Dependence Of Surface Tension Research Articles

Surface temperature measurement of cooling and heating droplets by rainbow refractometry.

Rainbow refractometry was used to measure the temperature and size of transparent spherical particles. In practice, however, there are limitations to the application of heating and cooling droplets, as the temperature measured is neither the average nor the surface or core temperature of the droplet. Reported here is an exploitation of this technique for droplet surface temperature determination. Droplet surface tension was measured by detecting the evolution of interference fringes of oscillating droplets. The dependence of surface tension on temperature facilitated the study of surface temperature of an evaporating droplet with time. Moving ethanol, n-heptane, and n-decane droplets were investigated under heating and cooling conditions. The capabilities and limitations of rainbow refractometry were verified by comparing the droplet temperature values measured directly by rainbow refractometry with the surface temperature.

The role of plate geometry and boundary type in global plate ductility and mantle convection

This paper tracks the role of plates in plate tectonics and mantle convection. Geometric and morphologic plate analyses are based on paleoreconstructions, beginning at 200 Ma, large-scale volcanic events, APWPs, and geoid data. Plates organize themselves to form a space-fitting geometry with a minimum perimeter/area (P/A) ratio (i.e., SA/V in three-dimensions) and a coordination number close to 5. Plates are either broken and subducted in order to remove plates with high P/A ratios or combined with other plates to reduce the total perimeter in the lithospheric plate mosaic. Various permutations of breaking and/or combining of high P/A plates are applied throughout earth's history to reduce the global P/A ratio. During this process, plates change their shape and/or size, which aids plate mobility to ultimately reach a stable geometry. Plates can only move with a suitable geometry and the global pattern keeps adjusting to reach a stable geometry. The lithospheric plates follow a pattern of ‘punctuated steady state’, where the global geometry cycles between ‘ductile’ periods, when the plates are moving to reach a new steady state geometry, to more static, or stable, periods, when the plates are relatively immobile and connected by a stable network of compressional stresses. Here, the Bénard-Marangoni theory is used to explain plate patterns in terms of surface tension because it allows for convection to be driven by temperature dependent surface tension. Mantle flow drives the temperature gradient at the surface, which results in a surface tension gradient. So, temperature dependent buoyancy and surface tension both play a role in convection. This suggests that there is feedback between the plates and the mantle, so neither is entirely passive.

Density, surface tension, and viscosity of Co-Cr-Mo melts measured using electrostatic levitation technique

Co-Cr-Mo (CCM) alloys, which are used in biomedical implants, are currently produced by additive manufacturing, for which accurate modeling of the process is required to attain the desired thermophysical properties of the melts. For the purpose of modeling, the density, surface tension, and viscosity of two CCM melts of distinct carbon content (0.05 and 0.25% by mass) were measured using an electrostatic levitation technique. The temperature dependence of both density and surface tension of the melts were assumed to be linear, whereas that for viscosity was assumed to have Arrhenius form, from which the activation energy corresponding to the viscous flow of each CCM melt was obtained. Using the Szyzkowski model along with our present and previous results, the influence of the partial pressure of oxygen on the surface tension of the two CCM melts was evaluated. No substantial difference in surface tension and viscosity between these melts was found.

Interfacial Properties of Deep Eutectic Solvents by Density Gradient Theory

Deep eutectic solvents (DES) are room-temperature liquid mixtures constituted of a hydrogen-bonding acceptor (HBA) and a hydrogen-bonding donor (HBD). They have high practical potential due to their versatility, quick preparation, and wide applications. Therefore, it is appropriate to have robust models to predict their properties. In this work, the density gradient theory has been combined with the perturbed-chain statistical associating fluid theory to model and understand the interfacial behavior in systems of deep eutectic solvents. DESs were modeled as mixtures of their constituents, and a methodology is proposed for estimating the chemical potential of DESs to extend their study to the interfacial properties. Available experimental data of hydrophilic and hydrophobic DESs were used to calculate the influence parameters, providing a way to linearize them in terms of the molecular parameters of HBDs and their molar ratio between HBD and HBA. This treatment has made it feasible to predict the thermal dependence of surface tension in most of the DESs analyzed with an average absolute relative deviation of 1.26%. Furthermore, density gradient theory and perturbed-chain statistical associating fluid theory were applied to predict the vapor–liquid surface tension in mixtures of organic compounds with DES. In particular, we have calculated the surface tension in mixtures of ChCl-glycerol and ChCl-lactic acid with water, ethanol, propanol, phenol, acetone, and ethyl acetate without fitting binary interaction parameters. The behavior of density profiles suggests that the surface is enriched with DES components for the DES + water mixtures. In contrast, it is enriched with diluent for the other ternary systems (ethanol, isopropanol, phenol, acetone, and ethyl acetate).

Temperature and composition dependent surface tension of binary liquid alloys

Surface tension is a fundamental parameter of binary liquid alloys (BLAs) for controlling the casting and welding processes. In this study, starting from the broken-bond rules, a theoretical model for the temperature-dependent surface tension (TDST) of BLAs was developed. Then combined with the classical ideal solution model, a surface tension model of BLAs related to temperature and composition was established. The model predictions are in good agreement with the available experimental data, which shows the rationality of our model. This research offers a simple method for the prediction of surface tension of BLAs with different component concentrations in a wide temperature range only by inputting the surface tension of pure components at a reference temperature and some basic thermodynamic data.

Mesoscale perspective on the Tolman length.

We demonstrate that the multiphase Shan-Chen lattice Boltzmann method (LBM) yields a curvature dependent surface tension σ as computed from three-dimensional hydrostatic droplets and bubbles simulations. Such curvature dependence is routinely characterized, at first order, by the so-called Tolman length δ. LBM allows one to precisely compute σ at the surface of tension R_{s} and determine the Tolman length from the coefficient of the first order correction. The corresponding values of δ display universality for different equations of state, following a power-law scaling near the critical temperature. The Tolman length has been studied so far mainly via computationally demanding Molecular Dynamics simulations or by means of Density Functional Theory approaches playing a pivotal role in extending Classical Nucleation Theory. The present results open a hydrodynamic-compliant mesoscale arena, in which the fundamental role of the Tolman length, alongside real-world applications to cavitation phenomena, can be effectively tackled. All the results can be independently reproduced through the "idea.deploy" framework.

О методических особенностях и ошибках измерения поверхностного натяжения водных суспензий

The paper analyzes the methodological features of measuring the surface tension of highly dispersed systems, which include bentonite suspensions. It is shown that bentonite suspensions arc complex nonequilibrium systems, when measuring the surface tension of which it is necessary to take into account the influence on its value of many factors, the main ones being dispersion and sedimentation. These factors have a significant effect on the measured value of surface tension. The non-equilibrium of the system under study leads to a time dependence of the surface tension, which significantly complicates the measurement of its dependence on temperature. To measure the surface tension of a bentonite suspension, a new method based on the superposition of measurement results obtained by two independent methods, the hanging drop method and the lying drop method, has been developed and tested. Sedimentation, when using these methods, leads to oppositely directed (relative to the surface) processes: in the first case, the surface of the drop enriches the particles of the solid phase, in the second -is impoverished. Experimental studies of the time dependences of surface tension have shown that in the hanging drop method there is a linear decrease in surface tension, in the lying drop method the surface tension increases linearly with time. Superposition of the results obtained by these methods allows us to find the value of surface tension at a given time. An analysis of surface tension measurement errors of the influence of various factors on the error in measuring surface tension of the developed method is carried out.

Onset of surface driven convection in selfrewetting fluid layer overlying a porous medium

The onset of thermocapillary convective motion in a self-rewetting fluid layer overlying a porous medium with thermally dependent surface tension is studied analytically. Surface tension is assumed to be a quadratic function of temperature. The top surface of a fluid layer is deformably free and the bottom is rigid. We considered boundaries to be insulating to temperature perturbations. The governing equation that satisfies the composite system is analyzed by the normal mode approach and solved by the regular perturbation technique for linear stability. A mathematical expression is derived for the critical Marangoni number by solving coupled equations. The influence of crispation number, thermal diffusivity ratio, and other physical parameters involved therein are analyzed for the convective stability of the bilayer system. It has been found that the start of convection is delayed when the crispation number goes down and the thermal diffusivity ratio goes up. Also, the impact of the ratio of the thickness of the fluid to the thickness of the porous matrix and the other physical parameters on controlling the convective motion of the configuration is examined in detail.

In English

The interfacial properties (dynamic and equilibrium surface tension, viscosity and elasticity moduli) of chitosan lactate have been studied at the liquid/air interface by the oscillating drop shape method. Isotherms of dynamic surface tension of chitosan lactate are similar to dependences for other polyelectrolyte solutions, in particular for proteins. Chitosan is a weak cationic polyelectrolyte which can change its conformation from a linear rod to a chaotic and compacted coil. Therefore, the experimental dependence of the equilibrium surface tension on concentration of chitosan lactate was analyzed with the adsorption model proposed earlier for proteins. This model accounts the possibility of polyelectrolyte molecules existence in surface layer in n states with different molar surface varying from the maximum value at very low surface coverage by polyelectrolyte molecules to a minimum value at high surface coverage. Good agreement between the calculated and experimental values of surface tension was observed. The dependences of the elasticity and viscosity moduli of chitosan lactate solutions on the drop oscillations frequency are conditioned by the influence of exchange processes both between the surface layer and the bulk solution and in the surface layer itself. An increase of the solution concentration intensifies the exchange processes, and an increase of the oscillation frequency suppresses them. It is shown that the dependence of the surface viscoelasticity modulus of chitosan lactate is extreme in nature with a pronounced maximum. The reason for such behavior is the possibility of changing the molar surface area of the polyelectrolyte at the interface dependent on the amount of adsorption and its structural properties. Attempt of theoretical description of the viscoelasticity modulus within the framework of model accounting mono- or bilayer adsorption did not lead to a satisfactory result, possibly due to barrier adsorption mechanism of chitosan. But bilayer model provide qualitative description of extreme behavior of surface viscoelasticity on concentration. The values of the surface viscoelasticity modulus of chitosan lactate occupy an intermediate position in comparison with the data available in the literature for globular and flexible-chain proteins, that is consistent with their molecular structure. In addition, the work shows the applicability of the adsorption model, developed earlier for proteins in the framework of a nonideal two-dimensional solution theory, for describing the surface properties of other polyelectrolytes. This makes it possible to obtain qualitative and quantitative information about the processes occurring in the systems under study.

Dependence of surface tension of fruit puree on temperature exposure

When developing food products with new properties using innovative technologies, it is important to obtain data on the physicochemical, thermal-physical and structural-mechanical properties of the processed food media. So, one of the key components in the selection of the mode of collapsing ultrasonic cavitation is the surface tension of vegetable purees. The paper presents research data (2020) on the effect of temperature on the surface tension coefficient of fruit puree of different viscosity. The objects of research are cherry plum, pear and apple puree, combined in a row by viscosity. The surface tension coefficient was determined by the stalagmometric method, for which the puree was preliminarily centrifuged. The measurements were carried out at temperatures of 25 and 35 °С. It was found that, under equal conditions of centrifugation of puree, the proportion of supernatant in pear puree is noticeably higher – 77.37 % to the weight of puree in comparison with cherry plum puree (67.20 %) and apple puree (52.75 %). This fact can be explained by the presence of stony cells in the former which form an incompressible sediment, which allows a greater separation of the dispersed phase (sediment) and the dispersion medium (supernatant). It was found that the coefficient of surface tension of fruit purees, despite the slight difference, decreases with increasing temperature. Analysis of the steepness of the slope of the curve characterizing the effect of temperature on the surface tension coefficient showed that temperature stabilization during technological processing is more required for pear puree.

Numerical simulation of the surfactants effect on the Taylor bubble in the PHP

Numerical simulation of the motion of a Taylor gas bubble in a heated small-diameter tube is carried out. Two models are used to describe the dependence of surface tension on temperature. In the first model, the surface tension decreases with temperature, and in the second, it increases, which corresponds to pure water and an aqueous surfactant solution. It is shown that the derivative sign affects the thickness of the liquid film around the bubble.

Impact of surface viscosity on the stability of a droplet translating through a stagnant fluid

This study examines the impact of interfacial viscosity on the stability of an initially deformed droplet translating through an unbounded quiescent fluid. The boundary-integral formulation is employed to investigate the time evolution of a droplet in the Stokes flow limit. The droplet interface is modelled using the Boussinesq–Scriven constitutive relationship having surface shear viscosity $\eta _\mu$ and surface dilatational viscosity $\eta _\kappa$ . We observe that, below a critical value of the capillary number, $Ca_C$ , the initially perturbed droplet reverts to its spherical shape. Above $Ca_C$ , the translating droplet deforms continuously, growing a tail at the rear end for initial prolate perturbations and a cavity for initial oblate perturbations. We find that surface shear viscosity inhibits the tail/cavity growth at the droplet's rear end and increases the $Ca_C$ compared with a clean droplet. In contrast, surface dilatational viscosity increases tail/cavity growth and lowers $Ca_C$ compared with a clean droplet. Surprisingly, both shear and dilatational surface viscosity appear to delay the time at which pinch off occurs, and hence satellite droplets form. Lastly, we explore the combined influence of surface viscosity and surfactant transport on droplet stability by assuming a linear dependence of surface tension on surfactant concentration and exponential dependence of interfacial viscosities on the surface pressure. We find that pressure-thinning/thickening effects significantly affect the droplet dynamics for surface shear viscosity but play a small role for surface dilatational viscosity. We lastly provide phase diagrams for the critical capillary number for different values of the droplet's viscosity ratio and initial Taylor deformation parameter.

Influence of oxygen adsorption from atmosphere on surface tension of liquid silicon

Influences of temperature and oxygen adsorption on the surface tension of liquid silicon were investigated by the oscillating droplet method using the electromagnetic levitation technique. Oxygen partial pressure in the vicinity of the liquid surface was controlled by the theoretically derived Ratto, Ricci, and Arato model and the effectiveness of which was experimentally confirmed from the in situ observation of oxidation and reduction behaviors of the droplet surface in this study. The surface tension of liquid silicon was decreased with increasing oxygen partial pressure in the vicinity of the liquid surface due to oxygen adsorption at low temperature, whereas the surface tension converged to a pure state value at high temperature regardless of the oxygen partial pressure due to a decrease in the equilibrium constant of oxygen adsorption reaction. As a result, “boomerang shape” temperature dependence of surface tension was observed; the gradient of the temperature dependence of surface tension was gradually increased with elevating temperature and then became a constant value at high temperature. The influences of oxygen adsorption and temperature on surface tension were successfully derived from the measurement result by using the Szyszkowski equation. Furthermore, the changes in enthalpy and entropy for oxygen adsorption on liquid silicon were also estimated.

Fluctuations in the nuclear pasta phase

Baryonic matter close to the saturation density is very likely to present complex inhomogeneous structures collectively known under the name of pasta phase. At finite temperature, the different geometric structures are expected to coexist, with potential consequences on the neutron star crust conductivity and neutrino transport in supernova matter. In the framework of a statistical multi-component approach, we calculate the composition of matter in the pasta phase considering density, proton fraction, and geometry fluctuations. Using a realistic energy functional from relativistic mean field theory and a temperature and isospin dependent surface tension fitted from Thomas-Fermi calculations, we show that different geometries can coexist in a large fraction of the pasta phase, down to temperatures of the order of the crystallization temperature of the neutron star crust. Quantitative estimates of the charge fluctuations are given.

Surface tension of binary and ternary polymer solutions: Experimental data of poly(vinyl acetate), poly(vinyl alcohol) and polyethylene glycol solutions and mixing rule evaluation over the entire concentration range

In order to assess the driving forces of Marangoni instabilities in drying polymer solution films, surface tension data over a wide concentration are necessary. While experimental data and mixing rule equations for the surface tension of liquid-liquid mixtures are readily available, data for polymer solutions are scarce. The aim of this work is to report surface tension data of methanol-toluene-poly(vinyl acetate), methanol-water-polyethylene glycol and water-poly(vinyl alcohol) solutions as well as to evaluate the applicability of available liquid-liquid mixing rule equations on polymer solutions despite an inevitable data gap at low solvent concentrations due to viscosity increase and solidification. The fit quality was assessed by calculating the averaged deviation as well as by manually checking for implausible curve shapes in the respective concentration data gaps. Several available but slightly modified equations are well equipped to describe the concentration and temperature dependent surface tension of the material systems under investigation. Recommendations are given for binary and ternary solutions.

Stability and energetics of two-dimensional surface crystals in liquid AuSi thin films and nanoscale droplets

Segregation at surfaces of metal-covalent binary liquids is often non-classical and in extreme cases such as AuSi, the surface crystallizes above the melting point. In this study, we employ atomic-scale computational frameworks to study the surface crystallization of AuSi films and droplets as a function of composition, temperature and size. For temperatures in the range $T_s^\ast=765-780$K above the melting point $(T_s^\ast\approx1.3\,T_m)$, both thin film and droplet surfaces undergo a first order transition, from a 2D Au$_2$Si crystalline phase to a laterally disordered yet stratified layer. The thin film surfaces exhibit an effective surface tension that increases with temperature and decreases with Si concentration. On the other hand, for droplets in the size range $10-30$ nm, the bulk Laplace pressure alters the surface segregation as it occurs with respect to a strained bulk. Above $T_s^\ast$ the size effect on the surface tension is small, while for $T<T_s^\ast$ the surface layer is strained and composed of 2D crystallites separated by extended grain boundary scars that lead to large fluctuations in its energetics. As a specific application, all-atom simulations of AuSi droplets on Si(111) substrate subject to Si surface flux show that the supersaturation dependent surface tension destabilizes the contact line via formation of a precursor wetting film on the solid-vapor interface, and has ramifications for size selection during VLS-based routes for nanowire growth. Our study sheds light on the interplay between stability and energetics of surfaces in these unique class of binary alloys and offers pathways for exploiting their surface structure for varied applications such as catalytic nanocrystal growth, dealloying, and polymer crystallization.

Dependence of the effective surface tension of liquid phase eutectic gallium indium on wrinkles of the surface oxide

We investigated the effective surface tension of liquid eutectic gallium indium (EGaIn) with oxide skin. Our visualization of the EGaIn interface during extension and compression indicated the compression causes the wrinkles on the oxide skin, which is then partially smoothed out by extension. We found that the creation of the interface was the combined result of tearing of the oxide skin and the unfolding of oxide wrinkles. Our experiments revealed that the effective surface tension depends on oxide wrinkle, and the value is 0.7 N/m in the absence of wrinkles, but can be as small as ∼0.5 N/m in the presence of surface wrinkles.

Stretch-Induced Cavitation: How Critical Cavity Radius and Barrier Energy, Radius, and Energy of a Stable Cavity Depend on the Stretching Factor.

Characteristics of tension-induced cavitation, such as free energy at the barrier for cavitation, the size of the critical (barrier) cavity, the stable cavity size, and the free energy of the stable cavity, depend on the amount of tension (stretch) and the initial size of the sample. In this work, we study how the characteristics of the cavitation mentioned above scale with the amount of applied tension. We consider two models characterizing the properties of cavitating liquid: (a) a simple model with a linear tension-strain relation and neglect of curvature dependence of cavity surface tension and (b) a more realistic model with a nonlinear tension-strain relation and curvature-dependent surface tension. For both models, we find the relevant scaling relations when we stretch the initial volume of the liquid sample in the interval between 1% and 20% of the initial volume. Specific numerical tests are performed for the case of liquid water when the initial volume of the sample is a sphere with a radius of 100 nm.

PECULARITIES OF MICELLE FORMATION OF PENTACYCLIC GLYCOSIDES IN AQUEOUS SOLUTIONS

The regularities of changes in structural characteristics during the formation of associates in micellar aqueous solutions of triterpene saponins Quillaja Saponin and Sapindus Mukorossi are considered. The dependence of surface tension and adsorption on the concentration of an aqueous saponin solution is analyzed, and the values of surface activity and parameters of the adsorption layer are calculated. The average values of diffusion coefficients for spherical and cylindrical micelles are determined based on the measurement of the solution viscosity. The effect of the electrolyte solution on the surface tension and viscosity of glycoside solutions is studied: when the electrolyte is introduced into the saponin solution, the surface tension decreases, which leads to a shift in the critical concentration of micelle formation towards lower concentrations. The introduction of potassium chloride electrolyte reduces the degree of ionization and, as a result of suppressing the electroviscosity effect, leads to a decrease in the viscosity of the solution. The dynamic light scattering method is used to determine the size of glycoside aggregates. It is established that there are aggregates of several sizes in an aqueous solution of saponin. The size and shape of aggregates were calculated using the concepts of micelle packing parameters. In the region of very low concentrations of glycoside solutions, when approaching the critical concentration of micelle formation in the solution, there are spherical micelles. A further increase in the saponin concentration in the solution leads to a decrease in the content of structures with a hydrodynamic radius of 50-80 nm and the appearance of larger agglomerates with sizes greater than 100 nm. It was found that micelles acquire a less hydrated and more densely packed cylindrical shape in the concentration range of 1.7-2.6 mmol/dm3. Compaction of associates leads to an increase in the content of particles with a hydrodynamic radius of 150-250 nm and larger ones, and their presence predicts the appearance of larger agglomerates. Analyzing the data obtained using the dynamic light scattering method, it can be concluded that aggregates of several sizes co-exist in the volume of aqueous saponin solutions at certain concentrations.

Extensive Databases and Group Contribution QSPRs of Ionic Liquid Properties. 3: Surface Tension

Quantitative structure–property relationships (QSPR) for calculating temperature dependence of surface tension (σ) of ionic liquids (ILs) in terms of group contributions (GCs) is proposed and broad...