Spinning Drop Apparatus Research Articles

New Interfacial Rheology Characteristics Measured Using a Spinning Drop Rheometer at the Optimum Formulation. Part 2. Surfactant–Oil–Water Systems with a High Volume of Middle‐Phase Microemulsion

AbstractThis article is a continuation of our first study on dilational interfacial rheology properties at optimum formulation for surfactant‐oil–water systems at low surfactant concentration just above the cμc. Here, we have investigated a high content of middle‐phase microemulsion with an optimum WIII phase behavior for a system containing sodium dodecyl sulfate, n‐pentanol, and kerosene. A new oscillating spinning drop interfacial rheometer was used to measure the interfacial properties. The very low dilational elasticity moduli and phase angle found at or near hydrophilic–lipophilic deviation (HLD) = 0 are related to the presence of the bicontinuous phase microemulsion and to the fast surfactant exchanges between the bulk and the interface, regardless of the phases involved in the measurement using the spinning drop apparatus, i.e., the two‐phase excess oil and excess water (O‐W) or the bicontinuous microemulsion and excess water (M‐W). We show that at or near optimum formulation, the interfacial tension and the dilational modulus for the M‐W case almost instantly reach equilibrium, because of the high surfactant content in the microemulsion and the fast exchanges between the bulk and the interface. In contrast, when both excess phases (O‐W) are measured, the changes in these properties are slower, due to the scarce presence of surfactants in both phases. The possibility of having almost all the surfactants trapped in the middle‐phase bicontinuous microemulsion could explain the emulsion instability in all the WIII range. This is behaving as if there were no surfactant available in the oil and water phases to stabilize the oil or water droplets thus formed.

Janus emulsions stabilized by phospholipids

Janus emulsions were formed by mixing three immiscible liquids; this implies two oil components (i.e. olive oil (OO) and silicone oil (SiO)) with water in presence of interfacial active components. The morphology and size of Janus droplets formed strongly depended on the type of surfactant used. In presence of a non-ionic surfactant, i.e. Tween 80, large engulfed Janus droplets were formed. By adding phospholipids to the system the droplet size was decreased and more stable Janus droplets formed. Interfacial tension measurements carried out using a spinning drop apparatus and a ring tensiometer demonstrate that interfacial tension is the most important factor controlling the size, morphology and stability of Janus droplets. When the interfacial tension between oil and water becomes ≤1mN/m, smaller Janus droplets are formed. Such conditions are fulfilled when phospholipids are used in combination with non-ionic surfactant Tween 80. The morphology of the double droplets is predominantly controlled by the viscosity and interfacial tension between the two oil phases. By using different types of phospholipids, i.e. asolectin and lecithin instead of a more concentrated phosphatidylcholine (phospholipon), the interfacial tension is decreased and different morphologies of engulfing can be observed.

Mechanical properties of liquid-filled shellac composite capsules

This paper describes the mechanical properties of thin-walled, liquid-filled composite capsules consisting of calcium pectinate and shellac. In a series of experiments we measured the deformation of these particles in a spinning drop apparatus. For different pH-values we studied the elastic properties of these particles and compared the obtained results with the mechanical response measured by squeezing capsule experiments. In analogy to these experiments, we also investigated liquid-filled unloaded calcium pectinate capsules without the addition of shellac. The deformation properties of these experiments and the surface Young moduli were in good agreement. Furthermore we investigated the liquid-filled calcium pectinate and the composite capsules by NMR microscopy. These experiments allowed investigations of the membrane thickness and the kinetics of membrane growing. Additional characterizations by stress controlled small amplitude surface shear experiments of similar composed gel layers provided coherent results for the surface Young modulus.

Deformation of liquid-filled calcium alginate capsules in a spinning drop apparatus

This paper describes the mechanical properties of thin-walled, liquid-filled calcium alginate capsules by measuring the deformation of these particles in a spinning drop apparatus. By variation of the guluronic acid content of the alginate, the polymerization time and the calcium and alginate concentration we systematically studied the elastic properties of these capsules. In a series of experiments we observed for the first time new types of irreversibly deformed capsules, which can be described by plastic deformation. For comparison purposes, we also investigated liquid-filled calcium alginate particles in squeezing capsule experiments. The qualitative and quantitative results of both experiments in terms of the deformation properties and the surface Young moduli were in good agreement. Furthermore we also investigated liquid-filled calcium alginate particles by NMR microscopy to characterize the capsules in view of their membrane thickness. These results, in combination with the spinning capsule experiments allowed us to measure the kinetics of surface gelation and the mechanism of membrane growing.

From two-dimensional model networks to microcapsules

The synthesis of microcapsules for technical, cosmetic, and pharmaceutical purposes has attracted much interest in recent years. The design of new capsules requires profound knowledge of their mechanical properties. Rheological studies provide interesting information on intrinsic membrane features and they can also be used to obtain information on bursting processes and shear-induced release of encapsulated compounds. In this article we shall discuss the basic rheological properties of different types of ultra-thin membranes, which can be used to form stable capsules walls. We have also analyzed the typical structures of these cross-linked films using Brewster-angle microscopy. Tiny oil or water droplets, which are surrounded by ultra-thin membranes, form simple types of microcapsules. In addition to the interface shear rheology, we have measured the Young's modulus (elongational modulus) and the Poisson ratio using a modified spinning drop apparatus. The shear-induced deformation and orientation of microcapsules was investigated in optical rheometers (rheoscopes). In the regime of small deformations the results were in fairly good agreement with a theoretical model recently proposed by Barthes-Biesel. Due to the simple synthesis and well-defined structure, microcapsules can also serve as model systems to understand the complicated flow properties of red blood cells (erythrocytes).

THE USE OF CARBOXYMETHYL ETHOXYLATE SURFACTANT TO DISSOLVE VITAMIN K1 AND TO OBTAIN LOW INTERFACIAL TENSION AND STABLE EMULSION SYSTEMS

The presence of vitamin K1 in human body is important for preventing the hemorrhagic disease. Due to its very long side chain, vitamin K1 is highly insoluble in water. We have successfully dissolve a substantial amount of vitamin K1 in solutions of a commercial surfactant containing carboxymethyl ethoxylates (Hüls B433) and obtained low interfacial tension (IFT) and stable emulsion systems. This paper will present the details of these experiments. The solubilization of vitamin K1 was estimated from UV absorption. The IFT values were measured by using a spinning drop apparatus and all particle sizes were determined by using laser light scattering. By using the Hüls B433 surfactant and an optimum amount of CaCl2, we can dissolve vitamin K1 in water and obtain low IFT systems in the order of 10−2 dyne/cm. The emulsions obtained in these systems are stable and contain droplet sizes below 65 nm. The dissolution of vitamin K1 and the IFT behavior in these systems follow the rules for crude oil and prefer larger surfactant micelles.

An empirical correlation between low interfacial tension and micellar size and solubilization for petroleum sulfonates in enhanced oil recovery

This paper describes some scientific methods for formulating ultralow interfacial tension systems for enhanced oil recovery. The recovery activity was judged by the solubilization of crude oil and the emulsion droplet size formed by the crude oil and the surfactant solutions. Dynamic light scattering was used in measuring the partical size. UV absorption measurement was applied to evaluate the solubilization capacity. Spinning drop apparatus was employed in determining the ultralow interfacial tension. Detailed procedures will be shown on: (1) to find a proper composition for preparing a petroleum sulfonate mixture; and (2) to find the optimum electrolyte concentration to achieve ultralow interfacial tension. The final ultralow interfacial tension systems will be proved by the spinning drop experiment. It was found that a surfactant system which can achieve ultralow interfacial tension has the following characteristics: (1) the surfactant solution contains micelles of around 100 nm in size; (2) the surfactant solution has high solubilization power; and (3) the emulsions formed by the surfactant solution and crude oil has droplet size below 200 nm. Under our experimental conditions, the process of lowering the interfacial tension seems to follow the diffusion controlled solubilization mechanism.

Deformation of a Capsule in a Spinning Drop Apparatus

This paper studies the rheological properties of ultrathin aminomethacrylate membranes that are synthesized at the interface between oil and water. We have measured the kinetics of the cross-linking reactions, the zero shear modulus, and the nonlinear rheological properties of those two-dimensional networks. The measurements were performed at a planar interface using a special surface rheometer. Once stabilized, the membranes exhibit rubber-elastic properties. In addition, we have formed small emulsion droplets using the same type of interfacial polymerization. In order to get more information on the mechanical properties of the resulting microcapsules, we have developed a new experimental technique that consists in measuring the deformation of a capsule in a spinning drop apparatus. A theoretical analysis of the deformation process allows an interface apparent elastic Young modulus to be calculated. From a comparison of the surface shear modulus with the Young modulus, it is then possible to estimate the surface Poisson ratio, which is here approximately zero. These results point to the existence of area compressible anisotropic membranes.

Coalescence and interfacial tension measurements for polymer melts: experiments on a PS-PE model system

A novel technique to measure coalescence phenomena in polymer blends was developed using a spinning drop apparatus. To date, coalescence experiments on polymers were performed by the slow process of gravity driven collisions. In comparison, the spinning drop method is more rapid and more versatile in its control of the contact radius and coalescent force. The governing parameters of the coalescence process, notably interfacial mobility and matrix film rupture thickness, can be assessed by testing a range of droplets of varying size. The relatively high mobility of the interface demonstrated by the experiments explains the dominant role played by coalescence in controlling the dispersion size in polymer melt blending. Estimates of the matrix film rupture thickness are in the order of 20–40 nm for the purified systems. This suggests that in the final stages of film drainage and rupture, entropic effects of the macromolecules play only a minor part. Commercial polymers were shown to coalesce considerably faster than a purified system. Here, impurities may lead to premature coalescence through lubrication of the interface (increasing its mobility) or by third-phase particles destabilising the matrix film.

Coalescence and interfacial tension measurements for polymer melts: A technique using the spinning drop apparatus

A novel technique that involves a spinning drop apparatus has been used to measure the interfacial tension of polymer melts on the basis of the shape of two colliding droplets. The technique combines the advantages of equilibrium techniques (accuracy and straightforward analysis) to a speed of measurement that is equal or faster than dynamic methods. For melt viscosity in the order of 10 4 Pas experimental time is in the order of 30 min. This is independent of viscosity ratio and interfacial tension itself, giving scope for investigating the effects of compatibilisers. Furthermore, the interfacial tension measurement is incorporated in a coalescence experiment. For the model systems chosen (PS/LDPE and PS/LLDPE) commercial polymers were shown to have reduced interfacial tension and increased scatter due to additives. When the polymers were purified the interfacial tension rose significantly.

Phase Behaviour of Ph-Dependent Microemulsions At High Temperature and Salinities

This paper describes the formulation principal for a model microemulsion system which exhibits pH dependent phase behaviour. The system investigated consists of octane, brine, alkyl ether carboxylic acid surfactants and short chain alcohols. The CMCs of these surfactants were lower in acid form of the surfactant (COOH) than for the salt form (COO-), also the micelles formed in acid solutions were smaller than for the salt. Furthermore the surface and interfacial tensions were found to increase with increasing pH. Increasing pH ionises the carboxylic acid head group thereby making the surfactant more hydrophilic. The effect of an increase in pH can be counterbalanced by increasing the electrolyte concentration. Measurements of ultralow interfacial tensions at different salinities and temperatures have been made using a spinning drop apparatus. Three phase microemulsion systems were studied as a function of temperature and pH. It was observed that the presence of ethylene oxide (EO) moiety in the surfactant molecule made the surfactants less sensitive to salinity than anionic surfactants. In addition, the carboxylic ionic head group made the surfactant more stable to temperature than simple EO nonionic surfactants. Thus these surfactants are more robust than either simple anionic or nonionic surfactants and thus these materials have potential in the field of surfactant flooding for tertiary oil recovery.

Evolution of a Liquid Drop in a Spinning Drop Tensiometer

To obtain desired material properties, a blend of two mostly incompatible polymers is often used. The blend morphology developed during the mixing process of molten polymers is strongly influenced by interfacial tension between the polymers. A spinning drop tensiometer is commonly used to measure the interfacial tension between two polymeric liquids. In this study a numerical method is developed which simulates the evolution of a liquid drop in a spinning drop apparatus. The Navier-Stokes equations are solved with a finite element formulation. A mixed Lagrangian and Eulerian technique is used to deal with the moving interface. The computation domain is remeshed and the flow field is interpolated to avoid mesh entanglement as drop deforms. The simulation generates relaxation curves for the radius and the length of the drop. The numerical results show that the shear stress on the drop surface is quite important. A simple theory of relaxation is then formulated which takes account of the shear stress on the surface of the cylindrical drop. It is found that the exponent for the relaxation of the drop depends on the interfacial tension, the equilibrium radius of the drop, the viscosities of both fluids, and the geometric ratios of the length to the radius of the drop and of the radius of the container to the radius of the drop.

Establishment of phase equilibria: temperature jump experiments in a spinning-drop apparatus

In a spinning-drop apparatus, used for the determination of interfacial tensions, it was investigated how phase-separated polymer solutions react on a rapid rise in temperature. These measurements, yielding an apparent interfacial tension as a function of time, demonstrate that new equilibria are achieved in four clearly separable steps. The first, very rapid one consists in the establishment of a local equilibrium within the interfacial area dividing the two coexisting liquids. During the second stage of much longer duration, solvent and solute are exchanged between the bulk material as a result of the gradients in the chemical potential that exist for both components in both phases; due to the higher mobility of the solvent, its flux dominates

From large surfactant micelle to low interfacial tension: A formulation principle applied to polyoxyethylene mono- n-dodecyl ether—hydrocarbon systems

This paper presents a method for achieving low interfacial tension in surfactant formulation. Large surfactant micelles of sizes around 100 nm were found in aqueous surfactant solutions yielding ultralow tension between an oil—water interface. The dynamic interfacial tensions of the non-ionic surfactant—hydrocarbon systems were measured as a function of time with a spinning drop apparatus. A series of polvoxyethylene mono- n-dodecyl ethers (C 12H 26O(CH 2CH 2O) x H. x = 3—6,8) and a series of hydrocarbons (C 8—C 15) were used in the experiments. The surfactant micelle size was measured by the dynamic light scattering technique using an He—Ne laser. At a spinning rate of 2000 rev min −1 and a surfactant concentration of 0.024%, the process of lowering the interfacial tension seems to undergo a diffusion-controlled solubilization mechanism. It is suggested that one way of achieving low interfacial tension is to build up large surfactant micelles which are effective in solubilization, in the surfactant formulation.

Spinning drop experiments on interfacial phenomena: Theoretical background and experimental evidence

Interfacial phenomena contribute strongly to structure formation in multiphase polymer blends. Spinning drop experiments allow not only to analyze the magnitude of the interfacial energy, but also to determine dynamic features such as coarsening or the break-up of elongated threads. This contribution reports the theoretical background of static and dynamic spinning drop experiments; it describes experimental evidence on the break-up dynamics of such elongated threads and it finally sketches a spinning drop apparatus designed for investigations of viscous polymer blends, even at elevated temperatures.

A spinning drop tensioextensometer

We examine some theoretical and experimental aspects of the measurement of interfacial tension, stress relaxation in elongational flow, and yield stresses in organic liquids, blends of polymer melts, and liquid crystal polymers. This study is based on an instrument which is an improved version of the spinning drop apparatus that is commonly used to measure interfacial tension between melted polymers. Problems of vibrations at high speed, heating of the bearings, high temperatures required to melt the polymers, outgassing at the reduced pressures generated by rotation, and other problems have been eliminated in the improved apparatus. This same instrument can be used to generate curves of volume expansion versus temperature for blended systems and to detect and interpret yield stresses which occur in some polymers and strongly influence the properties of blends. The instrument has been enhanced for accurate measurements of drop diameter, length and shape as a function of time and initial conditions. A theory of upper and lower bounds for interfacial tension and a theoretically based method of exponential fitting has been developed to help to overcome the problems of slow approach to equilibrium between highly viscous melts. We have developed and propose to develop further a theory of relaxation in which transient measurements of drop diameter can be used to obtain rheological properties like elongational and yield stresses and interfacial tension and more generally to interpret the curves of relaxation generated in the experiments.

Dynamic Interfacial Tension In Surfactant Enhanced Alkaline Flooding

Abstract Dynamic interfacial tension behaviour has been identified in a surfactant-enhanced alkaline flooding process using David Lloydminster crude oil, sodium carbonate, and the surfactant Neodol 25–35. The magnitude of this dynamic behaviour was found to vary with the surfactant concentration. Five linear corefloods in Berea sandstone were performed with different Neodol 25-3S concentrations. It was found that the initial interfacial tension value in each system, measured with the spinning drop apparatus, correlated with oil recovery efficiency. Further confirmation of this effect was found by comparison Son with literature values of oil recovery vs capillary number for linear Berea sandstone corefloods. Introduction In this paper, dynamic interfacial tension is shown to occur in surfactant-enhanced alkaline flooding. In such a process, the interfacial tension that occurs after initial oil/aqueous phase contact changes with time. The effect that this dynamic behaviour has on oil recovery in linear Berea sandstone cores is demonstrated. Dynamic interfacial tensions can occur when two immiscible liquid phases come into contact, provided one or both of the phases contains a surface-active material Interfacial tension between the two phases can change continuously with time until an equilibrium value is reached. During the course of attainment of equilibrium, the system may pass through an interfacial tension minimum. The possibility of this type of behaviour was mentioned by Wilson(1) and by Harkinsl21 in the 1920s. In 1952, the phenomenon was observed by Mansfield(3) with nujol/oleic acid in contact with a caustic solution, using the pendant-drop apparatus. England and Berg(4) described dynamic interfacial tension as the result of adsorptive accumulation of surface-active species at the interface, and observed the presence of adsorption and desorption barriers for the transfer of 1,5-pentanediol from white oil to water. Dynamic interfacial tensions have been observed repeatedly for crude oil/caustic systems. The phenomenon of interfacial tension (IFT) reduction in this system was first reported by Atkin-son(5) and Nutting(6) in 1927. A more detailed investigation was carried out by Reisburg and Doschert(7), who looked at the effect of interface age and of sodium hydroxide concentration on interfacial tension. Jennings(6) examined 164 crude oils from 78 oil fields and measured IFT as a function of sodium hydroxide concentration using the pendant-drop method. He defined the term "caustic coefficient" as "the number of square cycles on log-log paper bounded by the caustic interfacial tension curve between interfacial tension values of 0.01 and 1.0 dyne/cm and caustic concentrations between 0.001 and 1.0wt%. A poor correlation between caustic coefficient and crude oil total acid number was found. However, 90% of the oils tested showed their lowest IFT with a sodium hydroxide concentration of 0.1 wt%, Jennings did not measure dynamic IFT behaviour. McCaffrey(9) measured IFT between sodium hydroxide solutions and four crude oils using the spinning drop method(10). In some cases he found that IFT increased dramatically as the interface aged, which he attributed to the migration of soap products away from the interface after their initial formation.

THE EFFECT OF EQUILIBRATION TIME AND TEMPERATURE ON DROP-DROP COALESCENCE OF WILMINGTON CRUDE OIL IN A WEAKLY ALKALINE BRINE

Abstract The interfacial behavior of a Wilmington crude oil was studied as part of our investigations of enhanced oil recovery by weakly alkaline solutions. For some systems, the spinning drop apparatus can be used to measure transient interfacial tension (IFT) effects, coalescence times of oil drops, and film rigidity simultaneously, for rapid screening of chemical slug composition for the potential of improving oil recovery by the mechanisms of oil mobilization and oil bank formation. The experimental results presented include the effects of temperature, surface age, salinity, added surfactant, and polymer on coalescence time, film rigidity, and IFT behavior. Oil displacement tests were performed using surfactant-enhanced bicarbonate solutions formulated for improved mobility control and for improved oil mobilization and oil drop coalescence. The most significant result of this work was that we were able to measure the dynamics in IFT between 2 coalescing oil drops as perturbations in the equilibrium concentration of surfactant at the interface occurred during film drainage. The accuracy of the technique for measuring IFT and film rigidity improved as the contact radii between the oil drops increased.

The Static and Dynamic Interfacial Tensions Between Crude Oils and Caustic Solutions

Abstract One method to achieve EOR is chemical alteration of the reservoir environment so that previously trapped oil can begin to flow freely. Under certain conditions, caustic or alkaline solutions can do this. The work reported here shows that interfacial tension (IFT) between various crudes and caustics increases with time because of desorption of the surface-active species from the interface. The desorption rate is temperature-dependent. Four kinds of crude oil were used—a California crude, a Wyoming crude, an Illinois crude, and an Alaska crude. Only with crude oils with a high concentration of crude acids, such as the California crude, is the ultralow IFT maintained for any reasonable period of time, namely 24 hours. The presence of calcium ions at concentrations of 200 ppm or more destroys the capability of caustic to reduce the IFT's, even for the California crude. Mass-action relationships are presented that describe the equilibrium IFT at constant ionic strength between crude oils and sodium hydroxide solutions as a function of pH and calcium. Techniques are presented for evaluating time-dependent IFT's obtained by the spinning-drop apparatus. A transient mathematical model shows that IFT can increase by several orders of magnitude over a period of several days. Good agreement between the model and experimental data is obtained. The parameters obtained from these mathematical models describe crude reactivity to caustic more accurately than conventional crude acid numbers. The transient effects observed in the laboratory may or may not be significant in the field.

Buoyancy effects in the spinning-drop interfacial tensiometer

Interfacial tension measurements for the n-butanol/water system at 25.0°C were performed with a spinning-drop apparatus. At rotational frequencies above 5000 rpm the measured interfacial tension is found to be constant, independent of frequency and drop volume. At lower frequencies, the drop is displaced away from the rotation axis of the system by a combination of Coriolis and buoyancy forces. Measured displacements are in good agreement with a theoretical model, in which Ekman layers play a dominant role in the description of the drop behavior. However, the model is not capable of explaining the observed falloff in the apparent values of interfacial tension at low frequency.