3D printed mechanical robust cellulose derived liquid-free ionic conductive elastomer for multifunctional electronic devices

Green Manufacture of Hydrated Polymers Coatings with On-Demand Mechanics and Lubricity Based on Novel Biobased Polymerizable Deep Eutectic Solvents

The aging population necessitates a critical need for medical devices, where polymers-based surface lubrication coating is essential for optimal functionality. In fact, lubrication and mechanical requirements vary depending on the service environment of different medical devices. Until now, key mean is still blank for general preparation of hydrophilic polymers-based lubrication coatings with on-demand mechanics and lubricity. This study introduces a novel hydrophilic lubrication coating with tunable mechanical properties and lubricity, derived from eco-friendly polymerizable deep eutectic solvents (PDESs) containing betaine, hydroxyethyl acrylate, glycerol, and tannic acid. Unlike traditional high molecular weight polymers, this approach leverages small-molecule, high-biobased PDESs, thereby simplifying the synthesis process. The resulting coating demonstrates exceptional adhesion to a range of medical device materials─including glass, stainless steel, polyvinyl chloride, and polyurethane─thanks to the high content of hydroxyl groups and pyrogallol motifs from tannic acid. It also enables the precise tuning of mechanical strength, modulus, adhesion, hydrophilicity, and lubrication properties by varying the amounts of glycerol and tannic acid. Furthermore, the coating undergoes a hydration-induced transition from high-strength, high-friction to low-strength, low-friction states, maintaining repeatable performance. Additionally, the synergistic effects of betaine and tannic acid in the PDES contribute to its notable antimicrobial properties. In summary, these PDESs demonstrate significant potential for enhancing lubrication in a range of biomedical devices.

Green fabrication of biodegradable films: Harnessing the cellulosic residue of oat straw

Agricultural biomass is a sustainable source for developing biodegradable film to address mounting plastic perils. This study aims to investigate the influence of CaCl2 concentration on the properties of lignocellulose-based biodegradable film produced from oat straw biomass. Lignocellulose is extracted from oat biomass, and a green technique is employed to solubilize it in ZnCl2 solution and crosslinked with varying CaCl2 concentrations (200 mM-800 mM) to make films. The films containing 800 mM CaCl2 concentration demonstrated the lowest moisture content (12.81 ± 0.81 %), water solubility (43.91 ± 0.42), water vapor permeability (4.96 ± 0.14 × 10-11 g-1s-1Pa-1), visible light transmittance (53.27 ± 0.69 %), and moisture absorption (42.42 ± 1.32 %). The tensile strength has increased remarkably from 4.24 ± 0.76 to 17.24 ± 3.68 MPa due to increased CaCl2 concentration from 200 mM to 800 mM. They degraded up to 83 % in soil with 20 % moisture after 28 days. Overall, films made of lignocellulose from oat straw biomass films demonstrate high strength and moisture barrier capabilities, rendering them suitable for use as food packaging materials.

Ionic Liquid-Modified Copper for the Enhanced Thermal Conductivity and Mechanical Properties of Epoxy Resin/Expanded Graphite Composites

In this study, diglycidylether of bisphenol A (DGEBA)/expanded graphite (EG)/copper (Cu) powder composites with high thermal conductivity were prepared for use as thermal interface materials. To construct an excellent thermally conductive network, the Cu surface was modified using the ionic liquid 1-ethyl-3-methyl imidazolium dicyanamide. In addition, the effect of the Cu content on the thermal conductivity, thermal stability, flexural properties, impact strength, and morphologies of the DGEBA/EG/Cu composites was investigated. The results indicated that the addition of 10 wt % Cu increased the thermal conductivity of the composites from 7.35 to 9.86 W/(m·K). Conversely, the thermal stability of the composites decreased with the addition of Cu. The flexural strength and impact strength of the composites increased from 27.9 MPa and 0.81 kJ/m2 to 39.6 MPa and 0.96 kJ/m2, respectively, as the Cu content increased from 0 to 10 wt %. Moreover, the flexural modulus of the composites increased from 9632 to 11,309 MPa with the addition of 10 wt % Cu. Scanning electron microscopy analysis of the DGEBA/EG/Cu composites revealed sheet-shaped blocks with numerous microcracks on the fracture surfaces.

"Dissolve-on-Demand" 3D Printed Materials: Polymerizable Eutectics for Generating High Modulus, Thermoresponsive and Photoswitchable Eutectogels

Solvent-free photopolymerization of vinyl monomers to produce high modulus materials with applications in 3D printing and photoswitchable materials is demonstrated. Polymerizable eutectic (PE) mixtures are prepared by simply heating and stirring various molar ratios of N-isopropylacrylamide (NIPAM), acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA). The structural and thermal properties of the resulting mixtures are evaluated by 1D and 2D NMR spectroscopy as well as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV photocuring kinetics of the PE mixtures is evaluated via in situ photo-DSC and photorheology measurements. The PE mixtures cure rapidly and display storage moduli that are orders of magnitude greater than equivalent copolymers cured in an aqueous medium. The versatility of these PE systems is demonstrated through the addition of a photoswitchable spiropyran acrylate monomer, as well as applying the PE formulation as a stereolithography (SLA)-based 3D printing resin. Due to the hydrogen-bonding network in PE systems, 3D printing of the eutectic resin is possible in the absence of crosslinkers. The addition of a RAFT agent to reduce average polymer chain length enables 3D printing of materials which retain their shape and can be dissolved on demand in appropriate solvents.

Fabrication of liquid-free ionic conductive elastomer (ICE) from cellulose-rosin derived poly(esterimide) towards temperature-tolerant and solvent-resistant UV shadowless adhesive and sensor

Recently, the utilization of the cellulose to fabricate the multifunctional materials with aim to replace the petroleum-based product, is receiving significant attentions. However, the development of cellulose-based multifunctional materials with high mechanical strength and temperature resistance is still a challenge. Herein, the intrinsic feature and property of cellulose and rosin were creatively employed to fabricate a novel cellulose-rosin based poly(esterimide) (PEI) by esterification reaction and imidization reaction, and the obtained cellulose-rosin derived PEI exhibits superior thermal stability. Then the as-prepared cellulose-rosin derived PEI was dissolved in polymerizable deep eutectic solvents (PDES) and in-situ formed the ionic conductive elastomer (ICE) with via UV-induced polymerization. These cellulose-rosin based ICE exhibited excellent mechanical properties, solvent resistance, and temperature tolerance. By adjusting the mass ratio of cellulose-rosin derived PEI and PDES, the as-prepared liquid-free ICE functions as UV shadowless adhesive and wearable sensors. The bonding strength of UV shadowless adhesive could 1.52 MPa, which could be applied to fix the broken glass toy models. Furthermore, wearable sensors based those ICE could monitor the large and subtle movements even under extreme environmental condition, such as being soaked in organic solvent (such as tetrahydrofuran) or at low/high temperature (-25 °C or 80 °C). This work opens a new avenue for the next-generation of multifunctional ICE.

A tough, reversible and highly sensitive humidity actuator based on cellulose nanofiber films by intercalation modulated plasticization

Cellulose nanofiber was an ideal candidate for humidity actuators based on its wide availability, biocompatibility and excellent hydrophilicity. However, conventional cellulose nanofiber-based actuators faced challenges like poor water resistance, flexibility, and sensitivity. Herein, water-resistant, flexible, and highly sensitive cross-linked cellulose nanofibers (CCNF) single-layer humidity actuators with remarkable reversible humidity responsiveness were prepared by combining the green click chemistry modification and intercalation modulated plasticization (IMP). The incorporation of phenyl ring and the crosslinked network structure in CCNF films contributed to its improved water resistance and mechanical properties (with a stress increased from 85.9 ± 3.1 MPa to 141.2 ± 21.5 MPa). SEM analysis confirmed enhanced interlaminar sliding properties facilitated by IMP. This resulted in increased flexibility and toughness of CCNF films, with a strain of 11.5 % and toughness of 9.9 MJ/m3. These improvements efficiently enhanced humidity sensitivity for cellulose nanofiber, with a 4.8-fold increase in bending curvature and a response time of only 3.4 ± 0.1 s. Finally, the good humidity sensitivity of modified CNF can be easily imparted to carbon nanotubes (CNTs) via simple self-assembly method, thus leading to a high-performance humidity-responsive actuator. The click chemistry modification and IMP offer a new avenue to fabricate tough, reversible and highly sensitive humidity actuator based on cellulose nanofiber.

Self-healing, environmentally stable and adhesive hydrogel sensor with conductive cellulose nanocrystals for motion monitoring and character recognition

Conductive hydrogel-based sensors offer diverse applications in artificial intelligence, wearable electronic devices and character recognition management. However, it remains a significant challenge to maintain their satisfactory performances under extreme climatic conditions. Herein, a stretchable, self-adhesive, self-healing and environmentally stable conductive hydrogel was developed through free radical polymerization of hydroxyethyl acrylate (HEA) and poly(ethylene glycol) methacrylate (PEG) as the skeleton, followed by the incorporation of polyaniline-coated cellulose nanocrystal (CNC@PANI) as the conductive and reinforced nanofiller. Encouragingly, the as-prepared hydrogel (CHP) exhibited decent mechanical strength, satisfactory self-adhesion, prominent self-healing property (95.04 % after 60 s), excellent anti-freezing performance (below -60 °C) and outstanding moisture retention. The assembled sensor derived from CHP hydrogel possessed a low detection limit (0.5 % strain), high strain sensitivity (GF = 1.68) and fast response time (96 ms). Remarkably, even in harsh environmental temperatures from -60 °C to 80 °C, it reliably detected subtle and large-scale human motion for a long-term process (>10,000 cycles), manifesting its exceptional environmental tolerance. More interestingly, this hydrogel-based sensor could be assembled into a "writing board" for accurate handwritten numeral recognition. Therefore, the as-obtained multifunctional hydrogel could be a promising material applied in human motion detection and character recognition platforms even in harsh surroundings.

Recyclable and mechanically tough nanocellulose reinforced natural rubber composite conductive elastomers for flexible multifunctional sensor

The development of flexible wearable multifunctional electronics has gained great attention in the field of human motion monitoring. However, developing mechanically tough, highly stretchable, and recyclable composite conductive materials for application in multifunctional sensors remained great challenges. In this work, a mechanically tough, highly stretchable, and recyclable composite conductive elastomer with the dynamic physical-chemical dual-crosslinking network was fabricated by the combination of multiple hydrogen bonds and dynamic ester bonds. To prepare the proposed composite elastomers, the polyaniline-modified carboxylate cellulose nanocrystals (C-CNC@PANI) were used as both conductive filler to yield high conductivity of 15.08 mS/m, and mechanical reinforcement to construct the dynamic dual-crosslinking network with epoxidized natural rubber latex to realize the high mechanical strength (8.65 MPa) and toughness (29.57 MJ/m3). Meanwhile, the construction of dynamic dual-crosslinking network endowed the elastomer with satisfactory recyclability. Based on these features, the composite conductive elastomers were used as strain sensors, and electrode material for assembling flexible and recyclable self-powered sensors for monitoring human motions. Importantly, the composite conductive elastomers maintained reliable sensing and energy harvesting performance even after multiple recycling process. This study provides a new strategy for the preparation of recyclable, mechanically tough composite conductive materials for wearable sensors.

Solid-state, liquid-free ion-conducting elastomers: rising-star platforms for flexible intelligent devices

Soft ionic conductors have emerged as a powerful toolkit to engineer transparent flexible intelligent devices that go beyond their conventional counterparts. Particularly, due to their superior capacities of eliminating the evaporation, freezing and leakage issues of the liquid phase encountered with hydrogels, organohydrogels and ionogels, the emerging solid-state, liquid-free ion-conducting elastomers have been largely recognized as ideal candidates for intelligent flexible devices. However, despite their extensive development, a comprehensive and timely review in this emerging field is lacking, particularly from the perspective of design principles, advanced manufacturing, and distinctive applications. Herein, we present (1) the design principles and intriguing merits of solid-state, liquid-free ion-conducting elastomers; (2) the methods to manufacture solid-state, liquid-free ion-conducting elastomers with preferential architectures and functions using advanced technologies such as 3D printing; (3) how to leverage solid-state, liquid-free ion-conducting elastomers in exploiting advanced applications, especially in the fields of flexible wearable sensors, bioelectronics and energy harvesting; (4) what are the unsolved scientific and technical challenges and future opportunities in this multidisciplinary field. We envision that this review will provide a paradigm shift to trigger insightful thinking and innovation in the development of intelligent flexible devices and beyond.