyaniline, 36% hydrochloride (HCl), sodium bisulfite, phenol, sodium hydroxide, 1 ‐bromoundecane, potassium iodide, potassium carbonate, ethyl alcohol, and hexamethyltriphosphotriamine were used to prepare monomer AZO11 by diazotization reaction, alkylation reaction, recrystallization, and silica gel column chromatography. Similarly, using p ‐aminobenzyl carbinol as the reagent could obtain another monomer AZO‐diOH.…”