Ionic polymer–metal composites (IPMC)—constructed using an ionic polymer sandwiched between metal electrodes—have shown great potential for the fabrication of soft actuators. IPMC architectures have many advantages including low actuation voltage, fast response, basic control, and relatively light weight. Poly(acrylic acid) (PAA)‐based ion exchange membranes are of particular interest for IPMC devices due to their large ion exchange capacity and ease of preparation; however, they suffer from relatively weak mechanical strength. Here, PAA‐based soft actuators are synthesized with enhanced mechanical properties and proton conductivity through the incorporation of hydrogen bonding interactions with imidazolium groups via copolymerization with 1‐vinylimidazole. In addition to examining the impact of composition on physiochemical (swelling, glass transition, decomposition, Young's modulus, etc.) and electrochemical (specific capacitance) properties, an additive manufacturing process, digital light projection (DLP), is utilized to fabricate complex geometries demonstrating the potential for the fabrication of IPMC devices with complex actuation modalities. Planar DLP 3D‐printed IPMC actuators of varied polymer compositions are fabricated with activated carbon and copper electrodes, and their actuation performance is evaluated in air, where large bending deformation is observed (14°–37°).
The development of biobased resins with high-bonding performance has gained considerable attention in the wood industry. In this study, we developed biobased novolacs phenol-formaldehyde (BNPF) resins by partially replacing petroleum-based phenol and formaldehyde with lignin derived from kraft biorefinery and modified kraft biorefinery-derived lignin, respectively. We first performed a mild and efficient chemical modification of the lignin through the periodate oxidation process. Sodium periodate was used to oxidize the hydroxyl functional groups present in the interunit linkages (β-O-4 bond) in the lignin structure and convert lignin partly to quinones. This was assessed by Fourier-transform infrared spectroscopy, elemental analysis, solid-state 1H–13C 2D HETCOR NMR, and aldehyde content analysis. We synthesized a series of BNPF resins by replacing phenol with lignin, then by replacing formaldehyde with oxidized lignin, and finally by replacing both phenol and formaldehyde with lignin and oxidized lignin. The structural characterization results of the NPF resins revealed the formation of methylene linkages in the phenolic rings. Before application as wood adhesives, we studied the curing behavior of the formulated adhesive via differential scanning calorimetry. The adhesion strength of the adhesive was determined using the tensile shear strength analysis. The bonding performance tests indicated that BNPF resin adhesives have high adhesion strengths (>0.7 MPa). The outcome of this research provides a promising perspective to utilize natural polymers such as lignin for the synthesis of biobased wood adhesives.
Supercapacitors are an attractive technology for energy storage applications as they allow for fast charging of devices. The fabrication of flexible supercapacitors by additive manufacturing is a promising approach to produce energy storage components for applications where material flexibility and complex geometries are desirable. In this work, digital light projection (DLP) additive manufacturing is used to fabricate polymer electrolytes for flexible supercapacitors based on crosslinked poly(acrylic acid‐co‐vinylimidazole) (PAAVim). Ion gels are prepared through equilibration with 4M lithium chloride (LiCl) in ethylene glycol, deionized (DI) water and ethylene glycol/DI water mixtures. Flexibility and stretchability varied depending on the equilibration solvent with prepared PAAVim/LiCl polymer electrolytes exhibiting up to ˜700% elongation at break. Subsequent flexible supercapacitors fabricated by sandwiching the ion gel between carbon cloth electrodes delivered 60 F/g specific capacitance at the scan rate of 0.2 A/g with an energy density of 8.3 Wh/kg and a power density of 99.8 W/kg. Overall, this work demonstrates the fabrication of flexible capacitors through DLP additive manufacturing, where the resulting material physical and electrochemical properties can be varied through control over the resin chemistry.
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