The growth of laser-induced nanocarbons, referred to here as laser-induced nanocarbon (LINC) for short, directly on polymeric surfaces is a promising route toward surface engineering of commercial polymers. This paper aims to demonstrate how this new approach can enable achieving varied surface properties based on tuning the nanostructured morphology of the formed graphitic material on commercial polyimide (Kapton) films. We elucidate the effects of tuning laser processing parameters on the achieved nanoscale morphology and the resulting surface hydrophobicity or hydrophilicity. Our results show that by varying lasing power, rastering speed, laser spot size, and line-to-line gap sizes, a wide range of water contact angles are possible, i.e., from below 20 deg to above 110 deg. Combining water contact angle measurements from an optical tensiometer with LINC surface characterization using optical microscopy, electron microscopy, and Raman spectroscopy enables building the process–structur–property relationship. Our findings reveal that both the value of contact angle and the anisotropic wetting behavior of LINC on polyimide are dependent on their hierarchical surface nanostructure which ranges from isotropic nanoporous morphology to fibrous morphology. Results also show that increasing gap sizes lead to an increase in contact angles and thus an increase in the hydrophobicity of the surface. Hence, our work highlight the potential of this approach for manufacturing flexible devices with tailored surfaces.

The unique capabilities of Aerosol Jet ® technology for noncontact material deposition with in-flight adjustment of ink rheology in microdroplets are explained based on first principles of physics. The suitable range of ink droplet size is determined from the effectiveness for inertial impaction when depositing onto substrate and convenience for pneumatic manipulation, in-flight solvent evaporation, etc. The existence of a jet Reynolds number window is shown by a fluid dynamics analysis of impinging jets for Aerosol Jet ® printing with long standoff between nozzle and substrate, which defines the operation range of gas flow rate according to the nozzle orifice diameter. The time scale for ink droplets to remove volatile solvent is shown to just coincide that for them to travel in the nozzle channel toward substrate after meeting the coflowing sheath gas, enabling the in-flight manipulation of ink properties for high aspect-ratio feature printing. With inks being able to solidify rapidly, 3D structures, such as tall micropillars and thin-wall boxes, can be fabricated with Aerosol Jet ® printing. Having mist droplets in the range of 1–5 μ m also makes it possible to print lines of width about 10 μ m.

The method for fast fabrication of superhydrophobic surfaces was proposed to resist the formation of biofilm of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) for orthopedic and dental implants. Laser beam machining with nanosecond pulsed laser (Nd:YAG) was used to fabricate pit structure on Grade-5 Ti–6Al–4V alloy followed by annealing (at 300 °C with different time scales) in order to reduce the transition time from hydrophilic to superhydrophobic surface generation. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) techniques were used to characterize the textured samples. The surface wettability of plain and textured samples was measured by the sessile drop method using goniometer. The biofilm formation was qualitatively and quantitatively evaluated by FE-SEM and crystal violet binding assay, respectively. The biofilm formation was observed on plain (hydrophilic) surface for both the types of bacteria, whereas significantly less biofilm formation was observed on the laser textured (superhydrophobic) surfaces. The proposed method helps in reducing the risk of infection associated with implants without using cytotoxic bactericidal agents.

The importance of coatings in modern science and industry is great, and the system presented in this manuscript attempts to provide a method of creating high quality nanoparticle coatings with in situ sintering of nanoparticles. Dual regime nozzle creates close to optimum conditions for particle delivery and deposition and the addition of in situ thermally assisted coating makes it more productive. Preliminary results show systems uniform coating and in situ sintering capability.

Altering the wetting characteristics of copper will positively impact numerous practical applications. The contact angle (CA) of a water droplet on the polished copper surface is usually between 70 deg and 80 deg. This paper discusses a facile, scalable, tuned bulk micromanufacturing approach for altering the surface topology of copper concomitantly at the micro- and nano-length scales, and thus significantly influence its wetting characteristics. The resultant copper surfaces were found to be robust, nontoxic, and exhibited ultra-omniphilicity to various industrial liquids. This extreme wetting ability akin to a paper towel (CA of zero for multiple liquids) was achieved by tuning the bulk micromanufacturing process to generate connected hierarchical micro- and nano-roughness with nanocavities within the embryos of microcavities. With an adsorbed coating of ester, the same ultra-omniphilic copper surfaces were found to exhibit robust super-hydrophobicity (CA ∼ 152 deg for water).

Thermal fiber drawing has emerged as a novel process for the continuous manufacturing of semiconductor and polymer nanoparticles. Yet a scalable production of metal nanoparticles by thermal drawing is not reported due to the low viscosity and high surface tension of molten metals. Here, we present a generic method for the scalable nanomanufacturing of metal nanoparticles via thermal drawing based on droplet break-up emulsification of immiscible polymer/metal systems. We experimentally show the scalable manufacturing of metal Sn nanoparticles (<100 nm) in polyethersulfone (PES) fibers as a model system. The underlying mechanism for the particle formation is revealed, and a strategy for the particle diameter control is proposed. This process opens a new pathway for scalable manufacturing of metal nanoparticles from liquid state facilitated solely by the hydrodynamic forces, which may find exciting photonic, electrical, or energy applications.

A computational model to investigate the flushing of electric discharge machining (EDM) debris from the interelectrode gap during the spray-EDM process is developed. Spray-EDM differs from conventional EDM in that an atomized dielectric spray is used to generate a thin film that penetrates the interelectrode gap. The debris flushing in spray-EDM is investigated by developing models for three processes, viz., dielectric spray formation, film formation, and debris flushing. The range of spray system parameters including gas pressure and impingement angle that ensure formation of dielectric film on the surface is identified followed by the determination of dielectric film thickness and velocity. The debris flushing in conventional EDM with stationary dielectric and spray-EDM processes is then compared. It is observed that the dielectric film thickness and velocity play a significant role in removing the debris particles from the machining region. The model is used to determine the spray conditions that result in enhanced debris flushing with spray-EDM.

One of the challenges in making layered metal composites reinforced at interfaces has been controlling the dispersion and microstructure of the reinforcement particles. The reinforcement elements are typically applied at the interface by manual spreading using brush or by immersing the substrate in a suspension. In this study, an ultrasonic spraying technique has been used to deposit silicon carbide (SiC) nanoparticles on aluminum 6061 (Al6061) substrate foils to fabricate a laminate metal composite to control the deposited structure. The suspension parameters and the spraying parameters were investigated, and their influence on the deposited microstructure was analyzed. The laminate composite was consolidated using hot compaction, and a three-point bend test was performed to evaluate the mechanical properties. The yield and ultimate flexural strengths of the laminate composite reinforced with SiC nanoparticles increased by 32% and 15%, respectively, compared with those of the unreinforced sample prepared at the same condition.

Part II of this paper is focused on studying the droplet spreading and the subsequent evaporation/film-formation characteristics of the graphene oxide colloidal solutions that were benchmarked in Part I. A high-speed imaging investigation was conducted to study the impingement dynamics of the colloidal solutions on a heated substrate. The spreading and evaporation characteristics of the fluids were then correlated with the corresponding temperature profiles and the subsequent formation of the residual graphene oxide film on the substrate. The findings reveal that the most important criterion dictating the machining performance of these colloidal solutions is the ability to form uniform, submicron thick films of graphene oxide upon evaporation of the carrier fluid. Colloidal suspensions of ultrasonically exfoliated graphene oxide at concentrations < 0.5 wt.% are best suited for micromachining applications since they are seen to produce such films. The use of thermally reduced (TR) graphene oxide suspensions at concentrations < 0.5 wt.% results in nonuniform films with thickness variations in the 0–5 μ m range, which are responsible for the fluctuations seen in the cutting force and temperatures. At concentrations ≥ 0.5 wt.%, both the TR and ultrasonically exfoliated graphene oxide solutions result in thicker and nonuniform films that are detrimental for machining results. The findings of this study reveal that the characterization of the residual graphene oxide film left behind on a heated substrate may be an efficient technique to evaluate different graphene oxide colloidal solutions for cutting fluids applications in micromachining.

Atomization-based cutting fluid systems (ACFs) are increasingly being used in micromachining applications to provide cooling and lubrication to the tool–chip interface. In this research, a shielding nozzle design is presented. A computational fluid dynamic model is developed to perform parameter analysis of the design. The numerical simulations were accomplished using the Eulerian approach to the continuous phase and a Lagrangian approach for droplet tracking. Based on the results of the simulations it is determined that the shielding nozzle is effective at providing droplets to the cutting surface at an appropriate speed and size to create a lubricating microfilm.

In an electrospray, large electric potentials are used to generate a spray of highly charged droplets. Colloidal dispersions, consisting of nanoparticles in a volatile solvent, can be atomized using electrospray. Printing occurs by directing the emitted droplets toward a target substrate (TS). The solvent evaporation is rapid and dry nanoparticles are produced before reaching the surface. In this study, we investigate the structure of nanoparticle deposits printed using electrospray. Using dark field microscopy, four regimes are identified that mark the evolution of the deposit structure at early times. Electrospray imparts an excess electric charge onto the emitted particles. It is shown that the mutual Coulombic interaction between the particles governs their transport and ultimately the microstructure of the printed deposits. Electrospray offers enhanced control over the microstructure of printed nanomaterial deposits compared to traditional printing techniques. This has significant implications for the manufacturing of flexible electronic and photonic devices.

Near-field electrohydrodynamic jet (E-jet) printing has recently gained significant interest within the manufacturing research community because of its ability to produce micro/submicron-scale droplets using a wide variety of inks and substrates. However, the process currently operates in open-loop and as a result suffers from unpredictable printing quality. The use of physics-based, control-oriented process models is expected to enable closed-loop control of this printing technique. The objective of this research is to perform a fundamental study of the substrate-side droplet shape-evolution in near-field E-jet printing and to develop a physics-based model of the same that links input parameters such as voltage magnitude and ink properties to the height and diameter of the printed droplet. In order to achieve this objective, a synchronized high-speed imaging and substrate-side current-detection system is implemented to enable a correlation between the droplet shape parameters and the measured current signal. The experimental data reveals characteristic process signatures and droplet spreading regimes. The results of these studies served as the basis for a model that uses the measured current signal as its input to predict the final droplet diameter and height. A unique scaling factor based on the measured current signal is used in this model instead of relying on empirical scaling laws found in prior E-jet literature. For each of the three inks tested in this study, the average error in the model predictions is under 10% for both the diameter and the height of the steady-state droplet. While printing under nonconducive ambient conditions of low relative humidity and high temperature, the use of the environmental correction factor in the model is seen to result in a 17% reduction in the model prediction error.

A recent development in cooling and lubrication technology for micromachining processes is the use of atomized spray cooling systems. These systems have been shown to be more effective than traditional methods of cooling and lubrication for extending tool life in micromachining. Typical nozzle systems for atomization spray cooling incorporate the mixing of high-speed gas and an atomized fluid carried by a gas stream. In a two-phase atomization spray cooling system, the atomized fluid can easily access the tool–workpiece interface, removing heat through evaporation and lubricating the region by the spreading of oil micro-droplets. The success of the system is determined in a large part by the nozzle design, which determines the atomized droplet's behavior at the cutting zone. In this study, computational fluid dynamics are used to investigate the effect of nozzle design on droplet delivery to the tool. An eccentric-angle nozzle design is evaluated through droplet flow modeling. A design of simulations methodology is used to study the design parameters of initial droplet velocity, high-speed gas velocity, and the angle change between the two inlets. The system is modeled as a steady-state multiphase system without phase change, and droplet interaction with the continuous phase is dictated in the model by drag forces and fluid surface tension. The Lagrangian method, with a one-way coupling approach, is used to analyze droplet delivery at the cutting zone. Following a factorial experimental design, deionized water droplets and a semisynthetic cutting fluid are evaluated through model simulations. Statistical analysis of responses (droplet velocity at tool, spray thickness, and droplet density at tool) show that droplet velocity is crucial for the nozzle design and that modifying the studied parameters does not change droplet density in the cutting zone.

Superhydrophobicity in nature is the result of multiscale (hierarchical) roughness which consists of nano-asperities superimposed on micrometer scale roughness. A low-cost superhydrophobic surface was prepared by depositing soot on Vaseline coated glass substrates. The surface was rapidly prepared without any sophisticated fabrication facilities. The surface exhibited a remarkably high water contact angle of 161 deg and a roll-off angle of 3 deg. Atomic force microscopy (AFM) of the surface was done which revealed a very rough surface. The roughness features with nano-asperities superimposed on micrometer scale roughness enhance the water repellency. The micrometer scale peaks on the surface support the water droplet in a Cassie–Baxter state with the nano-asperities sheltering a composite interface below the droplet. The work of adhesion for the surface was also low at 18 nJ. The study will enable easy preparation of a cost effective superhydrophobic surface.