Range Of Surface Tensions Research Articles

Universality of Droplet Impingement: Low-to-High Viscosities and Surface Tensions

When a droplet impinges on a solid surface, its kinetic energy is mainly converted to capillary energy and viscous dissipation energy, the ratio of which depends on the wettability of the target surface and the liquid properties. Currently, there is no experimental or theoretical evidence that suggests which types of liquids exhibit the capillary energy-dominated impingement behavior. In this paper, we reported the droplet impingement behavior for a wide range of liquid viscosities, surface tensions and target surface wettabilities. Then, we showed that a recently developed energy balance equation for the droplet impingement behavior can be universally employed for predicting the maximum spreading contact area diameter of a droplet for Newtonian liquids in deposition process by modelling the droplet surface deformation. Subsequently, applicability limitations of recent existing models are discussed. The newly developed model demonstrated that the capillary energy-dominated impingement behavior can be observed at considerably low viscosities of liquid droplets such as that of the superfluid of liquid helium.

Mesoscopic model for soft flowing systems with tunable viscosity ratio

We propose a mesoscopic model of binary fluid mixtures with tunable viscosity ratio based on a two-range pseudo-potential lattice Boltzmann method, for the simulation of soft flowing systems. In addition to the short range repulsive interaction between species in the classical single-range model, a competing mechanism between the short-range attractive and mid-range repulsive interactions is imposed within each species. Besides extending the range of attainable surface tension as compared with the single-range model, the proposed scheme is also shown to achieve a positive disjoining pressure, independently of the viscosity ratio. The latter property is crucial for many microfluidic applications involving a collection of disperse droplets with a different viscosity from the continuum phase. As a preliminary application, the relative effective viscosity of a pressure-driven emulsion in a planar channel is computed.

Experimental study of aerosol release following liquid leaks of fission products concentrates simulants

Abstract This article presents an experimental study that encompasses a need for nuclear safety on the consequences of a leakage of fission products (FP) concentrates in a failed vessel during spent fuel reprocessing operations. Particulate airborne release fractions (ARFs), as the result of liquid FP simulants impacting a rigid surface, were assessed for two circular leakage geometries of 1 and 2 mm diameter. The detailed analysis of these ARFs which are between 2.7 × 10 −5 and 5.2 × 10 −5 for the different experimental configurations revealed their dependence on the surface tension and the viscosity of the solutions, as well as on the impacting jet diameter. The study also makes it possible to develop an empirical correlation that links the ARFs with the dimensionless Ohnesorge and Weber numbers in the considered surface tension and viscosity range.

Surface Dilatational Elasticity of Pulmonary Surfactant Solutions in a Wide Range of Surface Tensions

This work is devoted to the dynamic properties of adsorption films of pulmonary surfactant and a spread monolayer of dipalmitoylphosphatidylcholine, which is the main component of the mixed surfactant. The surface dilatational elasticity of the aforementioned systems has been determined using a recently proposed approach, which is based on the analysis of a response of a system to large deformations of a surface, and a modified Langmuir trough, which excludes solution leakage under barriers. At low surface tensions (below 30 mN/m) corresponding to those in pulmonary alveoles, the surface elasticity of a pulmonary surfactant adsorption film is half that of the spread dipalmitoylphosphatidylcholine monolayer. This may, in the former case, be related to the displacement of components with lower surface activity from the surface upon film compression.

Linear stability analysis of a liquid jet in a weak crossflow

In an effort to better understand the primary breakup mechanism of liquid jets in crossflow, a theoretical model for three-dimensional spatial linear stability of a viscous liquid jet injected in a weak gaseous crossflow is developed. The results are presented for the behavior of jet instabilities in the range of crossflow-to-jet momentum flux ratio of less than 0.01. In this range, the deformation of the liquid column allows a parallel base flow which is described by a modified viscous potential flow analysis. Focusing on the early stages of the jet evolution, a characteristic equation accounting for the growth of columnar waves is obtained and the most dominant wavelength and the corresponding growth rates are calculated. The predicted results for the asymptotic case of free jet flow are examined against the results available in the literature. Symmetric and asymmetric modes of liquid jet disturbance are investigated for a wide range of viscous, surface tension, and aerodynamic force ratios.

Modelling levitated 2-lobed droplets in rotation using Cassinian oval curves

A simple model of rotating 2-lobed droplets is proposed by setting the outline shape of the droplet to the Cassinian oval, a mathematical curve that closely resembles in shape. By deriving the governing equation of the proposed model and obtaining its stationary solutions, the relationship between the angular velocity of rotation and the maximum deformation length is explicitly and precisely calculated. The linear stability analysis is performed for the stationary solutions, and it is demonstrated that the stability of the solutions depends only on the ratio of the deformation length to the radius of the central cross-section of the droplet, which is independent of the physical properties of the droplet. Via comparison with an experimental study, it is observed that the calculated result is consistent with the deformation behaviour of actual 2-lobed droplets in the range where the stationary solution of the proposed model is linearly stable. Therefore, the proposed model is a suitable model for reproducing the steady deformation behaviour of 2-lobed droplets in a wide range of viscosities, surface tensions, densities and initial radii of the droplet, and especially if the viscosity of the droplet is low, the entire process of deformation of the 2-lobed droplet, including the unsteady breakup process, can be very well reproduced by the proposed model.

A novel method for the surface tension estimation of ionic liquids based on COSMO-RS theory

In the presented study, COSMO-RS sigma moments were utilized in a nonlinear multivariate QSPR model for the estimation of the temperature dependent surface tension of various ionic liquids in wide surface tension (15.5–65.1 mN m−1) and temperature (268–533 K) range. The developed model is supposed to be a generally applicable, robust and accurate method for the prediction of ionic liquid's surface tension. 880 data points ensure its reliability, which values were used to establish, validate and test the method. An artificial neural network was developed, optimized and used as regression model. The prediction power of the proposed model was validated with an external data set, with a squared correlation coefficient R2 = 0.97 and a mean absolute error MAE = 1 mN m−1. The estimation ability of the model was compared against widely known methods. Furthermore, the factor sensitivity analyses of the utilized molecular descriptors allowed shedding light on the intermolecular basis of ionic liquid's surface tension. Results showed that the kind of skewness of the sigma profile, the electrostatic interaction energy and the hydrogen bonding acceptor function play the most important roles in the formation of ionic liquid's surface tension.

Smooth, All-Solid, Low-Hysteresis, Omniphobic Surfaces with Enhanced Mechanical Durability.

The utility of omniphobic surfaces stems from their ability to repel a multitude of liquids, possessing a broad range of surface tensions and polarities, by causing them to bead up and either roll or slide off. These surfaces may be self-cleaning, corrosion-resistant, heat-transfer enhancing, stain-resistant or resistant to mineral- or biofouling. The majority of reported omniphobic surfaces use texture, lubricants, and/or grafted monolayers to engender these repellent properties. Unfortunately, these approaches often produce surfaces with deficiencies in long-term stability, durability, scalability, or applicability to a wide range of substrates. To overcome these limitations, we have fabricated an all-solid, substrate-independent, smooth, omniphobic coating composed of a fluorinated polyurethane and fluorodecyl polyhedral oligomeric silsesquioxane. Liquids of varying surface tension, including water, hexadecane, ethanol, and silicone oil, exhibit low-contact-angle hysteresis (<15°) on these surfaces, allowing liquid droplets to slide off, leaving no residue. Moreover, we demonstrate that these robust surfaces retained their repellent properties more effectively than textured or lubricated omniphobic surfaces after being subjected to mechanical abrasion.

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

An entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace’s law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results. Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.

Stable Liquid Jets Bouncing off Soft Gels.

A liquid jet can stably bounce off a sufficiently soft gel by following the contour of the dimple created upon impact. This new phenomenon is insensitive to the wetting properties of the gels and was observed for different liquids over a wide range of surface tensions, γ=24-72 mN/m. In contrast, other jet rebound phenomena are typically sensitive to γ: only a high γ jet rebounds off a hard solid (e.g. superhydrophobic surface) and only a low γ jet bounces off a liquid bath. This is because an air layer must be stabilized between the two interfaces. For a soft gel, no air layer is necessary and the jet rebound remains stable even when there is direct liquid-gel contact.

Lubricant-Infused Surfaces for Low-Surface-Tension Fluids: Promise versus Reality.

The past few decades have seen substantial effort for the design and manufacturing of hydrophobic structured surfaces for enhanced steam condensation in water-based applications. Such surfaces promote dropwise condensation and easy droplet removal. However, less priority has been given to applications utilizing low-surface-tension fluids as the condensate. Lubricant-infused surfaces (LISs) or slippery liquid-infused porous surfaces (SLIPSs) have recently been developed, where the atomically smooth, defect-free slippery surface leads to reduced pinning of water droplets and omniphobic characteristics. The remarkable results of LISs and SLIPSs with a range of working fluid droplets give hope of their viability with low-surface-tension condensates. However, the presence of the additional liquid in the form of lubricant brings other issues to consider. Here, in an effort to study the dropwise condensation potential of LISs and SLIPSs, we investigate the miscibility of a range of low-surface-tension fluids with widely used lubricants in LIS and SLIPS design. We consider a wide range of condensate surface tensions (12-73 mN/m) and different categories of lubricants with varied viscosities (5-2700 cSt), namely, fluorinated Krytox oils, hydrocarbon silicone oils, mineral oil, and ionic liquids. In addition, we use both theory and pendant drop experiments to predict the cloaking behavior of the lubricants and immiscible condensate working fluid pairs. Our work not only shows that careful attention must be paid to lubricant-condensate selection to create long-lasting LISs or SLIPSs but also develops lubricant selection design guidelines for stable LISs and SLIPSs for enhanced condensation in applications utilizing low-surface-tension working fluids.

Superamphiphobic Coatings from Combination of a Biomimetic Catechol‐Bearing Fluoropolymer and Halloysite Nanotubes

AbstractSuperamphiphobic coatings with remarkable water and oil repellency are prepared by the combination of a biomimetic catechol‐bearing fluoropolymer, poly{2‐(perfluorooctyl)ethyl acrylate‐co‐N‐(3,4‐dihydroxyphenethyl) acrylamide} (P(FAC8‐co‐DOPAm)), and naturally available halloysite nanotubes (HNTs). They are based on surface modification of HNTs with P(FAC8‐co‐DOPAm). A procedure to attain stable affinity between silica and the copolymer is established, and used for surface modification of HNTs. Superamphiphobic coatings are obtained by casting the suspension of P(FAC8‐co‐DOPAm)‐modified HNTs onto substrates. The superamphiphobic coatings exhibit Cassie–Baxter's wetting to liquids with a wide range of surface tension, because of the extremely low surface free energy and the unique micro‐/nanohierarchical surface topography, as well as the re‐entrant curvature of HNTs. These superamphiphobic coatings are environmentally and chemically durable, and can resist water scouring. The abundance of HNTs in nature and the easily controlled process of this method ensure an efficient approach for large‐scale production of superamphiphobic coatings for various applications.

Performances of Guerbet Alcohol Ethoxylates for Surfactant–Polymer Flooding Free of Alkali

Two series of double-chain single-head nonionic surfactants, Guerbet alcohol ethoxylates (CmGA–En; m = 16 and 20, n = 5.7–24.0), were synthesized, and their performances as surfactants for surfactant–polymer (SP) flooding free of alkali were evaluated. The products have relatively low critical micelle concentrations [(6.8 × 10–7)–(1.0 × 10–5 mol/L)] and a wide range of surface tensions at the critical micelle concentration (γcmc) values (30.3–38.0 mN/m) at 25 °C, depending on both the alkyl-chain length and the number of ethylene oxide (EO) units. When used alone, these nonionic surfactants are not efficient for reducing crude oil/connate water interfacial tension (IFT), but their binary mixtures with a highly hydrophobic zwitterionic surfactant, didodecylmethyl hydroxylpropyl sulfobetaine (diC12HSB), are very efficient in reducing Daqing crude oil/connate water IFTs. Ultralow IFTs can be achieved in a wide total concentration range (0.3–10 mM) at 45 °C, and the low limit (0.3 mM) can be further reduced t...

Vapor-Enabled Propulsion for Plasmonic Photothermal Motor at the Liquid/Air Interface.

This paper explores a new propulsion mechanism that is based on the ejection of hot vapor jet to propel the motor at the liquid/air interface. For conventional photothermal motors, which mostly are driven by Marangoni effect, it is challenging to propel those motors at the surfaces of liquids with low surface tension due to the reduced Marangoni effect. With this new vapor-enabled propulsion mechanism, the motors can move rapidly at the liquid/air interface of liquids with a broad range of surface tensions. A design that can accumulate the hot vapor is further demonstrated to enhance both the propulsion force as well as the applicable range of liquids for such motors. This new propulsion mechanism will help open up new opportunities for the photothermal motors with desired motion controls at a wide range of liquid/air interfaces where hot vapor can be generated.

Coalescence-Induced Self-Propulsion of Droplets on Superomniphobic Surfaces

We utilized superomniphobic surfaces to systematically investigate the different regimes of coalescence-induced self-propulsion of liquid droplets with a wide range of droplet radii, viscosities, and surface tensions. Our results indicate that the nondimensional jumping velocity Vj* is nearly constant (Vj* ≈ 0.2) in the inertial-capillary regime and decreases in the visco-capillary regime as the Ohnesorge number Oh increases, in agreement with prior work. Within the visco-capillary regime, decreasing the droplet radius R0 results in a more rapid decrease in the nondimensional jumping velocity Vj* compared to increasing the viscosity μ. This is because decreasing the droplet radius R0 increases the inertial-capillary velocity Vic in addition to increasing the Ohnesorge number Oh.

Autonomous Control of Fluids in a Wide Surface Tension Range in Microfluidics.

In this paper, we report the preparation of anisotropic wetting surfaces that could control various wetting behaviors of liquids in a wide surface tension range (from water to oil), which could be employed as a platform for controlling the flow of liquids in microfluidics (MFs). The anisotropic wetting surfaces are chemistry-asymmetric "Janus" silicon cylinder arrays, which are fabricated via selecting and regulating the functional groups on the surface of each cylinder unit. Liquids (in a wide surface tension range) wet in a unidirectional manner along the direction that was modified by the group with large surface energy. Through introducing the Janus structure into a T-shaped pattern and integrating it with an identical T-shaped poly(dimethylsiloxane) microchannel, the as-prepared chips can be utilized to perform as a surface tension admeasuring apparatus or a one-way valve for liquids in a wide surface tension range, even oil. Furthermore, because of the excellent ability in controlling the flowing behavior of liquids in a wide surface tension range in an open system or a microchannel, the anisotropic wetting surfaces are potential candidates to be applied both in open MFs and conventional MFs, which would broaden the application fields of MFs.

Estimating the Temperature-Dependent Surface Tension of Ionic Liquids Using a Neural Network-Based Group Contribution Method

A neural network-based group contribution method was developed in order to estimate the temperature-dependent surface tension of pure ionic liquids. A metaheuristic algorithm called gravitational search algorithm was employed in substitution of the traditional backpropagation learning algorithm to optimize the update weights of our neural network model. A total of 2307 experimental data points from 229 data sets of 162 different ionic liquid types, such as imidazolium, ammonium, phosphonium, pyridinium, pyrrolidinium, piperidinium, and sulfonium, were collected from the specialized literature. In this database, a wide temperature range from 263 to 533 K, and a wide surface tension range from 0.015 to 0.062 N·m–1, were covered. The input parameters contained the following properties: absolute temperature, the molecular weight of the ionic liquid, and 46 structural groups that composed the molecule. The accuracy of the proposed method was checked using the mean absolute percentage error (MAPE) and the corre...

Development of a group contribution method for estimating surface tension of ionic liquids over a wide range of temperatures

A group contribution method for estimating the surface tension of ionic liquids as a function of the absolute temperature, is presented. A total of 2286 experimental data points from 226 data sets of 154 ionic liquids were collected from the specialized literature. This database covers a temperature range of 263–533K and a surface tension range of 0.015–0.062N⋅m−1, for a heterogeneous set of ionic liquid-types such as imidazolium, ammonium, phosphonium, pyridinium, pyrrolidinium, and piperidinium. A correlation set containing the 75% of the overall database was used in order to calculate the contribution values of 10 structural cation groups and 30 structural anion groups. Then, a prediction set containing the other 25% of the overall database with data sets not used in the correlation phase was used in order to test the capabilities and accuracy of the proposed method. The results show that the proposed method can estimate the surface tension of several ionic liquids with a better accuracy than other methods available in the literature, with an average absolute relative deviation of 2.8% and a correlation coefficient of 0.98.

Influence of hydrophobicity distribution of particle mixtures on emulsion stabilization

Whilst emulsions stabilized by uniform particles are well established, the emulsification behavior of heterogeneous mixtures of particles with varying hydrophobicity is rarely examined. Consequently, the influence of the distribution of particle hydrophobicity on oil-water emulsion stabilization is poorly understood. In the present work, the wettability of the bitumen froth fine solids from Alberta oil sands was studied by film flotation and toluene-water emulsification tests, before and after a hydrothermal treatment at 300–420°C. This approach provided a series of populations of particles with different distributions of hydrophobicity. The initial fine particles in the bitumen froth had a critical surface tension ranging from 26 to 56mN/m, with a mean value of 39mN/m. Hydrothermal treatment at 300–420°C progressively shifted the hydrophobicity distribution of the fine particles, resulting in a lower mean critical surface tension and a narrower critical surface tension range. The emulsifying capacity of the fine particle mixtures, as indicated by the volume of the produced toluene-water emulsions, was unrelated to the mean critical surface tension. Instead, emulsification depended on the proportion of a specific sub-fraction of particles with a critical surface tension of 27–30mN/m. This sub-fraction of particles, with intermediate hydrophobicity, dominated the emulsification behavior of the particle mixtures.

Tear fluid-eye drops compatibility assessment using surface tension

Objective: To evaluate the compatibility of commercially available eye drop surface tension with the tear film physiological range and to characterize commonly used ophthalmic excipients in terms of their surface activity under eye-biorelevant conditions.Significance: There are a number of quality requirements for the eye drops (e.g. tonicity, pH, viscosity, refractive index) that needs to comply with the physiological parameters of the eye surface. However, the adjustment of surface tension properties of the eye drops to the normal range of surface tension at the air/tear fluid interface (40–46 mN/m) has received rather less attention thus far. Yet, the surface tension at the air/tear fluid interface is of vital importance for the normal function of the eye surface.Methods: The surface tension compatibility of the isotonic aqueous solutions of commonly used ophthalmic excipients as well as 18 approved eye drops with the tear fluid have been evaluated using surface tension method.Results: Each ophthalmic ingredient including the preservatives, solubilizing agents and thickening agents can influence the surface tension of the final formulation. In case of complex ophthalmic formulations one should also consider the possible interactions among excipients and consequent impact on overall surface activity. Out of 18 evaluated eye drops, three samples were within, 12 samples were below and three samples were above the physiological range of the tear fluid surface tension.Conclusions: Our results provide a rationale for clinical studies aiming to assess the correlation between the eye drops surface tension and the tear film (in)stability.