Variation Of Interfacial Tension Research Articles

Thermal- and Magnetic-Sensitive Particle Flocking Motion at the Air-Water Interface.

Collective self-motion of particulate systems provides novel opportunities for developing flocking and sensing functions from seemingly inanimate objects. In this paper, we report videos documenting spontaneous collective flocking of multiple irregularly shaped macroscopic benzoquinone (BQ) particles at the air-water interface. Self-propulsion occurs due to the Gibbs-Marangoni effect surface tension gradients generated by the BQ particles. The air-water interface develops inhomogeneous interfacial tension fields created by differential dissolution at points and edges of BQ particles, causing interfacial tension variations along the solid-liquid-air interfaces. Responses of irregularly shaped BQ particles to these driving forces do not result in random motion but lead to a cooperative hydrodynamic flocking. Curiously, the flocking behavior was very evident for irregularly shaped particles but not observed for symmetric circular BQ disks. The flock responds to changes in its local environment as it forages for interfacial free energy. It exhibits warm and cool thermotaxis and thus can sense local temperature changes. Also, though a single magnetic bead is not confined to a part of the Petri dish by an applied magnetic field, when this magnetic bead is a member of a flock in which all of the other beads are not magnetic, the flock as a whole moves and hovers around the region where the field is maximum. In other words, the magnetic bead becomes a kind of "sensor" for the flock to respond to a magnetic field, the response being a drift in the direction of the field.

Computational Modeling of Adiabatic Bubble Growth Dynamics From Submerged Capillary-Tube Orifices in Aqueous Solutions of Surfactants

The growth dynamics of isolated gas bubbles from a submerged capillary-tube orifice in a pool of an aqueous surfactant (sodium dodecyl sulfate or SDS) solution is computationally investigated. The governing equations for surfactant mass transport in the bulk liquid and interfacial adsorption–desorption are solved simultaneously with the Navier–Stokes equations, employing the volume-of-fluid (VOF) technique to track the deforming liquid–air interface. The VOF method tends to spread the liquid–air interface over two to three computational cells, creating an interface region with finite thickness. A new numerical treatment is developed to determine the surfactant transport and adsorption/desorption in the interface region. From the variation of the surfactant interfacial concentration, the spatio-temporal variation in interfacial tension is determined and the shape of the growing bubble is predicted. To validate the numerical model, experimental measurements of bubble shape and size are carried out using high speed videography. Because of the decrease in surface tension with surface age, bubble departure diameters in SDS–water solutions are smaller than those obtained in pure water, and they are a function of bubble frequency. At higher air-flow rates (smaller surface age), the bubble departure diameters tend toward those in pure water, whereas at low flow rates (larger surface age), they are significantly smaller than those in water and are closer in size to those in a pure liquid having surface tension equal to the equilibrium value in SDS solution. Furthermore, the nonuniform surfactant adsorption–desorption at the evolving interface results in variation in interfacial tension around the bubbles, and thus their shapes in surfactant solution are different from those in a pure liquid.

PH-Switchable IFT variations and emulsions based on the dynamic noncovalent surfactant/salt assembly at the water/oil interface.

Additional HCl can facilely control the dynamic noncovalent interaction between anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and additional organic matter, 4,4'-oxydianiline (ODA), at the water/oil interface. At low HCl concentration (ODA/HCl molar ratio (r) = 1 : 1.5, [ODA] = 250 mg L-1), the ODA+ ions effectively enhanced the SDBS ability to reduce the water/oil interfacial tension (IFT) by about two orders of magnitude, while the (SDBS)2/ODA2+ gemini-like surfactants could be constructed at a relatively high HCl concentration (r = 1 : 4, [ODA] = 250 mg L-1), which could largely reduce the IFT to 1.19 × 10-3 mN m-1. Molecular simulation was employed to explore the interfacial activity of ODAn+ (ODA+/ODA2+) ions and the SDBS/ODAn+ interaction. The control experiments used another three surfactants to verify the proposed model. The pH-switchable gradual protonation of amino groups in ODA molecules determined the SDBS/ODA interfacial assembly, which was responsible for the reversal of IFT variations and the related emulsion behaviors.

Nanoscale Resolution of Electric-field Induced Motion in Ionic Diblock Copolymer Thin Films.

Understanding the responses of ionic block copolymers to applied electric fields is crucial when targeting applications in areas such as energy storage, microelectronics, and transducers. This work shows that the identity of counterions in ionic diblock copolymers substantially affects their responses to electric fields, demonstrating the importance of ionic species for materials design. In situ neutron reflectometry measurements revealed that thin films containing imidazolium based cationic diblock copolymers, tetrafluoroborate counteranions led to film contraction under applied electric fields, while bromide counteranions drove expansion under similar field strengths. Coarse-grained molecular dynamics simulations were used to develop a fundamental understanding of these responses, uncovering a nonmonotonic trend in thickness change as a function of field strength. This behavior was attributed to elastic responses of microphase separated diblock copolymer chains resulting from variations in interfacial tension of polymer-polymer interfaces due to the redistribution of counteranions in the presence of electric fields.

Variation of interfacial tension of the steam-foam drive in heavy oil reservoirs

The reservoir could be divided into three zones: steam zone with saturated steam temperature, condensate zone and reservoir temperature zone. Experiments were conducted to investigate influence of mass fraction of foaming agent and temperature on interfacial tension at reservoir pressure and temperature, by means of high temperature and high pressure interfacial tension instrument. The results showed that increasing mass fraction of foaming agent and temperature would result in decreasing minimum dynamic interfacial tension and steady interfacial tension. As temperature increased, it would take less time for the system to reach minimum dynamic interfacial tension. In steam zone and condensate zone, the interfacial tensions between water and heavy oil all keep magnitude of 10-2mN/m, but it keeps magnitude of 10-1mN/m in reservoir temperature zone. So the foaming agent has better displacement efficiency for heavy oil in steam zone and condensate zone.

Interfacial tension induced-transport in shale: A pore-scale study

While unconventional reservoirs have quickly become a main contributor to oil and gas production, the transport mechanism in shale is not well understood. Although water does not imbibe into oil-wetted rock matrix, it has been observed in laboratory measurements that it can. The amount of water imbibed into the rock matrix increases when the salinity of the injected water decreases. Wettability alteration is often considered as the main reason for this phenomenon. One of the physical mechanisms for the imbibition of low salinity water into an oil-wetted rock matrix is the variation of the interfacial tension and the contact angle. The change of salinity initiates the change of interfacial tension driving the movement of the interface imbibing water into oil-wetted pores.The imbibition of the water into the rock matrix is a complicated process requiring a comprehensive understanding of the mass transport at pore scale. Hence, pore scale modeling was used in this research study for understanding the physics of transport at pore scale caused by interfacial tension variation or interfacial tension-induced transport. First, a simplified pore-scale model is presented to simulate the imbibition of water into an oil-wetted pore. Next, a numerical solution and procedure are outlined to simulate the transient mass transport in the pore as the result of interfacial tension variation due to salinity. The results indicate that the interfacial tension-induced transport is a very important mechanism for water imbibition into oil-wetted pores. How fast the water imbibes into the pore depends on the salinity gradient and the type of solute used. When salinity at the inlet of the pore is low, more solute diffuses out of the pore resulting in higher cumulative recovery from the pore. Reducing the interfacial tension between oil and water forces oil out of the pores and improve the oil recovery. Hence, low salinity water is recommended for low salinity water injection enhanced oil recovery.

Investigation of ionic liquids based on pyridinium and imidazolium as interfacial tension reducer of crude Oil−Water and their synergism with MgCl2

Ionic liquids (ILs) can be tailored as chemical surfactants and surface active agents to reduce the interfacial tension (IFT) of crude oil/aqueous solutions for enhanced oil recovery processes. The current investigation was aimed to explore the nature of ingenious active agents in crude oil, including asphaltene and resin, and their possible interactions with two families of ILs, namely pyridinium and imidazolium, on the IFT of crude oil/aqueous solutions, both in the presence and absence of MgCl2. To the best of our knowledge, the effect of crude oil type on the IFT of crude oil/aqueous solution containing salts and IL has not been ever investigated. Accordingly, IFTs of light, medium and heavy crude oils (labeled as LCO, MCO and HCO, respectively) and two ILs, i.e. [C8mim] [Cl] and [C8Py] [Cl] were measured. In addition, the effects of the total acid number of crude oils, the amount of ingenious active agents in the crude oils as well as their major structural, molecular parameters such as hydrogen/carbon ratio and type and amount of heteroatoms (i.e. nitrogen, sulfur and oxygen) were investigated. The obtained results indicated that the performance of ILs was influenced by the crude oil and IL types. In details, the aromatic section of cationic part and their interactions with heteroatoms of crude oil showed the most influential role on the IFT variation.

Influence of capillarity and gravity on confined Faraday waves

Experiments characterizing the influence of gravity and interfacial tension on Faraday instability in immiscible, confined fluid layers are presented. The variation in interfacial tension was obtained by controlling the temperature of a suitable binary fluid pair while the influence of gravity was analyzed through a series of terrestrial and microgravity (parabolic flight) experiments. These experiments confirm the existence of a crossover frequency, on either side of which gravity plays opposing roles. The current experiments also reveal that the neutral stability curves under Earth's gravity drift toward lower frequencies as the temperature of the liquid pair approaches its upper consolutal value, i.e., the temperature of complete miscibility. Such drifts in the low frequency range are shown to occur primarily due to the reduction in density difference between the layers, whereas at very high frequencies they are controlled by the lowering of interfacial tension. In the absence of gravity, the Faraday waves are characterized by larger wave numbers, and, as in terrestrial conditions, the instability thresholds at high frequencies increase with an increase of temperature, i.e., reduction in interfacial tension value. This surprising stabilization originates from the lowering of the critical wavelength that leads to increased viscous dissipation.

The improvement of the cationic/anionic surfactant interfacial activity via the selective host-guest recognition

Supramolecular chemistry proposed a controllable and convenient approach to construct the desired complexes used in various fields, including chemical enhanced oil recovery. β‑cyclodextrin (β-CD) can effectively enclose the surfactants to fabricate the stable inclusion complexes via the host-guest recognition. In the present report, the β‑CD effects on the interfacial activities of the mixed surfactant system consisting of N‑dodecyl‑N‑methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS) were systematically evaluated. Interestingly, the additional β-CD molecules greatly reduced the interfacial tension (IFT) between the L12/SDS aqueous solution and model oil (toluene and n-decane, v/v = 1:1). Due to the electrostatic attraction of L12/SDS, the β-CD molecules could selectively enclose the majority surfactants to improve the intensive arrangements of mixed surfactants at the interface. In general, the host-guest recognition facilitates the fabrications of β-CD/surfactant inclusions and decrease surfactant interfacial concentrations. The competition between the host-guest recognition and the electrostatic attraction dominates the IFT variations. Then we changed the molar ratio of L12/SDS, the dissolved order of chemicals and explored the variations of the mixed surfactants hydrophile-lipophile balance to further confirm the proposed mechanism. Moreover, the salinity and temperature effects on the IFT were systematically investigated.

Simulations of Interfacial Tension of Liquid-Liquid Ternary Mixtures Using Optimized Parametrization for Coarse-Grained Models.

In this work, liquid-liquid systems are studied by means of coarse-grained Monte Carlo simulations (CG-MC) and Dissipative Particle Dynamics (DPD). A methodology is proposed to reproduce liquid-liquid equilibrium (LLE) and to provide variation of interfacial tension (IFT), as a function of the solute concentration. A key step is the parametrization method based on the use of the Flory-Huggins parameter between DPD beads to calculate solute/solvent interactions. Parameters are determined using a set of experimental compositional data of LLE, following four different approaches. These approaches are evaluated, and the results obtained are compared to analyze advantages/disadvantages of each one. These methodologies have been compared through their application on six systems: water/benzene/1,4-dioxane,water/chloroform/acetone, water/benzene/acetic acid, water/benzene/2-propanol, water/hexane/acetone, and water/hexane/2-propanol. CG-MC simulations in the Gibbs (NVT) ensemble have been used to check the validity of parametrization approaches for LLE reproduction. Then, CG-MC simulations in the osmotic (μsoluteNsolventP zzT) ensemble were carried out considering the two liquid phases with an explicit interface. This step allows one to work at the same bulk concentrations as the experimental data by imposing the precise bulk phase compositions and predicting the interface composition. Finally, DPD simulations were used to predict IFT values for different solute concentrations. Our results on variation of IFT with solute concentration in bulk phases are in good agreement with experimental data, but some deviations can be observed for systems containing hexane molecules.

A simple apparatus to study the effect of lithology, permeability, and wettability on spontaneous imbibition

The spontaneous imbibition phenomenon is an important process in hydrocarbon recovery. Laboratory study of imbibition is affected by many parameters including, rock characteristics, boundary conditions, length of the sample, variable interfacial tension, and sample heterogeneity. Investigating spontaneous imbibition enhances our understanding of the imbibition mechanism and, hence, helps improve waterflooding used in the oil industry. A simple apparatus has been developed to resemble naturally fractured reservoirs. Using the developed apparatus, the effects of lithology, permeability, and wettability on spontaneous imbibition have been experimentally investigated. Some encountered unexpected technical problems during the experiments are overcome and reported in this paper. Details of the developed apparatus are shown and spontaneous imbibition results are presented. First, the effect of permeability on the oil recovery rate is presented. In addition, obtained curves of oil recovery by water spontaneous imbibition using different lithology are presented. Finally, results of oil recovery from Berea sandstone core sample before and after wettability alteration are shown.

Effects of asphaltene, resin and crude oil type on the interfacial tension of crude oil/brine solution

In recent years, the behavior of crude oil interfacial tension (IFT) as a function of salt concentration have been investigated. The results found in literature are highly controversial, thus the current experimental study aimed to clarify the reasons behind this by developing a methodology based on extracting asphaltene and resin from three different crude oils and performing elemental analysis on them. In addition, the effect of salinity on the IFT of three studied crude oil was compared with the synthetic crude oil consisted of different weight percent (wt%) of asphaltene and resin in toluene. The obtained results revealed that the IFT of crude oil as a function of salinity depended not only on the wt% of asphaltene and resin fractions but also on the aromaticity of asphaltene and resin. In fact, as the aromaticity of asphaltene increased, the performance of asphaltene decreased as a function of salinity while the aromaticity of resin led to a revers trend on IFT variation.

Synergetic interfacial adsorption of protein and low-molecular-weight emulsifiers in aerated emulsions

Whipped creams (aerated emulsions) are a complex emulsion-foam system whose oil-stabilizing potential and aeration capacity are determined by the surface activity of proteins and small surfactants. In this study, the interaction between three low-molecular-weight (LMW) emulsifiers [sodium stearoyl lactylate (SSL), phospholipid (PL), and sucrose ester (SE)] with caseinate was investigated to elucidate the mechanism of formation and stability of whipped creams. Competitive adsorption, interfacial tension, droplet aggregation, viscosity, and morphological variations of the emulsions were examined, and aeration capacity, hardness, and microstructure of whipped creams were measured. The combination of surfactants (0.05–1.0% w/w) with caseinate (0.6% w/w) produced concerted effects on the stability of emulsions. Water-soluble surfactant (SE) adsorbed more strongly than oil-soluble surfactants (SSL and PL) onto oil droplets. The lesser protein adsorption in the SE emulsion enabled a strong foaming activity in the subsequent aeration. Protrusions of triacylglycerol crystals and aggregation of oil droplets into an interactive colloidal matrix with considerable hardness and viscosity were prominently observed in SE creams. On the other hand, shear thinning followed by thickening was observed when PL was added to form the caseinate-based emulsion while no foaming was produced, and SSL, known to form α-gel at the interface, produced no stable foam. The improved emulsion stability yet the propensity to coalesce induced by cooperative actions of casein molecules and hydrophilic surfactant played a crucial role in producing aerated emulsions.

Surfactant Variations in Porous Media Localize Capillary Instabilities during Haines Jumps.

We use confocal microscopy to measure velocity and interfacial tension between a trapped wetting phase with a surfactant and a flowing, invading nonwetting phase in a porous medium. We relate interfacial tension variations at the fluid-fluid interface to surfactant concentration and show that these variations localize the destabilization of capillary forces and lead to rapid local invasion of the nonwetting fluid, resulting in a Haines jump. These spatial variations in surfactant concentration are caused by velocity variations at the fluid-fluid interfaces and lead to localization of the Haines jumps even in otherwise very uniform pore structure and pressure conditions. Our results provide new insight into the nature of Haines jumps, one of the most ubiquitous and important instabilities in flow in porous media.

Estimation of Interfacial Tension in Mixtures of Linear Hydrocarbons and Immiscible Organic Liquids with Water by Dissipative Particle Dynamics (DPD)

Petroleum systems have a high level of complexity due to the presence of a huge variety of organic compounds, mainly hydrocarbons. These characteristics, not only make difficult its recovery but also its study. In this sense, the study of parameters, such as the local variation of interfacial tension (IFT) is essential to understanding the behavior of different interfaces that arise through the extraction, transport and oil refining processes. Accordingly, in the present study, theoretical estimations of IFTs of linear-hydrocarbon-water, linear-hydrocarbon-glycerol, and mixtures of 11 types of organic-liquid with water were performed. The system elements were built by using coarse-graining technique and the dynamics were carried out by the Dissipative Particle Dynamics (DPD). With this technique was possible to reproduce, in a systematic way, an important set of IFT values for systems of oil industrial interest, which reproduced trends obtained from experimental analogous conditions.

Effects of Impurities on CO2 Sequestration in Saline Aquifers: Perspective of Interfacial Tension and Wettability

In recent years, the reduction of CO2 emissions has become a joint effort throughout the world, and carbon capture and sequestration (CCS) is an effective approach to solving the problem of CO2 emissions. In the present study, the effects of adding CH4, Ar, and H2S to CO2 on the interfacial tension (IFT) and wettability (contact angle, CA) of the CO2/water/silica system have been investigated using molecular dynamics simulation methods at 20 MPa and 318 K when the molar concentration of impurity gas was fixed at 20%. For the conditions studied, (1) CH4 has no significant effect; (2) Ar leads to a higher IFT, a larger CA on silica surfaces with a high hydroxyl density, and a smaller CA on silica surfaces with a low hydroxyl density; and (3) H2S causes a decrease of the IFT and an increase of the CA. Capillary pressure and gas storage capacity were predicted using IFT and CA data, and the variation of IFT and CA were explained based on density profiles normal to the gas/water and gas/silica interfaces. Thes...

Size Distribution and Dispersion of Droplets Generated by Impingement of Breaking Waves on Oil Slicks

AbstractThis laboratory experimental study investigates the temporal evolution of the size distribution of subsurface oil droplets generated as breaking waves entrain oil slicks. The measurements are performed for varying wave energy, as well as large variations in oil viscosity and oil‐water interfacial tension, the latter achieved by premixing the oil with dispersant. In situ measurements using digital inline holography at two magnifications are applied for measuring the droplet sizes and Particle Image Velocimetry (PIV) for determining the temporal evolution of turbulence after wave breaking. All early (2–10 s) size distributions have two distinct size ranges with different slopes. For low dispersant to oil ratios (DOR), the transition between them could be predicted based on a turbulent Weber (We) number in the 2–4 range, suggesting that turbulence plays an important role. For smaller droplets, all the number size distributions have power of about −2.1, and for larger droplets, the power decreases well below −3. The measured steepening of the size distribution over time is predicted by a simple model involving buoyant rise and turbulence dispersion. Conversely, for DOR 1:100 and 1:25 oils, the diameter of slope transition decreases from ∼1 mm to 46 and 14 µm, respectively, much faster than the We‐based prediction, and the size distribution steepens with increasing DOR. Furthermore, the concentration of micron‐sized droplets of DOR 1:25 oil increases for the first 10 min after entrainment. These phenomena are presumably caused by the observed formation and breakup oil microthreads associated with tip streaming.

Linear stability of two-layer Couette flows

The stability of two-layer Couette flow is investigated under variations in viscosity ratio, thickness ratio, interfacial tension and density ratio. The effects of the base flow on eigenvalue spectra are explained. A new type of interfacial mode is discovered at low viscosity ratio with properties that are different from Yih’s original interfacial mode (Yih, J. Fluid Mech., vol. 27, 1967, pp. 337–352). No unstable Tollmien–Schlichting waves were found over the range of parameters considered in this work. The results for thin films with different thicknesses can be collapsed onto a single curve if the Reynolds number and wavenumber are suitably defined based on the parameters of the thin layer. Interfacial tension always has a stabilizing effect, but the effects of density ratio cannot be so easily generalized. Neutral stability curves for water–alkane and water–air systems are presented as an initial step towards better understanding the effects of flow stability on the longevity and performance of liquid-infused surfaces and superhydrophobic surfaces.

Dissolution of commercial nanoscale silica particles in electrolyte solution: The importance of the solid-solvent-ratio to physical and chemical properties of the solid-liquid interface

Dissolution experiments of silica nanoparticles (NPs) were performed in an aqueous TRIS buffer system (pH=7.6) at 25°C and the effect of the particles to solvent ratio (PSR) was studied. Increasing the PSR distinctly promotes the kinetic size effect described previously, which leads to solute concentrations exceeding the thermodynamic saturation concentration under the respective conditions considerably. The striking experimental observations readily are rationalized by analysis of the Gibbs free energy (GFE) of the system. In the extended model approach the dissolution and Ostwald ripening is described using gradient curves of GFE, which have been calculated considering a variable interfacial tension of the solid-liquid-interface, γ. The GFE analysis provides size, RP, and concentration, ZP, of NPs as a function of dissolution time. The variation of the interfacial tension with particle size, γ(RP), is a consequence of the properties of the electric double layer, surface charge and surface potential, around the NPs. Suggestions are made how to predict the dissolution process from properties of the initial system solid-solution. Any meaningful report of dissolution experiments should include the saturation concentration of the material that forms the NPs as thermodynamic criterion, and the time necessary to obtain half of the saturation concentration in the system considered as kinetic criterion. Both aforementioned criteria are accessible from experiments without any model considerations.

Molecular Gibbs Surface Excess and CO2-Hydrate Density Determine the Strong Temperature- and Pressure-Dependent Supercritical CO2-Brine Interfacial Tension.

In CO2 geological storage, the interfacial tension (IFT) between supercritical CO2 and brine is critical for the storage capacitance design to prevent CO2 leakage. IFT relies not only on the interfacial molecule properties but also on the environmental conditions at different storage sites. In this paper, supercritical CO2-NaCl solution systems are modeled at 343-373 K and 6-35 MPa under the salinity of 1.89 mol/L using molecular dynamics simulations. After computing and comparing the molecular density profile across the interface, the atomic radial distribution function, the molecular orientation distribution, the molecular Gibbs surface excess (derived from the molecular density profile), and the CO2-hydrate number density under the above environmental conditions, we confirm that only the molecular Gibbs surface excess of CO2 molecules and the CO2-hydrate number density correlate strongly with the temperature- and pressure-dependent IFTs. We also compute the populations of two distinct CO2-hydrate structures (T-type and H-type) and attribute the observed dependence of IFTs to the dominance of the more stable, surfactant-like T-type CO2-hydrates at the interface. On the basis of these new molecular mechanisms behind IFT variations, this study could guide the rational design of suitable injecting environmental pressure and temperature conditions. We believe that the above two molecular-level metrics (Gibbs surface excess and hydrate number density) are of great fundamental importance for understanding the supercritical CO2-water interface and engineering applications in geological CO2 storage.