Solid-liquid Interfacial Tension Research Articles

Calculation of the work of adhesion of polyisoprene on graphite by molecular dynamics simulations

ABSTRACT Elastomeric compounds are reinforced with fillers such as carbon-black and silica to improve mechanical, dynamical, and tribological properties. The stability and physical properties of these materials are dominated by the intermolecular interactions occurring at the polymer/particles interface that determine the magnitude of the polymer/particles adhesion. Using molecular dynamics simulations, in this work, we evaluate the solid–liquid interfacial tension and the corresponding work of adhesion for a system composed of graphite/Polyisoprene 100% cis-1,4 within a range of molar masses and temperatures. We employ a simulation strategy for estimating the surface tension of fluid/vacuum and fluid/solid interfaces that use directly the local stress fields in the Irving–Kirkwood formalism. Using such procedure, we decompose the stress field into the individual components of the stress tensor and correlate them with the values of the work of adhesion in the different systems analyzed. Abbreviation: PI (100% 1,4); MD: molecular dynamics; PT lateral component of the stress; PN normal component of the stress.

Wetting and adhesion behavior on apple tree leaf surface by adding different surfactants

ObjectiveThis study was conducted to investigate the wetting behavior of different surfactant solutions on the leaf surfaces of apple during the fruit formation stage. MethodsFive surfactants, including C12E5, Tween-20, Triton X-100, DTAB, and SDS were evaluated in this study. The contact angle, surface tension, adhesion tension, work of adhesion, and solid-liquid interface tension of droplets on the leaf surface were determined by the drop method. ResultsThe results showed that the nonionic surfactants C12E5 and Triton X-100 had better wetting effects than other surfactants. Moreover, when the concentration of C12E5 and Triton X-100 was 1 × 10−3 mol/L, the leaves reached a completely wet state. Toxicity measurement showed that the incubation rate of Carposina niponensis eggs decreased gradually with increasing content of C12E5 or Triton X-100. Additionally, field efficacy analysis showed that adding C12E5 or Triton X-100 significantly improved the beta-cyfluthrin 3% water emulsion (EW) against C. niponensis. ConclusionsThese results indicate that the surfactants C12E5 and Triton X-100 can significantly improve pesticide application, which will be helpful for reducing pesticide use and developing new pesticides.

Effect of Electrolytes on Gas Oversolubility and Liquid Outflow from Hydrophobic Nanochannels.

We have experimentally studied the effect of electrolytes on gas oversolubility and liquid outflow from hydrophobic nanochannels. By immersing nanoporous material with the same porous structure and surface properties into four different aqueous electrolyte solutions with the same surface tension, the excessive solid-liquid interfacial tension of the resulted liquid nanofoam (LN) systems has been set as a constant. Upon unloading, partial liquid outflow has been observed and quantified. As the four LN systems show different degrees of recoverability, it suggests that the degree of liquid outflow is highly sensitive to the ion species. In addition, different from bulk phase scenario, the anions have a more profound effect than cations on gas oversolubility. Lower bulk gas solubility and larger gas oversolubility factor lead to higher degree of liquid outflow and recoverability of the LN systems. This fundamental understanding on the mechanism of liquid outflow enables the development of nanofluidics-based system into reusable energy absorbers.

Derivation of a pH Dependent Solid-Liquid Interfacial Tension and Theoretical Interpretation of the Physicochemistry of Dewetting in the CO2-Brine-Silica System

The solid-liquid interfacial tension is a fundamental parameter in areas of wettability pertaining to adhesive bonds and petroleum engineering practice. In wettability issues related to surface functionalized polymeric materials design to achieve specific adhesive properties, the solid-liquid interfacial tension can be pH dependent due to amphoteric behavior. In this paper, we have used the theory of pH dependent surface charging and the 2-pk model as well as the site binding model of the electric double layer theory to derive a pH dependent solid-liquid interfacial tension equation. 
 
 Following the fundamental relationship between solid-liquid interfacial tension and contact angle in light of Young’s equation, we have extended the theoretical basis of the derivation. Consequently, we have also derived a pH dependent cosine of the thermodynamic contact angle. Both equations give satisfactory explanations for observed experimental data available in the literature.

Effect of surface wettability on tribological properties of Al2O3/TiC ceramic under wet lubrication

The effect of surface wettability on the friction properties of Al2O3/TiC ceramic was investigated to improve the friction and wear of Al2O3/TiC ceramic tool surfaces. The surface wettability of Al2O3/TiC ceramic was changed by preparing different microgroove arrays on its surface. The surface contact angles of the different samples were measured to characterize surface wettability. The reciprocating linear friction tests were implemented under liquid lubrication by a ball-disc type friction machine and the friction coefficient was measured. The worn surface characteristics of Al2O3/TiC ceramic were observed using SEM. Results showed that the surface wettability effectively improved the friction and wear properties of Al2O3/TiC ceramic. The friction coefficient of Al2O3/TiC ceramics decreased as surface wettability was enhanced. The surface wettability enhancement of 86.8% corresponds to a reduction in the friction coefficient of 73.6%. The better the wettability, the smoother the worn surface. The mechanism responsible was explained as micro-textures promoted capillary adsorption of lubricating fluid on the surface of Al2O3/TiC ceramic. The additional capillary adsorption force reduced the solid-liquid interfacial tension, thereby enhancing the surface wettability of the Al2O3/TiC ceramic, which promoted spreading ability of lubricating fluid. Therefore, the lubricating fluid can form a continuous lubricating film at the friction interface to achieve the effect of reducing the friction.

Interaction Between Liquid Steel and AlN Substrate Containing Al-Y-Oxides

Reactions between molten iron, molten silicon steel, and ceramic materials are of great importance from the perspective of the corrosion of refractory material in the steelmaking and continuous casting processes. Reactions between liquid steel and aluminum nitride (AlN) substrate containing Al-Y-oxides were investigated using the sessile drop method at 1833 K (1560 °C). The liquid–substrate interface was observed with the increasing holding time, and the reaction mechanism was studied. In the case of the liquid iron and the silicon steel on the AlN substrate containing Al-Y-oxides, the reaction products on the steel side of the interface between the steel and the substrate were Al-rich Al-Y-oxides and Al2O3 particles. For silicon steel and pure AlN substrate, Al2O3 particles were the main products. Contact angles were lower for liquid iron than for silicon steel due to the higher oxygen content in iron. In addition, the solid–liquid interfacial tension and the work of adhesion between AlN and steel were measured.

Investigation of semi-solid microstructures of an A356 alloy containing rare-earth Gd during isothermal heat treatment

AbstractThe effects of isothermal heat treatment on microstructures of an A356 alloy containing rare-earth gadolinium (Gd) were investigated to obtain an optimum semi-solid structure. Our results revealed that the primary α-Al phase of the semi-solid A356 alloy containing Gd was significantly refined and that its morphology was spherical or near-spherical. Increases in holding temperature and prolongation of holding time led to an initial decrease in size during the primary α-Al phase, followed by a gradual increase. Solid–liquid interfacial tension resulted in the spheroidization of the primary α-Al phase.

Research on Hydrophobic Properties of Grating Structure on Monocrystalline Silicon Fabricated Using Micromachining

In this paper, micromilling was used to process the surface of single crystal silicon, and six different structural parameters of the grating structure were tested to get the contact angle in a different wettability. The contact angle obtained by the experiment was compared with the theoretical values of the Wenzel and Cassie model optimized based on the characteristics of micromilling. The relationship between structural parameters and wettability was verified. First, the contact angle of the parallel grating structure was greater than the vertical direction, which was influenced by the solid-liquid interface tension. Second, the hydrophobicity of the specimen was in good agreement with the predicted trend of the optimized prediction model C when the width of the convex is reduced. The support of the theoretical model to the experimental results is instructive to the construction of the structure. In addition, the molecular dynamics were used to verify the hydrophobicity of grating structures from a molecular point of view.

Correction to "Equilibrium Contact Angle and Adsorption Layer Properties with Surfactants".

The last line in eq 27 on page 7213 should read (Formula Presented) In the caption for Figure 2a on page 7213 it should read (a) In the macroscopic approach, the equilibrium contact angle is determined by the solid-liquid interfacial tension γsl and the liquid-gas and solid-gas interfacial tensions γ and γ sg that depend on the respective surfactant concentrations Gd and Ga on the droplet and the adsorption layer. (Formula Presented).

Interpretation of Young's equation for a liquid droplet on a flat and smooth solid surface: Mechanical and thermodynamic routes with a simple Lennard-Jones liquid.

In this study, we carried out molecular dynamics simulations of a cylindrical Lennard-Jones droplet on a flat and smooth solid surface and showed that Young's equation as the relation among solid-liquid, solid-vapor, and liquid-vapor interfacial tensions γSL, γSV, and γLV, respectively, was applicable only under a very restricted condition. Using the fluid stress-tensor distribution, we examined the force balance in the surface-lateral direction exerted on a rectangular control volume set around the contact line. As the mechanical route, the fluid stress integrals along the two control surfaces normal to the solid-fluid interface were theoretically connected with γSL and γSV relative to the solid-vacuum interfacial tension γS0 by Bakker's equation extended to solid-related interfaces via a thought experiment, for which the position of the solid-fluid interface plane was defined at the limit that the fluid molecules could reach. On the other hand, the fluid stress integral along the control surface lateral to the solid-fluid interface was connected with γLV by the Young-Laplace equation. Through this connection, we showed that Young's equation was valid for a system in which the net lateral force exerted on the fluid molecules from the solid surface was zero around the contact line. Furthermore, we compared γSL - γS0 and γSV - γS0 obtained by the mechanical route with the solid-liquid and solid-vapor works of adhesion obtained by the dry-surface method as one of the thermodynamic routes and showed that both routes resulted in a good agreement. In addition, the contact angle predicted by Young's equation with these interfacial tensions corresponded well to the apparent droplet contact angle determined by using the previously defined position of the solid-fluid interface plane; however, our theoretical derivation indicated that this correspondence was achieved because the zero-lateral force condition was satisfied in the present system with a flat and smooth solid surface. These results indicated that the contact angle should be predicted not only by the interfacial tensions but also by the pinning force exerted around the contact line.

Calculation of the interfacial tension of the graphene-water interaction by molecular simulations.

We report the calculation of the solid-liquid interface tension of the graphene-water interaction by using molecular simulations. Local profiles of the interfacial tension are given through the mechanical and thermodynamic definitions. The dependence of the interfacial tension on the graphene area is investigated by applying both reaction field and Ewald summation techniques. The structure of the interfacial region close to the graphene sheet is analyzed through the profiles of the density and hydrogen bond number and the orientation of the water molecules. We complete this study by plotting the profiles of the components of the pressure tensor calculated by the Ewald summation and reaction field methods. We also investigate the case of a reaction field version consisting in applying a damped shifted force in the case of the calculation of the pressure components.

Analytical derivation of a pH dependent contact angle equation and the relationship to industrial processes of energy concerns

Regarding Young's equation, three fundamental interfacial energies of interfacial tensions can be identified. One of these interfacial energies relevant to our purpose is that related to the solid-liquid interface and it can be pH dependent. Intermolecular theory of surface tension links the solid-liquid interfacial tension or energy to surface charge species of solids. These species are electrostatic and depend on the pH of the aqueous medium in contact with the solid surface. Therefore, a theoretical relationship between contact angle and pH of some kind is worth exploring based on the fundamental theories of pH dependent solid-liquid interfacial tension, given the pH dependent electric double layer.A review of the literature dealing with the pH-dependent contact angle shows that polynomial curves have been fitted to contact angle versus pH data. Based on established theoretical works dealing with surface charge theories related to the electric double layer found in the literature, we have derived a pH dependent contact angle equation that describes trends in published experimental data with a high degree of regression coefficient. We have also theoretically and experimentally validated our model. The industrial significance of our model lies in the fact that the solution for pH, when the derivative is equated to zero, gives the point of zero charge pH of solid surface, which is an approach that has already been used in published works without any theoretical justification. The relationship of our model to industrial operations of energy and environmental significance has been discussed.

The Role of Interfacial Energy and Specific Interactions on the Behavior of Poly(propylene glycol) Derivatives under 2D Confinement

The effect of the chemical modification of poly(propylene glycol) (PPG) end groups on the molecular dynamics under 2D confinement and the polymer/matrix interactions (including interfacial energies) was investigated by a combination of differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), surface tension and contact angle measurements. The replacement of −OH groups in native PPG allowed to modify the interactions with the hydroxyl groups attached to the pore walls of nanoporous aluminum oxide (AAO) membranes of various pore diameter. It was found that the observed reduction in the glass transition temperature (Tg) of the core polymers correlates well with a general trend (the higher the solid–liquid interfacial tension, γSL, the lower Tg,confined) reported earlier. Moreover, we demonstrated that although the interfacial solid–liquid energy seems to be almost the same for each studied herein material, a clear change in the crossover temperature (Tc), related to the vitrification...

A rapid method for interfacial tension calculation between rock plug and crude oil based on contact angles, application for EOR

ABSTRACTInterfacial tension and contact angle are two specific important parameters to take decisions for enhanced oil recovery, for instance, proper chemicals to use for surface tension reduction, expected wettability of solids, interaction between crude oil and rock. For this purpose, the article presents a method for easy calculation of the solid-liquid interfacial tension based on contact angle measurements applying Neumann's correlation and Young's equation. The main idea stands on the calculation of the rock parameters, like wettability, with known substances and extend these results to crude oils. It was possible, based on the results obtained, to establish a relationship between solid-liquid interfacial tension and contact angle for the crude oil – rock system, which can definitively be used for the calculation of interfacial tension of any other fluid spread out on the same kind of rock. A linear regression was obtained with an accuracy as good as R2 = 0.9989. Viscosity as a function of contact angle could also be obtained for the studied crude oils in the same kind of rock.

Multiscale Simulation Method for Quantitative Prediction of Surface Wettability at the Atomistic Level.

The solid-liquid interface is of great interest because of its highly heterogeneous character and its ubiquity in various applications. The most fundamental physical variable determining the strength of the solid-liquid interface is the solid-liquid interfacial tension, which is usually measured according to the contact angle. However, an accurate experimental measurement and a reliable theoretical prediction of the contact angle remain lacking because of many practical issues. Here, we propose a first-principles-based simulation approach to quantitatively predict the contact angle of an ideally clean surface using our recently developed multiscale simulation method of density functional theory in classical explicit solvents (DFT-CES). Using this approach, we simulate the surface wettability of a graphene and graphite surface, resulting in a reliable contact angle value that is comparable to the experimental data. From our simulation results, we find that the surface wettability is dominantly affected by the strength of the solid-liquid van der Waal's interaction. However, we further elucidate that there exists a secondary contribution from the change of water-water interaction, which is manifested by the change of liquid structure and dynamics of interfacial water layer. We expect that our proposed method can be used to quantitatively predict and understand the intriguing wetting phenomena at an atomistic level and can eventually be utilized to design a surface with a controlled hydrophobic(philic)ity.

A novel synthetic strategy of Fe@Cu core-shell microsphere particles by integration of solid-state immiscible metal system and low wettability

Herein, a novel preparation route of bimetallic spherical core-shell particles of immiscible metal system was developed and demonstrated through the synthesis of Fe@Cu core–shell microsphere particles. Copper ferrite (CuFe2O4) was used as precursor for the preparation of the Core–shell structured Fe@Cu microsphere using the solid-state immiscibility of Fe and Cu and the low wettability strategy of the liquid-solid interface of graphite at 1403 K. The results showed that phase separation occurred between Cu and Fe, where Cu tended to move towards the surface of the particles and Fe was more concentrated in the center of the particles, due to the lower surface energy of liquid Cu with respect to solid Fe. This was followed by formation of metal droplets located on loose graphite flakes on the spherical Fe@Cu due to the solid-liquid interfacial tension. The as-prepared Fe@Cu microsphere exhibited good spherical shapes and smooth surfaces. The cross-sectional micrographics and element mapping of the spherical particles confirmed the evenly distributions of the Fe-rich core and Cu-rich shell. This strategy is promising for the fabrication of core–shell structured spherical particles for immiscible alloys.

Molecular Dynamics Study of Hydrophilic Sphalerite (110) Surface as Modified by Normal and Branched Butylthiols.

Molecular dynamics simulation was used to study the wettability of the hydrophilic sphalerite (110) surface chemically modified by butylthiols made up of normal and branched alkyl tails, referred to as n-butylthiol and i-butylthiol hereafter, at different adsorption site coverages. Butylthiol molecules were grafted onto the adsorption sites of the surface in two different distributions-ordered and random. The results showed that for a given butylthiol at a given site coverage, random surface distribution yielded a slightly larger contact angle. This observation was attributed to the fact that average distances between the first and second nearest neighbors of butylthiol molecules are shorter in the case of random surface distribution, resulting in smaller patches of bare surface exposed to water molecules compared to those of the ordered surface distribution. Regardless of the tail structure, the random surface distribution exhibited hydrophobic character (i.e., contact angle ≥ 90°) at a relatively low site coverage of about 25%. The test area method and the Kirkwood and Buff approach were adopted to estimate surface energies (γSV) of the bare sphalerite (110) surface and the collector monolayer, respectively. Using the obtained γSV values of these two pure states, the apparent surface energy as a function of surface coverage was determined based on Cassie's law. This allowed us to estimate the corresponding values of solid-liquid apparent interfacial tension (γSL). Both γSV and γSL exhibit a linear inverse dependence on surface coverage with a crossover point at 25% site coverage (about 50% surface coverage), above which γSV falls below γSL, leading to contact angles greater than 90°. The results also revealed that contact angles of the two butylthiols are comparable at site coverages below ∼85%, but above that, they are significantly lower for the branched thiols compared to their normal counterparts. Considering the Lennard-Jones interaction energies between the water cluster and the butylthiols, stronger attractive interactions were present in the case of i-butylthiol due to the presence of two methyl groups in its alkyl chain. This difference was the most intense at site coverages above ∼85%.

Effect of Direct Current on Solid-Liquid Interfacial Tension and Wetting Behavior of Ga–In–Sn Alloy Melt on Cu Substrate

The effect of direct current (DC) on the wetting behavior of Cu substrate by liquid Ga–25In–13Sn alloy at room temperature is investigated using a sessile drop method. It is found that there is a critical value for current intensity, below which the decrease of contact angle with increasing current intensity is approximately linear and above which contact angle tends to a stable value from drop shape. Current polarity is a negligible factor in the observed trend. Additionally, the observed change in contact angles is translated into the corresponding change in solid-liquid interfacial tension using the equation of state for liquid interfacial tensions. The solid-liquid interfacial tension decreases under DC. DC-induced promotion of solute diffusion coefficient is likely to play an important role in determining the wettability and solid-liquid interfacial tension under DC.

Impact of Solid Surface Energy on Wettability of CO2-brine-Mineral Systems as a Function of Pressure, Temperature and Salinity

CO2 storage refers to the methods employed to inject CO2 in depleted oil and gas reservoirs and deep saline aquifers for long term storage of CO2 with the objective to reduce the anthropogenic CO2 emissions. Wettability and interfacial tension are two important multiphase parameters which are used to characterize the flow behavior of CO2 in reservoirs. Numerous studies have reported wettability data of CO2-brine systems on various rock forming minerals as function of pressure, temperature and salinity. However, the associated trends have not been physically well-understood and require considerable attention which is objective of our present work.In this work, we apply Neumann's equation of state method to our measured contact angle data for CO2-brine-mica systems and contact angle data of CO2-brine-quartz from Sarmadivaleh et al., 2015.Our results indicate that for mica, solid-CO2 interfacial tension decrease with pressure and salinity and increase with temperature. Moreover, solid-liquid interfacial tension decrease with temperature and decrease with salinity. For quartz, although the solid-CO2 interfacial tension decrease with pressure and increase with temperature, yet solid-liquid interfacial tension increase with temperature which explains the increase in contact angle with temperature for quartz. Overall, we find that results are in accordance with wettability data as function of pressure, temperature and salinity. We thus conclude that hotter reservoirs with lower injection pressure and lower brine salinities exhibit relatively better water wetting state and hence better seal capacity leading to higher CO2 storage potential. We also conclude that solid surface energy approach adequately explains the dependency of wettability on pressure, temperature and salinity.

Wettability of a nano-droplet in an electric field: A molecular dynamics study

The wettability of water droplets on solid substrates with external electric fields is a driving mechanism in many technologies. Here, the wettability of water nano-droplets on Si (100) substrates subjected to a perpendicular electric field was studied using molecular dynamics simulations (MD). The effects of the electric field on the liquid-vapor and solid-liquid interfacial tensions were investigated. The simulations show that the water contact angle decreases with increasing electric field on the Si (100) substrate. The MD results also show that the liquid-vapor interfacial tension decreases slightly with electric field strength and is insensitive to the field direction. However, the solid-liquid interfacial tension is significantly affected by the field direction and decreases in an upward but increases in a downward electric field. This directionally dependent solid-liquid interfacial tension causes the contact angle of the water droplet in a downward electric field to be larger than that in an upward electric field with the same field strength. The wettability of the solid surface also affects the effects of the electric field. For a hydrophobic substrate, the contact angle decreases with the field strength while for a hydrophilic substrate, the contact angle increases with increasing field strength.