Variation Of Surface Tension Research Articles

Solutal Marangoni effect influencing bubble dynamics with varied electrolyte compositions

In the photoelectrochemical (PEC) water splitting system, the intricate interplay between bubble evolution and charge transfer at the electrode-electrolyte interface underscores the paramount importance of studying electrolyte properties. In this paper, the bubble dynamics and gas-liquid interface mass transfer on TiO2 nanorod and nanotube film electrodes are investigated by changing the cation types (K+, Na+, Li+) and concentrations (0.1 M-1.5 M) in alkaline electrolytes. The results indicate that the photocurrent and gas production follow the order of K+ > Na+ > Li+ under the same concentration, which is affected by the solvation of metal cations in aqueous solution and the adsorption on the photoanode surface. Compared with the nanotube electrode, the nanorod electrode enables the bubble to detach at a smaller size and faster rate. The trend of bubble detachment diameter variation with concentration in different cation electrolytes is the same, and follows the order of K+ > Na+ > Li+, which indicates that the force caused by Marangoni effect shows similar rules. The results reveal that the surface tension variation rate induced by ion concentration gradient varies significantly under different cation concentrations, while the variation rate driven by temperature gradient remains notably stable. This confirms that the bubble growth and detachment depend on the solutal Marangoni effect caused by the surface tension variation rate of different alkaline electrolytes with concentration. Therefore, the suitable choice of electrolyte composition is pivotal for regulating the bubble evolution at the electrode-electrolyte interface and improving the PEC system efficiency.

TwoPhaseInterTrackFoam: an OpenFOAM module for Arbitrary Lagrangian/Eulerian Interface Tracking with Surfactants and Subgrid-Scale Modeling

We provide an implementation of the unstructured Finite-Volume Arbitrary Lagrangian / Eulerian (ALE) Interface-Tracking method for simulating incompressible, immiscible two-phase flows as an OpenFOAM module. In addition to interface-tracking capabilities that include tracking of two fluid phases, an implementation of a Subgrid-Scale (SGS) modeling framework for increased accuracy when simulating sharp boundary layers is enclosed. The SGS modeling framework simplifies embedding subgrid-scale profiles into the unstructured Finite Volume discretization. Our design of the SGS model library significantly simplifies adding new SGS models and applying SGS modeling to Partial Differential Equations (PDEs) in OpenFOAM. Program summaryProgram Title: twoPhaseInterTrackFoamCPC Library link to program files:https://doi.org/10.17632/6b49wb7fvd.1Developer's repository link:https://gitlab.com/interface-tracking/twophaseintertrackfoamreleaseLicensing provisions: GPLv3Programming language: C++Nature of problem: Two-phase flow problems involving surface-active agents (surfactants), variable surface tension force and very sharp boundary layers.Solution method: An OpenFOAM implementation of the Arbitrary Lagrangian / Eulerian Interface Tracking method.

Marangoni-Induced Honeycomb Structures in Spin-Coated Polymer Nanocomposite Films.

This study investigates Marangoni effect-induced structural changes in spin-coated polymer nanocomposite (PNC) films composed of poly(methyl methacrylate)-grafted silica nanoparticles (NPs) and poly(styrene-ran-acrylonitrile). Films cast from methyl isobutyl ketone (MIBK) solvent exhibit distinct hexagonal honeycomb cells with thickness gradients driven by surface tension variations. Atomic force microscopy reveals protruded ridges and junctions at cell intersections, where NP concentration is the highest. Upon annealing at 155 °C, NPs segregate to the surface due to their lower surface energy, and the initially protruding features flatten and eventually form depressed channels while maintaining higher NP density than surrounding areas. Time-of-flight secondary ion mass spectrometry corroborated these findings, highlighting enhanced surface segregation of NPs in MIBK films. These defects can be eliminated using methyl isoamyl ketone (MIAK) as a solvent that produces homogeneous films of uniform thickness. This study highlights the impact of the Marangoni effect on the microstructure and surface properties of PNC films, providing insights for enhancing film quality and performance.

Breakage dynamics and scaling of wet aggregates of rigid particles

The mechanical behaviour of wet particle aggregates is crucial in many granular processes such as wet granulation and soil degradation. However, the interplay of capillary and viscous forces for aggregate stability and breakage have remained elusive due to the complexity of granular dynamics. We use particle dynamics simulations to analyse the deformation and breakage of wet aggregates colliding with a flat wall. The aggregates are composed of spherical particles and the effect of liquid bonds is modelled through capillary and lubrication forces acting between particles. We perform an extensive parametric study by varying surface tension, impact velocity and liquid viscosity in a broad range of values. We show that when lubrication force is neglected, aggregate breakage is fully controlled by the reduced kinetic energy $\xi$ , defined as the ratio of incident kinetic energy to the initial capillary energy. At low values of $\xi$ , the aggregate deforms without breakage due to inelastic energy loss induced by rearrangements and loss of capillary bonds, whereas above a critical value of $\xi$ it breaks into smaller aggregates due to the transfer of kinetic energy from aggregate to fragments. In the presence of lubrication forces, the crossover from capillary to viscous regime is controlled by the capillary number, defined as the ratio of viscous dissipation to capillary energy. We find that the critical value of $\xi$ for aggregate breakage in the viscous regime increases as a power law with capillary number while the effective restitution coefficient follows the same trend as in the capillary regime.

Investigation of surfactant-laden bubble migration dynamics in self-rewetting fluids using lattice Boltzmann method

Self-rewetting fluids (SRFs), such as aqueous solutions of long-chain alcohols, show anomalous nonlinear (quadratic) variations of surface tension with temperature involving a positive gradient in certain ranges, leading to different thermocapillary convection compared to normal fluids (NFs). They have recently been used for enhancing thermal transport, especially in microfluidics and microgravity applications. Moreover, surface-active materials or surfactants can significantly alter interfacial dynamics by their adsorption on fluid interfaces. The coupled effects of temperature- and surfactant-induced Marangoni stresses, which arise due to surface tension gradients, on migration bubbles in SRFs remain unexplored. We use a robust lattice Boltzmann method based on central moments to simulate the two-fluid motions, capture interfaces, and compute the transport of energy and surfactant concentration fields, and systematically study the surfactant-laden bubble dynamics in SRFs. When compared to motion of bubbles in NFs, in which they continuously migrate without a stationary behavior, our results show that they exhibit dramatically different characteristics in SRFs in many different ways. Not only is the bubble motion directed toward the minimum temperature location in SRFs, but, more importantly, the bubble attains an equilibrium position. In the absence of surfactants, such an equilibrium position arises at the minimum reference temperature occurring at the center of the domain. The addition of surfactants moves the equilibrium location further upstream, which is controlled by the magnitude of the Gibbs elasticity parameter that determines the magnitude of the surface tension variation with surfactant concentration. The parabolic dependence of surface tension in SRF is parameterized by a quadratic sensitivity coefficient, which modulates this behavior. The lower this quantity, the greater is the role of surfactants modifying the equilibrium position of the bubble in SRF. Furthermore, the streamwise gradient in the surfactant concentration field influences the transient characteristics in approaching the terminal state of the bubble. These findings provide new means to potentially manipulate the bubble dynamics, and especially to tune its equilibrium states, in microchannels and other applications by exploiting the interplay between surfactants and SRFs.

Variation of Surface Tension of Liquid Metal with Fluorides in Tungsten Inert Gas Welding

Real-time measuring and obtaining surface tension of liquid metal during the arc welding process is critical for studying the behavior of the weld pool, such as Marangoni flow and flow velocity. The dynamic variation of surface tension of weld pool during tungsten inert gas welding process with and without fluoride flux was measured by weld pool oscillation sensing system, and the effect of fluoride flux on surface tension and pool behavior was analyzed. The results show that the surface tension gradient of liquid metal can convert from a negative to a positive value in a critical arc time. The flow velocity of liquid metal and critical arc time significantly increased and decreased, respectively, with fluoride flux. The variation of surface tension, flow velocity, and critical arc time with fluoride flux was induced by arc temperature increasing.

Numerical study of two equal-sized miscible drops undergoing head-on collision

The numerical analysis focuses on investigating head-on collisions between two miscible drops composed of distinct fluids, specifically ethanol and water. The simulations are performed using a coupled level set and volume of fluid approach with different Weber numbers to study the effect of drop inertia. The code is validated against experimental and numerical results from earlier investigations. Additionally, a comparative study involving both water drops and ethanol–water drops is conducted to explore the impact of varying surface tension ratios on collision outcomes. Results show that when miscible drops collide, the merged liquid drop exhibits asymmetric behavior, such as an asymmetric combined drop shape in cases of permanent coalescence or an asymmetric end droplet breakup in cases of reflexive separation. The collision outcome undergoes significant variation as the Weber number changes. At lower Weber numbers, permanent coalescence is observed, while at medium Weber numbers, reflexive separation occurs without the formation of a secondary drop. For medium to large Weber numbers, reflexive separation with the generation of one secondary drop becomes prominent, and in the case of very large Weber numbers, multiple satellite drops form. The maximum vertical elongation of the merged drop and corresponding surface energy increase as the surface tension ratio rises, irrespective of the Weber number. However, for a fixed surface tension ratio, the maximum vertical elongation and associated surface energy vary with an increase in the Weber number. The findings also shed light on the enhanced internal mixing arising from the mismatched surface tension of the colliding drops as the Weber number increases. Furthermore, the study explores the effect of drop inertia on various aspects, including asymmetric collision behavior, energy budget, and mixing index.

Multi‐Level Wettability Patterned Porous Matrix for Advanced Optical Information Encryption

AbstractIn the rapidly evolving landscape of information security, the demand for optical encryption techniques based on wettability patterning, which allows decryption without sophisticated devices and complex procedures, is progressively increasing. However, conventional approaches based on binary wettability patterned surfaces impose significant constraints in their practical use for high‐level information security. Herein, a novel approach to optically encrypt information through multi‐level wettability patterning is introduced on a porous polymer matrix synthesized from vinyl methacrylate (VMA) and poly(ethylene glycol) diacrylate (PEGDA). By employing the thiol‐ene click reaction, precise patterning of functional groups is achieved that exhibit distinct wettability responses to aqueous solutions with varying surface tensions, as well as pH‐responsive and fluorescent markers. This multi‐level wettability system surpasses traditional binary hydrophilic/hydrophobic patterns by providing enhanced control over wettability states, resulting in higher‐level encryption of information. The integration of pH and fluorescence responsivity further elevates the complexity and security of the encrypted information, making it decipherable only under specific and controlled conditions. The innovative approach offers a highly secure, robust, and customizable encryption method, redefining the potential of optical encryption technologies.

Highly stable nanobubbles in the reduction of apparent viscosity of liquids during UF process

Nano-bubbles (NBs) have attracted more attention in various chemical processes due to their different physicochemical properties from macro-bubbles. However, little attention has been paid to the variations in physicochemical properties of the liquids caused by NBs. In this study, stable NBs in the range of 120–360 nm (mean diameters of 221 nm) are generated at an air pressure of 0.3 MPa. Meanwhile, the surface tension of H2O and sodium dodecyl sulfate (SDS) solution decrease with increasing amounts of NBs, indicating that NBs altered the physicochemical properties of liquids. Consistent with the variations in surface tension, the apparent viscosity of pure H2O and 400 mg L−1 sodium alginate (SA) solutions decreased by 5.6 % and 6.6 % after bubbling for 180 min, respectively, which can be attributed to the long retention time of NBs in the mixture of NB-liquids. The correlations between the apparent viscosity of the gas–liquid mixture (μ) and the gas holdups (V) are then deduced as μ=μ0(1-αV), where μ0 is the apparent viscosity of liquid in the absence of NBs and α is the correction factor. The CFD results further confirm that the apparent viscosity of the gas–liquid mixture decreases with increasing gas holdups. During the UF process, NBs significantly increase the normalized flux of NB-H2O from 1.00 to 1.35 and from 0.72 to 1.02 for NB-10 mg L−1 SA solution, which from the other side confirms that NBs decrease the apparent viscosity of the gas–liquid mixture, thus improving the normalized flux of filtrates. This study provides valuable clues for the significance of NBs in chemical processes.

Hydrodynamic instability of shear imposed falling film over a uniformly heated inclined undulated substrate

Linear and weakly nonlinear stability analyses of an externally shear-imposed, gravity-driven falling film over a uniformly heated wavy substrate are studied. The longwave asymptotic expansion technique is utilized to formulate a single nonlinear free surface deflection equation. The linear stability criteria for the onset of instability are derived using the normal mode form in the linearized portion of the surface deformation equation. Linear stability theory reveals that the flow-directed sturdy external shear grows the surface wave instability by increasing the net driving force. On the contrary, the upstream-directed imposed shear may reduce the surface mode instability by restricting the gravity-driving force, which has the consequence of weakening the bulk velocity of the liquid film. However, the surface mode can be stabilized/destabilized by increasing the temperature-dependent density/surface-tension variation. Furthermore, the bottom steepness shows dual behavior on the surface instability depending upon the wavy wall's portion (uphill/downhill). At the downhill portion, the surface wave becomes more unstable than at the bottom substrate's uphill portion. Moreover, the multi-scale method is incorporated to obtain the complex Ginzburg–Landau equation in order to study the weakly nonlinear stability, confirming the existence of various flow regions of the liquid film. At any bottom portion (uphill/downhill), the flow-directed external shear expands the supercritical stable zones, which causes an amplification in the nonlinear wave amplitude, and the backflow-directed shear plays a counterproductive role. On the other hand, the supercritical stable region decreases or increases as long as the linear variation of density or surface tension increases with respect to the temperature, whereas the sub-critical unstable region exhibits an inverse trend.

Growth of a vapour bubble in a viscous, superheated Nanofluid under Effect of Variations in Surface Tension

This study analyzes the growth of a vapour bubble in a superheated nanofluid with variable surface tension at the bubble interface. The governing equations describing the problem are formulated, converted to a single integrodifferential equation, and solved analytically. The results are implemented in one of the favorable nanofluids, namely, Al2O3/water, since it is widely used in nanofluid applications, which include self-cooling devices and as a coolant in newly designed photovoltaic/thermal systems, because it has higher thermal and electrical physical properties than the base fluid and a lower economical preparation cost. The results showed that the growth process is proportional to the thermal diffusivity and the Jakob number, while it is inversely proportional to surface tension, dynamic viscosity, initial bubble radius, coefficient of the initial pressure difference, initial void fraction, and nanoparticle volume fraction. Moreover, we conducted a comparison to the experimental data obtained by Hamda and Hamed (2016), and our results achieved a better agreement with these data than some famous studies for both experiments for superheated Al2O3/water nanofluid and pure water (base fluid), because our model considered the effects of several parameters that were ignored in the previous theories, which have been derived as special cases of our result. Furthermore, the effects of nanoparticle characteristics and slip mechanisms; base fluid type and temperature; and the addition of surfactants on bubble growth rates are investigated. Implications drawn from this study may have consequences for the optimum design of thermal systems/devices based on nanofluid technology.

Jumping behavior of water nanodroplets on a superhydrophobic surface in high Ohnesorge number (Oh) regime

The coalescence-induced jumping of nanodroplets on superhydrophobic surfaces has recently gained research attention due to its application in energy harvesting, self-cleaning, and cooling of nanoscale electronic devices. This study aims to investigate the jumping behavior of water nanodroplets in a high Ohnesorge number regime, where 0.45 < Oh < 1 and identify the critical size of droplets where jumping terminates. The study utilized molecular dynamics simulations to analyze the jumping characteristics of droplets ranging from 1.5 nm to 7 nm in radius. The findings of this research developed a universal jumping mechanism for droplets of all sizes, identified the lower limit of droplet size, below which coalescence-induced jumping does not occur, and explained a special phenomenon of jumping velocity becoming maximum before it approaches zero. The study also investigated how jumping terminates due to the size difference between droplets. These findings align well with prior micro-scale studies and experimental predictions. Surface energy, viscous dissipation, kinetic energy, and varying surface tension have been identified as the dominating factors influencing nanoscale droplet jumping at such a high Oh regime. The findings will provide insights for developing various applications at this scale.

Bubble rising in the presence of a surfactant at very low concentrations

This paper analyzes experimentally and numerically the steady bubble rising in water with a surfactant dissolved at very low concentrations. We explain how traces of surfactant can significantly change the bubble dynamics. The tiny surface tension variation produced by the surfactant monolayer has a negligible effect on the capillary pressure. However, this variation occurs within an extremely thin diffusive boundary layer, which produces a Marangoni stress three orders of magnitude larger than the tangential viscous stress in a surfactant-free bubble. Although the Marangoni stress is confined within the surface boundary layer, it manages to immobilize most of the bubble's south hemisphere. The increase in skin friction and the reduction of the terminal velocity cannot be attributed to the viscous stress exerted on the immobilized interface but to the stress in the diffusive surface boundary layer. The stagnant-cap approximation applies despite the small surfactant concentration considered.

Droplet motion driven by humidity gradients during evaporation and condensation

The motion of droplets on solid surfaces in response to an external gradient is a fundamental problem with a broad range of applications, including water harvesting, heat exchange, mixing and printing. Here we study the motion of droplets driven by a humidity gradient, i.e. a variation in concentration of their own vapour in the surrounding gas phase. Using lattice-Boltzmann simulations of a diffuse-interface hydrodynamic model to account for the liquid and gas phases, we demonstrate that the droplet migrates towards the region of higher vapour concentration. This effect holds in situations where the ambient gradient drives either the evaporation or the condensation of the droplet, or both simultaneously. We identify two main mechanisms responsible for the observed motion: a difference in surface wettability, which we measure in terms of the Young stress, and a variation in surface tension, which drives a Marangoni flow. Our results are relevant in advancing our knowledge of the interplay between gas and liquid phases out of thermodynamic equilibrium, as well as for applications involving the control of droplet motion.Graphic abstract

DNS of Marangoni effects on a suspension of droplets in microgravity using the unstructured conservative level-set method

The multi-marker unstructured conservative level-set (UCLS) method for two-phase flow with variable surface tension is used for the Direct Numerical Simulation of thermocapillary-driven motion of a bi-dispersed suspension of droplets in microgravity. The so-called Marangoni stresses induced by surface tension gradients on the interface lead to a coupling of the momentum transport equation and the thermal energy transport equation. The finite-volume method discretizes the transport equations on three-dimensional collocated unstructured meshes. The UCLS method performs interface capturing with mass conservation of the fluid phases, whereas the multiple marker approach circumvents the numerical coalescence of fluid particles. The fractional-step projection method solves the pressure-velocity coupling. Unstructured flux-limiters schemes discretize the convective term in transport equations. Numerical and physical findings are reported.

Possible physical mechanisms of the high echogenicity of lipid coated nanobubbles

Lipid coated nanobubbles (NBs) have attracted a great level of interest as ultrasound (US) contrast agents due to their ability to extravagate through leaky tumor vasculature. Their linear resonance frequency is in the range of ∼50 M Hz–200 MHz, leading to confusion over their observed strong contrast in diagnostic US frequencies. By solving the Marmottant model, the dynamics of uncoated and lipid coated NBs and microbubbles (MBs) are studied over the frequency and pressure ranges (6–12 MHz, 0.1–1.2 MPa) generally used in diagnostic US. A novel bifurcation analysis in tandem with the analysis of the frequency component of the scattered pressure are conducted. Results show that despite the increased linear resonance frequency and viscous damping due to the lipid shell, buckling and rupture of the shell enhances the generation of the 2nd and 3rd harmonic resonances at pressures as low as 0.2 MPa, not observed with uncoated NBs. The generation of the harmonic resonances are concomitant with an abrupt increase in the 2nd and 3rd harmonic frequency component of the scattered pressure with their pressure threshold (PT) increasing with decreasing NBs size. For the same gas volume, and above the PT, the maximum non-destructive 2nd and 3rd harmonic powers of NBs can become higher than the 2–4 μm MBs. Similar to the lower subharmonic pressure threshold of MBs, the dynamic variation of the NBs effective surface tension due to buckling and rupture may be the potential reason behind the observed harmonic echogenicity.

Numerical analysis of thermophoretic particle deposition in a magneto-Marangoni convective dusty tangent hyperbolic nanofluid flow – Thermal and magnetic features

Abstract In the current study, we focus on the Magneto-Marangoni convective flow of dusty tangent hyperbolic nanofluid (TiO2 – kerosene oil) over a sheet in the presence of thermophoresis particles deposition and gyrotactic microorganisms. Along with activation energy, heat source, variable viscosity, and thermal conductivity, the Dufour-Soret effects are taken into consideration. Variable surface tension gradients are used to identify Marangoni convection. Melting of drying wafers, coating flow technology, wielding, crystals, soap film stabilization, and microfluidics all depend on Marangoni driven flow. This study’s major objective is to ascertain the thermal mobility of nanoparticles in a fluid with a kerosene oil base. To improve mass transfer phenomena, we inserted microorganisms into the base fluid. By using similarity transformations, the resulting system of nonlinear partial differential equations is converted into nonlinear ordinary differential equations. Using a shooting technique based on RKF-45th order, the numerical answers are obtained. For various values of the physical parameters, the local density of motile microorganisms, Nusselt number, skin friction, and Sherwood number are calculated. The findings demonstrated that as the Marangoni convection parameter is raised, the velocity profiles of the dust and fluid phases increase, but the microorganisms, concentration, and temperature profiles degrade in both phases.

OFFSET COALESCENCE BEHAVIOR OF IMPACTING LOW-SURFACE TENSION DROPLET ON HIGH-SURFACE-TENSION DROPLET

The impact of droplets of varying surface tension and subsequent spreading over a solid surface are inherent features in printing applications. In this regard, an experimental study of the impact of two drops of varied surface tension is carried out where the sessile water droplet on a hydrophilic substrate is impacted upon by another droplet of sequentially lowered surface tension. The impacts are studied for different impact velocities and offsets with respect to the mid-plane of the two colliding droplets. Sodium dodecyl sulfate is used to: (i) alter the surface tension without altering the viscosity, (ii) study the various parameters affecting the spreading length viz. the surface tension, (iii) offset between the drops, and (iv) impact velocity. The spreading lengths are obtained through image processing of the captured footage of the impact dynamics by a high-speed camera. It is found out that upon lowering the surface tension, the maximum and equilibrium spreading length varies to a significant extent, and the nature of the spreading dynamics changes. Both side- and top-view imaging are performed to understand the overall hydrodynamics. There is also a substantial change in "drawback" when dissimilarity in surface tension between the impacting droplets exists. Finally, a fit model is obtained to predict the maximum spread length of the various cases.

Hydrodynamics and Heat Transfer of Cavitation Bubble in Nanoparticles/Water Nanofluids Based on the Effects of Variable Surface Tension and Viscous Forces

This paper aims to investigate the unsteady oscillatory flow of water-based nanofluids MoS2 and SiO2 past a parallel plate channel filled with a saturated porous medium. The basic equations are solved analytically using the perturbation technique subject to the appropriate boundary conditions. A numerical evaluation of the analytical results is performed, and the effects of various physical parameters on velocity, temperature, and concentration profiles within the boundary layer are analyzed. Molybdenum disulfide MoS2 nanoparticles are well known for their low friction coefficient, good catalytic activity, and excellent physical properties. At the same time, Silicon dioxide (SiO2) nanoparticles are treated to have a porous structure, very high surface activity, and adsorption properties, which makes them suitable for developing high-capacity antimicrobial agents. Hence these nanoparticles can be considered for Nanoscale elements’ performance to make rigorous thermal quality nano liquids. Thus from engineering curiosity, the skin friction coefficient, Nusselt number, and Sherwood numbers are evaluated for significant parameters at cold and heated walls by utilizing MoS2 and SiO2 nanoparticles. It would give rise to novel features that can revolutionize biology, medicine, catalysis, and other smart fields. Furthermore, graphs and tables are used to describe a comparative study of the water-based nanofluids MoS2 and SiO2. It is found that when the radiation parameter Ra is increased by 200%, the average heat transfer rate at the heated channel wall containing MoS2 and SiO2 nanoparticles in the base fluid is decreased by 6.9% and 8.3%, respectively. Further, it is found that SiO2-water nanofluid has more effectiveness towards heat transfer compared to MoS2-water nanofluid.

Performance Improvement of an STS304-Based Dispensing Needle via Electrochemical Etching.

In this study, we explored the formation of micro-/nanosized porous structures on the surface of a needle composed of STS304 and examined the effect of conventional needles and needles capable of liquid ejection. Aqua regia, composed of HCl and HNO3, was electrochemically etched to form appropriately sized micro-/nanoporous structures. We observed that when dispensing liquids with low surface tension, they do not immediately fall downward but instead spread over the exterior surface of the needle before falling. We found that the extent of spreading on the surface is influenced by an etched porous structure. Furthermore, to analyze the effect of surface tension differences, we dispensed liquids with varying surface tensions using etched needles. Through the analysis, it was confirmed that, despite the low surface tension, the ejected droplet volume and speed could be stably maintained on the etched needle. This indicates that the spreading phenomenon of the liquid on the needle surface just before ejection can be controlled by the micro/nanoporous structure. We anticipate that these characteristics of etched needles could be utilized in industries where precision dispensing of low-surface-tension liquids is essential.