Laser-engineered heavy hydrocarbons: Old materials with new opportunities

Laser-upgraded coal tar for smart pavements in road and bridge monitoring applications

The implementation of an intelligent road network system requires many sensors for acquiring data from roads, bridges, and vehicles, thereby enabling comprehensive monitoring and regulation of road networks. Given this large number of required sensors, the sensors must be cost-effective, dependable, and environmentally friendly. Here, we show a laser upgrading strategy for coal tar, a low-value byproduct of coal distillation, to manufacture flexible strain-gauge sensors with maximum gauge factors of 15.20 and 254.17 for tension and compression respectively. Furthermore, we completely designed the supporting processes of sensor placement, data acquisition, processing, wireless communication, and information decoding to demonstrate the application of our sensors in traffic and bridge vibration monitoring. Our novel strategy of using lasers to upgrade coal tar for use as a sensor not only achieves the goal of turning waste into a resource but also provides an approach to satisfy large-scale application requirements for enabling intelligent road networks.

Highly conductive, conformable ionic laser-induced graphene electrodes for flexible iontronic devices

Iontronic devices, recognized for user-friendly soft electronics, establish an electrical double layer (EDL) at the interface between ion gels and electrodes, significantly influencing device performance. Despite extensive research on ion gels and diverse electrode materials, achieving a stable interfacial formation remains a persistent challenge. In this work, we report a solution to address this challenge by employing CO2 irradiation as a bottom-up methodology to directly fabricate highly conductive, conformable laser-induced graphene (LIG) electrodes on a polyimide (PI)-based ion gel. The PI ion gel exhibits exceptional EDL formation at the electrode interface, primarily attributable to efficient ion migration. Particularly, ionic laser-induced graphene (i-LIG) electrodes, derived from the PI ion gel as a precursor, yield high-quality graphene with enhanced crystallinity and an expanded porous structure in the upward direction. This outcome is achieved through a pronounced thermal transfer effect and intercalation phenomenon between graphene layers, facilitated by the presence of ionic liquids (ILs) within the PI ion gel. Ultimately, in comparison to alternative soft electrode-based vertical capacitors, the utilization of i-LIGs and PI ion gels in the vertical capacitor demonstrates reduced interfacial resistance and increased EDL capacitance, emphasizing the extensive potential of iontronic devices. These results not only highlight these features but also introduce a new perspective for advancing next-generation iontronic devices.

A Flexible Wearable Sensor Based on Laser-Induced Graphene for High-Precision Fine Motion Capture for Pilots

There has been a significant shift in research focus in recent years toward laser-induced graphene (LIG), which is a high-performance material with immense potential for use in energy storage, ultrahydrophobic water applications, and electronic devices. In particular, LIG has demonstrated considerable potential in the field of high-precision human motion posture capture using flexible sensing materials. In this study, we investigated the surface morphology evolution and performance of LIG formed by varying the laser energy accumulation times. Further, to capture human motion posture, we evaluated the performance of highly accurate flexible wearable sensors based on LIG. The experimental results showed that the sensors prepared using LIG exhibited exceptional flexibility and mechanical performance when the laser energy accumulation was optimized three times. They exhibited remarkable attributes, such as high sensitivity (~41.4), a low detection limit (0.05%), a rapid time response (response time of ~150 ms; relaxation time of ~100 ms), and excellent response stability even after 2000 s at a strain of 1.0% or 8.0%. These findings unequivocally show that flexible wearable sensors based on LIG have significant potential for capturing human motion posture, wrist pulse rates, and eye blinking patterns. Moreover, the sensors can capture various physiological signals for pilots to provide real-time capturing.

The evolution of atomistic structure and mechanical property of coke in the gasification process with CO2 and H2O at different temperatures: A ReaxFF molecular dynamics study

CONTEXT

An atomistic coke carbon model was constructed to simulate the structural evolution in the gasification and stretching process. The coke model was placed in a box with different CO2/H2O content to investigate the evolution of the atomistic structure of coke during the gasification. It was found that different atmospheric concentrations had different effects on the structure and reaction sites of the coke model. The CO2 molecules tended to dissolve on the surface of coke and disrupt its surface structure, while H2O molecules were more likely to enter the coke model to disrupt the internal structure. For tensile simulation, it was found that CO2 and H2O had different effects on the tensile resistance of the coke model. Controlling the composition content of the reaction gas can effectively influence the tensile strength of the coke model. By revealing the behavior of coke model at the micro scale, it provides a theoretical basis for the industrial coke application process.

METHODS

Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) was used to conduct the molecular dynamics using the reactive force field (ReaxFF). The atomistic model of coke carbon was constructed using the well-known annealing and quenching method, and its composition is determined according to the element analysis of industrial coke. The structural evolution in the gasification with CO2/H2O and the stretching process were analyzed in detail. Molecular dynamics simulations with reactive force field (ReaxFF-MD) were used to simulate the coke dissolution reaction under CO2/H2O atmosphere and the coke stretching process. The atmosphere ratio was modified to investigate the changes in coke structure under different atmosphere conditions. The Packmol software was used to place gas and coke models into the same box. During the reaction process, the Ovito software was used to perform corresponding visualization analysis on the changes in the atomic structure of coke.

Printing Three-Dimensional Refractory Metal Patterns in Ambient Air: Toward High Temperature Sensors

Refractory metals offer exceptional benefits for high temperature electronics including high-temperature resistance, corrosion resistance and excellent mechanical strength, while their high melting temperature and poor processibility poses challenges to manufacturing. Here this work reports a direct ink writing and tar-mediated laser sintering (DIW-TMLS) technique to fabricate three-dimensional (3D) refractory metal devices for high temperature applications. Metallic inks with high viscosity and enhanced light absorbance are designed by utilizing coal tar as binder. The printed patterns are sintered into oxidation-free porous metallic structures using a low-power (<10 W) laser in ambient environment, and 3D freestanding architectures can be rapidly fabricated by one step. Several applications are presented, including a fractal pattern-based strain gauge, an electrically small antenna (ESA) patterned on a hemisphere, and a wireless temperature sensor that can work up to 350 °C and withstand burning flames. The DIW-TMLS technique paves a viable route for rapid patterning of various metal materials with wide applicability, high flexibility, and 3D conformability, expanding the possibilities of harsh environment sensors.

Effect of Methyl Groups on Formation of Ordered or Layered Graphitic Materials from Aromatic Molecules

Developing functionally complex carbon materials from small aromatic molecules requires an understanding of how the chemistry and structure of its constituent molecules evolve and crosslink, to achieve a tailorable set of functional properties. Here, molecular dynamics (MD) simulations are used to isolate the effect of methyl groups on condensation reactions during the oxidative process and evaluate the impact on elastic modulus by considering three monodisperse pyrene-based systems with increasing methyl group fraction. A parameter to quantify the reaction progression is designed by computing the number of new covalent bonds formed. Utilizing the previously developed MD framework, it is found that increasing methylation leads to an almost doubling of bond formation, a larger fraction of the new bonds oriented in the direction of tensile stress, and a higher basal plane alignment of the precursor molecules along the direction of tensile stress, resulting in enhanced tensile modulus. Additionally, via experiments, it is demonstrated that precursors with a higher fraction of methyl groups result in a higher alignment of molecules. Moreover, increased methylation results in the lower spread of single molecule alignment which may lead to smaller variations in tensile modulus and more consistent properties in carbon materials derived from methyl-rich precursors.

Bayesian-Optimization-Assisted Laser Reduction of Poly(acrylonitrile) for Electrochemical Applications

Laser reduction of polymers has recently been explored to rapidly and inexpensively synthesize high-quality graphitic and carbonaceous materials. However, in past work, laser-induced graphene has been restricted to semiaromatic polymers and graphene oxide; in particular, poly(acrylonitrile) (PAN) is claimed to be a polymer that cannot be laser-reduced successfully to form electrochemically active material. In this work, three strategies to surmount this barrier are employed: (1) thermal stabilization of PAN to increase its sp² content for improved laser processability, (2) prelaser treatment microstructuring to reduce the effects of thermal stresses, and (3) Bayesian optimization to search the parameter space of laser processing to improve performance and discover morphologies. Based on these approaches, we successfully synthesize laser-reduced PAN with a low sheet resistance (6.5 Ω sq^-1) in a single lasing step. The resulting materials are tested electrochemically, and their applicability as membrane electrodes for vanadium redox flow batteries is demonstrated. This work demonstrates electrodes that are processed in air, below 300 °C, which are cycled stably over 2 weeks at 40 mA cm^-2, motivating further development of laser reduction of porous polymers for membrane electrode applications such as RFBs.

Graphitization by Metal Particles

Graphitization of carbon offers a promising route to upcycle waste biomass and plastics into functional carbon nanomaterials for a range of applications including energy storage devices. One challenge to the more widespread utilization of this technology is controlling the carbon nanostructures formed. In this work, we undertake a meta-analysis of graphitization catalyzed by transition metals, examining the available electron microscopy data of carbon nanostructures and finding a correlation between different nanostructures and metal particle size. By considering a thermodynamic description of the graphitization process on transition-metal nanoparticles, we show an energy barrier exists that distinguishes between different growth mechanisms. Particles smaller than ∼25 nm in radius remain trapped within closed carbon structures, while nanoparticles larger than this become mobile and produce nanotubes and ribbons. These predictions agree closely with experimentally observed trends and should provide a framework to better understand and tailor graphitization of waste materials into functional carbon nanostructures.

Quantification of Methane-Induced Asphaltene Precipitation in a Multiple Contact Process

A unique experiment design is proposed to study the asphaltene precipitation caused by multiple contact processes during gas injection. The newly proposed experiment quantified the asphaltene precipitation at different methane contact steps. Twenty times methane contacts and corresponding asphaltene precipitation states are measured using a light scattering setup under reservoir condition. The amount of the asphaltene precipitation, the composition changes, and the physical properties changes are measured for the 20 times methane contacts. After verifying the asphaltene precipitation in the static experiments, the formation damage caused by the asphaltene precipitation is studied by core flooding tests for three different permeability cases. We found that the primary asphaltene precipitation mechanism in the multiple contact process during methane injection is not the composition change caused by methane extraction. The methane-induced asphaltene stability loss during the multiple contact process is vital. The size and the structure of asphaltene precipitation particles in the crude oil change with the methane contacts. We found that the mechanism of permeability reduction caused by asphaltene precipitation is different depending on the porous media pore throat size and the asphaltene precipitation particle size. Under our experimental condition, the asphaltene precipitation acts as a conformance control method, leading to well-distance optimization considerations in field applications.

Sustainable valorization of asphaltenes via flash joule heating

The refining process of petroleum crude oil generates asphaltenes, which poses complicated problems during the production of cleaner fuels. Following refining, asphaltenes are typically combusted for reuse as fuel or discarded into tailing ponds and landfills, leading to economic and environmental disruption. Here, we show that low-value asphaltenes can be converted into a high-value carbon allotrope, asphaltene-derived flash graphene (AFG), via the flash joule heating (FJH) process. After successful conversion, we develop nanocomposites by dispersing AFG into a polymer effectively, which have superior mechanical, thermal, and corrosion-resistant properties compared to the bare polymer. In addition, the life cycle and technoeconomic analysis show that the FJH process leads to reduced environmental impact compared to the traditional processing of asphaltene and lower production cost compared to other FJH precursors. Thus, our work suggests an alternative pathway to the existing asphaltene processing that directs toward a higher value stream while sequestering downstream emissions from the processing.

Wetting Properties of Clathrate Hydrates in the Presence of Polycyclic Aromatic Compounds: Evidence of Ion-Specific Effects

Polycyclic aromatic hydrocarbons (PAHs) have attracted remarkable multidisciplinary attention due to their intriguing π-π stacking configurations, showing enormous opportunity for their use in a variety of advanced applications. To secure progress, detailed knowledge on PAHs' interfacial properties is required. Employing molecular dynamics, we probe the wetting properties of brine droplets (KCl, NaCl, and CaCl₂) on sII methane-ethane hydrate surfaces immersed in various oil solvents. Our simulations show synergistic effects due to the presence of PAHs compounded by ion-specific effects. Our analysis reveals phenomenological correlations between the wetting properties and a combination of the binding free-energy difference and entropy changes upon oil solvation for PAHs at oil/brine and oil/hydrate interfaces. The detailed thermodynamic analysis conducted upon the interactions between PAHs and various interfaces identifies molecular-level mechanisms responsible for wettability alterations, which could be applicable for advancing applications in optics, microfluidics, biotechnology, medicine, as well as hydrate management.

Laser Processing of Flexible In-Plane Micro-supercapacitors: Progresses in Advanced Manufacturing of Nanostructured Electrodes

Flexible in-plane architecture micro-supercapacitors (MSCs) are competitive candidates for on-chip miniature energy storage applications owing to their light weight, small size, high flexibility, as well as the advantages of short charging time, high power density, and long cycle life. However, tedious and time-consuming processes are required for the manufacturing of high-resolution interdigital electrodes using conventional approaches. In contrast, the laser processing technique enables high-efficiency high-precision patterning and advanced manufacturing of nanostructured electrodes. In this review, the recent advances in laser manufacturing and patterning of nanostructured electrodes for applications in flexible in-plane MSCs are comprehensively summarized. Various laser processing techniques for the synthesis, modification, and processing of interdigital electrode materials, including laser pyrolysis, reduction, oxidation, growth, activation, sintering, doping, and ablation, are discussed. In particular, some special features and merits of laser processing techniques are highlighted, including the impacts of laser types and parameters on manufacturing electrodes with desired morphologies/structures and their applications on the formation of high-quality nanoshaped graphene, the selective deposition of nanostructured materials, the controllable nanopore etching and heteroatom doping, and the efficient sintering of nanometal products. Finally, the current challenges and prospects associated with the laser processing of in-plane MSCs are also discussed. This review will provide a useful guidance for the advanced manufacturing of nanostructured electrodes in flexible in-plane energy storage devices and beyond.

Pressure-Strengthened Carbon Fibers from Mesophase Pitch Carbonization Processes

Little attention has been devoted to studying the pressures during the mesophase pitches carbonization processes and their effects on the as-produced carbon fibers' mechanical properties. Herein, we study the pressure-enhanced graphitization of mesophase pitch and the promoted tensile stresses of the produced carbon fibers using full atomistic simulations based on reactive force fields. Results show that pressures increase the tensile stress of as-produced fibers by 3.7-11 times under 1-6 GPa isotropic compressing pressure. The highest tensile stress can reach 4.39 GPa in carbonized coal tar pitch at 4000 K under 6 GPa. In experimental work, the pressurized laser-processed mesophase pitch generates less gas and shows more ordered carbonized structures in Raman spectra. This work provides a fundamental understanding of the reaction mechanism of carbon fiber production under pressure, and also illustrates a promising method to manufacture mesophase pitch-based carbon fibers with exceptional mechanical properties.

Atoms to fibers: Identifying novel processing methods in the synthesis of pitch-based carbon fibers

Understanding and optimizing the key mechanisms used in the synthesis of pitch-based carbon fibers (CFs) are challenging, because unlike polyacrylonitrile-based CFs, the feedstock for pitch-based CFs is chemically heterogeneous, resulting in complex fabrication leading to inconsistency in the final properties. In this work, we use molecular dynamics simulations to explore the processing and chemical phase space through a framework of CF models to identify their effects on elastic performance. The results are in excellent agreement with experiments. We find that density, followed by alignment, and functionality of the molecular constituents dictate the CF mechanical properties more strongly than their size and shape. Last, we propose a previously unexplored fabrication route for high-modulus CFs. Unlike graphitization, this results in increased sp³ fraction, achieved via generating high-density CFs. In addition, the high sp³ fraction leads to the fabrication of CFs with isometric compressive and tensile moduli, enabling their potential applications for compressive loading.

Electronic, Structural, and Magnetic Upgrading of Coal-Based Products through Laser Annealing

Most coal-to-product routes require complex thermal treatment to carbonize the raw materials. However, the lack of unified comparison of products made from different kinds of coals downplays the role of initial coal chemistry in high-temperature reactions. Here, we used a CO₂ laser to investigate the roles that aromatic content and maturity play in the structural evolution and doping of coals during annealing. Results show that a bituminous coal (DECS 19) with aromatic content and maturity in between higher rank, more mature anthracite (DECS 21) and lower rank, lower maturity lignite (DECS 25) leads to more graphite-like structure observed from the highest 2D peak on the Raman spectrum and conductivity (sheet resistance ∼30 ohm sq^-1) after lasing. When nitrogen dopants are incorporated with saturated urea dopants into coals through laser ablation, nitrogen preferentially incorporates at the edge sites of graphitic grains. Furthermore, oxide nanoparticles can be incorporated into the graphitic backbone of coal to modify their electronic and magnetic properties through laser annealing. Leveraging tunable magnetic behavior, we demonstrate a soft actuator using both conductive and magnetic coal-Fe/Co oxide. Through laser annealing, we propose a paradigm to understand and control coal chemistry toward flexible and tunable doping and magnetism.

Fingerprint-Inspired Strain Sensor with Balanced Sensitivity and Strain Range Using Laser-Induced Graphene

Sensitivity and strain range are two mutually exclusive features of strain sensors, where a significant improvement in flexibility is usually accompanied by a reduction in sensitivity. The skin of a human fingertip, due to its undulating fingerprint pattern, can easily detect environmental signals and enhances sensitivity without losing elasticity. Inspired by this characteristic, laser-induced graphene (LIG) with a fingerprint structure is prepared in one step on a polyimide (PI) film and transferred into an Ecoflex substrate to assemble resistive strain sensors. Experimentally, the fingerprint-inspired strain sensor exhibits a superfast response time (∼70 ms), balanced sensitivity and strain range (a gauge factor of 191.55 in the 42-50% strain range), and good reliability (>1500 cycles). Self-organized microcracks, initiated in weak mechanical areas, cause prominent resistance changes during reconnection/disconnection but irreversibly fail after excessive stretching. The robust function of fingerprint-inspired sensors is further demonstrated by real-time monitoring of tiny pulses, large body movements, gestures, and voice recognition.

Laser-Induced Tar-Mediated Sintering of Metals and Refractory Carbides in Air

Refractory metals and their carbides possess extraordinary chemical and temperature resilience and exceptional mechanical strength. Yet, they are notoriously difficult to employ in additive manufacturing, due to the high temperatures needed for processing. State of the art approaches to manufacture these materials generally require either a high-energy laser or electron beam as well as ventilation to protect the metal powder from combustion. Here, we present a versatile manufacturing process that utilizes tar as both a light absorber and antioxidant binder to sinter thin films of aluminum, copper, nickel, molybdenum, and tungsten powder using a low power (<2W) CO₂ laser in air. Films of sintered Al/Cu/Ni metals have sheet resistances of ∼10^-1 ohm/sq, while laser-sintered Mo/W-tar thin films form carbide phases. Several devices are demonstrated, including laser-sintered porous copper with a stable response to large strain (3.0) after 150 cycles, and a laserprocessed Mo/MoC_(1-x) filament that reaches T ∼1000 °C in open air at 12 V. These results show that tar-mediated laser sintering represents a possible low energy, cost-effective route for engineering refractory materials and one that can easily be extended to additive manufacturing processes.