This study compares fluid velocity magnitude and direction for three different glassy carbon (GC) electrode systems effecting alternating current (AC) electroosmotic pumping. The flow behavior is analyzed for electroosmotic pumping performed with asymmetric coplanar electrodes. Subsequently, effects of adding microposts array of two different heights (40 μ m and 80 μ m) are studied. Experimental results demonstrate that as peak-to-peak voltage is increased above 10 V peak-to-peak, the flow reversal is achieved for planar electrodes. Utilization of microposts-enhanced asymmetric electrodes blocks the flow reversal and alters the magnitude of the fluid velocity at the application of larger voltages (above 10 V peak-to-peak). Understanding of the consequences of three-dimensional geometry of asymmetric electrodes would allow designing the electrode system for AC electroosmotic pumping and mixing, as well as bidirectional fluid driving with equal forward and backward flow velocities.

In drilling, chip-clogging results in increased drilling temperature, excessive tool wear, and poor hole quality. Especially, in microdrilling, low rigidity of the tool and inability of cutting fluid to penetrate narrower tool–workpiece interface significantly reduce the drilling performance. A novel bubble-mixed cutting fluid delivery method proposed in this research aims toward achieving a high-performance micro deep-hole drilling process with a significant reduction in the consumption of cutting fluid. Experimental results show that the bubble-mixed cutting fluid delivery method achieves lower thrust force during drilling, higher drilled depth before tool breakage, and lower dimensional and circularity errors when machining deep holes in comparison with dry cutting or conventional flood delivery method. It is also found that the smaller-sized bubbles effectively penetrate the tool–workpiece interface during the drilling producing deeper holes by better chip evacuation and cooling.

Magnesium alloys have a good potential as structural biomaterials for temporary implant applications because of their self-degradation properties and biocompatibility. The surface condition is important for such applications, and lasers are often used to modify the surface characteristics of such components. In this context, the media through which the laser beam passes before reaching the surface to be irradiated is also of interest. In particular, laser irradiation in liquids affects the thermal energy delivery to the surface of the material, which in turns influences the formation of surface structures. In this work, rare earth containing WE54 Mg alloy has been irradiated under air and through a simulated body fluid (SBF) layer using a 500 watt pulsed Nd: YAG laser. As compared to direct laser surface treatment through air, laser irradiation through SBF generates new surface structures and deposition of ions issued from the SBF solution. Scanning electron microscope combined with energy dispersive spectroscopy (EDS) was used for the examination of surface structures formation and determination of elemental composition. Mesenchymal stem cells (MSC) culture was performed on laser modified WE54 alloy surface, and the MSC cytocompatibility on SBF-treated substrates was evaluated by the PrestoBlue™ assay test method. Cell reproducibility was observed on the SBF laser-treated surface which indicated that cell viability was improved by the surface treatment. The deposition of calcium and phosphorus ions on the WE54 surface was beneficial for cell viability. These results motivate the potential use of SBF-based films for biomedical purposes.

Foam-core meniscus coating is being used to retrofit 100 nm-scale sol–gel anti-reflective coatings (ARCs) onto in-field solar panels through the deposition, evaporation, and curing of wet films. Advantages of this technique include the means to control fluid flow relative to substrate motion and the ability to conform to large, warped substrates. While simple in practice, no models exist for predicting critical outcomes such as film thickness. In this paper, preliminary experiments are used to identify important process parameters, and an analytical model is developed and validated for predicting the thickness of silica sol–gel films deposited on solar glass.

Multiscale and multimaterial three-dimensional (3D) printing is new frontier in additive manufacturing (AM). It has shown great potential to implement the simultaneous and full control for fabricated object including external geometry, internal architecture, functional surface, material composition and ratio as well as gradient distribution, feature size ranging from nano-, micro-, to macro-scale, embedded components and electrocircuit, etc. Furthermore, it has the ability to construct the heterogeneous and hierarchical structured object with tailored properties and multiple functionalities which cannot be achieved through the existing technologies. That paves the way and may result in great breakthrough in various applications, e.g., functional tissue and organ, functionally graded (FG) material/structure, wearable devices, soft robot, functionally embedded electronics, metamaterial, multifunctionality product, etc. However, very few of the established AM processes have now the capability to implement the multimaterial and multiscale 3D printing. This paper presented a single nozzle-based multiscale and multimaterial 3D printing process by integrating the electrohydrodynamic jet printing and the active mixing multimaterial nozzle. The proposed AM technology has the capability to create multifunctional heterogeneously structured objects with control of the macroscale external geometry and microscale internal structures as well as functional surface features, particularly, the potential to dynamically mix, grade, and vary the ratios of different materials. An active mixing nozzle, as a core functional component of the 3D printer, is systematically investigated by combining with the theoretical analysis, numerical simulation, and experimental verification. The study aims at exploring a feasible solution to implement the multiscale and multimaterial 3D printing at low cost.

This paper presents a computational approach for simulating the motion of nanofibers during fiber-filled composites processing. A finite element-based Brownian dynamics simulation (BDS) is proposed to solve for the motion of nanofibers suspended within a viscous fluid. We employ a Langevin approach to account for both hydrodynamic and Brownian effects. The finite element method (FEM) is used to compute the hydrodynamic force and torque exerted from the surrounding fluid. The Brownian force and torque are regarded as the random thermal disturbing effects which are modeled as a Gaussian process. Our approach seeks solutions using an iterative Newton–Raphson method for a fiber's linear and angular velocities such that the net forces and torques, including both hydrodynamic and Brownian effects, acting on the fiber are zero. In the Newton–Raphson method, the analytical Jacobian matrix is derived from our finite element model. Fiber motion is then computed with a Runge–Kutta method to update fiber position and orientation as a function of time. Instead of remeshing the fluid domain as a fiber migrates, the essential boundary condition is transformed on the boundary of the fluid domain, so the tedious process of updating the stiffness matrix of finite element model is avoided. Since the Brownian disturbance from the surrounding fluid molecules is a stochastic process, Monte Carlo simulation is used to evaluate a large quantity of motions of a single fiber associated with different random Brownian forces and torques. The final fiber motion is obtained by averaging numerous fiber motion paths. Examples of fiber motions with various Péclet numbers are presented in this paper. The proposed computational methodology may be used to gain insight on how to control fiber orientation in micro- and nanopolymer composite suspensions in order to obtain the best engineered products.

This paper is aimed at investigating the effects of graphene oxide platelet (GOP) geometry (i.e., lateral size and thickness) and oxygen functionalization on the cooling and lubrication performance of GOP colloidal suspensions. The techniques of thermal reduction and ultrasonic exfoliation were used to manufacture three different types of GOPs. For each of these three types of GOPs, colloidal solutions with GOP concentrations varying between 0.1 and 1 wt.% were evaluated for their dynamic viscosity, thermal conductivity, and micromachining performance. The ultrasonically exfoliated GOPs (with 2–3 graphene layers and lowest in-solution characteristic lateral length of 120 nm) appear to be the most favorable for micromachining applications. Even at the lowest concentration of 0.1 wt.%, they are capable of providing a 51% reduction in the cutting temperature and a 25% reduction in the surface roughness value over that of the baseline semisynthetic cutting fluid. For the thermally reduced GOPs (TR GOPs) (with 4–8 graphene layers and in-solution characteristic lateral length of 562–2780 nm), a concentration of 0.2 wt.% appears to be optimal. The findings suggest that the differences seen between the colloidal suspensions in terms of their droplet spreading, evaporation, and the subsequent GOP film-formation characteristics may be better indicators of their machining performance, as opposed to their bulk fluid properties.

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.

Traditionally, micromixing has been thought to be governed by molecular diffusion. However, the authors consider that advection is important in the mixing enhancement and applicable to micromixing devices in many industrial fields. Here, the Marangoni convection, a type of shear flow induced at gas–liquid free interfaces, is introduced as an additional source for micromixing. To evaluate the proposal, two liquids with different surface tensions values were mixed in a capillary channel fabricated by the photolithography technique. The utility of Marangoni convection was confirmed in rapid mixing by the flow experiments.

The advancement of micro tube hydroforming (THF) technology has been hindered by, among others, the lack of robust microdie systems that could facilitate hydroforming of complex parts that require both expansion and feeding. This paper proposes a new micro-THF die assembly that is based on floating a microdie-assembly in a pressurized chamber. The fluid pressure inside the chamber which surrounds the dies and punches is the same as the pressure required to hydroform the tube. The fluid pressure intensity in the chamber varies in accordance with the predetermined pressure loading path required to successfully hydroform the part. The system was built, and hydroforming experiments were carried out for various micro- and meso-scale shapes, including bulge-shapes, Y-shapes, and T-shapes.

A reverse oscillatory flow (ROF) mixing system is discussed having a reaction channel 460 μm high by 152 mm wide for high flow rate processing of nanoparticle (NP) chemistries. The ROF system is demonstrated to produce CdS nanoparticles at a production rate of 115.7 g/h with a coefficient of variation (CV) for particle size down to 19%. These production rates are substantially higher than those achieved using other microchannel mixers while maintaining comparable size distributions. Advantages of the ROF approach include the use of larger microchannels which make the reactor easier to fabricate and less vulnerable to clogging.

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.