Nozzle-substrate Distance Research Articles

UV Resistance and Wetting of PLA Webs Obtained by Solution Blow Spinning.

In this work, the resistance of polylactide-based non-wovens produced by solution blow spinning to environmental factors was investigated. An average contact angle of up to 136° was achieved with an average fiber diameter of 340 nm at the optimal material density and nozzle-substrate distance. When exposed to ultraviolet (UV) radiation, the polylactide non-wovens rapidly lose their hydrophobic properties due to changes in surface morphology resulting from fiber melting. It was demonstrated that the influence of surface structural features on hydrophobicity is greater than that of the material itself. The stability of the wetting properties under UV irradiation was assessed using the derivative parameters of the Owens-Wendt technique, which can serve as an additional method for estimating surface polarity.

Surface properties and antibacterial characteristics of polyurethane modified by corona discharge for food processing industry

Thermal properties and durability make polyurethane (PU) ideal for conveyor belts in food processing industry. On the other hand, its susceptibility to adhesion of pathogens subjects him to surface treatment techniques. In this study, substrates of PU were exposed to corona discharge using air as treatment gas. The process parameters, such as treatment time and nozzle-substrate distance, and the microbicidal effects of the polymer surfaces against Staphylococcus aureus and Escherichia coli were examined. Changes in surface hydrophobicity occurred at short treatment times due to the introduction of polar groups, as proofed by X-ray Photoelectron Spectroscopy (XPS), while the surface morphology suffered minor changes as revealed by Scanning Electron Microscopy (SEM) imaging. Moreover, the hydrophilicity of plasma treated PU was minimal affected by the variation of nozzle-substrate distance, as long as the discharge was in contact with the polymer surface. The hydrophilic surfaces developed a very good resistance to bacteria adherence in few hours after incubation.

Conformal aerosol jet printing using a 3-axis printer

Conformal patterning using contact printing methods has been problematic, owing to the complex topography of realistic surfaces and the sensitivity of print quality to the nozzle-substrate distance. Motion planning for such printing configurations is also a challenge, with conventional methods using tessellated representations to generate conformal toolpaths. However, these representations are often subject to truncation errors, thus diminishing the accuracy of the printed part. We propose and demonstrate a novel method to perform conformal aerosol jet printing on curved and topographically complex surfaces. We begin with a non-uniform rational B-spline (NURBS) definition of a surface, perform patch selection (i.e., area of interest) and extract its associated points and normals, and then generate GCode for conformal printing. We make use of a serpentine toolpath that resembles a strain-sensor pattern, thus suggesting the generalization of this method to conformal printing of circuits for applications in sensing, chemical analysis, thermal management, and pharmaceutical delivery with relative ease.

Deposition mechanism of alumina particles in aerosol deposition based on the kinetic energy of particles

In this study, the aerosol deposition process was used to deposit the α-Al2O3 coating on Mo substrate under various conditions, i.e., particle size, type of carrier gas, gas flow rate and a nozzle–substrate distance. The formation behaviors of the α-Al2O3 coating in terms of deposition rate, microstructure and texture were studied in a correlation with the kinetic energy of the particles forming the coating. The fully dense and crystalline α-Al2O3 coatings were observed with the average grain size of 20 nm, significantly smaller than the particle sizes of 0.14 and 1.0 μm. The coating layers under all conditions were examined with a fiber texture with the (0001) plane tilted about 15° away from the coating plane. The microstructure and texture formation were resulted by fragmentation and plastic deformation of the particles during the deposition. The deposition formation of the particle collisions with the coating was simulated by the finite element analysis with the fragmentation model. The model suggested that the particles fracture at the boundary of the maximum shear strain generated by the particle impact. The deposit is formed by the lower part of the fracture particle. The strain energy in the deposited area of retained particles is considered to be equivalent to the kinetic energy, which includes the effects of the particle characteristics and physical properties. The result indicated that the changes of the deposition rate and texture formation can be well explained as a function of the strain energy. Regardless of the strain energy, the density of the α-Al2O3 coatings was almost the same as that of the bulk α-Al2O3 material. It was found that the high strain energy can lead to both high deposition rate and high indentation hardness.

Precision coating of ocular devices/contact lenses by nanoelectrospray additive printing

Eye drops are widely used for treating ocular diseases, but with poor bioavailability less than 5%. Drug-eluting contact lenses (DECLs) have been proven to improve the efficacy of treatment. For the manufacturing of DECLs, no method can directly deposit drug formulation on commercial lenses. In this work, a novel additive manufacturing approach, nanoelectrospray (nES), and a custom-built nES printing system was developed to directly deposit drug formulations on the surfaces of commercial contact lenses. As a demonstration, nES was used to coat the model biopolymer, zein, onto commercial lenses. Precise deposition of a ring-shaped polymer layer only on the peripheral region was achieved. For printing optimisation, the spraying width is primarily controlled by the nozzle substrate distance. The coating thickness, which can be used to directly control the drug dose, is subject to the polymer concentration in the formulation, dosing speed and the number of rotations. By using the spray current transient and established scaling law, the predicted spray volume is highly correlated to the experimental results. This study built a firm technological foundation for using nES as a novel additive manufacturing method to produce DECLs with drug coating at the surfaces of contact lenses in pre-defined patterns and locations.

Optimizing ultrasonic mist vapor deposition parameters toward facile synthesis of tungsten oxide nanofibers

Thanks to its high surface area, excellent condition for light absorption and scattering and suitable charge transport directions, nanofibrous morphology is a fascinating candidate for many important application fields. Herein as the first report, Tungsten oxide (WO2.92) thin films have been prepared via ultrasonic mist vapor deposition (UMVD) method. The effects of important growth parameters namely substrate-nozzle distance (D = 3, 5 and 8 cm), deposition time (t = 3, 6 and 18 min), substrate temperature (Ts = 130, 200 and 400 °C) and angle (θ = 0, 25 and 45°) on surface morphology of prepared thin films were investigated systematically. The analyses results revealed that Ts and θ played more determining roles affecting on tungsten oxide thin film morphology. Interestingly, very clear and obvious tungsten oxide nanofibers were deposited uniformly over the whole of substrate surface when high deposition time and angle (t = 18 min, θ = 45°) and mild substrate temperature (Ts = 200 °C) were utilized. The average diameter of grown nanofibers increased from 297 nm for θ = 0° to 429 nm for θ = 45°. No fibrous morphology was observed for the layers prepared with both low Ts = 130 and high Ts = 400 °C. Considering all of the results, a mechanism was proposed describing how the nanofibers were grown via UMVD method. obtaining fine tungsten oxide nanofibers via such a simple method is very interesting to use them as electrochromic coatings, sensors, photoelectrochemical electrodes etc.

Facile preparation of hazy Ga-doped ZnO electrodes by atmospheric pressure plasma jet

Increasing the optical path length without degrading optoelectronic properties of front electrodes of solar cells is promising to enhance the power conversion efficiency. This can be achieved by increasing the haze (H) of the electrode through texturing, while retaining high transmittance (Tt) and low sheet resistance (Rs). However, it is challenging to balance these properties simultaneously since they are mutually influenced. Here, we present a facile, low-cost, and single-run method of preparing gallium-doped zinc oxide (GZO) with high H (>25%), high Tt (>90% in the visible range, referenced to glass), and low Rs (6.62 Ω sq−1) using atmospheric pressure plasma jet. First, we increase the nozzle-substrate distance, or working distance (WD), to deposit a thin, rough GZO as a haze enhance (HE) layer and immediately deposit a standard GZO layer using the same apparatus. By tailoring the roughness of the HE layer using WD and scanning pitch, we successfully produce high-quality hazy GZO that have competitive figures of merit of 6.3 × 10−2 Ω−1 (referenced to the glass) and 2.1 × 10−2 Ω−1 (overall), and H = 25%. Also, unlike conventional methods, our approach does not require vacuum, etching, additional materials, or change of machine/tooling, which can significantly reduce the operational complexity.

Optimization of extrusion process for 3D hard candy manufacture

In the domain of 3D food printing, previously developed 3D candy printers focused majorly on soft candy materials, such as chocolate, gum, and jelly. These techniques also presented limitations in terms of reproducibility and model diversity. Accordingly, this study aimed to address these problems via investigation of the behavior of sugar, a printing material, with respect to the extrusion process of 3D hard candy manufacture and analysis of the reproducibility. Moreover, the relationship among the nozzle movement speed, extrusion speed, and pattern spacing was analyzed to derive the optimal conditions for the extrusion process for reproducing a 3D virtual model. It was observed that the pattern spacing was optimized at 0.9 mm, considering a stable manufacturing process and manufacturing speed. The optimized parameter values of nozzle diameter, nozzle-substrate distance, pneumatic pressure, control temperature, printing speed, and standoff distance were computed through a correlation analysis conducted with pattern spacing. Under these conditions, moldings with a total height of 6 cm could be built. Moreover, a considerably high reproducibility of the 3D model was achieved on consideration of changes in the pattern thickness according to the nozzle movement speed and extrusion speed. Overall, this study contributes to literature and bridges a gap therein by presenting a process technology for guaranteeing the reproducibility of 3D models. It also demonstrates that the production of personalized custom shapes will be effective and feasible in the future.

Conformal 3D printing of non-planar antennas on wrinkled and folded kapton films using point cloud data

We report a reverse engineering-driven method for conformal microextrusion three-dimensional (3D) printing of functional materials on complex 3D structures and thin films of near-arbitrary topography. A non-planar tool path programming algorithm for conformal microextrusion 3D printing based on point cloud data representations of object geometry is presented. We show that the optimal nozzle-substrate standoff distance for quality 3D printing depends on the substrate’s local geometric features (i.e. slope and curvature) and the tool trajectory. The impact and utility of the novel conformal microextrusion 3D printing process were demonstrated by fabrication of 3D spiral and Hilbert-curve loop antennas on various non-planar substrates, including wrinkled and folded Kapton films and origami. 3D-printed conformal antennas exhibited resonant frequencies ranging from 1.5 to 2.7 GHz with S 11 less than 10 db. This work provides a new method for conformal 3D printing on one-of-a-kind objects and non-planar films.

Control of Porous Layer Thickness in Thermophoretic Deposition of Nanoparticles.

The film thickness plays an important role in the performance of materials applicable to different technologies including chemical sensors, catalysis and/or energy materials. The relationship between the surface and volume of the functional layers is key to high performance evaluations. Here we demonstrate the thermophoretic deposition of different thicknesses of the functional layers designed using flame combustion of tin 2-ethylhexanoate dissolved in xylene, and measurement of thickness by scanning electron microscopy and focused ion beam. The parameters such as spray fluid concentration (differing Sn2+ content), substrate-nozzle distance and time of the spray were considered to investigate the layer growth. The results showed ≈ 23, 124 and 161 μm thickness of the SnO2 layer after flame spray of 0.1, 0.5 M and 1.0 M tin 2-EHA-Xylene solutions for 1200 s. While Sn2+ concentration was 0.5 M for all the flame sprays, the substrates placed at 250, 220 and 200 mm from the flame nozzle had layer thicknesses of 113, 116 and 132 µm, respectively. Spray time dependent thickness growth showed a linear increase from 8.5 to 152.1 µm when the substrates were flame sprayed for 30 s to 1200 s using 0.5 M tin 2-EHA-Xylene solutions. Changing the dispersion oxygen flow (3–7 L/min) had almost no effect on layer thickness. Layers fabricated were compared to a model found in literature, which seems to describe the thickness well in the domain of varied parameters. It turned out that primary particle size deposited on the substrate can be tuned without altering the layer thickness and with little effect on porosity. Applications depending on porosity, such as catalysis or gas sensing, can benefit from tuning the layer thickness and primary particle size.

Self-powered cadmium chalcogenide photodetectors by pressurized air blast spraying

Self-powered photodetectors (SPDs) have great application potential in next-generation instruments that operate wirelessly and independently. Hence, there is a strong market demand for more efficient, easier, cheaper, and faster SPDs fabrication methods and tools. Specially, spray pyrolysis (SS) is an extensively used technique because of its simplicity, cost-effectiveness, and high deposition rate. Furthermore, in a SS system, parameters such as the chamber temperature, air pressure, substrate temperature, and nozzle-substrate distance must be precisely selected since they determine the deposited film quality. Otherwise, pressurized air blast spraying is a standard atomization method implemented in economical and multi-use micro airbrush guns that can be used in conjunction with a substrate heater to complete the SS process. In this study, a fabrication procedure, complemented with a micro airbrush gun as an easy, inexpensive, and efficient tool for film deposition was developed and implemented to obtain a single and a parallel connection of four SPDs based on cadmium chalcogenides (CC). A comprehensive analysis of the optical and electrical properties of the obtained devices confirms the functionality of the implemented fabrication procedure. All fabricated SPDs devices show responsivity and specific detectivity in the visible spectrum demonstrating their capability for self-powered photodetection applications.

Facile preparation of ZnO nanostructured thin films via oblique angle ultrasonic mist vapor deposition (OA-UMVD): a systematic investigation

Ultrasonic mist vapor deposition (UMVD) is a widely used facile technique to prepare ZnO thin films. The surface properties of prepared thin films can be tuned via easily controllable UMVD deposition parameters. Herein, we utilized an oblique angle (OA) geometry in UMVD system named as OA-UMVD. The angle between incident flow and substrate (θs) was changed from 0° to 45°. Alteration of θs as well as substrate temperature (Ts) resulted in the deposition of ZnO thin films with different morphologies. For mild nozzle–substrate distance (D = 3 cm), fine vertical ZnO nanosheets with length of 123 nm and thickness of 23 nm were obtained for low Ts (330 °C) and small θs (≈ 0°). By increasing both Ts and θs, ZnO nanorods gradually appeared on the surface. Both nozzle–substrate distance (D) and Ts showed similar effect on deposition rate (Rd), and Rd decreased by increase of D and Ts, while deposition rate increased for larger θs. Confocal microscopy results revealed that using low Ts (330 °C), short distance (D = 1.5 cm) and large θs (45°) resulted in high macroscopic surface roughness (MRs) of 98 nm, while high Ts (500 °C), long D (5 cm) and small θs (≈ 0○) created compact and smooth surface with low MRs of 5 nm, in accordance with transmittance results. The ZnO wurtzite crystal structure was approved via X-ray diffraction patterns. The crystallite size in the layers was affected only by Ts, and θs had no significant effect on the layers’ crystallinity. Obtaining different ZnO nanostructures with different MRs via easily and accurately controllable growth parameters is a great advantage for our employed OA-UMVD system, which could be used to prepare ZnO thin films with desired morphologies for widespread application fields.

Ni-Doped ZnO Thin Films Deposited by Pneumatic Spray Pyrolysis

The objective of the present work is the study the Ni concentration effect on the optical, structural and electrical properties of ZnO:Ni thin films deposited by pneumatic spray pyrolysis method. Un-doped and Ni-doped ZnO thin films were prepared from zinc acetate dihydrate and nickel chloride hexahydrate dissolved in distilled water onto glass substrates by pneumatic spray pyrolysis method. Solution concentration, substrate temperature and nozzle-substrate distance were kept constant during all deposition processes. Effect of nickel content on the optical, structural and electrical properties of as-prepared films obtained was investigated by UV–Vis-NIR spectrophotometry, X-ray diffraction and four-point probe technique. The results indicate that the deposited films are well adherent to the substrates, present surface roughness and have a preferential growth in the (002) direction. The observed transmittance in the visible region was situated between 60% and 70%. For Ni-doped ZnO, there are two separate phases. The Urbach energy, grain size, and electrical conductivity increase with Ni content. The same behavior for both the optical energy gap and the ZnO:Ni lattice parameters.

Facile preparation of various ZnO nanostructures via ultrasonic mist vapor deposition: a systematic investigation about the effects of growth parameters

ZnO thin films with various surface morphologies were deposited on glass substrate via a facile and well-controllable method so-called ultrasonic mist vapor deposition (UMVD). The effects of important growth parameters namely substrate temperature (Ts), nozzle-substrate distance (D) and nozzle aperture diameter (d) on optical, electrical and surface properties (both in micro and macro-scale) of synthesized thin films were carefully investigated. In case of d = 10 mm and D = 6 cm, ZnO nanoseeds and nanorods were grown at Ts = 330 and 500 °C, respectively. Interestingly, ZnO nanosheets were grown perpendicular to the substrate when d = 10 mm, D = 9 cm and Ts = 400 °C. More rough surfaces (in macroscopic scale) were grown for small D (6 and 9 cm) and lower substrate temperature (Ts = 330 and 400 °C) while for Ts = 500 °C a smooth and uniform surface can be obtained at any distance. The layer prepared with d = 10 mm, has the lowest roughness (33 nm) which is one order of magnitude lower than other samples. Increment of Ts, d and also D reduced the electrical sheet resistance. The growth mechanisms leading to obtain various morphologies for different samples were also proposed and discussed.

Electrohydrodynamic printing process monitoring by microscopic image identification.

Electrohydrodynamic printing (EHDP) is able to precisely manipulate the position, size, and morphology of micro-/nano-fibers and fabricate high-resolution scaffolds using viscous biopolymer solutions. However, less attention has been paid to the influence of EHDP jet characteristics and key process parameters on deposited fiber patterns. To ensure the printing quality, it is very necessary to establish the relationship between the cone shapes and the stability of scaffold fabrication process. In this work, we used a digital microscopic imaging technique to monitor EHDP cones during printing, with subsequent image processing algorithms to extract related features, and a recognition algorithm to determine the suitability of Taylor cones for EHDP scaffold fabrication. Based on the experimental data, it has been concluded that the images of EHDP cone modes and the extracted features (centroid, jet diameter) are affected by their process parameters such as nozzle-substrate distance, the applied voltage, and stage moving speed. A convolutional neural network is then developed to classify these EHDP cone modes with the consideration of training time consumption and testing accuracy. A control algorithm will be developed to regulate the process parameters at the next stage for effective scaffold fabrication.

Effect of Spraying Parameters on the Morphology of Spray-Coated Active Layers for Organic Solar Cells

Over the past decade, organic solar cells (OSCs) have demonstrated their great potential for the low-cost mass production of renewable energy. However, the conventional active layer deposition technique (spin-coating) is not suitable for mass production due to its incompatibility with the roll-to-roll process. Spray-coating is a promising candidate for in-line production of OSCs but parameters such as distance between the spray nozzle and substrate, applied pressure and number of sprays should be optimized to produce adequate film thickness and morphology. Here, we verified how these processing parameters influence the thin film properties and observed that film thickness increases with decreasing nozzle-substrate distance, increasing number of sprays or applied pressure. The processing parameters were adjusted to produce spray-coated films with similar properties to the spin-coated ones thus confirming that spray-coating could replace spin-coating for mass production of OSC devices.

Direct-Ink-Writing of Degradable Carboxymethylcellulose

Additive manufacturing with degradable polymers have recently drawn significant attention due to its promising biomedical applications including artificial tissue engineering, surgical, and orthopedic devices etc. This paper experimentally investigates the direct-ink-writing of one of the widely used degradable polymers, carboxymethlycellulose. Through printing and geometric characterization of simple test structures, effect of ink concentration, substrate material and direct-ink-writing process parameters including printing pressure, printing speed and nozzle substrate distance on the process outcome is studied. Preliminary findings on printing of micro-scale structures using nozzles as small as 10 μm in diameter are also presented.

Effect of the Nozzle-Substrate Distance on the Structural and Optical Properties of ZnO Thin Films Deposited by Spray Pyrolysis Technique

In the present work, zinc oxide (ZnO) thin films were deposited by pyrolysis spray technique on glass substrate temperature 350°C, using the zinc acetate with a molarity of 0.1M. Our interest is on the investigation of the nozzle-substrate distance on the structural and optical properties of the films. Structural analysis by X-ray diffraction showed that the deposited films have a preferred orientation along the direction (002) and are relatively uniform. The spectrophotometer UV-Visible confirms that it is possible to get good transparent ZnO films with a transmission of 80 to 95% in the visible. The values of optical gaps Eg deduced from the spectra of UV-Visible transmissions vary between 3.21 and 3.25 eV.

Improvement of mechanical properties of polylactic acid adhesion joints with bio‐based adhesives by using air atmospheric plasma treatment

ABSTRACTThe packaging industry generates a high volume of wastes; so that, there is a high demand of biodegradable materials, which do not damage the environment. Nowadays, there is an interesting consumption of polylactic acid (PLA) due to its biodegradable features. This work focuses on the improvement of mechanical properties of PLA adhesion joints for uses in the packaging industry. In order to achieve that purpose, atmospheric plasma treatment is used to selectively modify PLA surface properties. The obtained experimental results show that the atmospheric plasma treatment is suitable to increase the mechanical performance of PLA–PLA adhesive joints. Optimum conditions for the atmospheric plasma treatment were obtained with a nozzle–substrate distance of 10 mm and an advance rate in the 100–300 mm s−1range; for these particular conditions, the effectiveness of the surface modification is the highest. The main plasma‐acting mechanisms are microetching together with the insertion of polar groups which lead to an interesting synergy that causes a remarkable increase in mechanical properties of adhesion joints. In particular, the shear strength of untreated PLA–PLA adhesion joints is close to 50 N cm−2and this value is increased up to values of about 168.7 N cm−2with optimum plasma treatment conditions. This indicates that atmospheric plasma treatment is both a technical and an environmental friendly technique to improve mechanical performance of PLA adhesive joints. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 42391.

LPG sensing characteristics of electrospray deposited SnO2 nanoparticles

In this study, SnO2 films were fabricated on conductive substrate such as aluminum and platinum coated alumina using electro-spray deposition (ESD) method for gas sensor applications. Solution flow rate, coating time, substrate–nozzle distance and solid/alcohol ratio were studied to optimize SnO2 film structure. The morphology of the deposited films was characterized by stereo and scanning electron microscopy (SEM). The gas sensing properties of tin oxide films were investigated using liquid petroleum gas (LPG) for various lower explosive limit (LEL). The results obtained from microscopic analyses show that optimum SnO2 films were evaluated at flow rate of 0.05ml/min, at distance of 6cm, for 10min deposition time, for 20gSnO2/Lethanol ratio and at 7kV DC electric field. By the results obtained from the gas sensing behavior, the sensitivity of the films was increased with operating temperature. The films showed better sensitivity for 20 LEL LPG concentration at 450°C operating temperature.