Solid Surface Tension Research Articles

Dynamic Solid Surface Tension Causes Droplet Pinning and Depinning.

The contact line of a liquid drop on a solid exerts a nanometrically sharp surface traction. This provides an unprecedented tool to study highly localized and dynamic surface deformations of soft polymer networks. One of the outstanding problems in this context is the stick-slip instability, observed above a critical velocity, during which the contact line periodically depins from its own wetting ridge. Time-resolved measurements of the solid deformation are challenging, and the mechanism of dynamical depinning has remained elusive. Here we present direct visualisations of the dynamic wetting ridge formed by water spreading on a PDMS gel. Unexpectedly, it is found that the opening angle of the wetting ridge increases with speed, which cannot be attributed to bulk rheology, but points to a dynamical increase of the solid's surface tensions. From this we derive the criterion for depinning that is confirmed experimentally. Our findings reveal a deep connection between stick-slip processes and newly identified dynamical surface effects.

Sorption isotherm and length change behavior of autoclaved aerated concrete

We conducted an experimental study on the sorption isotherm and length change behavior of autoclaved aerated concrete (AAC) in both desorption and adsorption processes. Three types of AAC with different bulk densities were used to study the length change mechanism. The experimental results show that the expansion of AAC during the adsorption process is mostly larger than the shrinkage in the first desorption process even though the water content in the adsorption process is lower. Interestingly, a clear expansion in the desorption process in a range of relative humidity (RH) from about 90% to 65% and a significant difference in the length change strain between the desorption and adsorption processes (shrinkage hysteresis) at high RH are observed. Based on these experimental results, we propose a model to represent the mechanism of the hygral length change of AAC, taking into account the changes in surface free energy of the solid surface and capillary tension. The model reasonably explains the significantly different length change behaviors of AACs with different pore structures.

Effect of Polysorbates on Solids Wettability and Their Adsorption Properties

The wettability of solids is important from both practical and theoretical viewpoints. In this study, we measured the contact angle of aqueous solutions of polysorbates (Tween 20, Tween 60, and Tween 80) on polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), polyamide (nylon 6), and quartz. Based on the obtained results, the adsorption of Tween 20 (T20), Tween 60 (T60), and Tween 80 (T80) at the solid-water interface was determined based on the structure and size of their molecules. Next, the tendency of polysorbates to adsorb at the solid-water interface was considered based on the Gibbs standard free energy of adsorption (ΔGadso). This energy was evaluated using various methods, including a method we propose based on the critical micelle concentration (CMC) and the contact angle of water and solution at the CMC, as well as their surface tension. The ΔGadso values obtained by this method were comparable to those calculated from the Langmuir equation. Taking into account the Tweens tendency to adsorb at the solid-water interface, the measured contact angle, the components and parameters of surface tension of Tweens solutions and solids, and the surface tension of water and its Lifshitz-van der Waals component that we determined, the wetting process in the solid-solution drop-air system was analyzed. The results based on the mentioned parameters showed that it is possible to predict the wettability of apolar, monopolar, and bipolar solids using the aqueous Tweens solution and their solution adhesion.

Macroscopic and Microscopic Properties of Some Surfactants and Biosurfactants.

The adsorption of surfactants at the water-air and solid-water interfaces and their wetting properties decide their practical applications. Therefore the adsorption of monorhamnolipid, surfactin, n-octyl-β-d-glucopyranoside, n-dodecyl-β-d-glucopyranoside, n-dodecyl-β-d-maltoside, sucrose monodecanoate, sucrose monododecanoate, Tween 20, Tween 60, and Tween 80 at the water-air, polytetrafluoroethylene-water, polyethylene-water, poly(methyl methacrylate)-water, polyamide-water, and quartz-water interfaces, their tendency to form micelles as well as their wetting properties, were considered in the light of their microscopic properties. For this purpose, the components and parameters of the surfactant tail and head, water and solids surface tension, and surfactant contactable area with adherent medium were applied for prediction of surfactant-surfactant and surfactant-solid interactions through the water phase with regard to their adsorption, micellization, and wetting processes. Next, the Gibbs free energy of interactions was compared to the Gibbs free energy of surfactant adsorption at the water-air and solid-water interfaces as well as the micellization. It appeared that from the surfactant-surfactant and surfactant-solid interactions through the water phase determined on the basis of the tail and head of surfactant surface tension, it is possible to predict the surfactant tendency to adsorb at the water-air and solid-water interfaces, as well as to form micelles.

Influence of Surface Properties of Minerals on Rebellious Ore Disintegration

The processes of rebellious ore disintegration with regard to the surface properties of minerals and rocks are discussed. The methods are proposed for the experimental determination of surface tension of solids during evaluation of dispergating efficiency, and the calculation procedure of the surface layer thickness during ore disintegration is offered. The calculations of the fusion temperatures of nanoparticles obtained in nonconventional disintegration of rebellious ore are presented. The calculations are performed for the nanoparticles with possible content of the most metals from the periodic chart.

Wetting and adhesion properties of rhamnolipid and surfactin

The measurements of the contact angle of the aqueous solution of rhamnolipid (RL) and surfactin (SF) on polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), nylon 6 and quartz were performed. The obtained values of the contact angle were analyzed by applying the components and parameters of the surface tension of aqueous solution of surfactants, PTFE, PE, PMMA, nylon 6 and quartz. This analysis showed that the contact angle of the solution on the hydrophobic solids can be predicted theoretically knowing the Lifshitz-van der Waals component of the water surface tension, the surface tension of the solids and that of the solution. Based on the contact angle values the critical surface tension of studied solids wetting, the adsorption of surfactants at the solid-water interface, the standard Gibbs free energy of adsorption as well as the work of adhesion of solutions to PTFE, PE, PMMA, nylon 6 and quartz surfaces were determined. It proved that the critical surface tension of wetting of the studied solids is different from their surface tension and that the work of adhesion of the aqueous solutions of RL and SF to PTFE, PE, PMMA, nylon 6 and quartz surfaces can be predicted from the components and parameters as well as the total surface tension of solids and solutions.

Numerical multiscale modelling of nonlinear elastowetting

Abstract We investigate here the static finite deformation of two (or more) three-dimensional nonlinear elastic solids which merge in a third medium, defining a triple line ( tl ). The total energy, accounting for elastic, surface and possible gravity potentials is then minimized numerically in order to solve two physical problems of interest: (i) a soft incompressible axisymmetric drop at rest on a stiffer substrate and (ii) a stiff drop at rest upon a softer substrate, both in situations of strong substrate surface tension effects. Because of the interplay between surface and bulk properties, the behavior of the tl is related to another smaller length-scale (typically micrometre scale) than the elastic solids length-scale (typically millimetre scale). A unified deformability parameter relating all scales is introduced and an adaptive finite element discretization of the domain is used. A first example approached by our model is the elasto-wetting problem in which a very soft drop sits on a stiffer elastic solid. The numerical predictions of our model are compared with the analytical results of the linear elastic theory. In particular, our computations show that Laplace pressure , together with the asymmetry of the solid surface tensions (between the wet and dry part of the interface), well account for the rotation of the cusp of the ridge. In the second example, motivated by indentation problems of a nonlinear elastic substrate by a stiff sphere, we analyse the interplay of the solid surface tensions and elasticity at small-scale. The numerical results also show that gravity might have an important effect and must be included in any micro-scale modelling.

High dielectric acrylonitrile-butadiene rubber with excellent mechanical properties by filling with surface-modified barium/strontium inorganic functional powders

Acrylonitrile-butadiene rubber (NBR) filled with surface-modified barium titanate (MBT), strontium titanate (MST) and barium strontium titanate (MBxS1−xT) was used to prepare the polymer dielectrics. BxS1−xT powders (x = 0.8, 0.7, 0.5 and 0.3) were synthesized via solid-state method. The crystal structure was observed by X-ray diffraction. The morphology and particle size of different powders were characterized by scanning electron microscopy (SEM). The contact angle test verified the hydrophobicity of the inorganic functional powders modified with bis-(γ-triethoxysilylpropyl)-tetrasulfide (KH845-4) improved obviously. The ratio of the dispersive solid surface tension and polar solid surface tension between inorganic filler and NBR matrix became closer after surface modification. The NBR/MBT/MST and NBR/MBxS1−xT systems were designed to improve the dielectric properties and enhance the mechanical properties. The curing characteristic of all NBR gums was tested. The dispersion of surface-modified functional filler in NBR was observed great according to the images of SEM. The mechanical properties of NBR/filler composites reinforced markedly compared with the neat NBR. For dielectric properties, the NBR/MB0.7S0.3T composites had the highest dielectric constant and the NBR/MST composites had the lowest dielectric loss factor at room temperature. They were suitable to be applied under the different frequency in oily environment for a long time. The oil resistance of all composites was also tested.

Rheological characterization and jet printing performance of Sn–58Bi solder pastes

The rheological character and jet printing performance of the lead-free solder paste (Sn–58Bi) with four solid phases were investigated. The rheology tests, containing oscillation test, creep recovery test, viscosity test and thixotropic loop test, were conducted by an Anton Paar MCR302 rheometer. Jet printing technology is a new packaging method with many advantages such as high precision, customization, low cost, etc. The jet printing test was carried out with the spray nozzle heated to 50 °C. From this study, it is found that the G″/G′ ratio of the pastes obtained by the oscillation stress test can influence the jet printing performance of the pastes. Paste 2 with the lowest ratio of G″/G′ can form the most complete hemispherical droplet. In addition, the solder paste with better liquid-like character at the nozzle and more solid phase property and surface tension when crashing on the base plate could be reverted to the hemispherical morphology easily. As the demand for pastes applied to jet printing increases, rheological measurement can assist with the research of the new high viscosity lead-free solder pastes.

Comprehensive Modeling of Capillary Condensation in Open-Ended Nanopores: Equilibrium, Metastability, and Spinodal

Capillary condensation within open-ended cylindrical nanopores is modeled thermodynamically and kinetically, in order to provide reasonable estimates of both the equilibrium phase transition pressure and capillary condensation pressure from a metastable state. The thermodynamic model is established by adding to the conventional Derjaguin–Broekhoff–de Boer model the effects of curvature on the fluid–solid interaction potentials and surface tension at the vapor–liquid interface. The equilibrium vapor–liquid phase transition pressure estimated via the thermodynamic model is in close agreement with that from the nonlocal density functional theory. In contrast to the equilibrium phase transition, capillary condensation from a metastable state cannot be estimated by the conventional thermodynamic models, because it inherently includes an activated process. To overcome this challenge, we propose a kinetic model of metastable capillary condensation for the first time. The model is based on the finding in our previous molecular simulation study, that metastable capillary condensation occurs when the corresponding rate constant reaches a critical value. The proposed kinetic model allows us to quantitatively reproduce the experimental capillary condensation pressures over a wide range of temperatures and mesopore sizes without computationally expensive molecular simulations.

Crystallization behavior, tensile behavior and hydrophilicity of poly(vinylidene fluoride)/polyethylene glycol blends

In this study, polyethylene glycol (PEG) of different molecular weight was added into poly(vinylidene fluoride) (PVDF) through melt blending. The hydrophilicity, processability, mechanical properties of the blends were investigated. Moreover, to understand fully, the crystallization and melting behavior, crystalline structure, molecular interactions of the blends were also studied. Results revealed that the addition of PEG evidently enhances the ductile and reduces the rheological torque of PVDF, what’s more, the contact angle of the blends with water was greatly reduced. The solid surface tension γs, chromatic dispersion part γ s d and polar part γ s p suggested the surface tension of the blend gradually increased from 38.31 to 55.65 mJ/m2 with the increase of PEG-20000 content.Wherein the dispersion part of the tension changed little, the polar part of the tension increased significantly from 5.74 to 20.41 mJ/m2, indicating that the addition of PEG greatly enhanced the polar part of surface tension of the blend, and therefore evidently enlarged the hydrophilic property of the blends. Besides, to elucidate the related effecting mechanism, the crystallization and molecular interaction of the blends were also studied.

Effect of Spreading Time on Contact Angle of Nanofluid on the Surface of Stainless Steel AISI 316 and Zircalloy 4

The solid surface tension plays an important role in the heat and mass transfer system for heat exchanger equipment. In the nuclear power plant industry, the stainless steel AISI 316 and Zircalloy 4 have been used for long time as structure materials. The purpose of the experimental is to study solid state surface tension behavior by measure contact angle Nano fluid contain nano particle alumina on metal surface of stainless steel AISI 316 and Zircalloy 4 by sessile drop method. The experiment is to measure the static contact angle and drop nano fluid contains nano particle alumina on stainless steel 316 and zircalloy 4 with different spreading time from 1 to 30 minute. It was observed that stainless steel 316 and zircalloy 4 lose their hydrophobic properties with increasing elapsed time during drop of nano fluid on the surface of alloy. As a result the contact angle of nano fluid on surface of metal is decrease with increasing elapsed time. While the magnitude diameter of drop nano fluid and wetting surface is increase with increasing elapsed time on the surface of the stainless steel SS 316 and Zircalloy 4.

Elastic modulus, surface tension, adhesion, and ideal and real strengths of solids

Formulas for the surface tension coefficient, adhesion energy, elastic modulus, and strength of solids versus the atomic density have been derived. The theoretical values of these parameters have been confirmed by experimental data gathered from many metals, insulators, and semiconductors.

Some remarks on the solid surface tension determination from contact angle measurements

The measurements of water, formamide and diiodomethane contact angle (θ) on polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), nylon 6, quartz and silica were performed. Based on the θ values of these liquids obtained on PTFE, the Lifshitz-van der Waals and acid-base and/or dispersion and polar components of their surface tension (ST) were determined. In turn, the θ values for water, formamide and diiodomethane on PMMA were applied to calculate the electron-acceptor and electron-donor parameters of the Lewis acid-base component of the formamide ST. For this calculation the same values of the electron-acceptor and electron-donor parameters for water ST were used. Taking into account the values of components and parameters of water, formamide and diiodomethane ST obtained by us, van Oss et al. and from the water(formamide)-n-alkane and water-diiodomethane interface tension, the components and parameters of studied solids ST were calculated. To this end different approaches to the interface tension were considered. The obtained values were compared with those in the literature. It was concluded that for determination of solid ST components and parameters, those of water, formamide and diiodomethane ST obtained from the θ measurements on the model solids should be used.

Dynamic analysis of a recirculation system of micro functional fluids for ink-jet applications

The rise of ink-jet printing technology has led to numerous studies about functional fluids, which, in most cases, are made to change and improve the chemical and rheological properties. Besides this, there are several patents about the recirculation fluid system that help to prevent settling particles, and thus improving print quality without consequences in the chemical composition of the fluid. This paper presents a dynamic analysis of a recirculation circuit for ink-jet microsystems applications with fluids that contain a particle size of 40 nm to 10 $$\upmu$$μm. This analysis integrates multiple mathematical and experimental models, in regard to variables such as: viscosity change with temperature and solid volume fraction, sedimentation, surface tension and flow behavior. As a result, specific values of vacuum pressure for different drop-on-demand print heads with different ink-jet functional fluids, places of probable sedimentation and minimum pickup velocities to remove settled particles are given.

Effect of surface tension on the adhesion between a rigid flat punch and a semi-infinite neo-Hookean half-space

We study the effect of surface stress on the retraction of a rigid flat circular punch adhering to an incompressible neo-Hookean half space using a large deformation finite element model (FEM). The effect of surface stress is determined by the dimensionless elasto-capillary number, ω=σ/(Ea), where σ is the isotropic solid–air interface surface stress which we shall called surface tension, E is the small strain Young’s modulus and a is the radius of punch. Adhesion of the punch to the half space is characterized by work of adhesion Wad. Within the range of retraction displacement of this work (less or equal to the punch radius), the stiffness of the system is insensitive to retraction displacement and depends only on the elasto-capillary number. In general, surface tension increases the slope of load–displacement curve or the stiffness of the system. For a given work of adhesion, the pull-off force (displacement) increases (decreases) with surface tension. Our results show that the apparent contact angle is not 90 degrees, as predicted by linear elastic theory, but varies from 20 to 180 degrees and is very sensitive to ω when it is near zero. This result can be potentially used to measure solid surface tension.

Spreading of the nanofluid triple line in ink jet printed electronics tracks

One of the next avenues for Additive Manufacturing to develop is that of multi-material deposition in order to add functionality to the already complex geometries that are capable of being manufactured. However, for electronic applications the fidelity of the deposited electronic tracks is of utmost importance. The purpose of this study was to investigate the effects of solid surface tensions, σsg−σsl, on the quality of printed lines, using 30–40nm silver nanofluid ink. The solid surface tensions of silver ink on glass and polytetrofluoroethylene (PTFE) substrates were determined theoretically, knowing characteristics of droplet. Meanwhile, a Dimatix printer with nozzles of size of 21.5μm was used to print conductive lines on smooth glass and PTFE substrates. The printed lines on glass were observed to be continuous with high quality of triple line, which was attributed to the high solid surface tensions of silver nanofluid ink on glass substrates. The solid surface tensions of silver nanofluid ink were relatively low on PTFE, as results the printed lines were discontinuous. The solid surface tensions were introduced as a reliable criterion to predict the printability of nanofluids. The distribution of silver nanoparticles and layering phenomenon in silver nanofluid triple region on glass substrate was clearly observed, using environmental scanning electron microscopy (ESEM) for the first time. In addition to disjoining pressure, the size of droplet and affinity of nanofluid for substrate were observed to have important influences on spreading of nanoparticles in triple region.

Mesoscale Modeling of Nonlinear Influence of Ambient Relative Humidity on Drying Shrinkage of Concrete

Creep and shrinkage are complicated time-dependent processes taking place in cementitious materials. In typical concretes, the most significant part of shrinkage is represented by drying shrinkage; it is caused by a decrease in relative humidity of pores which leads to an increase in capillary tension of pore water and in the solid surface tension at pore walls.Experimental data indicate that the ultimate value of drying shrinkage measured on concrete and mortar specimens is a nonlinear function of the ambient relative humidity. The nonlinear behavior is partially caused by microcracking, and partially by creep of the cement matrix. On the other hand, drying shrinkage of hardened cement paste, measured on very thin specimens at gradually decreasing relative humidity, is found to be a linear function of relative humidity.The aim of this paper is to assess the nature of the macroscopic shrinkage computed employing finite element simulations at the meso-scale level in which the drying cement paste is described by a viscoelastic model with tensile cracking and with a constant shrinkage coefficient.

Empirical study and prediction of liquids retention on structured polymer surfaces

Liquids' contact angle hysteresis and critical retention volumes on five commonly used plastics with surface structures were studied. The chevron‐like groove structures, which are orthogonally arranged, make the liquid–solid contact line elongated while the droplet found staying in the Wenzel state. Various dimensions of surface structures were represented by contact length ratio σ. Advancing and receding contact angles of liquids on polymer surfaces with various conditions were reported. Reduced hysteresis H, which links between advancing and receding contact angles, was also studied and found to extend its availability on structured surfaces. The research found that surface structures have linear effects on liquids' advancing contact angles in the range of σ = 1.0 to 1.42. Linear regression analysis was hence proposed to predict advancing contact angles, and the results indicate that approximate 80% of data points have less than 6% error. An empirical model, which adopts liquid–solid surface tension as the source of liquids' retention force, was proposed to estimate liquids' critical retention volumes on inclined surfaces. The proposed model found good agreements with existing experiment data and demonstrated its superiority over previous ones. The present model provides an approach to predict liquids' storage/repellency on structured surfaces when the advancing contact angles are predictable. Copyright © 2016 John Wiley & Sons, Ltd.

To “the first application of legendre transforms to the surface tension of solids”

To “the first application of legendre transforms to the surface tension of solids”