A note on spark bubble drop-on-demand droplet generation: simulation and experiment

The fluid dynamics of the spark bubble-generated droplet is studied both experimentally and numerically. The emphasis is especially on the droplet behavior after pinch-off. Commercial inkjet printers often produce satellite droplets along with parent droplets which are not desirable from the viewpoint of printing efficiency. Furthermore, standard drop-on-demand droplet generators are normally restricted to the generation of droplets with the same size as the nozzle diameter. In the spark bubble droplet generation method, a spark-generated bubble induces droplet formation through a hole in a solid surface separating the liquid and air interfaces. Immediately after ignition occurs, a bubble forms and creates pressure waves as it expands and contracts in a nonsymmetrical fashion. These pressure waves, depending on the geometries of the bubble location, plate, and hole may cause a single droplet smaller than the plate aperture to form and break up. In this article, a combined numerical and experimental study has been conducted to investigate the droplet behavior created in this manner. A high-speed camera is utilized to capture the droplet formation process. The numerical simulations have been carried out using the boundary integral spatial solution coupled with the time integration, i.e., a mixed Eulerian–Lagrangian approach. There is reasonable agreement between the simulations and experiment.     

Halogen bonds in 2D supramolecular self-assembly of organic semiconductors

Weak interactions between bromine, sulphur, and hydrogen are shown to stabilize 2D supramolecular monolayers at the liquid-solid interface. Three different thiophene-based semiconducting organic molecules assemble into close-packed ultrathin ordered layers. A combination of scanning tunneling microscopy (STM) and density functional theory (DFT) elucidates the interactions within the monolayer. Electrostatic interactions are identified as the driving force for intermolecular BrBr and BrH bonding. We find that the SS interactions of the 2D supramolecular layers correlate with the hole mobilities of thin film transistors of the same materials.     

An Injectable Hybrid Hydrogel with Oriented Short Fibers Induces Unidirectional Growth of Functional Nerve Cells

To regenerate soft aligned tissues in living organisms, low invasive biomaterials are required to create 3D microenvironments with a structural complexity to mimic the tissue's native architecture. Here, a tunable injectable hydrogel is reported, which allows precise engineering of the construct's anisotropy in situ. This material is defined as an Anisogel, representing a new type of tissue regenerative therapy. The Anisogel comprises a soft hydrogel, surrounding magneto‐responsive, cell adhesive, short fibers, which orient in situ in the direction of a low external magnetic field, before complete gelation of the matrix. The magnetic field can be removed after gelation of the biocompatible gel precursor, which fixes the aligned fibers and preserves the anisotropic structure of the Anisogel. Fibroblasts and nerve cells grow and extend unidirectionally within the Anisogels, in comparison to hydrogels without fibers or with randomly oriented fibers. The neurons inside the Anisogel show spontaneous electrical activity with calcium signals propagating along the anisotropy axis of the material. The reported system is simple and elegant and the short magneto‐responsive fibers can be produced with an effective high‐throughput method, ideal for a minimal invasive route for aligned tissue therapy.     

Influence of Salt and Surfactant on Copper Removal by Xanthan Gum-g-Itaconic Acid/Bentonite Hydrogel Composite from Water Using Fractional Factorial Design

A novel xanthan gum-g-itaconic acid/bentonite (XG-g-PIA/BET) hydrogel composite was synthesized using free radical polymerization in the presence of ammonium persulfate as initiator and N,N’-methylenebis(acrylamide) as crosslinker. The Fourier transform infrared spectroscopy spectra of XG-g-PIA/BET composite before and after adsorption gave strong evidence of the successful adsorbance of copper ions with COOH groups. Influence of the presence of three typical salts (NaCl, CaCl₂, and FeCl₃) and three types of surfactants including anionic (Brij 35), cationic (N-Cetyl-N,N,N-trimethyl ammonium bromide), anionic (sodium dodecyl sulfate), and their two-term interactions on copper ions adsorption capacity were investigated using 32 experiments with fractional factorial experimental design. The analysis of variance (ANOVA) showed that the fitted model had a significant p value (<0.0001), and except FeCl₃, all other variables present in the aqueous solution increased the copper adsorption capacity. In addition, there was no significant two-term interaction between different variables.     

Electrodeposition of nickel–phosphorus from a highly conductive citrate bath for wire bonding applications

A highly conductive electrolytic nickel–phosphorus (Ni–P) plating bath was formulated as an alternative to electroless Ni–P deposition for aluminium wire bonding application. The Ni–P deposits were electroplated from nickel citrate baths containing sodium chloride, citric acid, nickel sulphate and sodium hypophosphite (SHP) using the DC plating. In comparison with Watts bath, the formulated highly conductive citrate bath had almost twice of cathodic current efficiency in low-current density regions and exhibited more uniform plating thickness. In addition, the formulated citrate bath did not have any boric acid as a component; and hence, eliminating the waste disposal issue related to boric acid.     

Multiobjective optimization for force and moment balance of a four-bar linkage using evolutionary algorithms

In this study, force and moment balance of a planar four-bar linkage is implemented using evolutionary algorithms. In the current problem, the concepts of inertia counterweights and physical pendulum are utilized to complete balance of all mass effects, independent of input angular velocity. A proposed multiobjective particle swarm optimization, and non-dominated sorting genetic algorithm II are applied to minimize two objective functions subject to some design constraints. The applied algorithms produced a set of feasible solutions called pareto optimal solutions for the design problem. Finally, a fuzzy decision maker is utilized to select the best solution among the obtained pareto solutions. The results show that optimal solutions minimize the weights of applied counterweights and eliminate both shaking forces and moments transmitted to the ground, simultaneously.     

Incorporation of zeolite and silica nanoparticles into electrospun PVA/collagen nanofibrous scaffolds: The influence on the physical,chemical properties and cell behavior

Cartilage is under extensive investigation in tissue engineering research. Herein, we evaluated scaffolds prepared by composites of polyvinyl alcohol (PVA) and collagen incorporated with zeolite and silica nanoparticles (nZe and nSi). The scaffolds were prepared by the electrospinning method. The mean diameters of nanofibers were 0.61 ± 0.34 µm for PVA/collagen versuss 0.62 ± 0.22 µm and 0.66 ± 0.25 µm for the PVA/collagen/nZe and the PVA/collagen/nSi scaffolds, respectively. DAPI staining results revealed that cell proliferations on the PVA/collagen/nZe and PVA/collagen/nSi were strikingly higher than on the pure PVA/collagen. The results encouraged further investigation of PVA/collagen/nSi scaffolds as biomimetic platform for chondrocyte cells in tissue engineering.