Effect Of Interfacial Tension Research Articles

Nanoclay compatibilization of phase separated polysulfone/polyimide films for oxygen barrier

Polyimide (PI) and Polysulfone (PSF) films are used in many applications ranging from electronic film capacitors to membranes for gas separation and water purification, yet their phase separation issues limit many potential synergistic blend film applications. To this end, we examine the potential of nanoclays as non-traditional compatibilizers and re-enforcing agents in these technologically important polymer blend films. Herein, we quantify the effect of a nanoclay, Cloisite 30B on the phase separated blend film morphology compatibilization of PSF/PI and associated changes in its mechanical properties and film surface energy. Addition of as little as 1 mass% of organoclay strongly compatibilized the blend phases at all compositions, reducing the scale of blend phase separation by ~5–10 times, and interestingly, the net discreet surface phase separated domain area converged to that observed in 50% blend composition for other off-symmetric blend compositions. Clay compatibilization effects also induced a notable reduction of aspect ratio of surface phase separated domains in thin film blends, attributed to a high degree of exfoliation of the nanoclay by the PSF component so that the effective PSF domain interfacial tension with PI is reduced. Surface modification effects on topography leveling and surface energy changes are only qualitatively similar to our previous observations of block copolymer compatibilizer effect on polymer thin film blend phase separation. Thermal decomposition (TGA) measurements of PSF/PI films showed a decrease in thermal stability upon adding C30B due to its surfactant modification, while film mechanical tensile modulus properties improved slightly by adding low concentration of C30B (~1 mass%), but higher nanoclay loading decreased tensile strength and elongation at break. Finally we note that in terms of processing, the viscosities of the polymer solutions dramatically changed with addition 1 mass% and 3 mass% of C30B. We anticipate that more generally, nanoclays can act similarly to traditional polymeric compatibilizers in many aspects in suppressing polymer thin film blend phase separation that can have ramifications for many advanced technological applications such as sensors and membranes. To this end, we present preliminary oxygen barrier properties of adding Cloisite 30B on PSF/PI blend films.

A lattice Boltzmann method for axisymmetric multicomponent flows with high viscosity ratio

A color-gradient lattice Boltzmann method (LBM) is proposed to simulate axisymmetric multicomponent flows. This method uses a collision operator that is a combination of three separate parts, namely single-component collision operator, perturbation operator, and recoloring operator. A source term is added into the single-component collision operator such that in each single-component region the axisymmetric continuity and momentum equations can be exactly recovered. The interfacial tension effect is realized by the perturbation operator, in which an interfacial force of axisymmetric form is derived using the concept of continuum surface force. A recoloring operator proposed by Latva-Kokko and Rothman is extended to the axisymmetric case for phase segregation and maintenance of the interface. To enhance the method's numerical stability for handling binary fluids with high viscosity ratio, a multiple-relaxation-time model is used for the collision operator. Several numerical examples, including static droplet test, oscillation of a viscous droplet, and breakup of a liquid thread, are presented to test the capability and accuracy of the proposed color-gradient LBM. It is found that the present method is able to accurately capture the phase interface and produce low spurious velocities. Also, the LBM results are all in good agreement with the analytical solutions and/or available experimental data for a very broad range of viscosity ratios.

Effects of interfacial heat transfer, surface tension and contact angle on the formation of plasma-sprayed droplets through simulation study

Abstract A comprehensive numerical study of the effects of interfacial heat transfer, surface tension (1.8 N/m, 1.647 N/m, 1.35 N/m and temperature-dependent values) and contact angles (60°, 90° and 120°) on the droplet spreading behaviour in the formation of the plasma-sprayed splats was conducted. The evolution of splat morphologies with time was accurately captured using a volume of fluid (VOF) model in a 2-D computational domain. The results show that bubbles form at the time of impact and decrease the heat transfer efficiency at the contact points. During spreading, solidification occurs at the droplet edge before maximum spreading. The rapid growth of the underlying solidified layer induces fluid instabilities for the upper liquid layer, which triggers material jetting. The interfacial heat transfer is the key parameter influencing the droplet cooling process and the final splat morphology. Increasing the substrate preheating temperatures (from 27 °C to 300 °C) delays solidification but increases the potential of substrate melting. A low surface tension (1.35 N/m) readily promotes liquid projections, while the contact angle is of less importance in changing the surface morphologies.

Investigating the effect of interfacial tension and contact angle on capillary pressure curve, using free energy Lattice Boltzmann Method

Two phase flow of gas and oil through a porous medium was simulated by Free Energy model of Lattice Boltzmann Method. Constant pressure boundary condition for Free Energy model was derived and then, capillary pressure curve was determined for high density ratio flow (gas and oil flow) through porous media. A validation test was carried out to calculate pore size distribution from determined capillary pressure curve. Good agreement between this pore size distribution and real pore size distribution of porous medium was seen. Finally, the effect of interfacial tension and contact angle on shape of capillary pressure curve was investigated. Comparison of these results with experimental results of literature in this field shows good consistency between trends of capillary pressure curves. The results confirm that Free Energy lattice Boltzmann method is capable of determining acceptable capillary pressure curve for gas and oil flow in porous media which is supposedly the first usage of Free Energy model for this objective.

The effects of interfacial tension, injection rate, and permeability on oil recovery in dilute surfactant flooding

ABSTRACTSurfactant flooding as a potential enhanced oil recovery technology in depleted reservoirs after water flooding has been documented for several decades and has attracted extensive attention. This research explored the effect of interfacial tension among crude oil and surfactant, injection rate, and permeability on oil recovery in dilute surfactant flooding. The results indicated that the additional oil recovery increased with the reduction of the interfacial tension and the increase of the permeability. The additional oil recovery increased and later decreased with the increase of injection rate. The research is instructive for surfactant flooding application for enhanced oil recovery.

Internal gravity–capillary solitary waves in finite depth

We consider a two‐dimensional inviscid irrotational flow in a two layer fluid under the effects of gravity and interfacial tension. The upper fluid is bounded above by a rigid lid, and the lower fluid is bounded below by a rigid bottom. We use a spatial dynamics approach and formulate the steady Euler equations as a Hamiltonian system, where we consider the unbounded horizontal coordinate x as a time‐like coordinate. The linearization of the Hamiltonian system is studied, and bifurcation curves in the (β,α)‐plane are obtained, where α and β are two parameters. The curves depend on two additional parameters ρ and h, where ρ is the ratio of the densities and h is the ratio of the fluid depths. However, the bifurcation diagram is found to be qualitatively the same as for surface waves. In particular, we find that a Hamiltonian‐Hopf bifurcation, Hamiltonian real 1:1 resonance, and a Hamiltonian 02‐resonance occur for certain values of (β,α). Of particular interest are solitary wave solutions of the Euler equations. Such solutions correspond to homoclinic solutions of the Hamiltonian system. We investigate the parameter regimes where the Hamiltonian‐Hopf bifurcation and the Hamiltonian real 1:1 resonance occur. In both these cases, we perform a center manifold reduction of the Hamiltonian system and show that homoclinic solutions of the reduced system exist. In contrast to the case of surface waves, we find parameter values ρ and h for which the leading order nonlinear term in the reduced system vanishes. We make a detailed analysis of this phenomenon in the case of the real 1:1 resonance. We also briefly consider the Hamiltonian 02‐resonance and recover the results found by Kirrmann. Copyright © 2016 John Wiley & Sons, Ltd.

Numerical study on transient response of droplet deformation in a steady electric field

The transient response of droplet deformation in a steady electric field is investigated by the numerical simulation and the motion of interface is captured by level-set method. The numerical scheme is validated and found to be in good agreement with classic analytical solutions. The effects of electric field intensity, interfacial tension, oil viscosity and droplet size on the transient deformation process are systematically discussed. The numerical results show that electric field intensity can accelerate the deformation of the droplet, while interfacial tension and oil viscosity damp it. Furthermore, the relation between electric capillary number and dimensionless deformation time is obtained.

Shear modulus of structured electrorheological fluid mixtures.

Some immiscible blends under a strong electric field often exhibit periodic structures, bridging the gap between two electrodes. Upon shear, the structures tilt, and exhibit an elastic response which is mostly governed by the electric energy. Assuming a two-dimensional stripe structure, we calculate the Maxwell stress, and derive an expression for the shear modulus, demonstrating how it depends on the external electric field, the composition, and the dielectric properties of the blend. We also suggest the notion of effective interfacial tension, which renormalizes the effect of the electric field. This leads to a simple derivation of the scaling law for the selection of the wavelength of the structure formed under an electric field.

Direct Observation of Formation Behavior of Metal Emulsion in Sn/Salt System

Using two systems with different interfacial tensions, the behavior of metal emulsions during bottom blowing was observed directly with a high-speed camera. The interfacial tension between molten salt (KCl-LiCl-NaCl) and molten Sn was measured by a pendant drop method, and it decreased to about 100 mN/m when the Te content in Sn increased from 0 to 0.5 pct. In both systems, two types of metal emulsion behaviors were observed. In Mode A, fine metal droplets were formed after the metal film ruptured at the interface. In Mode B, the formation of coarse droplets was observed after the disintegration of the column generated by the rising bubble, and the number of droplets increased with the gas flow rate compared to that in Mode A. The generating frequency of each mode revealed that Mode B became dominant with increasing gas flow rate. In the pure Sn/salt system, the numbers of droplets of Mode B showed a local maximum at high gas flow rates, but the numbers of droplets in Sn-0.5 pctTe/salt increased continuously even in the same flow range. Regarding the size distribution, the percentage of coarse metal droplets in the Sn-0.5 pctTe alloy/salt was larger than that in the pure Sn/salt. Furthermore, the effect of interfacial tension on the variation in surface area and volume of the droplets showed a similar tendency for the column height. Therefore, a decrement of the interfacial tension led to an increment of the column height when Mode B occurred and finally resulted in a higher interfacial area.

Experimental study and thermodynamic modelling of methane and mixed C1 + C2 + C3 clathrate hydrates in the presence of mesoporous silica gel

In this communication, methane and synthetic gas mixture [CH4 (93.25 mol%) + C2H6 (4.8 mol%) + C3H8 (2 mol%)] hydrate dissociation conditions above the ice point of water were measured in a synthetic porous media of silica gel with different pore radii of 10 and 15 nm in the temperature and pressure ranges of (273.3–287.0) K and (3.30–6.22), respectively. The predictions of a thermodynamic model based on the solid solution theory of van der Waals and Platteuw (vdWP) considering the effects of interfacial tension and capillary forces are then compared with the obtained experimental data. It is shown that the model results are in good agreement with the corresponding data.

Gas/Oil Relative Permeability Normalization: Effects of Permeability, Wettability, and Interfacial Tension

Summary Relative permeabilities (kr) are crucial flow functions governing the fluid distribution within and production from petroleum reservoirs under various oil-recovery methods. To obtain these important reservoir parameters, conventionally, it is required to take rock samples from the reservoir and perform appropriate laboratory measurements. Although kr is expressed as a function of fluid saturation, it is now well-known that kr values are affected by pore structure and distribution, absolute permeability, wettability, interfacial tension (IFT), and saturation history. These rock/fluid properties often change from one region of the reservoir to another, but it would be impossible to perform kr measurements for all regions of a reservoir. Generally, performing experiments on a core with higher permeability is faster and easier than a low-permeability rock. Therefore, assuming all other parameters such as wettability, IFT, and displacement direction are the same for two rocks with different permeabilities, the question becomes how do we estimate the kr of a rock with lower permeability from available (measured) kr of a higher-permeability rock? How do we account for wettability and IFT differences? A normalization technique has been proposed to remove the effect of irreducible water and trapped saturations, which would be different under different conditions. The relative permeabilities can then be denormalized and assigned to different regions (rock types) of the reservoir on the basis of their own irreducible water and trapped saturations. The objective of this study is to introduce a methodology to predict the gas/oil kr for new rock/fluid conditions (such as permeability, wettability, and IFT) by use of existing gas/oil kr data measured at different conditions. By use of measured data from coreflood experiments, we show that by applying an appropriate normalization technique one can adequately predict kr of rocks with different permeability and wettability conditions in two-phase gas/oil flow. However, the results show that the effect of IFT change cannot be captured by normalization techniques. To improve the methodology, a new hypothesis is introduced and proposed here on the basis of dynamic trap saturation. Finally, by use of our experimental data, we evaluate the validity of the Coats (1980) IFT scaling method. We demonstrate the shortcomings of the method and offer an improvement to its prediction.

Droplet dynamics in confinement

This study is to understand confinement effect on the dynamical behaviour of a droplet immersed in an immiscible liquid subjected to a simple shear flow. The lattice Boltzmann method, which uses a forcing term and a recolouring algorithm to realize the interfacial tension effect and phase separation respectively, is adopted to systematically study droplet deformation and breakup in confined conditions. The effects of capillary number, viscosity ratio of the droplet to the carrier liquid, and confinement ratio are studied. The simulation results are compared against the theoretical predictions, experimental and numerical data available in literature. We find that increasing confinement ratio will enhance deformation, and the maximum deformation occurs at the viscosity ratio of unity. The droplet is found to orient more towards the flow direction with increasing viscosity ratio or confinement ratio. Also, it is noticed that the wall effect becomes more significant for the confinement ratios larger than 0.4. Finally, the critical capillary number, above which the droplet breakup occurs, is found to be mildly affected by the confinement for the viscosity ratio of unity. Upon increasing the confinement ratio, the critical capillary number increases for the viscosity ratios less than unity, but decreases for the viscosity ratios more than unity.

Barite precipitation following celestite dissolution in a porous medium: A SEM/BSE and μ-XRD/XRF study

A reaction cell experiment was designed to examine mineral dissolution/precipitation processes both at the macroscopic and pore scale. A rectangular flow cell was filled with a reactive porous layer lying between two porous layers composed of quartz sand (SiO2). The reactive layer consisted of celestite (or celestine, SrSO4) with a bimodal grain size distribution (<63μm and 125–400μm). A barium chloride solution was then injected into the flow cell, leading to fast dissolution and replacement of celestite by barite (or baryte, BaSO4). Due to the higher molar volume of barite compared to celestite, the porosity decreased in the reactive layer. We concentrated on the refinement of post-mortem analysis and the investigation of the dissolution/precipitation mechanisms at the pore scale (10–100μm). The sequential evolution of mineral transformations occurring in the reactive layer was determined. Our analytical techniques, combining scanning electron microscopy and synchrotron X-ray microdiffraction/microfluorescence, showed that the small celestite grain fraction dissolved rapidly to form nano-crystalline barite filling the pore space, while large celestite grains were covered with a thin rim of epitaxial micro-crystalline barite. Two distinct nucleation mechanisms for barite precipitation were involved: homogeneous nucleation (nucleation of barite in the pore space) and heterogeneous nucleation (nucleation on the surface of a solid substrate). Classical nucleation theory, using well-established and estimated parameters (e.g. effective interfacial tension) describing barite nucleation, was applied to explain the mineralogical changes occurring in our system.

Effects of Surfactant Blend Formulation on Crude Oil-Brine Interaction and Wettability: An Experimental Study

Interfacial tension of reservoir fluids and wettability are important parameters in the process of enhanced oil recovery. These two parameters affect the fluid distribution within reservoir formation. The fluids distribution in the reservoir strongly affects the flow behavior and residual oil recovery. Interfacial tension plays an important role due to its relationship between foam surface energy and foam stability. The wettability by contact angle measurement provides a method for determining fluid interaction and is considered as a basic research than practical tool for analysis of reservoir formation. The main objective of this research study is to determine the effects of interfacial tension and wettability on foam surfactant blend formulations, brine and crude oil. Anionic and nonionic surfactant blend were selected. The interfacial tension test was performed at 85oC. Dynamic interfacial tension of blended surfactant formulations with Malaysian crude oil were measured in fixed brine salinity. The interfacial tension values of tested surfactant blends were found lower than the interfacial tension between brine and crude oil. Interracial tension between crude oil and foam forming surfactant was reduced by using different concentration of surfactant blend. Good values were obtained by the measurement of contact angle between solid and three foam surfactant blend formulations. The interfacial tension and contact angle experimental studies revealed that, the blend of Alpha Olefin Sulfonate and Sodium Dodecyl Sulfonate with Octylphenol Ethylene Oxide play an important role in reducing the interfacial tension at crude oil-brine interface. The reduced interfacial tension and more wetting surface effects indicated that, these foam surfactant formulations are of great importance in the process of residual oil recovery.

Janus hybrid silica/polymer nanoparticles as effective compatibilizing agents for polystyrene/polyamide-6 melted blends

Silica/polystyrene Janus hybrid nanoparticles (JHNPs) were synthesized at the gram scale via miniemulsion polymerization technique and then incorporated into polystyrene/polyamide-6 melted blends. Due to their intrinsic amphiphilic properties, the JHNPs migrate to the interface of the PS/PA6 blend during the mixing process and play the role of a compatibilizing agent. First, a significant decrease of the size of the dispersed nodules was observed even at low content of JHNPs, whereas an optimum content of JHNPs corresponding to the saturation of the polystyrene/polyamide-6 (PS/PA6) interface was found in the 3–5 phr range. Secondly, the rheological properties of the blends were also significantly modified. The complex viscosity increased as a function of JHNPs content over the entire frequency range studied. Up to 5 phr of JHNPs, a high increase of the viscosity at low frequencies was observed. This is attributed to the formation of a solid network through the matrix/nodules interface of the nanocomposite. Finally, the Palierne model extended to the field of immiscible polymer blends was used; an important decrease of the effective interfacial tension of the system was observed when JHNPs were added. The asymmetry of these nanoparticles allows the combination of a “Pickering effect” of a solid particle with a “copolymer effect” of an amphiphilic structure. The synthesis procedure of JHNPs developed in this work renders these silica/polymer JHNPs interesting as a route for the compatibilization of polymer blends.

Droplet Breakup in Expansion-contraction Microchannels.

We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices.

Effective interfacial tension effect on the instability of streaming Rivlin-Ericksen elastico-viscous fluid flow through a porous medium

The instability of the plane interface between two uniform, superposed and streaming Rivlin-Ericksen elastico-viscous fluids through porous media, including the ‘effective interfacial tension’ effect, is considered. In the absence of the ‘effective interfacial tension’ stability/instability of the system as well as perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if perturbations in the direction of streaming are ignored, whereas for perturbation in all other directions, there exists instability for a certain wave number range. The ‘effective interfacial tension’ is able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations, the medium porosity reduces the stability range given in terms of a difference in streaming velocities.

Point-source imbibition into dry aqueous foams

We use experiments, modeling and numerics to study the imbibition dynamics from a point source into a homogeneous dry aqueous foam. A distinctive feature of foams compared to solid porous material is that imbibition occurs in the liquid microchannels of the foam called Plateau borders, which have a volume varying in space and time. Dynamics is driven by the capillary pressure and resisted by the viscous and gravity forces in the liquid microchannels. Assuming a constant pressure in the imbibing liquid reservoir, we show that the imbibition front advances and flattens out in time due to gravity, the effect of which is quantified by introducing the Bond number B, which compares the gravitational effects to the capillary pressure using the mean bubble radius as the characteristic length. This evolution describes both miscible and immiscible imbibing liquids. For the latter, we introduce the idea of an effective interfacial tension to take the oil-water interfacial energy into account. The details of the imbibition process are confirmed by experiments and numerics using foams with tangentially immobile interfaces in the channel-dominated model.

Combining molecular dynamics and lattice Boltzmann simulations: a hierarchical computational protocol for microfluidics

A hierarchical computational protocol is introduced to investigate the role of interfacial and wetting properties to the fluid displacement in hydrophilic pore network models (PNMs). Based on the combination of molecular dynamics (MD) and lattice Boltzmann method (LBM) simulations at both nano- and microscales, we study the role of dispersed functionalized \(\hbox {SiO}_{2}\) nanoparticles (NP) in brine to the oil displacement process in a clay (montmorillonite—MMT) pore structure. Our MD calculations indicate that dispersion of NP, with different hydrophilic properties, in brine solution reduces the interfacial tension between oil and brine, followed by an increase in the contact angle. The lowest interfacial tension and highest contact angle are for the hydrophilic NP functionalized with polyethylene glycol groups. By mapping the properties obtained from MD into LBM simulation parameters, we explore the oil displacement process in hydrophilic PNMs at the microscale. For all systems, the Young–Laplace filling rules are obeyed and, due to the finger formation, the displacement efficiency decreases as the capillary number increases. It was observed that, with the inclusion of NP, a reduction in interfacial tension associated with an increase in the contact angle may enhance the oil displacement process in hydrophilic pore systems at the microscale. The proposed computational protocol can be a versatile tool to explore the potentialities of chemical additives, such as NP, for the oil recovery process and investigate the effects of interfacial tension and wetting properties on the fluid behavior at both nano- and microscales.

Effects of interfacial tension and emulsification on displacement efficiency in dilute surfactant flooding

This study provides an investigation on the effect of interfacial tension (IFT) and emulsification on displacement efficiency in dilute surfactant flooding.