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.

Electromechanical Origin of Phonon Dynamics Exhibiting Tunable Anisotropic Heat Transport in Layered Nanostructures.

Owing to the structural characteristics of 2D layered nanomaterials, anisotropic thermal conductivity is considered an attractive design factor for constructing efficient heat-transfer pathways. In this study, the electromechanical origin of anisotropic thermal conduction in Ti3 C2 O2 M (M = Li, Na, K) is investigated at the atomic scale using theoretical multiscale analysis. The results demonstrate that the acoustic and optical phonon modes drive interlayer and intralayer heat conduction, respectively. Further, the lower the atomic number of the alkali ions intercalated in the Ti3 C2 O2 layer, the more immediately it responds to externally applied oscillations owing to its low inertia and high electrostatic force. The Li-ion layer exhibits an instantaneous response to vibrational excitations from an external source, making it transparent to higher phonon modes under interlayer and intralayer thermal conduction. The electromechanical modulation properties of the ion layer are further elucidated, providing practical insights into the design of anisotropic thermal paths.

Ultraviolet Light Debondable Optically Clear Adhesives for Flexible Displays through Efficient Visible-Light Curing.

With growing sustainability concerns, the need for products that facilitate easy disassembly and reuse has increased. Adhesives, initially designed for bonding, now face demands for selective removal, enabling rapid assembly-disassembly and efficient maintenance across industries. This need is particularly evident in the display industry, with the rise of foldable devices necessitating specialized adhesives. A novel optically clear adhesive (OCA) is presented for foldable display, featuring a unique UV-stimulated selective removal feature. This approach incorporates benzophenone derivatives into the polymer network, facilitating rapid debonding under UV irradiation. A key feature of this method is the adept use of visible-light-driven radical polymerization for OCA film fabrication. This method shows remarkable compatibility with various monomers and exhibits orthogonal reactivity to benzophenone, rendering it ideal for large-scale production. The resultant OCA not only has high transparency and balanced elasticity, along with excellent resistance to repeated folding, but it also exhibits significantly reduced adhesion when exposed to UV irradiation. By merging this customized formulation with strategically integrated UV-responsive elements, an effective solution is offered that enhances manufacturing efficiency and product reliability in the rapidly evolving field of sustainable electronics and displays. This research additionally contributes to eco-friendly device fabrication, aligning with emerging technology demands.

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.

Observation of Highly Anisotropic Thermal Expansion of Polymer Films.

While dimensional change under thermal loading dictates various device failure mechanisms in soft materials, the interplay between microstructures and thermal expansion remains underexplored. Here, we develop a novel method to directly probe the thermal expansion for nanoscale polymer films using an atomic force microscope as well as confining active thermal volume. In a model system, spin-coated poly(methyl methacrylate), we find that the in-plane thermal expansion is enhanced by 20-fold compared to that along the out-of-plane directions in confined dimensions. Our molecular dynamics simulations show that the collective motion of side groups along backbone chains uniquely drives the enhancement of thermal expansion anisotropy of polymers in the nanoscale limit. This work unveils the intimate role of the microstructure of polymer films on its thermal-mechanical interaction, paving a route to judiciously enhance the reliability in a broad range of thin-film devices.

Engineering Silk Protein to Modulate Polymorphic Transitions for Green Lithography Resists.

Silk protein is being increasingly introduced as a prospective material for biomedical devices. However, a limited locus to intervene in nature-oriented silk protein makes it challenging to implement on-demand functions to silk. Here, we report how polymorphic transitions are related with molecular structures of artificially synthesized silk protein and design principles to construct a green-lithographic and high-performative protein resist. The repetition number and ratio of two major building blocks in synthesized silk protein are essential to determine the size and content of ß-sheet crystallites, and radicals resulting from tyrosine cleavages by the 193 nm laser irradiation induce the ß-sheet to α-helix transition. Synthesized silk is designed to exclusively comprise homogeneous building blocks and exhibit high crystallization and tyrosine-richness, thus constituting an excellent basis for developing a high-performance deep-UV photoresist. Additionally, our findings can be conjugated to design an electron-beam resist governed by the different irradiation-protein interaction mechanisms. All synthesis and lithography processes are fully water-based, promising green lithography. Using the engineered silk, a nanopatterned planar color filter showing the reduced angle dependence can be obtained. Our study provides insights into the industrial scale production of silk protein with on-demand functions.

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.

Emerging laser-assisted vacuum processes for ultra-precision, high-yield manufacturing.

Laser technology is a cutting-edge process with a unique photothermal response, precise site selectivity, and remote controllability. Laser technology has recently emerged as a novel tool in the semiconductor, display, and thin film industries by providing additional capabilities to existing high-vacuum equipment. The in situ and in operando laser assistance enables using multiple process environments with a level of complexity unachievable with conventional vacuum equipment. This broadens the usable range of process parameters and directly improves material properties, product precision, and device performance. This review paper examines the recent research trends in laser-assisted vacuum processes (LAVPs) as a vital tool for innovation in next-generation manufacturing processing equipment and addresses the unique characteristics and mechanisms of lasers exclusively used in each study. All the findings suggest that the LAVP can lead to methodological breakthroughs in dry etching, 2D material synthesis, and chemical vapor deposition for optoelectronic devices.

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.

Molecular mechanics of Ag nanowire transfer processes subjected to contact loading by a PDMS substrate.

Precise transfer and attachment of a single nanowire to a target substrate is an interesting technique in surface engineering. The spacing, which restrains the attachment of a nanowire to a substrate, and the bending strain that occurs when the nanowire detaches from the elastomeric donor are important design parameters. In this regard, in this study, all-atom molecular dynamics (MD) simulations were conducted to analyse the mechanical behaviour of a penta-twinned silver nanowire (AgNW) placed on a polydimethylsiloxane (PDMS) donor substrate to elucidate the relevant transfer process. The bow deformation of the AgNW at the delamination front of PDMS was characterized as a function of its diameter and aspect ratio. The mechanisms of dislocation slip and propagation as well as the internal stress distribution of the AgNW were then examined. The results showed that twin boundary formation during the bow deformation is a key factor affecting the strain hardening of the AgNW and leading to complete plastic strain recovery after the removal of the PDMS substrate. Furthermore, the process was demonstrated experimentally by a localized bonding and transfer of AgNWs by continuous-wave laser irradiation. Based on the computational and experimental findings, an empirical model considering the shape parameters of AgNWs that can ensure a successful transfer process was established, which is essential for high-performance AgNW electrode design.

From Chaos to Control: Programmable Crack Patterning with Molecular Order in Polymer Substrates.

Cracks are typically associated with the failure of materials. However, cracks can also be used to create periodic patterns on the surfaces of materials, as observed in the skin of crocodiles and elephants. In synthetic materials, surface patterns are critical to micro- and nanoscale fabrication processes. Here, a strategy is presented that enables freely programmable patterns of cracks on the surface of a polymer and then uses these cracks to pattern other materials. Cracks form during deposition of a thin film metal on a liquid crystal polymer network (LCN) and follow the spatially patterned molecular order of the polymer. These patterned sub-micrometer scale cracks have an order parameter of 0.98 ± 0.02 and form readily over centimeter-scale areas on the flexible substrates. The patterning of the LCN enables cracks that turn corners, spiral azimuthally, or radiate from a point. Conductive inks can be filled into these oriented cracks, resulting in flexible, anisotropic, and transparent conductors. This materials-based processing approach to patterning cracks enables unprecedented control of the orientation, length, width, and depth of the cracks without costly lithography methods. This approach promises new architectures of electronics, sensors, fluidics, optics, and other devices with micro- and nanoscale features.

Self-folding Structural Design Using Multiscale Analysis on the Light-absorption Folding Behaviour of Polystyrene Sheet.

Concentrated light-absorption on specific areas of polystyrene (PS) sheet induces self-folding behaviour. Such localized light-absorption control is easily realized by black-coloured line pattern printing. As the temperature in the line patterns of PS sheet increases differently due to the transparencies in each line pattern, localized thermal contraction generates folding deformation of the PS sheet. The light-activated folding technique is caused by the shape memory effect of PS sheet. The shape memory creation procedure (SMCP) is described by using molecular dynamic (MD) simulation, and the constitutive model of PS sheet is identified. This study employs the shell/cohesive line element for the folding deformation of PS sheet, and utilizes the constitutive model obtained from the MD simulation. Based on the continuum-model analysis of the PS sheet folding deformation activated by light, various self-folding structures are designed and manufactured.

Liquid-Crystalline Elastomers with Gold Nanoparticle Cross-Linkers.

Embedding nanoparticles in a responsive polymer matrix is a formidable way to fabricate hybrid materials with predesigned properties and prospective applications in actuators, mechanically tunable optical elements, and electroclinic films. However, achieving chemical compatibility between nanoparticles and organic matter is not trivial and often results in disordered structures. Herein, it is shown that using nanoparticles as exclusive cross-linkers in the preparation of liquid-crystalline polymers can yield long-range-ordered liquid-crystalline elastomers with high loadings of well-dispersed nanoparticles, as confirmed by small-angle XRD measurements. Moreover, the strategy of incorporating NPs as cross-linking units does not result in disruption of mechanical properties of the polymer, and this phenomenon was explained by the means of all-atom molecular dynamics simulations. Such materials can exhibit switchable behavior under thermal stimulus with stability spanning over multiple heating/cooling cycles. The presented strategy has proven to be a promising approach for the preparation of new types of hybrid liquid-crystalline elastomers that can be of value for future photonic applications.

Molecular Dynamics Study on the Photothermal Actuation of a Glassy Photoresponsive Polymer Reinforced with Gold Nanoparticles with Size Effect.

We investigated the optical and thermal actuation behavior of densely cross-linked photoresponsive polymer (PRP) and polymer nanocomposites containing gold nanoparticles (PRP/Au) using all-atom molecular dynamics (MD) simulations. The modeled molecular structures contain a large number of photoreactive mesogens with linear orientation. Flexible side chains are interconnected through covalent bonds under periodic boundary conditions. A switchable dihedral potential was applied on a diazene moiety to describe the photochemical trans-to-cis isomerization. To quantify the photoinduced molecular reorientation and its effect on the macroscopic actuation of the neat PRP and PRP/Au materials, we characterized the photostrain and other material properties including elastic stiffness and thermal stability according to the photoisomerization ratio of the reactive groups. We particularly examined the effect of nanoparticle size on the photothermal actuation by varying the diameter of the nanofiller (10-20 Å) under the same volume fraction of 1.62%. The results indicated that the insertion of the gold nanoparticles enlarges the photostrain of the material while enhancing its mechanical stiffness and thermal stability. When the diameter of the nanoparticle reaches a size similar to or smaller than the length of the mesogen, the interfacial energy between the nanofiller and the surrounding polymer matrix does not significantly affect the alignment of the mesogens, but rather the adsorption energy at the interface generates a stable interphase layer. Hence, these improvements were more effective as the size of the gold nanoparticle decreased. The present findings suggest a wider analysis of the nanofiller-reinforced PRP composites and could be a guide for the mechanical design of the PRP actuator system.

Nonlinear photomechanics of nematic networks: upscaling microscopic behaviour to macroscopic deformation.

A liquid crystal network whose chromophores are functionalized by photochromic dye exhibits light-induced mechanical behaviour. As a result, the micro-scaled thermotropic traits of the network and the macroscopic phase behaviour are both influenced as light alternates the shape of the dyes. In this paper, we present an analysis of this photomechanical behaviour based on the proposed multiscale framework, which incorporates the molecular details of microstate evolution into a continuum-based understanding. The effects of trans-to-cis photoisomerization driven by actinic light irradiation are first examined using molecular dynamics simulations, and are compared against the predictions of the classical dilution model; this reveals certain characteristics of mesogenic interaction upon isomerization, followed by changes in the polymeric structure. We then upscale the thermotropic phase-related information with the aid of a nonlinear finite element analysis; macroscopic deflection with respect to the wide ranges of temperature and actinic light intensity are thereby examined, which reveals that the classical model underestimates the true deformation. This work therefore provides measures for analysing photomechanics in general by bridging the gap between the micro- and macro-scales.

Light and thermal responses of liquid-crystal-network films: A finite element study.

As a polymeric system incorporating rigid molecules within its structure, the liquid-crystal network (LCN) has been envisaged as a novel heterogeneous material. Under the influence of external stimuli, the orientational order of the liquid-crystalline phase becomes dilute and overall anisotropy is hence decreased; the actinic light absorbed by photochromic molecules, for example, induces the geometric isomerization and subsequently yields internal stress within the local network. In this study we investigate light- and temperature-induced spontaneous deformations of the LCN structure via a three-dimensional finite element model that incorporates geometric nonlinearity with a photomechanical constitutive model. We first examine the bending behavior and its nonlinearity and then parametrically study the various behaviors that stem from different origins ranging from the microscale to the macroscale: (i) the geometry of the LCN film, (ii) the macroscopic global order, (iii) the distorted mesogenic orientation due to the Fredericks distortion, and (iv) defect-induced instability. These interrelated behaviors demonstrate both the simulation capability and the necessity of the presenting framework. By employing a nonlinear consideration along with a microscopic shape parameter r the present approach facilitates further understanding of photomechanical physics such as the deconvolution of various stimuli and the deformed shape obtained due to snap-through instability. Furthermore, this study may offer insight into the design of light-sensitive actuation systems by deepening our knowledge and providing an efficient measure.

Elastic stiffness and filler size effect of covalently grafted nanosilica polyimide composites: molecular dynamics study.

The filler size-dependent elastic stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young's and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in elastic stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization of the matrix polymer in the vicinity of the nanoparticles, which was confirmed by the self-diffusion coefficient, the highly grafted interface is found to bring about a greater reinforcing effect than the ungrafted interface.