Recent developments in selective laser processes for wearable devices

Recently,the increasing interest in wearable technology for personal healthcare and smart virtual/augmented reality applications has led to the development of facile fabrication methods.Lasers have long been used to develop original solutions to such challenging technological problems due to their remote,sterile,rapid,and site-selective processing of materials.In this review,recent developments in relevant laser processes are summarized under two separate categories.First,transformative approaches,such as for laser-induced graphene,are introduced.In addition to design optimization and the alteration of a native substrate,the latest advances under a transformative approach now enable more complex material compositions and multilayer device configurations through the simultaneous transformation of heterogeneous precursors,or the sequential addition of functional layers coupled with other electronic elements.In addition,the more conventional laser techniques,such as ablation,sintering,and synthesis,can still be used to enhance the functionality of an entire system through the expansion of applicable materials and the adoption of new mechanisms.Later,various wearable device components developed through the corresponding laser processes are discussed,with an emphasis on chemical/physical sensors and energy devices.In addition,special attention is given to applications that use multiple laser sources or processes,which lay the foundation for the all-laser fabrication of wearable devices.

Configuration-dependent stretchable all-solid-state supercapacitors and hybrid supercapacitors

Given the rise in the popularity of wearable electronics that are able to deform into desirable configurations while maintaining electrochemical functionality,stretchable and flexible(hybrid)supercapacitors(SCs)have become increasingly of interest as innovative energy storage devices.Their outstanding power density,long lifetime with low capacitance loss,and appropriate energy density,in particular in hybrid cases make them ideal candidates for flexible electronics.The aim of this review paper is to provide an in-depth discussion of these stretchable and flexible SCs ranging from fabrication to electro-mechanical properties.This review paper begins with a short overview of the fundamentals of charge storage mechanisms and different types of multivalent metal-ion hybrid SCs.The research methods leading up to the current state of these stretchable and flexible SCs are then presented.This is followed by an in-depth presentation of the challenges associated with the fabrication methods for different configurations.Proposed novel strategies to maximize the elastic and electrochemical properties of stretchable/flexible or quasi-solid-state SCs are classified and the pros and cons associated with each are shown.The advances in mechanical properties and the expected advancements for the future of these SCs are discussed in the last section.

Zinc-ion hybrid supercapacitors with ultrahigh areal and gravimetric energy densities and long cycling life

Zinc ion hybrid supercapacitor (ZIHSC) with promising energy and power densities is an excellent answer to the ever-growing demand for energy storage devices.The restricted lifespan due to the dendrite formation on metallic zinc (Zn) is one of the main roadblocks.Herein,we investigate the electrochemical capability of oxygen-enriched porous carbon nanofibers (A-CNF) and nitrogen,oxygen-enriched porous carbon nanofibers (N-CNF) cathode materials for structural ZIHSCs.To this end,a series of samples with different chemical compositions (N and O contents) are prepared to present deep insight into the electrochemical mechanism between N/O doping and Zn-ion storage.The as-prepared ZIHSC in the presence of N-CNF cathode and Zn Cl_(2) electrolyte offers a battery-level gravimetric energy density of 143.2 Wh kg^(-1)at a power density of 367.1 W kg^(-1).The free-standing N-CNF electrodes in ZIHSCs enjoy delivering an outstanding areal energy density of 110.4μWh cm^(-2)at 0.24 m W cm^(-2),excellent rate capability,and noticeable cycling stability over 10,000 cycles at 10 A g^(-1)with less than 7%decay.It was also concluded that active pyrrolic N dopants might deliver and facilitate more pseudocapacitance in ZIHSCs than other N configurations,resulting in higher adsorption/desorption and insertion/extraction process of Zn Cl^(+).Taking advantage of the beneficial properties of a free-standing continuous cathode,this novel generation of structural cathode material offers high areal and gravimetric energy densities and mechanical properties in a single zinc-ion-based package.

Polymer transfer film formation from cryogenic to elevated temperatures

This study reports on the tribological performance of aromatic thermosetting co-polyester(ATSP)and polyether ether ketone(PEEK)-based polymer composite coatings mixed with PTFE filler.The coatings were tested across a wide temperature range from−180 to 110℃ to simulate the environmental temperatures on Titan,Moon,and Mars,which are of particular interest for NASA’s future exploratory missions.An experimental setup was developed to conduct the pin-on-disk experiments under dry sliding conditions and extreme temperature and contact pressure.Transfer film formation and its characteristics were found to play significant roles in the tribological performance,and the characteristics of the film were temperature-dependent.The XPS and SEM analysis indicated the increase of the PTFE content in the transfer film as the temperature decreased to cryogenic conditions.The coefficient of friction did not follow a linear trend with temperature and was minimum at 110℃ and maximum at−180℃.ATSP coating showed superior performance with lower friction and unmeasurable wear at all temperatures,whereas PEEK coating exhibited maximum wear at 25℃ followed by−180,and 110℃.

A review of current understanding in tribochemical reactions involving lubricant additives

Lubricants have played important roles in friction and wear reduction and increasing efficiency of mechanical systems.To optimize tribological performance,chemical reactions between a lubricant and a substrate must be designed strategically.Tribochemical reactions are chemical reactions enabled or accelerated by mechanical stimuli.Tribochemically activated lubricant additives play important roles in these reactions.In this review,current understanding in mechanisms of chemical reactions under shear has been discussed.Additives such as oil-soluble organics,ionic liquids(ILs),and nanoparticles(NPs)were analyzed in relation to the tribochemical reaction routes with elements in metallic substrates.The results indicated that phosphorus,sulfur,fluorine,and nitrogen are key elements for tribochemical reactions.The resulting tribofilms from zinc dithiophosphates(ZDDP)and molybdenum dithiocarbamate(MoDTC)have been widely reported,yet that from ILs and NPs need to investigate further.This review serves as a reference for researchers to design and optimize new lubricants.

Bioactive superparamagnetic iron oxide-gold nanoparticles regulated by a dynamic magnetic field induce neuronal Ca^(2+)influx and differentiation

Treating neurodegenerative diseases,e.g.,Alzheimer’s Disease,remains a significant challenge due to the limited neuroregeneration rate in the brain.The objective of this study is to evaluate the hypothesis that external magnetic field(MF)stimulation of nerve growth factor functionalized superparamagnetic iron oxide-gold(NGF-SPIO-Au)nanoparticles(NPs)can induce Ca^(2+)influx,membrane depolarization,and enhance neuron differentiation with dynamic MF(DMF)outperforming static MF(SMF)regulation.We showed the that total intracellular Ca^(2+)influx of PC-12 cells was improved by 300%and 535%by the stimulation of DMF(1 Hz,0.5 T,30min)with NGF-SPIO-Au NPs compared to DMF alone and SMF with NGF-SPIO-Au NPs,respectively,which was attributed to successive membrane depolarization.Cellular uptake performed with the application of sodium azide proved that DMF enhanced cellular uptake of NGF-SPIO-Au NPs via endocytosis.In addition,DMF upregulated both the neural differentiation marker(β3-tubulin)and the cell adhesive molecule(integrin-β1)with the existence of NGF-SPIO-Au NPs,while SMF did not show these effects.The results imply that noninvasive DMF-stimulated NPs can regulate intracellular Ca^(2+)influx and enhance neuron differentiation and neuroregeneration rate.

Bayesian optimization with active learning of design constraints using an entropy-based approach

The design of alloys for use in gas turbine engine blades is a complex task that involves balancing multiple objectives and constraints.Candidate alloys must be ductile at room temperature and retain their yield strength at high temperatures,as well as possess low density,high thermal conductivity,narrow solidification range,high solidus temperature,and a small linear thermal expansion coefficient.Traditional Integrated Computational Materials Engineering(ICME)methods are not sufficient for exploring combinatorially-vast alloy design spaces,optimizing for multiple objectives,nor ensuring that multiple constraints are met.In this work,we propose an approach for solving a constrained multi-objective materials design problem over a large composition space,specifically focusing on the Mo-Nb-Ti-V-W system as a representative Multi-Principal Element Alloy(MPEA)for potential use in next-generation gas turbine blades.Our approach is able to learn and adapt to unknown constraints in the design space,making decisions about the best course of action at each stage of the process.As a result,we identify 21 Pareto-optimal alloys that satisfy all constraints.Our proposed framework is significantly more efficient and faster than a brute force approach.

Synergistic effects of zeolitic imidazolate frameworks(ZIFs)with different transition metals on intumescent flame-retarded polypropylene composites:A comparative study

The use of intumescent flame retardants(IFRs)is considered an environmentally friendly and cost-effective strategy to suppress potential fire hazards from synthetic polymers.However,some conventional IFRs are neither efficient in developing a thermally stable char layer nor reducing the release of toxic byproducts during polymer combustion.In this work,we aim to discuss the effects of zeolitic imidazolate frameworks(ZIFs)on synergistically improving the flame retardancy behaviors in polypropylene(PP)composites,including thermal degradation(evolved gas analysis),free radical reactions in the gaseous phase(in-situ chemiluminescent image analysis),and carbonaceous structure in the condensed phase(micro-morphology and composition analysis).It is found that the transition metals in ZIFs can catalytically accelerate the crosslinking reaction at a lower initial temperature and decrease the amount of hydrocarbon volatiles in the gaseous phase.Once ignited,the embedded ZIFs can firstly bridge adjacent phosphorus chains in the polymer matrix to expand crosslinking degrees and then they are anchored in the developed N-doped phospho-carbonaceous networks after pyrolysis.As a result,more compact char residue structures are observed in the condensed phase for ZIF-reinforced composites.For example,by replacing 2 wt%of IFR with ZIF-67,the peak heat release rate,peak smoke production rate,and peak CO production rate are reduced by 69%,80%,and 72%,respectively,when compared to the conventional composite.These results indicate an excellent solution to resolve inherent fire hazards associated with IFRs in polymers and achieve necessary efficiency for industrial applications.It also provides a new strategy for determining flammability characteristics and combustion mechanisms of polymer composites using in-situ chemiluminescence analysis.

Microencapsulated paraffin as a tribological additive for advanced polymeric coatings

Numerous tribological applications,wherein the use of liquid lubricants is infeasible,require adequate dry lubrication.Despite the use of polymers as an effective solution for dry sliding tribological applications,their poor wear resistance prevents the utilization in harsh industrial environment.Different methods are typically implemented to tackle the poor wear performance of polymers,however sacrificing some of their mechanical/tribological properties.Herein,we discussed the introduction of a novel additive,namely microencapsulated phase change material(MPCM)into an advanced polymeric coating.Specifically,paraffin was encapsulated into melamine-based resin,and the capsules were dispersed in an aromatic thermosetting co-polyester(ATSP)coating.We found that the MPCM-filled composite exhibited a unique tribological behavior,manifested as“zero wear”,and a super-low coefficient of friction(COF)of 0.05.The developed composite outperformed the state-of-the-art polytetrafluoroethylene(PTFE)-filled coatings,under the experimental conditions examined herein.