Dynamic Interfacial Properties Research Articles

Effects of asphaltenes and organic acids on crude oil-brine interfacial visco-elasticity and oil recovery in low-salinity waterflooding

Smart-water flooding has become increasingly more important as Enhanced-Oil Recovery technology in recent years. However, the observed incremental recovery varies significantly from case to case, even when the reservoir rock lithology, and water and oil characteristics are similar. In our earlier research, we proposed that a favorable crude-oil brine film visco-elasticity response reduces oil trapping during waterflooding and consequently increases oil recovery. We also advanced the idea that the film response depends upon a combination of crude oil and water characteristics. The purpose of this research is to show that the crude oil asphaltenic and acid fractions have a noticeable effect on interfacial rheology, while benefiting oil recovery in coreflooding experiments. In this work, 1HNMR (Proton Nuclear Magnetic Resonance) was used to track changes in organic acid concentration in aqueous phase-crude oil partitioning experiments. Interfacial visco-elasticity measurements were conducted on several brine-crude oil sets as well as crude oil/brine volumetric ratios. On the other hand, emulsion stability was examined through low-field NMR drop-size time courses to evaluate coalescence. Finally, carefully selected coreflooding experiments were run to measure oil recovery and pressure drop as functions of time. The crude oils analyzed exhibit differences in asphaltene content and bulk acid concentration partitioned into the aqueous phase. These differences contribute dissimilarly to interfacial rheological behavior. In all cases, interfacial visco-elasticity increases the greater the asphaltene concentration and decreases at higher acid concentration for a given brine. The elastic modulus reaches a plateau value after a time specific to each brine-crude oil system. The effects of acids and asphaltenes appear to depend on the volumetric crude oil-to-brine ratio. Coreflooding recovery factor results show a positive correlation with dynamic interfacial properties, though not a straightforward one. Emulsions stability turns out to also be a complex function of the aforementioned interfacial properties and does not directly correlate to oil recovery. Our findings reveal that the nature of the fluids in the oil reservoir makes a significant difference in terms of fluid-fluid interactions. These may affect multiphase flow in porous media and consequently the final oil recovery after waterflooding. When this is better understood, a better design strategy to achieve optimal brine modification can be proposed to increase the oil recovery.

Effects of molecular weight on the dynamic mechanical properties and interfacial properties of carbon fiber fabric-reinforced polyetherketone cardo composites

It’s a long-standing task to explore the toughening effect of fiber-reinforced thermoplastic composites, which could be used to produce new materials demanded by the aerospace field. In this work, we investigated the effects of the molecular weight of a thermoplastic resin, polyetherketone cardo (PEK-c), on the thermal, mechanical, and interfacial properties of the composite. Carbon fiber fabrics reinforced with PEK-c composite laminates were prepared by solution-processed prepreg and hot press molding. Scanning electron microscopic results showed that the fibers were distributed uniformly in the resin, with no visible flaws detected. The results of the dynamic mechanical analysis revealed that, according to the lower mobility of the polymer chain, the glass transition temperature of composite laminates increased with the increase in molecular weight. However, the tan δ values showed a lower peak value with a higher molecular weight due to the improved interfacial property between the resin and the fiber. The results on interlaminar shear strength also indicate that composites with resins of higher molecular weight have better interfacial adhesion. These results are closely interrelated with and contribute to our overall understanding of the effects of molecular weight on the properties of CFRP composites.

Excess Sorption of Supercritical CO2 within Cylindrical Silica Nanopores

Using Molecular Dynamics simulations, we examine structural and dynamical properties of supercritical CO2 confined within cylindrical hydrophobic nanopores of diameters 38 and 10 A. Computer simulations were performed along the isotherm T = 315 K, spanning CO2 densities from ρ/ρc = 2.22 down to ρ/ρc = 0.22. Radial and orientational distribution functions, analysis of interfacial dynamic properties, and estimatons for local diffusion and orientational relaxation times are presented. In agreement with previous experimental data, our simulation results reveal the presence of a dense phase adsorbed within the pores. The combination of low CO2 bulk densities and narrow pores leads to ρint/ρblk ≈ 5-fold enhancement of the global density of the confined fluid. These density increments gradually become much less marked as the external phase becomes denser. Contrasting, in that latter limit, we found that the trapped fluid may become less dense than the bulk phase. Adsorption behavior of CO2 onto hydrophilic-like ...

Correlation of the depletion layer with the Helmholtz layer in the anatase TiO2-H2O interface via molecular dynamics simulations.

Molecular dynamics simulations have been conducted to study the interaction between anatase TiO2(001), (100), and (101) surfaces and water at room temperature. The dynamic interfacial structure and properties of water on anatase TiO2 surfaces are obtained by analyzing the water density, the diffusion coefficient of water, the surface charge distribution, electric fields and the electrostatic potential distribution. The simulation results have revealed that a highly-ordered water layer structure can be formed near to the anatase TiO2 surface and have also given the Helmholtz layer width and potential drop at the water-TiO2 interface. By correlating the Helmholtz layer with the depletion layer, the depletion layer widths of three surfaces (001), (100), and (101) have been calculated as 474 Å, 237 Å and 99 Å, respectively. The resulting order of the photoelectrochemical activity of the anatase TiO2 surfaces is (001) > (100) > (101), which is consistent with the experimental results. This study may provide a useful correlation of the depletion layer with the Helmholtz layer based on simulations results for the prediction of the behavior and the control of photon-energy conversion devices.

Modulating interfacial dilatational properties by electrostatic sodium caseinate and carboxymethylcellulose interactions

The interactions between sodium caseinate (NaCas) and carboxymethylcellulose (CMC) in aqueous solution influenced by pH and CMC concentration were assessed by visual observation, measuring turbidity, ζ-potential, particle size and rheological tests. Effects of CMC on the interfacial dynamic properties of NaCas were investigated using an automatic pendant drop tensiometer. The results indicated that CMC adsorbed onto NaCas mainly through electrostatic interactions in solution at pH ≤ 5.5. and their interactions revealed a significant influence on the dynamic characteristics of NaCas adsorbed films. For surface pressure (π) and surface dilatational modulus (E) values, they were both changed in response to the presence of CMC in the bulk phase at pH 5.5 and 4. Especially for the E values of films, which showed a continuous increase as function of CMC concentration. However, the presence of CMC in the bulk phase had no significant effect on the adsorption of NaCas molecules at pH 7, indicating the interface was dominated by the protein.

Dynamic surface dilational properties of anionic Gemini surfactants with polyoxyethylene spacers

Abstract The dynamic interfacial dilational properties of anionic Gemini surfactants (oligooxa)-α,ω-bis( m -octylbenzene sulfonate) (C 8 E 4 C 8 and C 8 E 8 C 8 ) with polyoxyethylene spacers at the water–air interface were investigated by means of oscillating the drop profile method. The influences of temperature and salt on dilational properties were explored. The experimental results show that the special structure of surfactant C 8 E 8 C 8 is a principal factor to control the nature of interfacial adsorption film. The distinct two peak values appear in dilational modulus vs. time curves for surfactant C 8 E 8 C 8 , which is different from that of traditional surfactants with low molecular weight. The first peak is believed to be related to the molecular diffusion-exchange process between the bulk and interface, and the second peak may be due to the formation and collapse of interfacial sublayer by ethylene oxide groups. In addition, the temperature has obviously effect on the second peak value of dilatioanl modulus. However, there is nearly no effect on the value of the second peak by addition of NaCl. The mechanisms responsible for unique interfacial behaviors mentioned above have been provided schematically.

Corrigendum to “Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films” [Cont. Lens Anterior Eye 37 (2014) 368–376

Corrigendum to “Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films” [Cont. Lens Anterior Eye 37 (2014) 368–376

Microemulsion versus emulsion as effective carrier of hydroxytyrosol

Two edible Water-in-Oil (W/O) dispersions, an emulsion that remains kinetically stable and a microemulsion which is spontaneously formed, transparent and thermodynamically stable, were developed for potential use as functional foods, due to their ability to be considered as matrices to encapsulate biologically active hydrophilic molecules. Both systems contained Medium Chain Triglycerides (MCT) as the continuous phase and were used as carriers of Hydroxytyrosol (HT), a hydrophilic antioxidant of olive oil. A low energy input fabrication process of the emulsion was implemented. The obtained emulsion contained 1.3% (w/w) of surfactants and 5% (w/w) aqueous phase. The spontaneously formed microemulsion contained 4.9% (w/w) of surfactants and 2% (w/w) aqueous phase. A comparative study in terms of structural characterization of the systems in the absence and presence of HT was carried out. Particle size distribution obtained by Dynamic Light Scattering (DLS) technique and interfacial properties of the surfactants’ layer, examined by Electron Paramagnetic Resonance (EPR) spectroscopy indicated the involvement of HT in the surfactant membrane. Finally, the proposed systems were studied for the scavenging activity of the encapsulated antioxidant toward galvinoxyl stable free radical showing a high scavenging activity of HT in both systems.

Equilibrium and dynamic interfacial properties of protein/ionic-liquid-type surfactant solutions at the decane/water interface.

The interfacial behavior of β-casein and lysozyme solutions has been investigated in the presence of an ionic liquid-type imidazolium surfactant ([C16mim]Br) at the decane/water interface. The dynamic dilational properties of the protein/surfactant solutions are investigated by the oscillating drop method and interfacial tension relaxation method. The interfacial tension isotherms for the mixed adsorption layers indicate that the increased addition of [C16mim]Br to a pure protein changes the properties of the complex formed at the decane/water interface. Whereas the interfacial tension data of the protein/surfactant mixed layers do not clearly show differences with changing bulk composition, the dilational rheology provides undoubted evidence that the structure and, in particular, the dynamics of the adsorbed layers depend on the bulk surfactant concentration. The experiment data for β-casein/[C16mim]Br solutions indicate that at higher bulk [C16mim]Br concentrations, β-casein in the interfacial layer is subject to conformational changes, where it gives space to [C16mim]Br molecules in the form of coadsorb rather than replacement; in contrast, in lysozyme/[C16mim]Br solutions some lysozyme molecules desorb from the interface due to the competitive adsorption of free [C16mim]Br molecules. Experimental results related to the interfacial dilational properties of the protein/surfactant solutions show that the dilational modulus turns out to be more sensitive to the conformation of protein/surfactant mixture at the liquid interface than the interfacial tension.

Impact of ionic liquid-type imidazolium surfactant addition on dynamic properties of BSA adsorption layers at different pH.

The dynamic interfacial properties of mixed solutions of bovine serum albumin (BSA) and the ionic liquid-type imidazolium surfactant ([C16mim]Br) were measured as a function of the interface age, surfactant concentration and solution pH. Three BSA conformers were investigated: the normal N form as well as the fast F and aged A forms, corresponding to the different solution pH, respectively. The interfacial tension and the interfacial dilational elasticity isotherms for the mixed adsorption layers indicate that the addition of [C16mim]Br to the different structures of BSA isomers influences the properties of the adsorption layer at the decane/water interface. The addition of [C16mim]Br does not influence the structure of the protein at pH below the isoelectric point of BSA, but at higher solution pH, the addition of surfactants significantly influences the dynamic interfacial properties of BSA solutions due to the electrostatic interaction between the components.

Influence of various nanoparticle shapes on the interfacial chain mobility: a molecular dynamics simulation.

To fully understand the polymer-filler interfacial interaction mechanism, we use a coarse-grained molecular dynamics simulation to mainly investigate the interfacial dynamic properties by tuning the polymer-filler interaction, temperature, chain length, volume fraction of filler, and size and shape of filler. The polymer beads around the filler exhibit an obvious layering behavior and a gradient of polymer dynamics is observed for systems filled with three kinds of fillers (spherical, rod-like and sheet-like). By analyzing the dynamics of the interfacial beads in the first adsorbed layer, we find that the mobility of interfacial beads becomes greater at lower polymer-filler interaction strength and higher temperature. The adsorption/desorption dynamics of interfacial beads decreases with the increase of the chain length, and then becomes nearly unchanged when the chain length exceeds the entanglement molecular weight. It is found that the influence of the different size of nanospheres on the mobility of interfacial beads is just induced by the curvature. However, for systems filled with nanorods and nanosheets, besides the curvature, the force exerted on the polymer beads also plays an important role. For systems filled with three kinds of fillers, the mobility of interfacial beads is the slowest for the nanosheet filled system and only in this case the "glassy layer" exists for strongly attractive interfacial interaction. By comparing the dynamics of the adsorbed polymer beads for three different shapes of filler, it is concluded that it is the total force exerted on the polymer beads by the filler that determines the mobility of the interfacial beads. In short, this work could provide valuable information on the fundamental understanding of polymer-filler interfacial behavior, especially for systems filled with fillers of different shapes.

Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films.

To evaluate the influence of lens care solutions (LCS) on interfacial dynamics and rheological properties of human tear-lipid films. Tear lipids were extracted from Schirmer strips collected from 6 healthy subjects. Sessile bubble tensiometry was used to study interfacial properties at 22°C. Lipids were deposited on an air bubble immersed into electrolytes solution to form 90±20nm films. Lipid films were subjected to expansion-compression cycles for dynamic interfacial properties and to step-strain relaxations for assessments of rheological properties. LCS (BioTrue [BT], PureMoist [PM], Revitalens [RL], ClearCare [CC]) were injected into optical chamber and equilibrated for 2h without or with lipid films. Dynamic interfacial properties of films were measured. Then electrolyte solution was pumped through chamber and properties of films were re-evaluated. Equilibrium surface tension (EST), elasticity modulus (E), and relaxation times (τ) of tear lipids were 22±2.1mN/m, 10.7-14.8mN/m, and 80-150s, respectively. EST for LCS was 43.6±0.2 for CC, 38.3±0.2 for BT, 36.5±1.2 for RL, and 32.8±0.2mN/m for PM. [corrected]. E for LCS varied within 0.5-6.7mN/m, and τ varied from 49 to 68±5s. For mixed lipids+LCS films, EST remained unchanged whereas E and τ were reduced for all LCS types. Exposure to PM and RL noticeably altered the shape of lipid-film iso-cycles. These changes persisted after LCS washout. Some components of LCS bind irreversibly to lipid films and make them less viscous and less elastic. These findings suggest the possibility of tear-film destabilization upon LCS exposure.

Dilational rheological properties of sulphobetaines at the water–decane interface: Effect of hydrophobic group

The interfacial tensions and dilational properties of adsorbed films of two zwitterionic surfactants with different hydrophobic groups, alkyl sulphobetaine (ASB) and benzyl substituted alkyl sulphobetaine (BSB), at the decane–water interface have been investigated by the drop shape analysis method. The influences of dilational frequency and bulk concentration on the interfacial dilational modulus and phase angle were expounded. The effects of electrolyte NaCl on the interfacial tensions and dilational properties have also been researched. The experimental results show that the similar CMC and IFTCMC values for ASB and BSB indicate their similar interfacial activity. The Amin value of BSB is larger than that of ASB, which is due to the steric effect of benzene ring in BSB molecule. The dilational data show that betaines can form compact adsorption films due to their electric neutrality in experimental condition, which results in the higher maximum values of dilational moduli for both BSB and ASB than those of common surfactants. Moreover, the whole hydrophilic part, sulfonic group, hydroxyl and ammonium group, can response to the area variations by change the orientation between parallel to the interface and introduce to the aqueous instead of diffusion-exchange process, which can enhance the elasticity of the film. The electrolyte NaCl has a function of accelerating the diffusion-exchange process of surfactant molecules. As a result, the dynamic interfacial properties such as dilational properties show obvious variations, while the static interfacial property such as interfacial tension has little change after the addition of 1% NaCl.

Surface relaxations as a tool to distinguish the dynamic interfacial properties of films formed by normal and diseased meibomian lipids.

The surface properties of human meibomian lipids (MGS), the major constituent of the tear film (TF) lipid layer, are of key importance for TF stability. The dynamic interfacial properties of films by MGS from normal eyes (nMGS) and eyes with meibomian gland dysfunction (dMGS) were studied using a Langmuir surface balance. The behavior of the samples during dynamic area changes was evaluated by surface pressure-area isotherms and isocycles. The surface dilatational rheology of the films was examined in the frequency range 10(-5) to 1 Hz by the stress-relaxation method. A significant difference was found, with dMGS showing slow viscosity-dominated relaxation at 10(-4) to 10(-3) Hz, whereas nMGS remained predominantly elastic over the whole range. A Cole-Cole plot revealed two characteristic processes contributing to the relaxation, fast (on the scale of characteristic time τ < 5 s) and slow (τ > 100 s), the latter prevailing in dMGS films. Brewster angle microscopy revealed better spreading of nMGS at the air-water interface, whereas dMGS layers were non-uniform and patchy. The distinctions in the interfacial properties of the films in vitro correlated with the accelerated degradation of meibum layer pattern at the air-tear interface and with the decreased stability of TF in vivo. These results, and also recent findings on the modest capability of meibum to suppress the evaporation of the aqueous subphase, suggest the need for a re-evaluation of the role of MGS. The probable key function of meibomian lipids might be to form viscoelastic films capable of opposing dilation of the air-tear interface. The impact of temperature on the meibum surface properties is discussed in terms of its possible effect on the normal structure of the film.

Bubble in flow field: A new experimental protocol for investigating dynamic adsorption layers by using capillary pressure tensiometry

For many years the model of a dynamic adsorption layer (DAL) is well established as explanation for the behavior of rising bubbles in surfactant solutions. This model explains the velocity profile and the evolution of the shape of a rising bubble based on the hypothesis of the balance between the drag force and the structure of the adsorbed layer governed by Marangoni convection. However, direct measurements of interfacial properties of the bubble during rising are a real challenge. Here we present a new experimental protocol called “bubble in flow field” suitable for direct measurements of dynamic interfacial properties of a bubble surface using the capillary pressure tensiometry under liquid flow conditions. The experimental results for pure water demonstrate the applicability of the technique for measuring the surface tension of bubbles in a liquid flow field. The operational conditions including capillary tip geometry, liquid flow rate, bubble size and distance of the flow outlet to the bubble pole are optimized experimentally to achieve significant flow effects on a fixed bubble, while surface tension measurements are still reliable. The results for surfactant solutions (C12DMPO and CTAB) indicate respective effects depending on the flow conditions around a freshly formed bubble and evidence the formation of a dynamic adsorption layer. The adsorption equilibrium state is reached faster for higher liquid flow rates. However, the effect of the flow field is negligible on pre-aged bubble surfaces, i.e. no net desorption effects caused by the liquid flow are observed.

Impact of ionic liquid-type imidazolium surfactant additions on dynamic properties of β-casein adsorption layer

In this article, by means of interfacial dilational rheology and interfacial pressure methods, we have investigated the interfacial properties of adsorbed films at water/decane interface, formed by β-casein and a series of ionic liquid-type imidazolium surfactant [Cnmim]Br (n = 12, 14, 16). The results obtained demonstrate that the addition of ionic liquid-type imidazolium surfactant [Cnmim]Br strongly influenced the dynamic interfacial properties of β-casein solutions due to the β-casein/[Cnmim]Br complex formation. The β-casein/[Cnmim]Br complex has been formed by different charged ions of protein and surfactant, so there is competitive adsorption between the complex and surfactant. In the beginning, the surfactant molecules can adsorb to the interfacial freely according to their higher diffusion coefficient, and the β-casein/[Cnmim]Br complex was not influenced as well. As the interfacial pressure increasing, the interfacial concentration of the complex increases gradually and interactively. At higher surfactant concentrations, the complexes were formed owing to the hydrophobic interactions between the component and the complexes structure have changed. Consequently, the adsorption layer structure and the dynamic elasticity properties also changed. Because of the hydrophobic interactions, the complex became relatively hydrophilic and unstable, the ratio of the free surfactant molecules to the complexes also increased. Moreover, due to the stronger attraction with aromatic rings through π–π interaction resulting from the existence of imidazolium head group, the elasticity of β-casein/[Cnmim]Br system are much higher than that of the traditional surfactant, indicating that the adsorption layer formed by β-casein/[Cnmim]Br are much stronger.

Characterization methods for liquid interfacial layers

Liquid interfaces are met everywhere in our daily life. The corresponding interfacial properties and their modification play an important role in many modern technologies. Most prominent examples are all processes involved in the formation of foams and emulsions, as they are based on a fast creation of new surfaces, often of an immense extension. During the formation of an emulsion, for example, all freshly created and already existing interfaces are permanently subject to all types of deformation. This clearly entails the need of a quantitative knowledge on relevant dynamic interfacial properties and their changes under conditions pertinent to the technological processes. We report on the state of the art of interfacial layer characterization, including the determination of thermodynamic quantities as base line for a further quantitative analysis of the more important dynamic interfacial characteristics. Main focus of the presented work is on the experimental possibilities available at present to gain dynamic interfacial parameters, such as interfacial tensions, adsorbed amounts, interfacial composition, visco-elastic parameters, at shortest available surface ages and fastest possible interfacial perturbations. The experimental opportunities are presented along with examples for selected systems and theoretical models for a best data analysis. We also report on simulation results and concepts of necessary refinements and developments in this important field of interfacial dynamics.

Interface-Induced Disassembly of a Self-Assembled Two-Component Nanoparticle System

We present a study of static and dynamic interfacial properties of self-assembled polyelectrolyte complex nanoparticles (size 110-120 nm) containing entrapped surfactant molecules at a fluid/fluid interface. Surface tension vs time measurements of an aqueous solution of these polyelectrolyte complex nanoparticles (PCNs) show a concentration-dependent biphasic adsorption to the air/water interface while interfacial microrheology data show a concentration-dependent initial increase in the surface viscosity (up to 10(-7) N·m/s), followed by a sharp decrease (10(-9) N·m/s). Direct visualization of the air/water interface shows disappearance of particles from the interface over time. On the basis of these observations, we propose that the PCNs at fluid/fluid interfaces exist in two states: initial accumulation of PCNs at the air/water interface as nanoparticles, followed by interface induced disassembly of the accumulated PCNs into their components. The lack of change in particle size, charge, and viscosity of the bulk aqueous solution of PCNs with time indicates that this disintegration of the self-assembled PCNs is an interfacial phenomenon. Changes in energy encountered by the PCNs at the interface lead to instability of the self-assembled system and dissociation into its components. Such systems can be used for applications requiring directed delivery and triggered release of entrapped surfactants or macromolecules at fluid/fluid interfaces.

Evolution of the water-monomer dynamic interfacial properties during methyl methacrylate radical polymerization in a single monomer droplet: dependence on the chemical structure of the surfactant

This paper deals with the monitoring of the methyl methacrylate (MMA) droplet interface during its polymerization in one single monomer droplet by using a drop tensiometer. The droplet is stabilized by various molecular and polymer surfactants, in particular Pluronic® F68 and pullulan-block-Jeffamine®. The polymerization in one single droplet of the tensiometer can be seen as a way to study the interface of polymer nanoparticles during a mini-emulsion polymerization assuming the concept of a perfect nanoreactor. It was found that the experimental results (surface tension and interfacial rheology) can be connected with MMA radical polymerization. These results demonstrate that the drop tensiometer technique enables interface evolution to be followed during polymer polymerization. © 2013 Society of Chemical Industry

Effects of bulk aggregation on PEI–SDS monolayers at the dynamic air–liquid interface: depletion due to precipitation versus enrichment by a convection/spreading mechanism

The dynamic interfacial adsorption from mixtures of high molecular weight poly(ethylene imine) (PEI) and sodium dodecyl sulfate (SDS) has been studied by neutron reflectometry and ellipsometry at the expanding air–water interface created by an overflowing cylinder. Aggregation of PEI and SDS in the bulk solution has very different consequences on the dynamic interfacial properties depending on the polyelectrolyte charge density. At high pH, where PEI has low charge density, bulk aggregation depletes the solution of surface-active monomers and small complexes; the aggregates do not adsorb to the dynamic liquid interface as a result of their slow diffusion, and the surface excess is depleted. At low pH, where PEI has a high charge density, bulk aggregates reach the surface and reorganise to spread thin transient patches of material across the interface, enriching rather than depleting the surface excess. This study highlights that in order to optimise the performance of polymer–surfactant mixtures under conditions relevant to processing and applications, further work is required to understand their behaviour under non-equilibrium conditions.