A Bioinspired Design of Protective Al2O3/Polyurethane Hierarchical Composite Film Through Layer-By-Layer Deposition.

Structural materials such as ceramics, metals, and carbon fiber-reinforced plastics (CFRP) are frequently threatened by large compressive and impact forces. Energy absorption layers, i.e., polyurethane and silicone foams with excellent damping properties, are applied on the surfaces of different substrates to absorb energy. However, the amount of energy dissipation and penetration resistance are limited in commercial polyurethane foams. Herein, a distinctive nacre-like architecture design strategy is proposed by integrating hard porous ceramic frameworks and flexible polyurethane buffers to improve energy absorption and impact resistance. Experimental investigations reveal the bioinspired designs exhibit optimized hardness, strength, and modulus compared to that of polyurethane. Due to the multiscale energy dissipation mechanisms, the resulting normalized absorbed energy (≈8.557 MJ m-3) is ≈20 times higher than polyurethane foams under 50% quasi-static compression. The bioinspired composites provide superior protection for structural materials (CFRP, glass, and steel), surpassing polyurethane films under impact loadings. It is shown CFRP coated with the designed materials can withstand more than ten impact loadings (in energy of 10 J) without obvious damage, which otherwise delaminates after a single impact. This biomimetic design strategy holds the potential to offer valuable insights for the development of lightweight, energy-absorbent, and impact-resistant materials.

Current and Future Trends for Polymer Micro/Nanoprocessing in Industrial Applications.

Polymers are widely used in optical devices, electronic devices, energy-harvesting/storage devices, and sensors, owing to their low weight, excellent flexibility, and simple fabrication process. With advancements in micro/nanoprocessing techniques and more demanding application requirements, it is becoming necessary to realize high-resolution fabrication of polymers to prepare miniaturized devices. This is particularly because conventional processing technologies suffer from high thermal stress and strong adhesion/friction, which can irreversibly damage the micro/nanostructures of miniaturized devices. In addition, although the use of advanced fabrication methods to prepare high-resolution micro/nanostructures is explored, these methods are limited to laboratory research or small-batch production. This review focuses on the micro/nanoprocessing of polymeric materials and devices with high spatial precision and replication accuracy for industrial applications. Specifically, the current state-of-the-art techniques and future trends for micro/nanomolding, high-energy beam processing, and micro/nanomachining are discussed. Moreover, an overview of the fabrication and applications of various polymer-based elements and devices such as microlenses, biosensors, and transistors is provided. These techniques are expected to be widely applied for multiscale and multimaterial processing as well as for multifunction integration in next-generation integrated devices, such as photoelectric, smart, and biodegradable devices.

Enhanced Electromechanical Response in PVDF-BNBT Composite Nanofibers for Flexible Sensor Applications.

Wearable energy harvesters and sensors have recently attracted significant attention with the rapid development of artificial intelligence and the Internet of Things (IoT). Compared to high-output bulk materials, these wearable devices are mainly fabricated by thin-film-based materials that limit their application. Therefore, the enhancement of output voltage and power for these devices has recently become an urgent topic. In this paper, the lead-free bismuth titanate-barium titanate (0.93(Na0.5Bi0.5)TiO3-0.07BaTiO3(BNBT)) nanoparticles and nanofibers were embedded into the PVDF nanofibers. They produced high inorganic electrical voltage coefficients, high electromechanical coupling coefficients, and environmentally friendly properties that enhance the electromechanical performance of pure PVDF nanofibers, and they are all the critical requirements for modern flexible pressure sensors. In detail, PVDF and PVDF-based composites nanofibers were prepared by electrospinning, and different flexible sandwich composite devices were fabricated by the PDMS encapsulation method. As a result, the six-time enhancement maximum output voltage was obtained in a PVDF-BNBT (fiber)-based composite sensor compared to the pure PVDF one. Our results indicate that the output voltage of the pressure sensors has been significantly enhanced, and the development gate is enabled by analyzing the related physical process and influence mechanism.

A Numerical Simulation Method for the One-Step Compression-Stamping Process of Continuous Fiber Reinforced Thermoplastic Composites.

Continuous fiber reinforced thermoplastic (CFRTP) composites have many advantages, such as high strength, high stiffness, shorter cycle, time and enabling the part consolidation of structural components. However, the mass production of the CFRTP parts is still challenging in industry and simulations can be used to better understand internal molding mechanisms. This paper proposes a three-dimensional simulation method for a one-step compression-stamping process which can conduct thermoplastic compression molding and continuous fiber reinforced thermoplastic composite stamping forming in one single mold, simultaneously. To overcome the strongly coupled non-isothermal moving boundary between the polymer and the composites, arbitrary Lagrangian-Eulerian based Navier-Stokes equations were applied to solve the thermoplastic compression, and a fiber rotation based objective stress rate model was used to solve for the composite stamping. Meanwhile, a strongly coupled fluid structure interaction framework with dual mesh technology is proposed to address the non-isothermal moving boundary issue between the polymer and the composites. This simulation method was compared against the experimental results to verify its accuracy. The polymer flow fronts were measured at different molding stages and the error between simulation and experiment was within 3.5%. The final composites' in-plane deformation error was less than 2.5%. The experiment shows that this work can accurately simulate the actual molding process.

High-strength cellulose films obtained by the combined action of shear force and surface selective dissolution.

Cellulose is a promising and advantageous material because it is low-cost, abundant and biodegradable. Nonetheless, dealing with this material is extremely challenging because cellulose cannot dissolve in most solvents or melt at any temperature or pressure in the air owing to strong hydrogen-bonding networks. In this work, a surface selective dissolution with shear force process was proposed to prepare cellulose films with high strength from microcrystalline cellulose powders. The tensile strength reached 94 MPa and the thermal decomposition temperature improved by 64 °C compared with that of regenerated cellulose. A mechanism of surface dissolution and reconnection was proposed to explain the process. The outstanding mechanical property attributes to tight reconnection of the undissolved cores via dissolved surfaces in cellulose powders, and the improved thermal decomposition temperature is due to preserved cellulose Ⅰ crystalline structure of microcrystalline cellulose. We believe that this cost-effective and facile method holds promise for industrial-scaleproduction of cellulose materials.