Interfacial Shear Viscosity Research Articles

Liquid Drainage in Single Plateau Borders of Foam

This paper reports on an investigation of the influence of the interfacial shear viscosity on the liquid drainage in single Plateau borders of foam. The simplified Navier–Stokes equation governing the liquid flow is solved for the liquid velocity by the numerical computational method. The numerical results show significant influence of the interfacial shear viscosity on the liquid velocity in the Plateau border. Comparison of the numerical results for the average velocity over the cross-section area of the Plateau border to the available analytical solution shows that the available analytical solution underestimates the average velocity. New, simple yet accurate correlations for the dependence of the average velocity on the radius of the cross section of the Plateau border, the pressure gradient, and the interfacial shear viscosity are obtained using the asymptotic analysis and the numerical data.

Interfacial film properties of asphaltenes and resins

Interfacial film properties of asphaltenes and resins have been studied by interfacial shear viscosity measurements. The results show that the structure of the asphaltene film at the interface between oil and water is changed from two-dimensional to three-dimensional network as the concentration of the asphaltene at the interface increased. The film can be divided into three types namely expanded liquid film, condensed liquid film and solid-like three-dimensional network film. Furthermore, the structures of the interfacial films formed by asphaltene molecules and asphaltene particles are different and the strengths of these films are also different. The adsorption and migration processes of asphaltene molecules and migration process of asphaltene particles at the interface are different.

Effect of interfacial properties on the drop size distribution of high internal phase ratio emulsions

Interfacial properties of polyoxyethylene(2) oleyl ether and drop size distributions of emulsions prepared with this surfactant are investigated experimentally in this work; 80, 88 and 94% (v) internal phase ratio W/O type emulsions were prepared, where the aqueous phase was 1% sorbitol solution and the oil phase, a 1:1 v/v mixture of surfactant and paraffin oil. Experimental evidence indicated an interaction between the hydrocarbon chains of surfactant molecules and the solvent paraffin oil through van der Waals forces and between the ethoxylate groups and sorbitol, a polyalcohol, in the aqueous phase through hydrogen bonds, notably below the transition temperature. Continuous phase liquid present in the plateau borders was found to act as a reservoir of surface active agents, minimizing the effect of stretching of the film under shear. In cases where the amount of liquid hold up in plateau borders is negligible, the drop size distributions were found to be very sensitive to shearing rate. Interplay between the interfacial shear viscosity and the interfacial tension was found to control the rate of coalescence of drops less than 0.48 μm only in the case of 94% emulsions, corresponding to maximum stretching of interfacial area. In other cases, interfacial film stability seems to control the rate of coalescence.

Interfacial shear rheology of aged and heat-treated beta-lactoglobulin films: displacement by nonionic surfactant.

Interfacial shear rheology of adsorbed beta-lactoglobulin films (bulk protein concentration 10(-)(3) wt %) has been studied over the temperature range 20-90 degrees C using a two-dimensional Couette-type viscometer. Effects of the type of interface (air-water, triolein-water, and n-dodecane-water), the pH (2.0, 5.6, 6.0, 7.0, and 9.0), and the extent of the heat treatment have been assessed via measurements of changes in the apparent interfacial shear viscosity and elasticity before and after the addition of increasing amounts of nonionic surfactant Tween 20 (polyoxyethylene sorbitan monolaurate). The highest interfacial viscosities were obtained at the n-dodecane-water interface and the lowest at the air-water interface. Competitive displacement of protein from the interface by Tween 20 was easier at the air-water and n-dodecane-water interfaces as compared to the triolein-water interface. The surface shear viscosity was higher and the displacement by Tween 20 more difficult as the isoelectric point of the protein was approached, which is in agreement with the presence of a more strongly cross-linked protein network at the interface. The effect of heat treatment was dependent on the pH of the aqueous solution. No simple relationship between the surface rheological characteristics and the ease of displacement by Tween 20 could be inferred.

Viscoelastic theory for nematic polymer interfaces

Full Paper: A macroscopic theory for the dynamics of compressible nematic polymer-viscous fluid interfaces is developed from first principles. The theory is used to define and characterize the basic interfacial viscoelastic material properties of the ordered interfaces. The theory is based on a decomposition of the kinematic fields and nematic tensor order parameter that takes into account the symmetry breaking of the interface. The interfacial rate of entropy production used to identify the interfacial viscoelastic modes is given in terms of surface rate of deformation tensor and the surface Jaumann derivative of the tangential component nematic tensor order parameter. The derived surface viscous stress tensor is asymmetric and thus describes surface flow-induced changes in the tensor order parameter. Consistency with the Boussinesq surface fluid appropriate for Newtonian interfaces is established. The interfacial material functions are identified as the dynamic surface tension, the interfacial dilational viscosities, and the interfacial shear viscosities. The interfacial material functions depend on the surface tensor order parameter and as a consequence anisotropy is their characteristic feature. Two characteristic interfacial tensions and two dilational viscosities are predicted depending on the director orientation. In addition six interfacial shear viscosities arise as the directors sample the velocity, velocity gradient, and vorticity directions. Finally the theory provides for the necessary theoretical tools needed to describe the interfacial dynamics of nematic polymer interfaces, such as capillary instabilities, Marangoni flows, and wetting phenomena.

Viscoelastic theory for nematic interfaces

A complete macroscopic theory for compressible nematic-viscous fluid interfaces is developed and used to characterize the interfacial elastic, viscous, and viscoelastic material properties. The derived expression for the interfacial stress tensor includes elastic and viscous components. Surface gradients of the interfacial elastic stress tensor generates tangential Marangoni forces as well as normal forces. The latter may be present even in planar surfaces, implying that in principle static planar interfaces may accommodate pressure jumps. The asymmetric interfacial viscous stress tensor takes into account the surface nematic ordering and is given in terms of the interfacial rate of deformation and interfacial Jaumann derivative. The material function that describes the anisotropic viscoelasticity is the dynamic interfacial tension, which includes the interfacial tension and dilational viscosities. Viscous dissipation due to interfacial compressibility is described by the anisotropic dilational viscosity, and it is shown to describe the Boussinesq surface fluid appropriate for Newtonian interfaces when the director is homeotropic. Three characteristic interfacial shear viscosities are defined according to whether the surface orientation is along the velocity direction, the velocity gradient, or the unit normal. In the last case the expression reduces to the interfacial shear viscosity of the Boussinesq surface fluid. The theory provides a theoretical framework to study interfacial stability, thin liquid film stability and hydrodynamics, and any other interfacial rheology phenomena.

Interactions between fat crystal networks and sodium caseinate at the sunflower oil‐water interface

AbstractA Couette‐type torsion wire surface shear viscometer was used to measure the apparent interfacial shear viscosity of pH 7 (I=0.05 M) buffered solutions of sodium caseinate in contact with sunflower oil. The sunflower oil contained 1% fat crystals in either the β or β′ polymorphic form, or was crystal free. In all cases, the fat crystals increased the interfacial shear viscosity synergistically, with the β′ crystals causing the biggest increase. Substituting the protein for a small‐molecule surfactant (Tween‐40) showed that this was not simply due to the protein lowering the interfacial tension. Sedimentation studies of the different fat crystal slurries suggested that the extent of the interfacial shear viscosity increase was related to the strength of crystal‐crystal interactions in the oil phase. It seems likely that when protein is present at the interface, it fixes the adsorbed layer of fat crystals to the cross‐linked protein film at the interface. When this film was sheared, the strength of the crystal‐crystal interactions in the oil phase became important. However, when Tween‐40 was in the aqueous phase instead of the protein, the crystal‐crystal interactions were not relevant, presumably because the Tween‐40 interfacial film simply flowed around the adsorbed crystals

Interactions between Tristearin Crystals and Proteins at the Oil–Water Interface

A Couette-type torsion wire surface shear viscometer was used to measure the apparent interfacial shear viscosity of pH 7 (I= 0.05M) buffered solutions of lysozyme, sodium caseinate, and Tween-40 in contact with eithern-tetradecane or purified sunflower oil at a planar interface. When proteins were present in the aqueous phase and tristearin crystals in the oil phase, there was a synergistic increase in the interfacial shear viscosity over the sum of each component in the absence of the other. The magnitude of the increase appeared to be independent of the type of protein but dependent on the nature of the oil phase. This increase in the interfacial shear viscosity was found not to be due simply to the protein reducing the interfacial tension and thus affecting the adsorption behavior of the fat crystals. When the aqueous phase contained a small-molecule surfactant (Tween-40) instead of protein, but at the same interfacial tension as the sodium caseinate system, a significantly smaller increase was observed in the interfacial shear viscosity than in the protein system. It therefore seems likely that when proteins are present, hydrophobic peptide residues interact with the tristearin crystals at the interface.

Effect of Interfacial Rheology on Foams Viscoelasticity, an Effective Medium Approach

We have computed in 3-dimensional foams the influence of interfacial rheology on the macroscopic foam viscoelasticity. We show that the two interfacial moduli play different roles. The dilational viscosity is not at all additive to the macroscopic modulus, while both the interfacial shear viscosity and the internal phase modulus are nearly additive. The dilational viscosity is shunted by a grid mode at high frequency. The calculations are done in a selfconsistent effective medium approximation.

Instability of a non-wetting film with interfacial viscous stress

The destabilization of a thin three-dimensional non-wetting film above a solid wall is examined for the special case in which surfactant is adsorbed onto the free surface of the film. Attention is restricted to the case of a Newtonian surface, with surfactant displaying rapid surface diffusion or exhibiting small Marangoni number, such that the dominant intrinsic interfacial stress is of a purely viscous origin. A surface-excess force approach is adopted for the purpose of incorporating into the analysis the attractive/repulsive dispersive forces acting between the solid wall and the film. Three coupled nonlinear partial differential equations are obtained that describe the ‘large-wavelength’ spatio-temporal evolution of the free film surface following a small initial disturbance. These equations are shown to reduce to results in the literature in the limit of zero interfacial viscosities. Employing linear stability analysis, an explicit dispersion equation is obtained relating the growth coefficient to interfacial viscosities. It is found, at least in the linear regime, that the sum of interfacial shear and dilatational viscosities – and not each separately – imparts a damping effect that in the most extreme case is four-fold relative to the case of no interfacial viscosities. Nonlinear stability analysis in the limiting case of a two-dimensional film indicates that interfacial viscosities may strongly hinder the onset of instability through large interfacial stresses that arise in the vicinity of trough and crest regions of the film.

Influence of Tristearin Crystals on the Apparent Interfacial Shear Viscosity of Aqueous Lysozyme-Hydrocarbon Model Systems

An automated Couette-type torsion-wire surface shear viscometer was used to measure the apparent interfacial shear viscosity of a pH 7 (1 = 0.05 M) phosphate-buffered lysozyme solution in contact with n-tetradecane at a planar interface. When tristearin crystals were present in the oil phase and lysozyme in the aqueous phase, a higher initial apparent interfacial shear viscosity resulted than would be expected from the individual contributions of lysozyme and crystals alone. It is suggested that this synergism is due to the adsorption of hydrophobic groups of the lysozyme to tristearin crystals at the interface. Interactions between proteins and fat crystals are thought to be of significance in the stabilization of many food emulsions.

The interfacial rheological behaviour of monolayers of PEO/PMMA graft copolymers spread at the air/water and oil/water interfaces

Dilatational and shear rheological properties of spread films of PEO/PMMA graft (comb) copolymers were examined at the air/water, toluene/water and toluene— n-heptane/water interfaces. The interfacial dilatational studies were carried out using the stress relaxation Fourier transformation method. The experimental measurement of the interfacial tension decay was performed by means of the Langmuir trough—Wilhelmy plate technique. The high values obtained for the characteristic times and the shape of the Cole—Cole plots indicate that the relaxation processes involve mainly rearrangement in the conformation of the molecules. The interfacial shear viscosity was measured by observing the damped oscillation of a torsion pendulum. The largest interfacial viscosity was exhibited by the monolayer spread at the toluene— n-heptane/water interface. Emulsions prepared with this system, in a separate study to be published, showed the lowest coalescence rate indicating that at this interface the graft copolymer forms a coherent film which retards interdroplet film drainage. The results show that films which exhibit larger values of the interfacial rheological parameters produced a more stable emulsion owing to an increase in the mechanical strength of the interfacial film and its ability to respond to local thickness variations.

Viscous coupling in two-phase flow in porous media and its effect on relative permeabilities

An idealized model of a porous rock consisting of a bundle of capillary tubes whose cross-sections are regular polygons is used to assess the importance of viscous coupling or lubrication during simultaneous oil-water flow. Fluids are nonuniformly distributed over tubes of different characteristic dimension because of the requirements of capillary equilibrium and the effect of interfacial viscosity at oil-water interfaces is considered. With these assumptions, we find that the importance of viscous coupling depends on the rheology of the oil-water interface. Where the interfacial shear viscosity is zero, viscous coupling leading to a dependence of oil relative permeability on oil-water viscosity ratio for viscosity ratios greater than one is important for a range of pore cross-section shapes and pore size distributions. For nonzero interfacial shear viscosity, viscous coupling is reduced. Using values reported in the literature for crude oil-brine systems, we find no viscous coupling.

Competitive displacement of proteins in oil-in-water emulsions containing calcium ions

The influence of calcium ions on the time-dependent competitive adsorption of phosvitin and β-casein at pH 7 has been investigated at the emulsion droplet surface by monitoring the protein content of the aqueous phase. In the absence of calcium ions, addition of β-casein to a phosvitin-stabilised oil-in-water emulsion (0.5 wt.% protein, 20 wt.% n-tetradecane) results in 70% of the originally adsorbed phosvitin becoming displaced within a few minutes, followed by the loss of a further 10% over a 48 h period. In contrast, when calcium ions are present at a concentration sufficient to cause droplet aggregation in the mixed emulsion, no phosvitin is desorbed, despite substantial adsorption of the added β-casein. But, when calcium ions are present in insufficient quantity to cause aggregation, displacement of phosvitin by β-casein is facilitated. The incorporation of calcium ions prior to homogenisation increases the amount of phosvitin at the emulsion droplet surface. The interfacial shear viscosity of an adsorbed phosvitin film at the planar oil—water interface is markedly increased when calcium ions are present.

INVESTIGATION OF EMULSIFICATION AND COALESCENCE PHENOMENA IN CRUDE OIL/ALKALINE WATER SYSTEMS

Abstract Emulsihcation and coalescence processes in crude oil/alkaline water systems were examined and their influence on alkaline Hood enhanced oil recovery was assessed. Emulsification mechanisms were investigated under static and dynamic conditions using microvisual techniques. Coalescence rates were measured using the inclined spinning drop tensiometer. The relative impact of interfacial viscosity on coalescence processes was determined through measurements of interfacial shear viscosities. In addition, the influences of chemical composition on ease of emulsification, coalescence rate, and interfacial shear viscosity were examined. Ease of emulsification was influenced by the composition of the crude oil, the electrolyte concentration, and the partitioning coefficient of surfactants. Coalescence was primarily affected by processes which disrupted the crude oil/water interface. Alkaline flood oil recovery efficiency was promoted by emulsification followed by rapid coalescence to form a stable oil bank.

Alcohol-assisted alkaline flooding for enhanced oil recovery

Alcohol additives were found to improve alkaline flood performance under certain conditions. Only crude oils that emulsified during alkaline flooding were more efficiently recovered with alcohol. Improved recovery with alcohol was attributed to modification of emulsion characteristics. Alcohol additives reduced emulsion viscosities and accelerated emulsion coalescence rates, which improved oil bank stability and promoted oil recovery. Oil recovery efficiency was affected by the chemical structure of the alcohol. Oil recovery generally improved with increasing molecular weight from methanol to butanol and then decreased for the less water soluble pentanol isomers. Alcohol additives were found to affect the interfacial shear viscosities (IFSV) and interfacial tensions (IFT) of crude oil/alkaline water systems. Improvements in recovery efficiency was found to correspond directly to reduced IFSV. Poor recovery was also related to elevated interfacial tensions.

Measuring nonlinear surface stress-deformation behavior for aqueous solutions of dodecyl sodium sulfate and dodecyl alcohol

It is demonstrated for the first time that aqueous solutions of dodecyl sodium sulfate and dodecyl alcohol exhibit nonlinear stress-deformation behavior that can be described by the generalized Boussinesq surface fluid model, at least for data from the deep channel and knife-edge interfacial viscometers. The apparent interfacial shear viscosities reported here are an order of magnitude larger than the interfacial shear viscosities reported previously in the context of the linear Boussinesq surface fluid model. While the reason for the difference is not clear, two cautions concerning interfacial viscosities measurements with this system are discussed.

MEASUREMENT OF LIQUID-LIQUID INTERFACIAL SHEAR VISCOSITY: THE UNSTEADY STATE DEFORMATION OF AN INTERFACE IN A CYLINDRICAL CELL

The theoretical background of a new method for the measurement of liquid-liquid interfacial shear viscosities is presented. The method is simple in design and conducive to routine measurements. Liquid-liquid interfacial shear viscosities are measured by observation of the unsteady state deformation of the interface after a slowly rotating cylindrical cell containing the liquids is abruptly halted. The deformation is established with tracer particles located at the interface between two liquids. Presented here are correlations which relate the traversed angle of the panicles to the interfacial shear viscosity, the viscosities and densities of the bulk phases, and the cup dimensions. Correlations show that the method is sufficiently sensitive to allow measurements of interfacial shear viscosities ranging from 0.001 to 1.0 surface poise (sp). Preliminary data showing good agreement between theoretical predictions and experimental observations for a system expected to show negligible interfacial shear viscosi...

Effect of alcohol on adsorption of casein at the oil—water interface

We report on the effect of added ethanol on time-dependent interfacial tensions and surface shear viscosities at 25°C for adsorbed films of sodium caseinate at the interface between n-hexadecane and an aqueous solution (pH 7, ionic strength 0.005 M) containing from 10 −4 wt% to 10 −1 wt% protein. Addition of 10 wt% ethanol causes changes in interfacial tension which vary from ~15 mN/m at short times to just 2–3 mN/m under steady-state conditions. The presence of 1 wt% ethanol inhibits the formation of a film with measurable surface viscosity. Experiments in which ethanol is added to the sub-phase below an aged protein film are explained in terms of a rapid displacement step, followed by slow accumulation of ethanol-aggregated protein in secondary layers if the bulk protein concentration is high enough.

Behaviour of adsorbed myosin at the oil-water interface

Interfacial tensions and surface shear viscosities are reported at 7 and 25°C for adsorbed films of myosin at the n-tetradecanebuffer interface (bulk protein concentration 10 −3 wt%, pH 6.5, 0.5 m KCl). Surface behaviour similar to that of other proteins is observed at 25°C, but unique surface behaviour is observed at 8°C. An unusual feature is a surface viscosity which increases with temperature-particularly in young films.