It is of great scientific and technical interests to conduct fundamental studies on the laser interactions with nanoparticles-reinforced metals. This part of the study presents the effects of nanoparticles on surface tension and viscosity, thus the heat transfer and fluid flow, and eventually the laser melting process. In order to determine the surface tension and viscosity of nanoparticles-reinforced metals, an innovative measurement system was developed based on the characteristics of oscillating metal melt drops after laser melting. The surface tensions of Ni/Al₂O₃ (4.4 vol. %) and Ni/SiC (3.6 vol. %) at ∼1500 °C were 1.39 ± 0.03 N/m and 1.57 ± 0.06 N/m, respectively, slightly lower than that of pure Ni, 1.68 ± 0.04 N/m. The viscosities of these Ni/Al₂O₃ and Ni/SiC MMNCs at ∼1500 °C were 13.3 ± 0.8 mPa·s and 17.3 ± 3.1 mPa·s, respectively, significantly higher than that of pure Ni, 4.8 ± 0.3 mPa·s. To understand the influences of the nanoparticles-modified thermophysical properties on laser melting, an analytical model was used to theoretically predict the melt pool flows using the newly measured material properties from both Part I and Part II. The theoretical analysis indicated that the thermocapillary flows were tremendously suppressed due to the significantly increased viscosity after the addition of nanoparticles. To test the hypothesis that laser polishing could significantly benefit from this new phenomenon, systematic laser polishing experiments at various laser pulse energies were conducted on Ni/Al₂O₃ (4.4 vol. %) and pure Ni for comparison. The surface roughness of the Ni/Al₂O₃ was reduced from 323 nm to 72 nm with optimized laser polishing parameters while that of pure Ni only from 254 nm to 107 nm. The normalized surface roughness reduced by nearly a factor of two with the help of nanoparticles, validating the feasibility to tune thermophysical properties and thus control laser-processing outcomes by nanoparticles. It is expected that the nanoparticle approach can be applied to many laser manufacturing technologies to improve the process capability and broaden the application space.

Future wearable electronics and smart textiles face a major challenge in the development of energy storage devices that are high-performing while still being flexible, lightweight, and safe. Fiber supercapacitors are one of the most promising energy storage technologies for such applications due to their excellent electrochemical characteristics and mechanical flexibility. Over the past decade, researchers have put in tremendous effort and made significant progress on fiber supercapacitors. It is now the time to assess the outcomes to ensure that this kind of energy storage device will be practical for future wearable electronics and smart textiles. While the materials, fabrication methods, and energy storage performance of fiber supercapacitors have been summarized and evaluated in many previous publications, this review paper focuses on two practical questions: Are the reported devices providing sufficient energy and power densities to wearable electronics? Are the reported devices flexible and durable enough to be integrated into smart textiles? To answer the first question, we not only review the electrochemical performance of the reported fiber supercapacitors but also compare them to the power needs of a variety of commercial electronics. To answer the second question, we review the general approaches to assess the flexibility of wearable textiles and suggest standard methods to evaluate the mechanical flexibility and stability of fiber supercapacitors for future studies. Lastly, this article summarizes the challenges for the practical application of fiber supercapacitors and proposes possible solutions.

It is of tremendous interest to apply laser to process nanoparticles-reinforced metals for widespread applications. However, little fundamental understanding has been obtained on the underlining physics of laser interactions with nanoparticles-reinforced metals. In this work, fundamental study was carried out to understand the effects of nanoparticles on the optical and thermophysical properties of the base metal, the corresponding heat transfer and melt pool flow processes, and the consequent surface property in laser melting. Part I presents both experimental and theoretical results on the effects of nanoparticles on the optical reflectivity, specific heat, and thermal conductivity. Electrocodeposition was used to produce nickel samples with nanoparticles. Using a power meter, the reflectivity of Ni/Al₂O₃ (1.8 vol. %) was measured to be 65.8% while pure Ni was at 67.4%, indicating that the Al₂O₃ nanoparticles did not change the reflectivity substantially. Differential scanning calorimetry was used to determine the heat capacity of the nanocomposites. The specific heat capacities of the Ni/Al₂O₃ (4.4 vol. %) and Ni/SiC (3.6 vol. %) at room temperature were 0.424 ± 0.013 J/g K and 0.423 ± 0.014 J/g K, respectively, close to that of pure Ni, 0.424 ± 0.008 J/g K. An experimental setup was developed to measure thermal conductivity based on the laser flash method. The thermal conductivities of these Ni/Al₂O₃ and Ni/SiC nanocomposites at room temperature were 84.1 ± 3.4 W/m K and 87.3 ± 3.4 W/m K, respectively, less than that of pure Ni, 91.7 ± 2.8 W/m K. Theoretical models based on the effective medium approximation theory were also used to predict the heat capacity and thermal conductivity of the nanoparticles-reinforced nickel. The theoretical results match well with the measurements. The knowledge of the optical and thermophysical properties of nanoparticles-reinforced metals would provide valuable insights to understand and control laser processing of metal matrix nanocomposites.

Thermal fiber drawing process has emerged as a promising nanomanufacturing process to generate high-throughput, well aligned, and indefinitely long micro/nanostructures. However, scalable fabrication of metal–polymer nanocomposite is still a challenge, since it is still very difficult to control metal core geometry at nanoscale due to the low-viscosity and high-surface energy of molten metals in cladding materials (e.g., polymer or glass). Here, we show that a scalable nanomanufacture of metal–polymer nanocomposite via thermal fiber drawing is possible. Polyethersulfone (PES) fibers embedded with Sn nanoparticles (<200 nm) were produced by the iterative size reduction thermal fiber drawing. A post-characterization procedure was developed to successfully reveal the metal core geometry at submicron scale. A three-stage control mechanism is proposed to realize the possible control of the metal nanoparticle morphology. This thermal drawing approach promises a scalable production of metal–polymer nanocomposite fibers with unique physicochemical properties for exciting new functionalities.