Introduction to subpressure-driven soft deformation method for removing inherent voids in green components manufactured by material extrusion.

This study introduces a post-treatment process, the subpressure-driven soft deformation method, to reduce inherent voids in Material Extrusion (MEX) components. By subjecting printed green components to heat treatment under subpressure, the process enhances viscosity, effectively filling voids formed between deposited tracks. The average porosities of the samples sintered from the green components without and with soft deformation are calculated to be 3.55% and 2.36%, respectively. A comparison of the tensile strengths and fracture surfaces of the sintered samples with and without soft deformation treatment indicated that the sintered samples with soft deformation treatment exhibited narrower standard deviation for the various mechanical properties. Capillary rheometer calculations indicate feedstock viscosity to be between 450.34 and 1018.31 Pa s under subpressure, diminishing inter-track voids without sizeable dimensional changes. Molecular dynamics simulation demonstrates a 3.7-fold increase in bond strength, indicating intertrack voids effectively eliminated. Reduced inter-particle distances facilitate necking, grain growth, and improved sintered density.

Omnidirectional Energy Harvesting Fleeces.

Underwater mechanical energy harvesters are of rising interest due to their potential for various applications, such as self-powered ocean energy harvesters, monitoring devices, and wave sensors. Pressure-responsive films and stretch-responsive fibers, which provide high electrical power in electrolytes and have simple structures that do not require packing systems, are promising as harvesters in the ocean environment. One drawback of underwater mechanical energy harvesters is that they are highly dependent on the direction of receiving external forces, which is unfavorable in environments where the direction of the supplied force is constantly changing. Here, we report spherical fleece, consisting of wool fibers and single-walled carbon nanotubes (SWCNTs), which exhibit repetitive electrical currents in all directions. No matter which direction the fleece is deformed, it changes the surface area available for ions to access SWCNTs electrochemically, causing a piezoionic phenomenon. The current per input mechanical stress of the fabricated SWCNT/wool energy harvester is up to 33.476 mA/MPa, which is the highest among underwater mechanical energy harvesters reported to date. In particular, it is suitable for low-frequency (<1 Hz) environments, making it ideal for utilizing natural forces such as wind and waves as harvesting sources. The operating mechanism in the nanoscale region of the proposed fleece harvester has been theoretically elucidated through all-atom molecular dynamics simulations.

Regeneration of interfacial bonding force of waste carbon fibers by light: Process demonstration and atomic level analysis.

Although interest in recycling carbon fibers is rapidly growing, practical applications of recycled carbon fibers (rCFs) are limited owing to their poor wettability and adhesion. Surface modification of CFs was achieved through intense pulsed light (IPL) irradiation, which functionalizes surface of rCFs. Surface energy, chemical composition, morphology, and interfacial shear strength (IFSS) of rCFs before and after IPL irradiation were investigated. The rCF IPL-irradiated at 1,200 V improved both polar and dispersive components of surface energy, and the IFSS significantly increased by 2.93 times in relation to that of the pristine rCF and reached 95% of that of high-grade commercial CFs. We proposed a mechanism by which oxygen functional groups on the rCF surface enhance the molecular bonding force with HDPE, and the model was validated from molecular dynamics simulations. IPL irradiation is a rapid and effective surface treatment method that can be employed for the manufacture of rCF-reinforced composites.

Chemo-Mechanical Energy Harvesters with Enhanced Intrinsic Electrochemical Capacitance in Carbon Nanotube Yarns.

Predicting and preventing disasters in difficult-to-access environments, such as oceans, requires self-powered monitoring devices. Since the need to periodically charge and replace batteries is an economic and environmental concern, energy harvesting from external stimuli to supply electricity to batteries is increasingly being considered. Especially, in aqueous environments including electrolytes, coiled carbon nanotube (CNT) yarn harvesters have been reported as an emerging approach for converting mechanical energy into electrical energy driven by large and reversible capacitance changes under stretching and releasing. To realize enhanced harvesting performance, experimental and computational approaches to optimize structural homogeneity and electrochemical accessible area in CNT yarns to maximize intrinsic electrochemical capacitance (IEC) and stretch-induced changes are presented here. Enhanced IEC further enables to decrease matching impedance for more energy efficient circuits with harvesters. In an ocean-like environment with a frequency from 0.1 to 1 Hz, the proposed harvester demonstrates the highest volumetric power (1.6-10.45 mW cm-3 ) of all mechanical harvesters reported in the literature to the knowledge of the authors. Additionally, a high electrical peak power of 540 W kg-1 and energy conversion efficiency of 2.15% are obtained from torsional and tensile mechanical energy.