Versatile Patterning of Liquid Metal via Multiphase 3D Printing.

This paper presents a scalable and straightforward technique for the immediate patterning of liquid metal/polymer composites via multiphase 3D printing. Capitalizing on the polymer's capacity to confine liquid metal (LM) into diverse patterns. The interplay between distinctive fluidic properties of liquid metal and its self-passivating oxide layer within an oxidative environment ensures a resilient interface with the polymer matrix. This study introduces an inventive approach for achieving versatile patterns in eutectic gallium indium (EGaIn), a gallium alloy. The efficacy of pattern formation hinges on nozzle's design and internal geometry, which govern multiphase interaction. The interplay between EGaIn and polymer within the nozzle channels, regulated by variables such as traverse speed and material flow pressure, leads to periodic patterns. These patterns, when encapsulated within a dielectric polymer polyvinyl alcohol (PVA), exhibit an augmented inherent capacitance in capacitor assemblies. This discovery not only unveils the potential for cost-effective and highly sensitive capacitive pressure sensors but also underscores prospective applications of these novel patterns in precise motion detection, including heart rate monitoring, and comprehensive analysis of gait profiles. The amalgamation of advanced materials and intricate patterning techniques presents a transformative prospect in the domains of wearable sensing and comprehensive human motion analysis.

Nanoparticle Assembly: From Self-Organization to Controlled Micropatterning for Enhanced Functionalities.

Nanoparticles form long-range micropatterns via self-assembly or directed self-assembly with superior mechanical, electrical, optical, magnetic, chemical, and other functional properties for broad applications, such as structural supports, thermal exchangers, optoelectronics, microelectronics, and robotics. The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. This article provides a comprehensive review of nanoparticle assembly formed primarily via the balance of forces at the nanoscale (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer). The review commences with a general overview of nanoparticle self-assembly, with the state-of-the-art literature review and motivation. It subsequently reviews the recent progress in nanoparticle assembly without the presence of surface templates. Manufacturing techniques for surface template fabrication and their influence on nanoparticle assembly efficiency and effectiveness are then explored. The primary focus is the spatial organization and orientational preference of nanoparticles on non-templated and pre-templated surfaces in a controlled manner. Moreover, the article discusses broad applications of micropatterned surfaces, encompassing various fields. Finally, the review concludes with a summary of manufacturing methods, their limitations, and future trends in nanoparticle assembly.

A versatile route for the fabrication of micro-patterned polylactic-acid (PLA)-based membranes with tailored morphology via breath figure imprinting.

Breath figure imprinting, based on surface instabilities combined with fast polymer evaporation in a humid environment, enables the creation of micro-patterned membranes with tailored pore sizes. Despite being a simple procedure, it is still challenging to fully understand the dynamics behind the formation of hierarchical structuring. In this work, we used the breath figure technique to prepare porous PLA-based (polylactic acid) membranes with two distinctive additives, polyvinylidene fluoride (PVDF) and zinc oxide nanoparticles (ZnO NPs). The selection of these additives was governed by their unique properties and the potential synergistic effects; when blended with PLA, the addition of NPs leads to more uniform structures with tunable characteristics and potential multifunctionality. This article sheds light on the multifaced interactions that intricate the interplays between PLA, PVDF, and ZnO, thus governing their assembly. Through a comprehensive investigation, we scrutinize the impact of blending PVDF and different concentrations of ZnO NPs on the morphology and chemical properties of the final self-assembled PLA membranes while presenting an advanced understanding of the potential applications of PLA-self-assembly porous membranes in various industrial sectors.

'Dark' CO2 fixation in succinate fermentations enabled by direct CO2 delivery via hollow fiber membrane carbonation.

Anaerobic succinate fermentations can achieve high-titer, high-yield performance while fixing CO2 through the reductive branch of the tricarboxylic acid cycle. To provide the needed CO2, conventional media is supplemented with significant (up to 60 g/L) bicarbonate (HCO3-), and/or carbonate (CO32-) salts. However, producing these salts from CO2 and natural ores is thermodynamically unfavorable and, thus, energetically costly, which reduces the overall sustainability of the process. Here, a series of composite hollow fiber membranes (HFMs) were first fabricated, after which comprehensive CO2 mass transfer measurements were performed under cell-free conditions using a novel, constant-pH method. Lumen pressure and total HFM surface area were found to be linearly correlated with the flux and volumetric rate of CO2 delivery, respectively. Novel HFM bioreactors were then constructed and used to comprehensively investigate the effects of modulating the CO2 delivery rate on succinate fermentations by engineered Escherichia coli. Through appropriate tuning of the design and operating conditions, it was ultimately possible to produce up to 64.5 g/L succinate at a glucose yield of 0.68 g/g; performance approaching that of control fermentations with directly added HCO3-/CO32- salts and on par with prior studies. HFMs were further found to demonstrate a high potential for repeated reuse. Overall, HFM-based CO2 delivery represents a viable alternative to the addition of HCO3-/CO32- salts to succinate fermentations, and likely other 'dark' CO2-fixing fermentations.

3D Printing-Enabled Design and Manufacturing Strategies for Batteries: A Review.

Lithium-ion batteries (LIBs) have significantly impacted the daily lives, finding broad applications in various industries such as consumer electronics, electric vehicles, medical devices, aerospace, and power tools. However, they still face issues (i.e., safety due to dendrite propagation, manufacturing cost, random porosities, and basic & planar geometries) that hinder their widespread applications as the demand for LIBs rapidly increases in all sectors due to their high energy and power density values compared to other batteries. Additive manufacturing (AM) is a promising technique for creating precise and programmable structures in energy storage devices. This review first summarizes light, filament, powder, and jetting-based 3D printing methods with the status on current trends and limitations for each AM technology. The paper also delves into 3D printing-enabled electrodes (both anodes and cathodes) and solid-state electrolytes for LIBs, emphasizing the current state-of-the-art materials, manufacturing methods, and properties/performance. Additionally, the current challenges in the AM for electrochemical energy storage (EES) applications, including limited materials, low processing precision, codesign/comanufacturing concepts for complete battery printing, machine learning (ML)/artificial intelligence (AI) for processing optimization and data analysis, environmental risks, and the potential of 4D printing in advanced battery applications, are also presented.

Unveiling the Multiradical Character of the Biphenylene Network and Its Anisotropic Charge Transport.

Recent progress in the on-surface synthesis and characterization of nanomaterials is facilitating the realization of new carbon allotropes, such as nanoporous graphenes, graphynes, and 2D π-conjugated polymers. One of the latest examples is the biphenylene network (BPN), which was recently fabricated on gold and characterized with atomic precision. This gapless 2D organic material presents uncommon metallic conduction, which could help develop innovative carbon-based electronics. Here, using first principles calculations and quantum transport simulations, we provide new insights into some fundamental properties of BPN, which are key for its further technological exploitation. We predict that BPN hosts an unprecedented spin-polarized multiradical ground state, which has important implications for the chemical reactivity of the 2D material under practical use conditions. The associated electronic band gap is highly sensitive to perturbations, as seen in finite temperature (300 K) molecular dynamics simulations, but the multiradical character remains stable. Furthermore, BPN is found to host in-plane anisotropic (spin-polarized) electrical transport, rooted in its intrinsic structural features, which suggests potential device functionality of interest for both nanoelectronics and spintronics.

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications.

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

Scalable Alignment and Selective Deposition of Nanoparticles for Multifunctional Sensor Applications.

Here reported is the layer-by-layer-based advanced manufacturing that yields a simple, novel, and cost-effective technique for generating selective nanoparticle deposition and orientation in the form of well-controlled patterns. The surface roughness of the three-dimensionally printed patterns and the solid-liquid-air contact line, as well as the nanoparticle interactions in dipped suspensions, determine the carbon nanofiber (CNF) alignment, while the presence of triangular grooves supports the pinning of the meniscus, resulting in a configuration consisting of alternating CNF and polymer channels. The polymer/nanoparticle composites show 10 times lower resistance along with the particle alignment direction than the randomly distributed CNF networks and 6 orders of magnitude lower than that along the transverse direction. The unidirectional alignment of the CNF also demonstrates linear piezoresistivity behavior under small strain deformation along with high sensitivity and selectivity toward volatile organic compounds. The reported advanced manufacturing shows broad applications in microelectronics, energy transport, light composites, and multifunctional sensors.

Spin Proximity Effects in Graphene/Topological Insulator Heterostructures.

Enhancing the spin-orbit interaction in graphene, via proximity effects with topological insulators, could create a novel 2D system that combines nontrivial spin textures with high electron mobility. To engineer practical spintronics applications with such graphene/topological insulator (Gr/TI) heterostructures, an understanding of the hybrid spin-dependent properties is essential. However, to date, despite the large number of experimental studies on Gr/TI heterostructures reporting a great variety of remarkable (spin) transport phenomena, little is known about the true nature of the spin texture of the interface states as well as their role on the measured properties. Here, we use ab initio simulations and tight-binding models to determine the precise spin texture of electronic states in graphene interfaced with a Bi2Se3 topological insulator. Our calculations predict the emergence of a giant spin lifetime anisotropy in the graphene layer, which should be a measurable hallmark of spin transport in Gr/TI heterostructures and suggest novel types of spin devices.

Fabricating Fibers of a Porous-Polystyrene Shell and Particle-Loaded Core.

Polystyrene (PS) polymers have broad applications in protective packaging for food shipping, containers, lids, bottles, trays, tumblers, disposable cutlery and the making of models. Currently, most PS products, such as foams, are not accepted for recycling due to a low density in the porous structure. This poses a challenge for logistics as well as creating a lack of incentive to invest in high-value products. This study, however, demonstrated the use of a dry-jet wet-spinning technique to manufacture continuous PS fibers enabled by an in-house designed and developed spinning apparatus. The manufactured fibers showed porosity in the shell and the capability to load particles in their core, a structure with high potential use in environmentally relevant applications such as water treatment or CO2 collections. A two-phase liquid-state microstructure was first achieved via a co-axial spinneret. Following coagulation procedures and heat treatment, phase-separation-based selective dissolution successfully generated the porous-shell/particle-core fibers. The pore size and density were controlled by the porogen (i.e., PEG) concentrations and examined using scanning electron microscopy (SEM). Fiber formation dynamics were studied via rheology tests and gelation measurements. The shell components were characterized by tensile tests, thermogravimetric analysis, and differential scanning calorimetry for mechanical durability and thermal stability analyses.

Ink-Based Additive Manufacturing of a Polymer/Coal Composite: A Non-Traditional Reinforcement.

Coal, a crucial natural resource traditionally employed for generating carbon-rich materials and powering global industries, has faced escalating scrutiny due to its adverse environmental impacts outweighing its utility in the contemporary world. In response to the worldwide shift toward sustainability, the United States alone has witnessed an approximate 50% reduction in coal consumption. Nevertheless, the ample availability of coal has spurred interest in identifying alternative sustainable applications. This research delves into the feasibility of utilizing coal as a nonconventional carbon-rich reinforcement in direct ink writing (DIW)-based 3D printing techniques. Our investigation here involves a thermosetting resin serving as a matrix, incorporating pulverized coal (250 µm in size) and carbon black as the reinforcement and a viscosity modifier, respectively. The ink formulation is meticulously designed to exhibit shear-thinning behavior essential for DIW 3D printing, ensuring uniform and continuous printing. Mechanical properties are assessed through the 3D printing of ASTM standard specimens to validate the reinforcing impact. Remarkably, the study reveals that a 2 wt % coal concentration in the ink leads to a substantial improvement in both tensile and flexural properties, resulting in enhancements of 35 and 12.5%, respectively. Additionally, the research demonstrates the printability of various geometries with coal as reinforcement, opening up new possibilities for coal utilization while pursuing more sustainable manufacturing and applications.

Coaxial Layered Fiber Spinning for Wind Turbine Blade Recycling.

Plastics' long degradation time and their role in adding millions of metric tons of plastic waste to our oceans annually present an acute environmental challenge. Handling end-of-life waste from wind turbine blades (WTBs) is equally pressing. Currently, WTB waste often finds its way into landfills, emphasizing the need for recycling and sustainable solutions. Mechanical recycling of composite WTB presents an avenue for the recovery of glass fibers (GF) for repurposing as fillers or reinforcements. The resulting composite materials exhibit improved properties compared to the pure PAN polymer. Through the employment of the dry-jet wet spinning technique, we have successfully manufactured PAN/GF coaxial-layered fibers with a 0.1 wt % GF content in the middle layer. These fibers demonstrate enhanced mechanical properties and a lightweight nature. Most notably, the composite fiber demonstrates a significant 24.4% increase in strength and a 17.7% increase in modulus. These fibers hold vast potential for various industrial applications, particularly in the production of structural components (e.g., electric vehicles), contributing to enhanced performance and energy efficiency.

Continuous Three-Dimensional Printing of Architected Piezoelectric Sensors in Minutes.

Additive manufacturing (AM), also known as three-dimensional (3D) printing, is thriving as an effective and robust method in fabricating architected piezoelectric structures, yet most of the commonly adopted printing techniques often face the inherent speed-accuracy trade-off, limiting their speed in manufacturing sophisticated parts containing micro-/nanoscale features. Herein, stabilized, photo-curable resins comprising chemically functionalized piezoelectric nanoparticles (PiezoNPs) were formulated, from which microscale architected 3D piezoelectric structures were printed continuously via micro continuous liquid interface production (µCLIP) at speeds of up to ~60 µm s-1, which are more than 10 times faster than the previously reported stereolithography-based works. The 3D-printed functionalized barium titanate (f-BTO) composites reveal a bulk piezoelectric charge constant d 33 of 27.70 pC N-1 with the 30 wt% f-BTO. Moreover, rationally designed lattice structures that manifested enhanced, tailorable piezoelectric sensing performance as well as mechanical flexibility were tested and explored in diverse flexible and wearable self-powered sensing applications, e.g., motion recognition and respiratory monitoring.

Crosslinked Polyethylene (XLPE) Recycling via Foams.

Efficient recycling of crosslinked polyethylene has been challenging due to manufacturing difficulties caused by chemical crosslinking. This study focuses on simple processing via solid waste powder generation and particle fining for the subsequent crosslinked polyethylene inclusion and dispersion in rigid polyurethane foam. In addition, the concentration effects of crosslinked polyethylene in polyurethane were studied, showing a well-controlled foam microstructure with uniform pores, retained strength, better thermal degradation resistance, and, more importantly, increased thermal capabilities. Thus, the simple mechanical processing of crosslinked polyethylene and chemical urethane foaming showed the massive potential of recycling large amounts of crosslinked polyethylene in foams for broad applications in food packaging, house insulation, and sound reduction.

Intrinsic Field-Induced Nanoparticle Assembly in Three-Dimensional (3D) Printing Polymeric Composites.

Nanoparticles (NPs) are materials considered to be 1-100 nm in size and are available in different dimensional shapes, geometrical sizes, physical morphologies, mechanical robustness, and chemical compositions. Irrespective of the dimensions (i.e., zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D)), NPs have a tendency to become entangled together, forming aggregations due to high attraction, making it hard to realize their full potential from their ordered counterparts. Many challenges exist to attain high-quality stabilized dispersion and long-range ordered assembly of NPs. Three-dimensional printing (3DP), also known as additive manufacturing (AM), is a technique dependent on layer-by-layer material addition for building 3D structures and encompasses a few categories based on the feedstock material types and printing mechanisms. One benefit from the 3DP procedures is their capability to produce anisotropic microstructural/nanostructural characteristics for desired mechanical reinforcement, transport phenomena, energy management, and biomedical implants. This paper briefly overviews relevant 3DP methods with an embedded nature to assemble nanoparticles without interference with external fields (e.g., magnetic or electrical). Our focus is the shear-field-induced nanoparticle alignment, covering material jetting-, electrohydrodynamic-, filament melting-, and ink writing-based 3DP. A concise summary of photopolymerization and its "optical tweezer" effects on nanoparticle confinement also inspires creative approaches in generating ordered nanostructures. The nanoparticles and polymers involved in this review are diverse, consisting of metallic, ceramic, and carbon nanoparticles in matrices or on surfaces of varying macromolecules. A short statement of challenges (e.g., low resolution, slow printing speed, limited material options) for 3DP-enabled nanoparticle orders provides some perspectives toward the enormous potential of 3DP in directing NPs assembly and fabricating high-performance polymer/nanoparticle composites.

Aligned Ti3C2Tx MXene for 3D Micropatterning via Additive Manufacturing.

Selective deposition and preferential alignment of two-dimensional (2D) nanoparticles on complex and flexible three-dimensional (3D) substrates can tune material properties and enrich structural versatility for broad applications in wearable health monitoring, soft robotics, and human-machine interfaces. However, achieving precise and scalable control of the morphology of layer-structured nanomaterials is challenging, especially constructing hierarchical architectures consistent from nanoscale alignment to microscale patterning to complex macroscale landscapes. This work demonstrated a scalable and straightforward hybrid 3D printing method for orientational alignment and positional patterning of 2D MXene nanoparticles. This process involved (i) surface topology design via microcontinuous liquid interface production (µCLIP) and (ii) directed assembly of MXene flakes via capillarity-driven direct ink writing (DIW). With well-managed surface patterning geometry and printing ink quality control, the surface microchannels constrained MXene suspensions and leveraged microforces to facilitate preferential alignment of MXene sheets via layer-by-layer additive depositions. The printed devices displayed multifunctional properties, i.e., anisotropic conductivity and piezoresistive sensing with a wide sensing range, high sensitivity, fast response time, and mechanical durability. Our fabrication technique shows enormous potential for rapid, digital, scalable, and low-cost manufacturing of hierarchical structures, especially for micropatterning and aligning 2D nanoparticles not easily accessible through conventional processing methods.

PMMA-TiO2 Fibers for the Photocatalytic Degradation of Water Pollutants.

Titanium dioxide (TiO2) is a promising photocatalyst that possesses a redox potential suitable for environmental remediation applications. A low photocatalytic yield and high cost have thus far limited the commercial adoption of TiO2-based fixed-bed reactors. One solution is to engineer the physical geometry or chemical composition of the substrate to overcome these limitations. In this work, porous polymethyl methacrylate (PMMA) substrates with immobilized TiO2 nanoparticles in fiber forms were fabricated and analyzed to demonstrate the influence of contaminant transport and light accessibility on the overall photocatalytic performance. The influences of (i) fiber porosity and (ii) fiber architecture on the overall photocatalytic performance were investigated. The porous structure was fabricated using wet phase inversion. The core-shell-structured fibers exhibited much higher mechanical properties than the porous fibers (7.52 GPa vs. non-testability) and maintained the same degradation rates as porous structures (0.059 vs. 0.053/min) in removing methylene blue with comparable specific surface areas. The highest methylene blue (MB) degradation rate (kMB) of 0.116 min-1 was observed due to increases of the exposed surface area, pointing to more efficient photocatalysis by optimizing core-shell dimensions. This research provides an easy-to-manufacture and cost-efficient method for producing PMMA/TiO2 core-shell fibers with a broad application in water treatment, air purification, and volatile sensors.

In situ alignment of graphene nanoplatelets in poly(vinyl alcohol) nanocomposite fibers with controlled stepwise interfacial exfoliation.

Hierarchically microstructured tri-axial poly(vinyl alcohol)/graphene nanoplatelet (PVA/GNP) composite fibers were fabricated using a dry-jet wet spinning technique. The composites with distinct PVA/GNPs/PVA phases led to highly oriented and evenly distributed graphene nanoplatelets (GNPs) as a result of molecular chain-assisted interfacial exfoliation. With a concentration of 3.3 wt% continuously aligned GNPs, the composite achieved a ∼73.5% increase in Young's modulus (∼38 GPa), as compared to the pure PVA fiber, and an electrical conductivity of ∼0.38 S m-1, one of the best mechanical/electrical properties reported for polymer/GNP nanocomposite fibers. This study has broader impacts on textile engineering, wearable robotics, smart sensors, and optoelectronic devices.

Reversible Self-Healing for Preserving Optical Transparency and Repairing Mechanical Damage in Composites.

This research concentrates on the healing of optical properties, roughness, contact angle hysteresis, and shallow scratches in polymer/nanoparticle composites. A series of ternary composite blends [epoxy/halloysite nanotubes (HNTs)/cellulose acetate butyrate (CAB)] with various CAB concentrations were fabricated and subjected to a series of mechanical damages. The optimized concentration of a nanoparticle is 1.0 vol %, and the CAB concentration is 3.0 vol % based on the mechanical reinforcement and wear resistance. Nanoscale scratching, microlevel falling-sand test, and macrolevel Taber abrasions were utilized to damage the surfaces. The induced damage (roughness and surface scratch up to hundreds of nanometers in depth) healed upon heating. At any temperatures above the softening transition of the semi-interpenetrating network structure of the polymer composites, CAB migrates into the microcracks, and the essential mechanical parameters (modulus, strength, strain to failure) are recovered; in our particular epoxy/HNTs/CAB system, optical transparency is also recovered efficiently. CAB also moves to the macroscopic air/specimen interface and favorably modifies the surface properties, reducing the roll-off angles of water droplets from ∼90° to ∼20°. Through an appropriate choice of CAB additives with different molecular weights, the healing temperature can be tailored.

Tailoring emergent spin phenomena in Dirac material heterostructures.

Dirac materials such as graphene and topological insulators (TIs) are known to have unique electronic and spintronic properties. We combine graphene with TIs in van der Waals heterostructures to demonstrate the emergence of a strong proximity-induced spin-orbit coupling in graphene. By performing spin transport and precession measurements supported by ab initio simulations, we discover a strong tunability and suppression of the spin signal and spin lifetime due to the hybridization of graphene and TI electronic bands. The enhanced spin-orbit coupling strength is estimated to be nearly an order of magnitude higher than in pristine graphene. These findings in graphene-TI heterostructures could open interesting opportunities for exploring exotic physical phenomena and new device functionalities governed by topological proximity effects.