Dynamic Surface Properties of Asphaltenes and Resins at the Oil-Air Interface

Interfacial tension and contact angle of asphaltenic and resinous model oil in the presence of binary salts mixtures

Using smart or low salinity waters known as green processes gained increasing attention due to their unique features and their positive impacts on the environment. In light of this fact and since there is limited knowledge about the effects of salts under engineered concentrations or binary mixtures and crude oil fractions on the interfacial tension (IFT) reduction and wettability alteration of the resinous (RSO) and asphaltenic synthetic oil (ASO), the current investigation is designed and performed for the first time. Moreover, the dynamic behavior of the IFT variation was carefully investigated and the relaxation time was obtained and modeled to see the impact of mono and divalent salts individually and in binary conditions. The relaxation times revealed that the lowest adsorption times were obtained for NaCl/CaCl2 brine regardless of the examined oil types of ASO and RSO due to the high movement affinity of the polar functional groups toward the interface consequently reducing the required time for coverage and packing of active agents at the interface. Finally, the measured contact angle values revealed a significant effect of binary salts on the wettability alteration toward strongly water-wet conditions, especially for the RSO and ASO compared with crude oil.

Amphiphilic Janus Particles for Aerobic Alcohol Oxidation in Oil Foams

Amphiphilic Janus silica particles, tunable with oleophobic-oleophilic properties and low fluorine content (8 wt % F), exhibited prominent foamability for a variety of aromatic alcohols at low particle concentrations (<1 wt %) compared to randomly functionalized silica particles. When selectively loaded with Pd nanoparticles on the oleophilic hemisphere, the particles displayed more than a 2-fold increase in catalytic activity for the aerobic oxidation of benzyl alcohol compared to nonfoam bulk catalysis under ambient O2 pressure. The particles were conveniently recycled with high foamability and catalytic activity maintained for at least five consecutive runs.

Ethanol Foams Stabilized by Isobutyl-Based POSS-Organosilica Dual-Particle Assemblies

Nonaqueous foams in low-surface tension solvents (<25 mN·m-1) are highly desired for applications in fire extinguishers and detoxification gels. However, their formation is a Holy Grail of the chemical industry due to the need for stabilizers with low surface energy and high recyclability. Herein, we disclose a new strategy to generate abundant foams in ethanol and a variety of low-surface tension solvents relying on the interfacial coadsorption of two different particles. The particles consist of surface-active fluorinated silica particles, used as a stabilizer, and a novel amphiphilic polyhedral oligomeric silsesquioxane (POSS) decorated with isobutyl cage substituents, used as a frother. The interaction between POSS and fluorinated particles at the ethanol-air interface was thoroughly investigated by combining physicochemical methods (contact angle, dynamic surface tension, and dynamic light scattering methods) and catalytic tests using the model aerobic oxidation reaction of benzyl alcohol. Both particles could be conveniently recycled for at least 5 consecutive runs with high foamability and catalytic activity.

Elastometry of Complex Fluid Pendant Capsules

Oil/water interfaces are ubiquitous in nature. Opposing polarities at these interfaces attract surface-active molecules, which can seed complex viscoelastic or even solid interfacial structure. Biorelevant proteins such as hydrophobin, polymers such as PNIPAM, and the asphaltenes in crude oil (CRO) are examples of some systems where such layers can occur. When a pendant drop of CRO is aged in brine, it can form an interfacial elastic membrane of asphaltenes so stiff that it wrinkles and crumples upon retraction. Most of the work studying CRO/brine interfaces focuses on the viscoelastic liquid regime, leaving a wide range of fully solidified, elastic interfaces largely unexplored. In this work, we quantitatively measure elasticity in all phases of drop retraction. In early retraction, the interface shows a fluid viscoelasticity measurable using a Gibbs isotherm or dilatational rheology. Further retraction causes a phase transition to a 2D elastic solid with nonisotropic, nonhomogeneous surface stresses. In this regime, we use new techniques in the elastic membrane theory to fit for the elasticities of these solid capsules. These elastic measurements can help us develop a deeper understanding not only of CRO interfaces but also of the myriad fluid systems with solid interfacial layers.

Use of a Geometric Parameter for Characterizing Rigid Films at Oil-Water Interfaces

Interfacial tension and dilatational rheology are often used to characterize the mechanical response of a liquid interface using axisymmetric drop shape analysis (ADSA). It is important to note that for systems dominated by adsorption/desorption of surfactants, the contributions of extra mechanical stresses are negligible; thus, the Young-Laplace equation remains valid. However, for interfaces dominated by extra stresses, as in the case of particle monolayers or asphaltenes that clearly exhibit a skin (a rigid film), the nature of the elastic response is fundamentally different and the validity of the equation is questionable. Calculation of the interfacial tension and dilatational elasticity using drop shape analysis depends critically on the drop shape following the Young-Laplace equation. If the interface becomes more like a solid, the drop shape will deviate from being purely Laplacian. Indeed, the drop will exhibit a wrinkled surface as collapse continues. The geometric parameter R_V/A, defined as the ratio (dV/V)/(dA/A) with V is the volume of the drop and A is the area of the interface), allows one to measure the deviation of the drop shape from purely Laplacian. For a simple interface (pure liquids or surfactant solutions), R_V/A is quite close to the theoretical value of 1.5 of a perfect sphere. Nevertheless, if the molecules adsorbed at the interface begin to interact strongly, the ratio can vary. In the limit of long-time-scale experiments, R_V/A of some drops approaches 2. We studied the evolution of the parameter R_V/A for different systems, from simple to complex, as a function of oscillation frequencies and amplitudes of drop volume. The results obtained were compared to the values of the interfacial moduli and drop shape behavior to better characterize the regime change.

Microscopic Mechanical Model Analysis and Visualization Investigation of SiO2 Nanoparticle/HPAM Polymer Foam Liquid Film Displacing Heavy Oil

In this paper, the microscopic mechanisms and macroscopic characteristics of polymer/nanoparticle foam flooding in a heavy oil reservoir environment were studied. Sodium dodecyl sulfate (SDS) surfactant was used as the foaming agent, and the foam was prepared by a combination of partially hydrolyzed polyacrylamide (HPAM) polymer and SiO₂ nanoparticles. By performing experiments with the microscopic model, the foam flooding dynamics in the heavy oil reservoir were simulated. Based on the experiments, the formula model was established to evaluate the physicochemical effects between the foam liquid film and oil surface. Finally, the macroscopic characteristics of foam flooding were studied by performing oil displacement experiments with a 2D visual model. The microscopic experiments demonstrated that the foam liquid film could exert multiple actions, such as adsorption, stretching, and cutting on the heavy oil in the reservoir pores. These actions were accompanied by force changes between the foam and heavy oil, and the addition of polymer and nanoparticles further strengthened them. The calculations of the formula model indicated that the polymer and nanoparticles amplified the force between the foam liquid film and heavy oil by 1.95 and 2.2 times, respectively. The 2D visual model experiments suggested that foam flooding could further develop heavy oil after water flooding through its liquid film effects, and the oil recovery efficiency increased from 42.43 to 57.82%. In addition, the polymer and nanoparticles further optimized the oil displacement effect of the foam liquid film, which made the oil recovery efficiency reach 64.77-68.16%.

Effect of interfacial rheology on drop coalescence in water-oil emulsion

Over the last years several studies have been conducted to understand emulsion formation and its behavior. In some applications, the aim is the phase separation of the emulsions through the coalescence of the drops, as in the oil industry. In this study, the relationship between rheological properties of oil-water interfaces and the drainage time of a thin oil film between two aqueous drops was investigated. Interfacial tension and dilatational rheology were measured using the axisymmetric drop shape analysis. We evaluated different concentrations of a nonionic surfactant (Span 80) dissolved in mineral oil (Primol 352) phase. The results indicate a direct relationship between the properties of the structure formed at the oil-water interface and the absence of droplet coalescence. For low surfactant concentrations, below the critical micelle concentration (CMC), the interface is weakly elastic (fluid-like) and the coalescence process always occurs; the draining time is not to related to the aging time of the interface. For surfactant concentrations above CMC, the elastic and viscous moduli showed significant changes with aging leading to the formation of a solid-like film at the interface preventing further coalescence. We used the characteristic times of change in interfacial rheological behavior to better explain the non-coalescence process.

Multiphase Microreactors Based on Liquid-Liquid and Gas-Liquid Dispersions Stabilized by Colloidal Catalytic Particles

Pickering emulsions, foams, bubbles, and marbles are dispersions of two immiscible liquids or of a liquid and a gas stabilized by surface-active colloidal particles. These systems can be used for engineering liquid-liquid-solid and gas-liquid-solid microreactors for multiphase reactions. They constitute original platforms for reengineering multiphase reactors towards a higher degree of sustainability. This Review provides a systematic overview on the recent progress of liquid-liquid and gas-liquid dispersions stabilized by solid particles as microreactors for engineering eco-efficient reactions, with emphasis on biobased reagents. Physicochemical driving parameters, challenges, and strategies to (de)stabilize dispersions for product recovery/catalyst recycling are discussed. Advanced concepts such as cascade and continuous flow reactions, compartmentalization of incompatible reagents, and multiscale computational methods for accelerating particle discovery are also addressed.

The Oscillatory Spinning Drop Technique. An Innovative Method to Measure Dilational Interfacial Rheological Properties of Brine-Crude Oil Systems in the Presence of Asphaltenes

The oscillatory spinning drop method has been proven recently to be an accurate technique to measure dilational interfacial rheological properties. It is the only available equipment for measuring dilational moduli in low interfacial tension systems, as it is the case in applications dealing with surfactant-oil-water three-phase behavior like enhanced oil recovery, crude oil dehydration, or extreme microemulsion solubilization. Different systems can be studied, bubble-in-liquid, oil-in-water, microemulsion-in-water, oil-in-microemulsion, and systems with the presence of complex natural surfactants like asphaltene aggregates or particles. The technique allows studying the characteristics and properties of water/oil interfaces, particularly when the oil contains asphaltenes and when surfactants are present. In this work, we present a review of the measurements of crude oil-brine interfaces with the oscillating spinning drop technique. The review is divided into four sections. First, an introduction on the oscillating spinning drop technique, fundamental and applied concepts are presented. The three sections that follow are divided according to the complexity of the systems measured with the oscillating spinning drop, starting with simple surfactant-oil-water systems. Then the complexity increases, presenting interfacial rheology properties of crude oil-brine systems, and finally, more complex surfactant-crude oil-brine systems are reviewed. We have found that using the oscillating spinning drop method to measure interfacial rheology properties can help make precise measurements in a reasonable amount of time. This is of significance when systems with long equilibration times, e.g., asphaltene or high molecular weight surfactant-containing systems are measured, or with systems formulated with a demulsifier which is generally associated with low interfacial tension.

Evolution of adsorbed layers of asphaltenes at oil-water interfaces: A novel experimental protocol

HYPOTHESIS

Asphaltenes can form rigid interfacial films surrounding water droplets rendering water separation from crude oil sluggish. Therefore, the quantitative characterization of such complex film formation is of great importance. As the adsorbed layers of asphaltene illustrate crumpling under compression at certain conditions, the evolution process from soft to rigid states of the film can be evaluated considering standard deviations from Young-Laplace shape fitting.

EXPERIMENTAL

In this study, novel experimental protocols are introduced to investigate the evolution of adsorbed asphaltene layer to a film of aggregates at model oil/water interface by means of dynamic interfacial tension (IFT) and dilational surface rheology measurements. In particular, the surface elasticity and standard deviation from the Young-Laplace shape fitting (YL-SD) are introduced as important indicators for the transformation of a regular asphaltene adsorbed layer to a film of aggregates. Different parameters affecting the film formation and stability, such as aging time, asphaltene concentration, and history of interfacial dynamics, are discussed and linked to emulsion stability.

FINDINGS

It is shown for the first time that the standard deviation of drop profile fitting from the Young-Laplace equation can be used as a rigorous parameter to reveal the properties of the interfacial asphaltene film, which cannot be recognized by regular IFT measurements. Via this novel technique, it is revealed that the transformation of an asphaltene adsorbed layer to a rigid film depends not only on the asphaltene concentration but also on the aging time and the interfacial area perturbations. The results of this new method are supported by measurements of the dilational surface elasticity, which is known as an important parameter for the characterization of complex adsorbed layers, and further verified by an emulsion stability analysis.

Experimental Investigation on Microscopic Force Measurement of Foam and Heavy Oil

This paper combined experiments with a theoretical model to simulate the behavior between a foam and heavy oil during contact pressing, separation, and adsorption. We discuss the changes in the elasticity and adsorption forces during the pressing and adsorption of the two fluids. The influence of the changes in temperature and pressure, the concentration of the sodium dodecyl sulfate surfactant, the heavy oil viscosity, and the addition of partially hydrolyzed polyacrylamide and hydrophobic SiO₂ nanoparticles was studied. The results showed that the overall increase in the elasticity and adsorption forces between the foam at 1 wt % surfactant and heavy oil was more than 2 times greater than those of the foam with 0.2 wt % surfactant. The increase in viscosity of heavy oil also increased various forces. The overall improvement in the adsorption force between fluids caused by nanoparticles during separation and adsorption stages reached 1.8 times, which was better than that obtained using the polymer (1.65 times). However, the polymer showed a 1.4 times higher elastic force during the fluid pressing stage than the nanoparticles and about 4 times higher than the control foam, and the increase in temperature greatly weakened the effect of the force, while the change in pressure did not cause much impact. An analytical model was built based on fluid mechanics, and the calculation results were consistent with the experimental data with an error of about 5-12%, suggesting that this model provides a good reference value.

On the rupture of thin films made from aqueous surfactant solutions

This short review describes the work on aqueous foam film stability with the important past contributions of Dotchi Exerowa and Dimo Platikanov, together with advances from other research groups. The review is focused on film rupture, for which few controlled experiments can be found in the literature and as a consequence, our understanding is still limited. The work on rupture of films in foams is described, together with the correlations with the rupture of isolated films. The review addresses mainly the case of aqueous films and foams, but analog studies of emulsions and emulsion films are also briefly discussed.

Chemical Reaction-Driven Spreading of an Organic Extractant on the Gas-Water Interface: Insight into the Controllable Formation of a Gas Bubble-Supported Organic Extractant Liquid Membrane

The extraction and recovery of low-concentration valuable metals from various complex aqueous solutions or industrial waste waters have attracted extensive interests in recent years. In our previous works, we suggested a novel technique called bubbling organic liquid membrane extraction by spreading and covering an organic extractant with extremely small volume on the surface of gas bubbles to form a layer of the gas bubble-supported organic liquid membrane for selective extraction and enrichment of low-concentration targets from dilute aqueous solutions. It was found that for successfully performing the bubbling organic liquid membrane extraction, a prerequisite is knowing how to control the formation of a stable organic liquid membrane covered on the surface of gas bubbles. However, once the organic extractant starts to spread on the surface of gas bubbles, the extraction chemical reaction at the interface between the organic extractant liquid membrane and the rare-earth aqueous solution will occur. In the present work, the spreading behavior of the organic extractant P507 on the surface of rare-earth aqueous solutions was investigated and was compared with the behaviors on the surface of deionized water. It was revealed that the spreading of the organic extractant P507 on the surface of aqueous solutions containing rare-earth ions was accelerated because of the occurrence of the chemical reactions at the gas-water interface. The difference in the spreading rate of organic extractant P507 liquid droplets on the surface of deionized water and on that of Er(III) aqueous solutions with an increase in the P507 concentration, the saponification degrees of the P507 extractant, and the preloading amount of Er(III) in the P507 extractant revealed that the chemical reaction at the interface between the spreading P507 thin liquid membrane and the Er(III) aqueous solution would result in the Marangoni convection along the interface, which is in favor of overcoming the resistance from the viscous force when the surface tension gradient replaces gravity as a dominant driving force for the spreading. The present work provides an experimental foundation toward understanding the effect of the interfacial chemical reaction on the spreading behavior of an organic oil droplet on the gas-water interface. It is beneficial for the development of our suggested new technique of bubbling organic liquid membrane extraction and to achieve a controllable generation of a stable gas bubble-supported organic liquid membrane for performing solvent extraction at large aqueous-to-oil phase ratios.

Asphaltenes at Oil/Gas Interfaces: Foamability Even with No Significant Surface Activity

In the oil industry, oil foams can be found at different steps from the crude oil treatment to the gas stations. Their lifetime can sometimes reach several hours and be much longer than the residence times available for gas/liquid separation. However, the conditions of formation and stability of such foams have been poorly studied in the literature, in contrast to the foamability of aqueous systems. On the fields, it is currently observed that crude oils enriched with asphaltenes form particularly stable foams. In this work, we have studied the influence of asphaltenes on the foamability of oil mixtures. All the experiments were performed on model systems of crude oils, that-is-to-say decane/toluene mixtures containing asphaltenes at concentrations ranging from 0.01 to 5 wt%. We in particular demonstrate that, within the investigated concentration range, asphaltenes from two different wells do not have any significant surface active properties despite their contribution to the foamability of oil mixtures. We show that the formation of an asphaltene layer at the interface with air that has been evidenced in the past results from solvent evaporation. Using a recently developed experiment based on the Marangoni effect with our model oils, we demonstrate that asphaltenes are not surface active in those oils. We further characterize the oil foamability by measuring the lifetime of the foam formed by blowing nitrogen through the liquid in a column. At concentrations larger than 1 wt%, asphaltenes significantly enhance the foamability of the oil mixtures. Moreover, the closer the asphaltenes are to their limit of precipitation the larger the foamability. However, we evidence that the oil mixtures themselves foam and we show the importance to consider that effect on the foamability. In addition, we observe that the foamability of the asphaltenes solutions unexpectedly varies with the initial height of the liquid in the column. We suggest that, although not significantly modifying the surface tension, the asphaltenes could be trapped at the oil/gas interface and thus prevent bubble coalescence.

Dynamic Asphaltene-Stearic Acid Competition at the Oil-Water Interface

Interfacial tension (IFT) is one of the major parameters which govern the fluid flow in oil production and recovery. This paper investigates the interfacial activity of different natural surfactants found in crude oil. The main objective was to better understand the competition between carboxylic acids and asphaltenes on toluene/water interfaces. Dynamic IFT was measured for water-in-oil pendant drops contrary to most studies using oil-in-water drops. Stearic acid (SA) was used as model compound for surface-active carboxylic acids in crude. The influence of concentration of these species on dynamic IFT between model oil and deionized water was examined. The acid concentrations were of realistic values (total acid number 0.1 to 2 mg KOH/g oil) while asphaltene concentrations were low and set between 10 and 100 ppm. In mixtures, the initial surface pressure was entirely determined by the SA content while asphaltenes showed a slow initial diffusion to the interface followed by increased adsorption at longer times. The final surface pressure was higher for asphaltenes compared to SA, but for binaries, the final surface pressure was always lower than the sum of the individuals. At high SA concentration, surface pressures of mixtures were dominated entirely by the SA, although, Langmuir isotherm analysis shows that asphaltenes bind to the interface 200-250 times stronger than SA. The surface area/molecule for both SA and asphaltenes were found to be larger than the values reported in recent literature. Various approaches to dynamic surface adsorption were tested, showing that apparent diffusivity of asphaltenes is very low, in agreement with other works. Hence, the adsorption is apparently under barrier control. A possible hypothesis is that at the initial phase of the experiment and at lower concentration of asphaltenes, the interface is occupied by stearic acid molecules forming a dense layer of hydrocarbon chains that may repel the asphaltenes.

Quasi-Phase Diagrams at Air/Oil Interfaces and Bulk Oil Phases for Crystallization of Small-Molecular Semiconductors by Adjusting Gibbs Adsorption

The temperature and concentration dependencies of the crystallization of two small-molecular semiconductors were clarified by constructing quasi-phase diagrams at air/oil interfaces and in bulk oil phases. A quinoidal quaterthiophene derivative with four alkyl chains (QQT(CN)4) in 1,1,2,2-tetrachroloethane (TCE) and a thienoacene derivative with two alkyl chains (C8-BTBT) in o-dichlorobenzene were used. The apparent crystal nucleation temperature (T_n) and dissolution temperature (T_d) of the molecules were determined based on optical microscopy examination in closed glass capillaries and open dishes during slow cooling and heating processes, respectively. T_n and T_d were considered estimates of the critical temperatures for nuclear formation and crystal growth, respectively. The T_n values of QQT(CN)4 and C8-BTBT at the air/oil interfaces were higher than those in the bulk oil phases, whereas the T_d values at the air/oil interfaces were almost the same as those in the bulk oil phases. These Gibbs adsorption phenomena were attributed to the solvophobic effect of the alkyl chain moieties. The temperature range between T_n and T_d corresponds to suitable supercooling conditions for ideal crystal growth based on the suppression of nucleation. The T_n values at the water/oil and oil/glass interfaces did not shift compared with those of the bulk phases, indicating that adsorption did not occur at the hydrophilic interfaces. Promotion and inhibition of nuclear formation for crystal growth of the semiconductors were achieved at the air/oil and hydrophilic interfaces, respectively.

The Effect of pH on the Properties of a Cationic Bitumen Emulsifier

Surfactants used in road surface treatments have an optimal application pH value which is an important condition for applications, otherwise stable bitumen emulsions with high solid contents are impossible to achieve. Therefore, a wide range of pH values were employed to investigate its effect on the bitumen/water interfacial properties of a cationic bitumen emulsifier. It is shown that interfacial tension and dilatational modulus have correlations with pH value. The lowest value of interfacial tension declined with the decrease of pH value. The strong acid system has the highest dilatational modulus while this modulus of the neutral system is the lowest. Compared with the neutral system, the maximum of the dilatational modulus also appears in the acid or alkaline system at a relatively low concentration. Physical properties of bitumen emulsions, including storage stability and Zeta potential, show the same changing rule as the interfacial rheology.

Interfacial behavior of asphaltenes

We review the existing literature on asphaltenes at various types of interfaces: oil-water, air-water, gas-oil and solid-liquid, with more emphasis on the oil-water interfaces. We address the role of asphaltene aggregation, recently clarified for asphaltenes in bulk by the Yen-Mullins model. We discuss the questions of adsorption reversibility and interfacial rheology, especially in connection with emulsion stability.

Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation

Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

Effect of Tween 40 and Tween 60 on the Properties of a Cationic Slow-Set Emulsifier

The properties of a cationic slow-set emulsifier named INDULIN SBT in the absence and presence of Tween 40 and Tween 60 is investigated in this paper. After adding Tween 40 and Tween 60, the interfacial tension and dilatational modulus of SBT have remarkable changes. Compared with the pure SBT system, the interfacial properties of the mixed surfactant systems are improved obviously, especially if the ratio of the mixtures is 1 : 1. The Zeta potentials are also the lowest with favorable storage stability in these systems. At suitable ratios, synergistic adsorption may take place, resulting in remarkable enhanced interfacial properties. The combination of SBT and Tween 40 as well as Tween 60 could be used as surfactant mixtures applied in asphalt emulsions.

Asphaltene-laden interfaces form soft glassy layers in contraction experiments: a mechanism for coalescence blocking

In previous studies, the adsorption kinetics of asphaltenes at the water-oil interface were interpreted utilizing a Langmuir equation of state (EOS) based on droplet expansion experiments.1-3 Long-term adsorption kinetics followed random sequential adsorption (RSA) theory predictions, asymptotically reaching ∼85% limiting surface coverage, which is similar to limiting random 2D close packing of disks. To extend this work beyond this slow adsorption process, we performed rapid contractions and contraction-expansions of asphaltene-laden interfaces using the pendant drop experiment to emulate a Langmuir trough. This simulates the rapid increase in interfacial asphaltene concentration that occurs during coalescence events. For the contraction of droplets aged in asphaltene solutions, deviation from the EOS consistently occurs at a surface pressure value ∼21 mN/m corresponding to a surface coverage ∼80%. At this point droplets lose the shape required for validity of the Laplace-Young equation, indicating solidlike surface behavior. On further contraction wrinkles appear, which disappear when the droplet is held at constant volume. Surface pressure also decreases down to an equilibrium value near that measured for slow adsorption experiments. This behavior appears to be due to a transition to a glassy interface on contraction past the packing limit, followed by relaxation toward equilibrium by desorption at constant volume. This hypothesis is supported by cycling experiments around the close-packed limit where the transition to and from a solidlike state appears to be both fast and reversible, with little hysteresis. Also, the soft glass rheology model of Sollich is shown to capture previously reported shear behavior during adsorption. The results suggest that the mechanism by which asphaltenes stabilize water-in-oil emulsions is by blocking coalescence due to rapid formation of a glassy interface, in turn caused by interfacial asphaltenes rapidly increasing in concentration beyond the glass transition point.

Long-term adsorption kinetics of asphaltenes at the oil-water interface: a random sequential adsorption perspective

Previous studies indicated that asphaltenes adsorbed as monomers on oil-water interfaces and the early stage kinetics of the process was controlled by diffusion and hence dependent on oil viscosity. By measuring interfacial tension (IFT) as a function of surface coverage during droplet expansions in pendant drop experiments, it was also concluded that the IFT data could be interpreted with a Langmuir equation of state (EoS), which was independent of oil viscosity, time of adsorption, and bulk asphaltenes concentration. The surface excess coverage was calculated to be ∼0.3 nm(2)/molecule, which suggested adsorption in face-on configuration of asphaltenes monomers at the interface and average PAH core per molecule of about 6 for the asphaltenes investigated, consistent with the Yen-Mullins model. The current study focuses on the kinetics of asphaltenes adsorption at longer times and higher interfacial coverage. Long-term IFT data have been measured by the pendant drop method for different asphaltenes concentrations and for different bulk viscosities of the oil phase (0.5-28 cP). The data indicate that when coverage reaches 35-40%, the adsorption rates slow down considerably compared to the diffusion-controlled rates at the very early stages. The surface pressure increase rate (or IFT decrease rate) at these higher coverages is now independent of oil viscosity but dependent upon both surface pressure itself and asphaltene monomer concentration. The long-term asymptotic behavior of surface coverage is found to be consistent with the predictions from surface diffusion-mediated random sequential adsorption (RSA) theory which indicates a linear dependency of surface coverage on 1/√t and an asymptotic limit very close to 2D random close packing of polydispersed disks (85%). From these observations RSA theory parameters were extracted that enabled description of adsorption kinetics for the range of conditions above surface coverage of 35%.

Dynamic Interfacial Tension Behavior of Alkyl Amino Sulfonate in Crude Oil-Brine System

The compatibility of surfactants, a series of alkyl amino sulfonate containing various the length of alkyl chain (dodecyl, tetradecyl, hexadecyl and octadecyl, developed in our laboratory), with formation water matching the Xinjiang Oil Field reservoir water and the dynamic interfacial tensions (DIT) behaviors between the crude oil and the formation water for a number of alkaline flooding systems were measured. These surfactants are found to be well compatible with formation water up to 0.10 g L−1 surfactant concentration, especially Dodec-AS and Tetradec-AS show a good compatibility with formation water over the full range of surfactant concentration investigated (0.01–0.20 g L−1). All surfactants exhibit the dynamic interfacial tension behavior, and can reach and maintain low interfacial tension at very low concentration. The time for reaching the equilibrium DIT (DITeq) is longer for surfactant with stronger lipophilicity, e.g. octadecyl-AS. It is interestingly found that the ratio value between DITeq and the tension at crude oil/reservoir water interface in the absence of surfactant is in the range of 10−4–10−3 mN m−1, accordingly based on which and the previous results, four surfactants individually or with other additives together may become potent candidates for enhanced oil recovery. Fortunately, the alkyl amino sulfonate combinational systems without alkali designed by our group can reduce the interfacial tension even to 10−4 mN m−1 at very low surfactant concentration. These surfactants or their systems have characteristic of “Green”, in addition to the excellent salt-tolerance and the less expensive cost for enhanced oil recovery, and therefore they are good oil-displacing reagents for enhanced oil recovery.

Interfacial rheology of asphaltenes at oil-water interfaces and interpretation of the equation of state

In an earlier study, oil-water interfacial tension was measured by the pendant drop technique for a range of oil-phase asphaltene concentrations and viscosities. The interfacial tension was found to be related to the relative surface coverage during droplet expansion. The relationship was independent of aging time and bulk asphaltenes concentration, suggesting that cross-linking did not occur at the interface and that only asphaltene monomers were adsorbed. The present study extends this work to measurements of interfacial rheology with the same fluids. Dilatation moduli have been measured using the pulsating droplet technique at different frequencies, different concentrations (below and above CNAC), and different aging times. Care was taken to apply the technique in conditions where viscous and inertial effects are small. The elastic modulus increases with frequency and then plateaus to an asymptotic value. The asymptotic or instantaneous elasticity has been plotted against the interfacial tension, indicating the existence of a unique relationship, between them, independent of adsorption conditions. The relationship between interfacial tension and surface coverage is analyzed with a Langmuir equation of state. The equation of state also enabled the prediction of the observed relationship between the instantaneous elasticity and interfacial tension. The fit by a simple Langmuir equation of state (EOS) suggests minimal effects of aging and of nanoaggregates or gel formation at the interface. Only one parameter is involved in the fit, which is the surface excess coverage Γ∞ = 3.2 molecules/nm(2) (31.25 Å(2)/molecule). This value appears to agree with flat-on adsorption of monomeric asphaltene structures consisting of aromatic cores composed of an average of six fused rings and supports the hypothesis that nanoaggregates do not adsorb on the interface. The observed interfacial effects of the adsorbed asphaltenes, correlated by the Langmuir EOS, are consistent with the asphaltene aggregation behavior in the bulk fluid expected from the Yen-Mullins model.

Adsorption kinetics of asphaltenes at the oil-water interface and nanoaggregation in the bulk

Asphaltenes constitute high molecular weight constituents of crude oils that are insoluble in n-heptane and soluble in toluene. They contribute to the stabilization of the water-in-oil emulsions formed during crude oil recovery and hinder drop-drop coalescence. As a result, asphaltenes unfavorably impact water-oil separation processes and consequently oil production rates. In view of this there is a need to better understand the physicochemical effects of asphaltenes at water-oil interfaces. This study elucidates aspects of these effects based on new data on the interfacial tension in such systems from pendant drop experiments, supported by results from nuclear magnetic resonance (NMR) and dynamic light scattering (DLS) studies. The pendant drop experiments using different asphaltene concentrations (mass fractions) and solvent viscosities indicate that the interfacial tension reduction kinetics at short times are controlled by bulk diffusion of the fraction of asphaltenes present as monomer. At low mass fractions much of the asphaltenes appear to be present as monomers, but at mass fractions greater than about 80 ppm they appear to aggregate into larger structures, a finding consistent with the NMR and DLS results. At longer times interfacial tension reduction kinetics are slower and no longer diffusion controlled. To investigate the controlling mechanisms at this later stage the pendant drop experiment was made to function in a fashion similar to a Langmuir trough with interfacial tension being measured during expansion of a droplet aged in various conditions. The interfacial tension was observed to depend on surface coverage and not on time. All observations indicate the later stage transition is to an adsorption barrier-controlled regime rather than to a conformational relaxation regime.

Surface force measurements on freely suspended liquid films

This paper reviews existing studies of freely suspended liquid films, focusing on the role of the forces between surfaces. The important role of kinetics phenomena is discussed. Examples of studies making use of solutions containing surfactants, proteins and particles are compared. The different aspects of film lifetime are discussed, from film formation to film rupture. A comparison with the few existing theories is also made.

The colloidal structure of bitumen: consequences on the rheology and on the mechanisms of bitumen modification

The use of bitumen as a construction material dates back to antiquity. The materials in use then were mostly naturally occurring in contrast to modern bitumens which have become highly technical artificial materials. This article reviews the current understanding of bitumen structure and the consequences in terms of properties, with a strong emphasis on the rheological properties. The links between chemistry, structure and mechanical properties are highlighted in the framework of an updated colloidal picture of bitumen. It shows that a simple solvation parameter allows quantifying the effect of the asphaltenes on the rheological properties of bitumen. This appears as a promising approach in order to understand more complex phenomena such as bitumen ageing or the diffusion of rejuvenating oils into an older bitumen. From this structural modelling, the effect of several modifiers, such as polymers, acids or mineral fillers, is explained using fundamental results from the mechanics of colloidal suspensions and multiphase materials through the Palierne model. Thus, relevant parameters describing polymer-bitumen or mineral fillers-bitumen interactions can be extracted, as detailed from literature data. In the case of mineral filler, volume fraction is the key parameter but particle size comes also into play when fine fillers are considered. In the case of polymer-modified bitumens, the swelling extent of the polymer controls all other parameters of importance: volume fraction of dispersed phase and mechanical properties of both dispersed and continuous phases. In addition, interesting rheological features due to droplet shape relaxations are described in polymer-modified bitumens. Although a general picture of bitumen structure is shown to emerge, the many fundamental points that remain to be addressed are discussed throughout the paper.