Multifunctional Laser-Induced Graphene Papers with Combined Defocusing and Grafting Processes for Patternable and Continuously Tunable Wettability from Superlyophilicity to Superlyophobicity

Ruthenium Anchored Laser-Induced Graphene as Binder-Free and Free-Standing Electrode for Selective Electrosynthesis of Ammonia from Nitrate

Developing effective electrocatalysts for the nitrate reduction reaction (NO3RR) is a promising alternative to conventional industrial ammonia (NH3) synthesis. Herein, starting from a flexible laser-induced graphene (LIG) film with hierarchical and interconnected macroporous architecture, a binder-free and free-standing Ru-modified LIG electrode (Ru-LIG) is fabricated for electrocatalytic NO3RR via a facile electrodeposition method. The relationship between the laser-scribing parameters and the NO3RR performance of Ru-LIG electrodes is studied in-depth. At -0.59 VRHE, the Ru-LIG electrode exhibited the optimal and stable NO3RR performance (NH3 yield rate of 655.9 µg cm-2 h-1 with NH3 Faradaic efficiency of up to 93.7%) under a laser defocus setting of +2 mm and an applied laser power of 4.8 W, outperforming most of the reported NO3RR electrodes operated under similar conditions. The optimized laser-scribing parameters promoted the surface properties of LIG with increased graphitization degree and decreased charge-transfer resistance, leading to synergistically improved Ru electrodeposition with more exposed NO3RR active sites. This work not only provides a new insight to enhance the electrocatalytic NO3RR performance of LIG-based electrodes via the coordination with metal electrocatalysts as well as identification of the critical laser-scribing parameters but also will inspire the rational design of future advanced laser-induced electrocatalysts for NO3RR.

Multifunctional Laser-Induced Graphene-Based Microfluidic Chip for High-Performance Oocyte Cryopreservation with Low Concentration of Cryoprotectants

Oocyte cryopreservation is essential in the field of assisted reproduction, but due to the large size and poor environmental tolerance of oocytes, cell freezing technology needs further improvement. Here, a Y-shaped microfluidic chip based on 3D graphene is ingeniously devised by combining laser-induced graphene (LIG) technology and fiber etching technology. The prepared LIG/PDMS microfluidic chip can effectively suppress ice crystal size and delay ice crystal freezing time by adjusting surface hydrophobicity. In addition, LIG endows the microfluidic chip with an outstanding photothermal effect, which allows to sharply increase its surface temperature from 25 to 71.8 °C with 10 s of low-power 808 nm laser irradiation (0.4 W cm-2). Notably, the LIG/PDMS microfluidic chip not only replaces the traditional cryopreservation carriers, but also effectively reduces the dosage of cryoprotectants (CPAs) needed in mouse oocyte cryopreservation. Even when the concentration of CPAs is cut in half (final concentration of 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO)), the survival rate of oocytes is still as high as 92.4%, significantly higher than the control group's 85.8%. Therefore, this work provides a novel design strategy to construct multifunctional microfluidic chips for high-performance oocytes cryopreservation.

Roll-to-Roll Manufacturing of Breathable Superhydrophobic Membranes

Self-cleaning and anti-biofouling are both advantages for lotus-leaf-like superhydrophobic surfaces. Methods for creating superhydrophobicity, including chemical bonding low surface energy molecular fragments and constructing surface morphology with protrusions, micropores, and trapped micro airbags by traditional physical strategies, unfortunately, have encountered challenges. They often involve complex synthesis processes, stubborn chemical accumulation, brutal degradation, or infeasible calculation and imprecise modulation in fabricating hierarchical surface roughness. Here, a scalable method to prepare high-quality, breathable superhydrophobic membranes is proposed by developing a successive roll-to-roll laser manufacturing technique, which offers advantages over conventional fabrication approaches in enabling automatically large-scale production and ensuring cost-effectiveness. Nanosecond laser writing and femtosecond laser drilling produce surface microstructures and micropore arrays, respectively, endowing the membrane with superior antiwater capability with hierarchical microstructures forming a barrier and blocking water infiltration. The membrane's breathability is carefully optimized by tailoring micropore arrays to allow for the adequate passage of water vapor while maintaining superhydrophobicity. These membranes combine the benefits of anti-aqueous corrosive liquid behaviors, photothermal effects, thermoplastic properties, and stretchable performances as promising comprehensive materials in diverse scenes.

Laser-induced transient conversion of rhodochrosite/polyimide into multifunctional MnO2/graphene electrodes for energy storage applications

Laser-induced graphene (LIG) has been extensively investigated for electrochemical energy storage due to its easy synthesis and highly conductive nature. However, the limited charge accumulation in LIG usually leads to significantly low energy densities. In this work, we report a novel strategy to directly transform natural rhodochrosite into ultrafine manganese dioxide (MnO2) nanoparticles (NPs) in the polyimide (PI) substrate for high-performance micro-supercapacitors (MSCs) and lithium-ion batteries (LIBs) through a scalable and cost-effective laser processing method. Specifically, laser treatment on rhodochrosite/polyimide precursors induces the thermal explosion, which splits rhodochrosite (10 μm) into MnO2 NPs (12-16 nm) on the carbon matrix of LIG due to the sputtering effect. Benefiting from largely exposed active sites from the ultrafine MnO2 and the synergetic effect from highly conductive LIG, the MnO2/LIG MSCs show a high specific capacitance of 544.0 F g-1 (154.3 mF cm-2; 14.16 F cm-3) at 3 A/g and 82.1% capacitance retention after 10,000 cycles at 5A/g, in contrast to pure LIG (<100 F g-1). Moreover, the MnO2/LIG-based LIBs show the highest reversible discharge capacity of ∼1097 mAh g-1 at 0.2 A/g and ∼ 866.4 mAh g-1 at 1.0 A/g. This study opens a new route for synthesizing novel LIG-based composites from natural minerals.

Droplet Transportation on Liquid-Infused Asymmetrically Structured Surfaces by Mechanical Oscillation and Viscosity Control

The transportation of droplets on solid surfaces has received significant attention owing to its importance in biochemical analysis and microfluidics. In this study, we propose a novel strategy for controlling droplet motion by combining an asymmetric structure and infused lubricating oil on a vibrating substrate. The transportation of droplets with volumes ranging from 10 to 90 μL was realized, and the movement speed could be adjusted from 1.45 to 10.87 mm/s. Typical droplet manipulations, including droplet transportation along a long trajectory and selective movement of multiple droplets, were successfully demonstrated. Through experimental exploration and theoretical analysis, we showed that the adjustment of droplet transport velocity involves an intricate interaction among the Ohnesorge number, droplet volume, and input amplitude. It can potentially be used for the more complex manipulation of liquid droplets in microfluidic and biochemical analysis systems.

Different Roles of Surface Chemistry and Roughness of Laser-Induced Graphene: Implications for Tunable Wettability

The control of surface wettability is a technological key aspect and usually poses considerable challenges connected to high cost, nanostructure, and durability, especially when aiming at surface patterning with high and extreme wettability contrast. This work shows a simple and scalable approach by using laser-induced graphene (LIG) and a locally inert atmosphere to continuously tune the wettability of a polyimide/LIG surface from hydrophilic to superhydrophobic (Φ ∼ 160°). This is related to the reduced amount of oxygen on the LIG surface, influenced by the local atmosphere. Furthermore, the influence of the roughness pattern of LIG on the wettability is investigated. Both approaches are combined, and the influence of surface chemistry and roughness is discussed. Measurements of the roll-off angle show that LIG scribed in an inert atmosphere with a low roughness has the highest droplet mobility with a roll-off angle of ΦRO = (1.7 ± 0.3)°. The superhydrophobic properties of the samples were maintained for over a year and showed no degradation after multiple uses. Applications of surfaces with extreme wettability contrast in millifluidics and fog basking are demonstrated. Overall, the proposed processing allows for the continuous tuning and patterning of the surface properties of LIG in a very accessible fashion useful for "lab-on-chip" applications.

Enhanced water transportation on a superhydrophilic serial cycloid-shaped pattern

Spontaneous and directional water transportation (SDWT) is considered as an ideal water transportation method and has a great prospect in the aerospace and ship fields. Nonetheless, the existing SDWT has the limitation of a slow water transportation velocity because of its geometry structure configuration, which hinders the practical application of the SDWT. To overcome this limitation, we developed a new superhydrophilic serial cycloid-shaped pattern (SSCP) which was inspired by the micro-cavity shape of the Nepenthes. First, we experimentally found that the water transportation velocity on the SSCP was faster than that on the superhydrophilic serial wedge-shaped pattern (SSWP) and analyzed the faster water transportation mechanism. Then, the influence of the SSCP parameters on the transportation velocity was investigated by a single-factor experiment. In addition, the water transportation velocity on the SSCP was enhanced to 289 mm s^-1 by combining the single-factor experiment, orthogonal optimization design, streamline junction transition optimization, and pre-wet pattern, which was the fastest in the SDWT. Moreover, the SSCP demonstrated its superior capability in long-distance water transportation, gravity resistant water transportation, heat transfer, and fog collection. This finding shows remarkable application prospects in the high-performance fluid transportation system.

Ultrasensitive Humidity Sensors with Synergy between Superhydrophilic Porous Carbon Electrodes and Phosphorus-Doped Dielectric Electrolyte

Capacitive humidity sensors have been used for human health monitoring, but their performance may be poor in terms of sensitivity and response time, because of limitations in sensing materials and insufficient knowledge about sensing mechanisms. Herein, a new combination of humidity sensing materials to assemble thin-film based capacitive-type sensors is proposed by using PA-doped polybenzimidazole (PA-PBI) as an electrolyte and laser-carbonized PA-PBI as a carbon electrode (PA-PBI-C). Based on PA involved laser scribing, the flexible sensor can reach excellent humidity-sensing performances with an ultrahigh sensitivity (1.16 × 106 pF RH%-1, where RH represents the relative humidity), a superior linearity (R2 = 0.9982), a fast response time (0.72 s), and a low hysteresis in a wide RH range from 1% to 95%. By further studying P-O decorated porous carbon electrode with superhydrophilicity and the solid-state dielectric electrolyte featured by a high dielectric constant, a synergistic sensing mechanism consisting of a "Water reservoir" and a "Bridge" is established to support advanced health-monitoring applications such as the respiration patterns and skin condition where both sensitivity and response time are critical.

Laser-Induced Graphene Enabled Additive Manufacturing of Multifunctional 3D Architectures with Freeform Structures

3D printing has become an important strategy for constructing graphene smart structures with arbitrary shapes and complexities. Compared with graphene oxide ink/gel/resin based manners, laser-induced graphene (LIG) is unique for facile and scalable assembly of 1D and 2D structures but still faces size and shape obstacles for constructing 3D macrostructures. In this work, a brand-new LIG based additive manufacturing (LIG-AM) protocol is developed to form bulk 3D graphene with freeform structures without introducing extra binders, templates, and catalysts. On the basis of selective laser sintering, LIG-AM creatively irradiates polyimide (PI) powder-bed for triggering both particle-sintering and graphene-converting processes layer-by-layer, which is unique for assembling varied types of graphene architectures including identical-section, variable-section, and graphene/PI hybrid structures. In addition to exploring combined graphitizing and fusing discipline, processing efficiency and assembling resolution of LIG-AM are also balanceable through synergistic control of lasing power and powder-feeding thickness. By further studying various process dependent properties, a LIG-AM enabled aircraft-wing section model is finally printed to comprehensively demonstrate its shiftable process, hybridizable structure, and multifunctional performance including force-sensing, anti-icing/deicing, and microwave shielding and absorption.

Bacterial surface attachment and fouling assay on polymer and carbon surfaces using Rheinheimera sp. identified using bacteria community analysis of brackish water

Biofouling on surfaces in contact with sea- or brackish water can severely impact the function of devices like reverse osmosis modules. Single species laboratory assays are frequently used to test new low fouling materials. The choice of bacterial strain is guided by the natural population present in the application of interest and decides on the predictive power of the results. In this work, the analysis of the bacterial community present in brackish water from Mashabei Sadeh, Israel was performed and Rheinheimera sp. was detected as a prominent microorganism. A Rheinheimera strain was selected to establish a short-term accumulation assay to probe initial bacterial attachment as well as biofilm growth to determine the biofilm-inhibiting properties of coatings. Both assays were applied to model coatings, and technically relevant polymers including laser-induced graphene. This strategy might be applied to other water sources to better predict the fouling propensity of new coatings.

Wettability Controlled Surface for Energy Conversion

To achieve clean and high-efficiency utilization of renewable energy, functional surfaces with controllable and patternable wettability are becoming a fast-growing research focus. In this work, a laser scribing strategy to fabricate patterned graphene surfaces that are capable of energy conversion in different forms is demonstrated. Using the laser raster-scanning and vector-scanning modes, two distinct surface structures are constructed on polybenzoxazine substrate, yielding a superhydrophilic (LSHL) surface and superhydrophobic (LSHB) surface, respectively. Of particular note is that the unique hierarchical structure of LSHB surface has endowed it with quite a robust superwetting behaviors. Further profiting from the flexibility of the processing method, wettability patterns with spatially resolved LSHL and LSHB regions are designed, achieving the conversion of surface energy to liquid kinetic energy. This also offers a tractable approach to fabricate wettability-engineered devices that enable the directional, pumpless transport of water by capillary pressure gradient and the selective surface cooling via jet impingement. In addition, the LSHB surface demonstrates the high conversion of electric-to-thermal energy (222 °C cm² W^-1 ) and light-to-thermal energy (88%). Overall, the material system and processing method present a promising step forward to developing easy-fabricated graphene surfaces with spatially controlled wettability for efficient energy utilization and conversion.

3D-Laminated Graphene with Combined Laser Irradiation and Resin Infiltration toward Designable Macrostructure and Multifunction

Macroscopic 3D graphene has become a significant topic for satisfying the continuously upgraded smart structures and devices. Compared with liquid assembling and catalytic templating methods, laser-induced graphene (LIG) is showing facile and scalable advantages but still faces limited sizes and geometries by using template induction or on-site lay-up strategies. In this work, a new LIG protocol is developed for facile stacking and shaping 3D LIG macrostructures by laminating layers of LIG papers (LIGPs) with combined resin infiltration and hot pressing. Specifically, the constructed 3D LIGP composites (LIGP-C) are compatible with large area, high thickness, and customizable flat or curved shapes. Additionally, systematic research is explored for investigating critical processing parameters on tuning its multifunctional properties. As the laminated layers are stacked from 1 to 10, it is discovered that piezoresistivity (i.e., gauge factor) of LIGP-C dramatically reflects an ≈3900% improvement from 0.39 to 15.7 while mechanical and electrical properties maintain simultaneously at the highest levels, attributed to the formation of densely packed fusion layers. Along with excellent durability for resisting multiple harsh environments, a sensor-array system with 5 × 5 LIGP-C elements is finally demonstrated on fiber-reinforced polymeric composites for accurate strain mapping.

Laser-Induced Graphene Superhydrophobic Surface Transition from Pinning to Rolling for Multiple Applications

The fabrication and applications of superhydrophobic surfaces (contact angle >150°, sliding angle <10°) have attracted worldwide interest with respect to materials and devices. In this work, the laser-induced graphene (LIG) superhydrophobic surface transition from pinning to rolling via an extremely simple solvent treatment of LIG in air is reported. By adding a certain solvent (e.g., ethanol) to the surface, the LIG superhydrophobic surface changes from pinning (sliding angle = 180°) to rolling (sliding angle <6°), which is attributed to the chemically changed surface properties and surface morphology of LIG. Three applications are demonstrated with the developed superhydrophobic LIG, including surface-enhanced Raman spectroscopy, water-oil separation, and anti-icing.

Design and fabrication of a large-range graphene/hexagonal boron nitride heterostructure based pressure sensor with poly(methyl methacrylate) substrate

Aiming at overpressure measurement, this paper presents a large-range graphene/hexagonal boron nitride (h-BN) heterostructure-based pressure sensor with a poly(methyl methacrylate) (PMMA) substrate. Graphene and h-BN are chosen as sensitive materials because they both have large Young's modulus, high intrinsic strength, high natural frequency, and atomic thickness at the same time. These characteristics provide favorable conditions for the application of the sensor in the high pressure and high frequency dynamic environment. Moreover, the photoresist-assisted transfer technology is proposed for transferring graphene from the growth substrate to the PMMA substrate and the lift-off method with exposure and development is developed to achieve metal patterning on the PMMA substrate. The sensor characterization results suggest that the graphene and h-BN films have good transfer qualities and the heterojunction possesses excellent electrical performance. The static pressure loading experiments confirm that the sensor has a pressure range of up to 85 MPa and its piezoresistive coefficient is 0.7 GPa^-1, which indicates that the designed sensor is suitable for overpressure fields. This study provides a novel method for determining overpressure and lays a foundation for the fabrication of graphene-based electronic devices with an organic substrate.