High Surface Tension Research Articles

Biocompatible Exfoliation and Modified Self-Assembly Deposition of Graphene Films for Electrodes Fabrication: Processing Parameters Vs. Electrochemical Performance

Liquid Phase Exfoliation (LPE) of graphite has been proposed as a scalable and low-cost method for graphene (G) production (A. O’Neill, U. Khan et al. Phys. Chem. C, 115, 5422–5428 (2011)). Ultrasonic mixing coupled with polymeric stabilizers effectively overcomes Van Der Walls forces between graphitic planes and isolating graphene flakes. The absence of strong oxidizing/reducing agents in the synthesis process allows the graphenic basal plane to preserve its sp2 character, with defects mainly concentrated at the flakes’ edges. In this work, we investigate the use of biocompatible solvents, ethanol (EtOH) and water, and stabilizing agents (cellulose acetate butyrate, CAB) to form stable liquid dispersions of graphene. Centrifugation of the EtOH/CAB/G mixture and removal of excess polymeric stabilizer followed the Ultrasonic Assisted Liquid Phase Exfoliation (UALPE) to obtain an optimal graphene dispersion. The resulting material is employed for the self-assembly-driven deposition of multi-layer graphene films on SiO2/Si substrates. According to the Marangoni effect principle, the low surface tension value of the graphene liquor can be exploited to induce a mass flow at the interface with a secondary high surface tension solvent (H2O). This phenomenon results in the formation of stable films of “compressed” graphene (X. Li et al., Adv. Funct. Mater., 26, 1322–1329 (2016)). Said material is deposited on the Si/SiO2 surface by a Langmuir-Shaefer/Blodgett hybrid approach with an ad hoc 3D printed sample holder. The graphene films are characterized via Raman, XPS, and SEM. Raman spectroscopy was the primary tool for the evaluation of the quality of graphene and its characteristics. The I(D)/I(G) and I(D)/I(D’) ratios confirm low-defectivity concentrated at the edges. The 2D peak shape and fit were instead used to indicate the number of graphene layers, estimated at 5-7. The same parameters were employed to analyze multi-layer graphene films, identifying the stacking of the material as electronically decoupled. The electrical properties are analyzed as a function of the coating iterations and UALPE duration to obtain conductivity data, showing the best results to be in the range of the 103 Sm.Electrochemical characterization of the deposits is evaluated by redox probing graphene in an appropriate electrolyte. A coordination complex couple like ferro/ferricyanide is used to evaluate the electrochemical performance of the graphene films as electrodes in standard cyclic voltammetry. The reversible nature of the [Fe(CN)6]3-/[Fe(CN)6]4- redox reaction allows the calculation of the Electrochemical Surface Area (ESA) by analyzing the voltammetric current1. (Y. Lei et al., J. Electroanal. Chem., 887, 115084 (2021)). The exfoliation parameters and iterations of self-assembly-driven electrode fabrication are related to the electrochemically active surface area (D. A. C. Brownson and C. E. Banks, The Handbook of Graphene Electrochemistry, p. 201, Springer London, London, (2014)). Electrochemical AFM (EC-AFM) is also utilized to assess the behavior of the carbonaceous deposits. EC-AMF in situ analysis is employed to investigate the evolution of the electrochemical phenomena on a micro/nanoscale and trace a correlation between the graphene synthesis variables and the response of the multi-layer graphene films.

Patterns of interfacial flow around a lubricated rolling point contact region

It is of great importance to develop an in-depth understanding of interfacial flow around a lubricated rolling point contact region (RPCR). Consideration of the flow patterns around an RPCR will be important for the lubrication, cooling, and cleaning of machine parts, such as rolling bearings and gearboxes. In this study, an experiment using laser-induced fluorescence and a simulation using computational fluid dynamics of interfacial flow around an oil-lubricated ball-on-disk RPCR are presented. The results show good agreement with each other, and the flow patterns are clearly classified. The forming mechanisms are analyzed in terms of force competition caused by inertia, viscosity, pressure gradient, and air–oil surface tension. Quantitative criteria are proposed to evaluate the behaviors at the air–oil interface and the transition of flow patterns. Analyses have shown that the competition between these forces drives the motion of the air–oil interface, and the formation of flow patterns can be considered a self-adjusting process for the air–oil interface toward the equilibrium positions of the forces. High surface tension is beneficial for maintaining interface stability and can prevent the meniscus from rupturing at an outlet and concaving at an inlet. High capillary numbers may increase the risk for outlet meniscus rupture and the degree of concavity of the inlet meniscus.

Ink Formulation and Optimum Surface Condition for a Printed Organic Light-Emitting Diode with High Boiling Point and Surface Tension Solvents

Ink formulation with the benzoate-type solvent mixture was designed to provide a mismatch in the surface tension, boiling point, and viscosity toward a stable jet printing on organic light-emitting diode (OLED) pixel pattern cell. Compared with a single component solvent ink, the mixtures showed smoother surface roughness and uniform line printed, while the dried film roughness was further improved by solvent-vapor annealing. Inkjet OLEDs on the 60 to 80 μm-scale pixels were fabricated, and the luminous quantum efficiency behavior of the printed OLEDs were characterized in terms of structural perfection of patterns and in-pixel coverage for different bank boundaries. With the optimum printing recipe and pattern-receptor surface condition, an external quantum efficiency of inkjet device was more than 82% of the value for spin-coating reference.

Differences in cortical contractile properties between healthy epithelial and cancerous mesenchymal breast cells

Cell contractility is mainly imagined as a force dipole-like interaction based on actin stress fibers that pull on cellular adhesion sites. Here, we present a different type of contractility based on isotropic contractions within the actomyosin cortex. Measuring mechanosensitive cortical contractility of suspended cells among various cell lines allowed us to exclude effects caused by stress fibers. We found that epithelial cells display a higher cortical tension than mesenchymal cells, directly contrasting to stress fiber-mediated contractility. These two types of contractility can even be used to distinguish epithelial from mesenchymal cells. These findings from a single cell level correlate to the rearrangement effects of actomyosin cortices within cells assembled in multicellular aggregates. Epithelial cells form a collective contractile actin cortex surrounding multicellular aggregates and further generate a high surface tension reminiscent of tissue boundaries. Hence, we suggest this intercellular structure as to be crucial for epithelial tissue integrity. In contrast, mesenchymal cells do not form collective actomyosin cortices reducing multicellular cohesion and enabling cell escape from the aggregates.

COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF TAYLOR BUBBLE RISE IN FLOWING LIQUIDS

Systematic analysis of the effect of gravitational, interfacial, viscous and inertia forces acting on a Taylor bubble rising in flowing liquids characterised by the dimensionless Froude (Uc), inverse viscosity (Nf ) and Eötvös numbers (Eo) is carried out using computational fluid dynamic finite element method. Particular attention is paid to cocurrent (i.e upward) liquid flow and the influence of the characterising dimensionless parameters on the bubble rise velocity and morphology analysed for Nf, Eo and Uc ranging between [40, 100], [20, 300] and [−0.20, 0.20], respectively. Analysis of the results of the numerical simulations showed that the existing theoretical model for the prediction of Taylor bubble rise velocity in upward flowing liquids could be modified to accurately predict the rise velocity in liquids with high viscous and surface tension effects. Furthermore, the mechanism governing the change in morphology of the bubble in flowing liquids was shown to be the interplay between the viscous stress and total curvature stress at the interface. Keywords: Taylor bubble, finite element, slug flow, CFD, rise velocity

Fabrication and durability characterization of superhydrophobic and lubricant-infused surfaces

HypothesisPractical applications of non-wetting surfaces require good mechanical durability in the wet environments for which they are intended to be used. Durability of non-wetting surfaces is influenced by the surface features, interaction with the functionalization agent, and the lubricant properties that can be tuned independently to identify optimal combination. ExperimentsIn this study, superhydrophobic and lubricant-infused surfaces are fabricated on copper tubes using chemical etching and electrodeposition texturing techniques, six different functionalizing agents, and five different infused lubricants. Through 180 fabrication combinations and 102 durability tests, each parameter is systematically studied for contributions to initial non-wetting behavior and its durability in heated, wet environment, under high-energy water jet impingement, and under accelerated flow conditions. FindingsAmong the adsorbing and curing functionalization agents investigated, n-Hexadecyl mercaptan that belongs to the sulfhydryl group and Sylgard-184, respectively, showed high durability in heated water immersion and under jet impingement tests. For lubricant-infused surfaces, lubricants with high surface tension demonstrated high durability in heated water immersion test, whereas durability in hydrodynamic conditions is closely correlated to lubricant viscosity. Results showed that a lubricant-infused surface will maintain its non-wetting properties in dropwise condensation conditions for approximately 1.5 years.

Design, analysis, and experimental performance of a novel micro-nozzle based liquid metal direct writing system

The use of liquid alloy micro-printing methods for stretchable conductors and sensors has become a hot topic of micromachining research because of its attractive properties. Due to the high surface tension and easy oxidation characteristics of liquid metal, it is difficult to be accurately processed. In this paper, a direct writing method based on micro-nozzles for Galinstan alloy is presented. In comparison with the existing liquid alloy printing methods, the size of metal drops is reduced to 83 by utilizing its wettability with the substrate and self-made micro-nozzles with the accuracy of micro order in a range from 13 to 87 inner diameter. This micro direct writing system was used to produce an array of alloy droplets, micro droplets and wires patterns, and a pile of alloy on account of the formation of the gallium-oxide layer which preserves their shapes. The diameter of droplets in an array is less than 83 and the line width is as small as 83 . This first demonstration of direct writing based on micro-nozzles provides a variety of liquid metal distribution strategies and improves the accuracy of alloy electronics. Also, attempts have been made to produce a vertical pile of droplets, by the shape protection of gallium-oxide skin. This method makes a good compromise between resolution, process simplicity, design flexibility, and fast delivery automaticity.

Falling film evaporation and pool boiling heat transfer of R1233zd(E) on thermal spray coated tube

• Falling film evaporation heat transfer of R1233zd(E) was experimentally investigated. • Up to 4.2-fold heat transfer enhancement could be obtained by thermal spray coating. • R1233zd(E) achieved a lower heat transfer coefficient than R134a at 20 °C. Falling film evaporators have been expected as an alternative to flooded evaporators for reducing the refrigerant usage. It is important for the enhancement of the film evaporation heat transfer to keep a liquid film and promote nucleate boiling in the liquid film. This study focused on nucleate boiling heat transfer in the liquid film by thermal spray coating that can be applied regardless of the material of heat transfer tubes. The heat transfer performance of falling film evaporation on a horizontal copper tube was experimentally evaluated. Since nucleate boiling phenomena, such as activation of nucleation sites and bubble behaviors in the liquid film, strongly depend on the physical properties of the refrigerant, the experimental results for R1233zd(E), one of the alternative refrigerants with low GWP, were compared with those for R134a. Two types of tubes were used: the smooth tube and the thermal spray coated tube fabricated by an arc wire spraying method, with the outer diameter of 19.05 mm and the heating length of 50 mm. Pool boiling experiments were also conducted to confirm the wall superheat for nucleate boiling. The heat transfer coefficients were evaluated with a film mass flow rate range of 8.5 × 10 −3 to 6.3 × 10 −2 kg/(m·s), a heat flux range of 10 to 85 kW/m 2 , and a saturation temperature at 20 °C. The effects of the structure of the heating surface, heat flux, and thermophysical properties of the refrigerant on the heat transfer performance are discussed. Results show that the heat transfer of the falling film became the nucleate boiling dominant with a sufficient heat flux and liquid film flow rate. The thermal spray coated surface enhanced not only the nucleate boiling but also the liquid spreading by the vapor bubbles in the liquid film, and thus the coated tube produced higher heat transfer coefficients of 2.1 to 4.8 times those for the smooth tube. The wall superheat at the onset of nucleate boiling was higher for R1233zd(E) than for R134a, because R1233zd(E) has a higher surface tension and lower vapor density. Thus, the pool boiling and falling film evaporation heat transfer coefficients were lower for R1233zd(E) than for R134a.

Antagonistic activity of lipopeptide-biosurfactant producing Bacillus subtilis AKP, against Colletotrichum capsici, the causal organism of anthracnose disease of chilli

Research for the development of biological control agents as an alternative to agrochemicals for controlling plant pathogens has gained considerable attention for the acquirement of agricultural sustainability. The present study reports a qualitative assessment of the potential of one promising antagonistic bacteria isolated from soil collected from Ultapani reserve forest, Assam, India, identified as Bacillus subtilis isolate AKP based on the morphological, biochemical, and molecular characteristic (NCBI GenBank Accession no. MW052029). The bacteria exhibited antagonistic activity against Chilli anthracnose fungus Colletotrichum capsici (61.5% growth inhibition in dual culture plate assay) which established the basis of further investigation. The strain AKP was found to exhibit biosurfactant producing ability with high emulsification index (83.1%) and surface tension reduction activity (83.8 to 21.9 ± 0.21). The crude extract from AKP strain also caused a significant reduction in disease incidence (anthracnose symptoms) by 16.66 ± 0.23% thus, providing good biocontrol efficiency against C. capsici based on in-vitro detached fruit assay. B. subtilis AKP showed the presence of surfactin (srfAA), iturin (ituC), and fengycin (fenD) antimicrobial biosynthetic genes in PCR assay. LC-MS analysis identified different homologues of surfactin, iturin, and fengycin lipopeptide biosurfactant from the methanolic fraction. Furthermore, the application of cell suspension-based B. subtilis also showed potentials for plant growth promotion both under in-vitro assays as well as in-vivo conditions in pot experiments. Our study revealed the potential of B. subtilis AKP in suppression of C. capsici as well as plant growth promotion which can be used on a commercial scale for the management of Anthracnose disease.

Degradative enzymes and biosurfactant mediated mechanism of diesel fuel and n-hexadecane biodegradation by Paenibacillus sp. D9

Hydrophobic pollutants remain a serious threat to animals, plants, humans, and the biological system at large if not reduced or removed from the environments. This study focused on the experimental degradation analysis of 2% each of diesel fuel and n-hexadecane utilized as a source of carbon and energy by Paenibacillus sp. D9. During the process, there was the removal of 98.4% and 61.2% n-hexadecane and diesel fuel, respectively, in the 14 days incubation period. There was involvement of degradative enzymes, namely alkane hydroxylase, alcohol dehydrogenase, and esterase as determined during the process of biodegradation. The activities of alkane hydroxylase (82 U), alcohol dehydrogenase (23 U), and esterase (0.220 U) were differentially produced, with enhanced biosurfactant activity, demonstrating their contribution to degradation of hydrocarbons. The outcomes were additionally reinforced as specific polymerase chain reaction primers were used to detect the presence of genes responsible for biodegradation and biosurfactant synthesis. The data revealed that the efficiency of the biosurfactant in accelerating the degradation and solubilization of these hydrocarbons was ensured with high hydrophobicity, emulsifying capacities, and surface tension reduction. Therefore, due to the production of enzymes, Paenibacillus sp. D9 strain was active than reported biosurfactant-producing bacteria in the biodegradation of hydrophobic pollutants.

Ultrastrong Spontaneous Surface Wetting of Room Temperature Liquid Metal on Treated Metal Surface

AbstractThe low melting gallium‐based liquid metal (LM) is showing tremendous potential in many technologies due to its unique properties. However, the high surface tensions as well as oxidations result in poor wetting capability on most solid surfaces, which limits its practical application. In this work, a simple chemical method is utilized to enable spontaneous wetting of LM on various metal surfaces, such as copper, nickel, and iron. It is found that LM can spread rapidly on the metal substrates treated with CuCl2 solution through reactive‐wetting and metallic bond‐enabled wetting mechanism. The redox reaction between Ga and copper compound and the formation of intermetallic compound via LM phagocytosis help drive LM to wet metal substrates spontaneously. Many factors affecting the wetting behaviors of LM, including surface roughness, crystal size, and ambient environment, are systematically studied. This finding provides a novel strategy to solve the wetting problem of LM and will enable wider applications.

Nanotip Formation from Liquid Metals for Soft Electronic Junctions.

Liquid metals and alloys with high-aspect-ratio nanodimensional features are highly sought-after for emerging electronic applications. However, high surface tension, water-like fluidity, and the existence of self-limiting oxides confer specific peculiarities to their characteristics. Here, we introduce a high accuracy nanometric three-dimensional pulling and stretching method to fabricate liquid-metal-based nanotips from room- or near-room-temperature gallium-based alloys. The pulling rate and step size were controlled with a resolution of up to 10 nm and yielded different nanotip morphologies and lengths as a function of the base liquid metal alloy composition and the pulling parameters. The obtained nanotips presented high aspect ratios over lengths of a few microns and apexes between 10 and 100 nm. The liquid metal alloys were found confined within nanotips with about 10 nm apexes when vertically pulled at 100 nm/s. An amorphous gallium oxide skin was shown to cover the surface of the nanotips, while the liquid core was composed of the initial liquid metal alloys. The electrical contact established at the nanotips was characterized under dynamic conditions. The liquid metal nanotips showed an Ohmic resistance when a continuous liquid metal channel was formed, and a controllable semiconductor state corresponding to a heterojunction formed at the junction between the liquid metal phase and the gallium oxide semiconductor skin. The variable threshold voltages of the heterojunction were controlled via stretching of the nanotips with a 10 nm step resolution. The liquid metal nanotips were also used for establishing soft electronic junctions. This novel method of liquid metal nanotip fabrication with Ohmic and semiconducting behaviors will lead to exciting avenues for developing electronic and sensing devices.

Preparation of ethanol and palm oil/palm kernel oil alternative biofuels based on property improvement and particle size analysis

With the continuous rise in fuel prices and the depletion of fossil fuel resources, the alternative biofuel which has good stability and is suitable for engine combustion is the focus of scientists' research. In this study, the method of mixing ethanol with palm oil (PO) and palm kernel oil (PKO) was used to improve the shortcomings of PO/PKO, such as high surface tension, high density and viscosity. Five co-solvents with a biological production background are selected: tetrahydrofuran (THF), polyoxymethylene dimethyl ether (PODE) and three butanol isomers to aid solubility. The results show that with the continuous dripping of the co-solvent, the PO/PKO and the ethanol gradually dissolve each other until the emergence of a single-phase liquid. Among the five co-solvents, the order of solubilization is THF > PODE > n-butanol > 2-butanol > iso-butanol. Also, with the increase in temperature, the solubility-assisting ability increases. When the particle size of the ternary blended fuel microemulsion system reaches the maximum value of 59.65 nm, the composition ratio of ethanol in the basic system is 50%. In addition, PKO has a stronger affinity with ethanol than PO; PKO can be completely miscible with ethanol when the experimental temperature is 35 °C. As the proportion of ethanol increases, the surface tension of the ternary system decreases by 36.2% at most. In terms of fuel property adjustment, THF has the best adjustment effect on solubility and viscosity. Butanol has the best adjustment effect on the density of blended fuel. PODE will corrode copper strips due to high oxygen content. In the future, according to the fuel demand in different scenarios, the proportion of each component in the blended fuel can be adjusted to achieve the optimum in practical applications.

Macroscopic Evidence of the Liquidlike Nature of Nanoscale Polydimethylsiloxane Brushes.

We report macroscopic evidence of the liquidlike nature of surface-tethered poly(dimethylsiloxane) (PDMS) brushes by studying their adhesion to ice. Whereas ice permanently detaches from solid surfaces when subjected to sufficient shear, commonly referred to as the material's ice adhesion strength, adhered ice instead slides over PDMS brushes indefinitely. When additionally methylated, we observe Couette-like flow of the PDMS brushes between the ice and silicon surface. PDMS brush ice adhesion displays a shear-rate-dependent shear stress, rheological behavior reminiscent of liquids, and is affected by ice velocity, temperature, and brush thickness, following scaling laws akin to liquid PDMS films. This liquidlike nature allows ice to detach solely by self-weight, yielding an ice adhesion strength of 0.3 kPa, 1000 times less than a low surface energy, perfluorinated monolayer. The methylated PDMS brushes also display omniphobicity, repelling essentially all liquids with vanishingly small contact angle hysteresis. Methylation results in significantly higher contact angles than previously reported, nonmethylated brushes, especially for polar liquids of both high and low surface tension.

Electrically Induced Wire‐Forming 3D Printing Technology of Gallium‐Based Low Melting Point Metals

AbstractLow‐melting point metals and alloys, as emerging 3D printing ink, have attracted more and more attention especially for flexible or intelligent conductors and electronics. However, achieving 3D continuity of liquid metal structures or patterns using a common method is still challenging and worth pursuing. In this study, a generalized method is proposed for 3D printing structures made of low melting gallium‐based alloys with diverse melting points, which should greatly expand their applications. The mechanism for shaping liquid metal inks relies on the combination actions between electrocapillarity and oxidation, which significantly reduces the high surface tension as well provides solid frame for the inner liquid metals. Taken galinstan as an example, the printing conditions, including the viscosity of hydrogel, positive voltage (0–15 V), calcium chloride concentration, and velocity (the movement speed of the printing head) are explored to optimize the process. The printed galinstan is characterized to observe the morphology and elemental analysis of the surface oxide layer. During the process, the chemical reagents are all safe and non‐toxic, which is in line with the green product requirements. This printing method shall have broad application prospect in flexible electronics, biosensors, biomedical engineering, contrast agent in vivo, and other fields.

Particle-Based Dynamic Water Drops with High Surface Tension in Real Time

Surface tension has a great influence on the shape of the fluid interface, and is an important physical characteristic in expressing not only liquids but also liquid metals such as mercury and gallium. In the field of physics-based particle fluid simulations, it is a challenging problem to express the high surface tension generated by fluid-air or fluid-solid interaction in real time. The main reasons for this are (1) The magnitude of the force that can be stably expressed in real-time fluid simulation is limited, so when the magnitude of the surface tension increases at a large time-step, the simulation stability decreases, and (2) If we use a small time-step, a stronger force can be expressed. However, it becomes difficult to operate in real time because the computational cost increases. Techniques were proposed to solve this problem for a few specific scenes, but there has not yet been a general approach that can reliably express high surface tension in various scenarios. In this paper, we propose a real-time particle-based fluid simulation framework that can efficiently and stably express high surface tension. Unlike the previous methods, we newly model the surface tension so that the strong surface tension force generated in the droplet area with a large curvature is applied evenly in the normal and tangent directions regardless of the size of the droplet. We also propose new pressure constraints that converge quickly and accurately using this force. Our method can be effectively used in various physics-based simulation scenarios because it can easily express and control surface tension effects that appear in materials such as liquid metal as well as water.

Heat capacity, density, surface tension, and contact angle for polyalphaolefins and ester lubricants

Thermophysical properties of lubricants are important to understand which ones are appropriated for the industrial conditions expected. Thermophysical properties of two different families of lubricants were analysed: polyalphaolefins (PAO6, PAO20, PAO32 and PAO40) and four ester-based lubricants. Specific heat capacity, density, surface tension, and contact angle were experimentally determined over a broad temperature range through methods such as μDSC, U-tube vibration, drop volume, and sessile drop method, respectively. A clear difference between the two families was observed due to their structure and composition, grouping by nature. Ester-based lubricants showed lower specific heat capacity but higher surface tension and density than polyalphaolefins. PAO6 clearly has the lowest density and surface tension and presents the highest specific heat capacity of all lubricants, and together with trimethylolpropane trioleate, TMPTO, presents the best wettability. Heat capacity values were used to test the validity of two predictive methods.

Facile preparation of super-oleophobic TiO2/SiO2 composite coatings by spraying method

Re-entrant geometries can effectively trap air pockets, increase air/liquid interface fraction, prevent the penetration of low surface tension organic liquids, and achieve super-oleophobic performance. However, the creation of re-entrant geometries usually involving expensive lithographic tools, or complicated chemical procedures, and cannot be applied on a large scale, such super-oleophobic surfaces are unsuitable for practical application. Constructing hierarchical micro/nanostructure on substrates is a feasible solution to achieve super-oleophobicity through facile spraying method. Herein, we report a super-oleophobic TiO2/SiO2 composite coatings by taking advantage of an exceedingly simple spraying method. The dendritic structures produced by spraying the TiO2/SiO2 mixture play the critical role in obtaining the re-entrant geometry required for oleophobic surface, and the introduction of micron-scale TiO2 particles and nano-scale SiO2 particles provide an enough dual-scale rough structure for the coating. The TiO2/SiO2 composite coatings exhibit superior repellence to high and low surface tension liquids as well long-term durability. This design strategy may provide useful guidelines for the fabrication of particle-based spray-coated super-oleophobic surfaces.

Performance of Two-Fluid Atomization of Gel Propellant

Two-fluid atomization of highly viscous and shear thinning non-Newtonian fluids must overcome the viscous resistance. Conventional air-blast atomizers address this requirement by operating at higher gas–liquid mass ratios (GLRs) at the cost of deteriorated efficiency. In this investigation, the atomization efficiency of a two-fluid atomizer is characterized. Fluidic design of the atomizer reduces the viscosity-induced dampening of disruptive inertia force and speeds up the breakup by providing kinetic energy of strategically positioned microjets of air. Three fluids of different viscosities and surface tensions were tested to examine the effects of properties on atomization efficiency. The presence of droplets and ligaments near the exit plane of the atomizer revealed that the atomizer enables prompt breakup of fluids without appreciable delay by viscosity. Consequently, it could break up complex non-Newtonian Jet A1 gel propellant with efficiency in the range of 0.015–0.1. Moreover, it is also capable of atomizing Newtonian fluids like water (high surface tension) with efficiency of 0.06–0.1 and Jet A1 (low surface tension) with efficiency of 0.02–0.08. Note that varied as ( to ) for the liquids tested in this work. The results of this investigation show that the deterioration in the performance of internally impinging atomizers at higher air and liquid throughputs is not determined by the viscosity of liquid but is predominantly due to the loss in kinetic energy of the excess air.

An Experimental Study of Graphene-Based Conductive Ink for Inkjet-Printable Electronics

The field of printable electronics and sensors has been experiencing increased interest and growth to meet the demands of low-cost, flexible, and lightweight devices. From this subset of devices, graphene-based printable electronics and sensors are of specific interest due to their transparency, flexibility, biocompatibility, and high conductivity. Among all modern ink printing technology, screen printing, spray coating, 3D printing, and inkjet printing are often utilized to fabricate flexible electronic applications from conductive ink. Compared with the other three, inkjet printing has received the most attention due to the simple printing process, high repeatability, economy, and time-savings compared to other printing techniques. However, inkjet printing often suffers from nozzle clogging due to aggregation of the particles in the conductive inks. In this research, a conductive graphene-based ink is developed to be used in a regular inkjet printer. Our goal is to fabricate this ink such that it is flexible, biocompatible, and easily manufacturable. This method seeks to create a low viscosity, high surface tension ink that addresses the clogging of the nozzle due to an aggregation of particles and is capable of being printed through a regular inkjet printer. By selectively choosing and modifying the composition and processes of ink formulation methodologies of past research, a graphene-based conductive ink that is compatible with inkjet printing is formulated. A flexible hydration sensor is printed out with this graphene-based conductive ink through which its conductivity and sensitivity are compared with the same sensor printed with commercially available graphene ink.