Dynamic Interfacial Tension Measurements Research Articles

Unraveling Early-Stage Dynamics of Cage-to-Covalent Organic Framework Transformation at Liquid-Liquid Interface.

Postsynthetic linker exchange (PLE) has emerged as an emerging synthetic strategy for constructing high-quality covalent organic frameworks (COFs) from preassembled entities such as linear polymers, amorphous networks, COFs, and porous organic cages by using the principles of dynamic covalent chemistry. The PLE strategy has recently been extended at the liquid-liquid interface to fabricate highly crystalline two-dimensional (2D)-COF membranes at a faster time scale (24 h). Examining the early stages of the interfacial PLE dynamics becomes essential to understanding the expedited COF growth process. In this regard, pendant drop tensiometry has been employed to probe the initial reaction dynamics of the imine cage-to-COF transformation through dynamic interfacial tension (IFT) measurements. The contrasting trends in IFT profiles between PLE-mediated (from cage) and direct COF synthesis (from parent monomers) are in qualitative agreement with the kinetics of bulk-scale interfacial polymerizations. Further, the distinct early-stage interfacial behaviors between the diverse synthetic routes have been experimentally demonstrated using tensiometry, optical microscopy, electron microscopy, and powder X-ray diffraction (PXRD) analysis. The pivotal role of in situ generated imine intermediates (ImIs) and the phenomenon of spontaneous emulsification toward accelerated interfacial COF growth process was delineated. The current study on deploying the pendant drop tensiometric technique to examine early-stage interfacial polymerization dynamics opens up a gripping avenue for mechanistic exploration in PLE-based COF synthesis. The generality of the developed methodology to study the initial COF growth kinetics was extended to a new interfacial PLE-mediated cage-to-COF transformation.

Dynamic Interfacial Tension Measurement for the Kinetic Study of Eu(III) Extraction in the NaNO3/Tributyl Phosphate System Based on an Increase in Interfacial Tension.

We demonstrated for the first time that interfacial tension measurements can be used to evaluate the kinetics of the solvent extraction of metal ions. The Eu(III) extraction mechanism in the nitrate ion/tributyl phosphate (TBP) system was investigated on the basis of dynamic interfacial tension. Interestingly, the interfacial tension of the TBP droplet (γ) increased with Eu(III) extraction. This behavior can be explained by the electrocapillary effect. The time dependence of γ was kinetically analyzed, and we demonstrated that the rate-determining process was the interfacial reaction of Eu(III). Furthermore, the dependence of the mass transfer rate constant upon the concentration of the nitrate ions revealed that two nitrate ions were involved in the interfacial reaction during Eu(III) extraction. However, no change in the rate constant upon TBP concentration was observed, because the change in the TBP concentration did not affect the electrocapillary effect. We determined the forward and backward reaction rates to be k1 = (1.5 ± 0.7) × 10-6 m M-2 s-1 and k-MT = (6.9 ± 3.9) × 10-7 m s-1. Therefore, for the first time, we demonstrated that dynamic interfacial tension, which is involved in the electrocapillary effect, can be used to elucidate the kinetics of Eu(III) extraction. We expect that this study will attract the attention of researchers in several fields, including physical and analytical chemistry.

Pore scale investigation of chelating agents flooding for enhanced oil recovery

Recently, laboratory tests have shown a positive response to chelating agent brines in sandstone and carbonate reservoirs as a new enhanced oil recovery technique. There is little research on direct and visual evidence of underlying mechanisms behind the chelating agent effects. In this study, a microfluidic method was established using glass micromodel to investigate the micro-mechanisms of displacement under ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) chelating agent at the pore-scale level. Furthermore, for the study of fluid/fluid interactions, EDTA brine and DTPA brine were brought into contact with two different crude oils to examine the possible compositional changes. For this purpose, sample tests, Fourier Transform Infrared Spectroscopy (FTIR), microscopic image analysis, and dynamic interfacial tension (IFT) measurements were conducted. The FTIR data showed EDTA brine and DTPA brine induced changes in the oil sample composition compared to seawater, which can be related to the formation of water-in-oil micro-dispersions. Microscopic image analysis on samples confirmed the formation of these micro-dispersions. The visual study by the micromodel demonstrated the micro-dispersion formation in the tertiary injection of EDTA and DTPA brine. Based on the observation made, the pore-scale mechanisms of chelating agent flooding involve the chelating agent brine penetrating the crude oil, resulting in micro-dispersion formation. These micro-dispersions tend to alter wettability to a more water-wet state, facilitate oil detachment from the surface, redistribution of oil saturation, and thus leading to improved oil recovery. The observed IFT reduction aids the penetration of EDTA and DTPA brine into the crude oil to form micro-dispersions.

Mechanisms and effects of amphiphilic lamellar nanofluid for enhanced oil recovery in low permeability reservoirs

Amphiphilic nanosheets have attracted more attention for enhanced oil recovery (EOR) owing to their unique properties. Here, the amphiphilic molybdenum disulfide (MoS2) nanosheets (AP-MDN) were prepared by functionalizing octadecyl amine (ODA) molecules onto the molybdenum disulfide nanosheets (MDN) surfaces. The dynamic stability and interfacial tension (IFT) measurements of AP-MDN nanofluid were evaluated. Besides, the mechanisms and effects of AP-MDN nanofluid for EOR were also systematically investigated and studied. Experimental results indicate that the dynamic stability of AP-MDN nanofluid is improved when MDN is successfully functionalized with ODA molecules. The IFT is decreased to 10-1 mN/m and micron-emulsions ranging from 1 µm ∼ 2 µm can be formed. In addition, the contraction rate of oil film exposed in ultra-low concentration AP-MDN nanofluid (50 mg/L) experiences two stages: a steep stage (8.5817 × 10-5 cm/s) and a gentle stage (0.6617 × 10-5 cm/s) owing to the generation of structuring disjoining pressure. Comprehensive mechanisms of AP-MDN nanofluid for EOR are also proposed and revealed. Moreover, oil washing efficiency of AP-MDN nanofluid is as high as 95.7 % when the soaking time is 6 hrs and temperature is 75 ℃. Core flooding experimental results demonstrate that the increase in shut-down time and the injection mode of multiple rounds with small slugs can better promote the interaction between AP-MDN nanofluid and crude oil in porous media. The highest oil recovery contributed by AP-MDN nanofluid is 19.1 %. These results are expected to promise AP-MDN nanofluid as an effective candidate for EOR.

Demulsification law of polyether demulsifier for W/O crude oil emulsion containing hydrophobically modified polyacrylamide in water

Hydrophobically modified polyacrylamide (HMPAM) is one of the commonly used polymers for polymer flooding. Because it is water soluble, there are many reports on the impact of HMPAM on the stability and treatment of produced water (it is O/W emulsion), but few reports on its influence on the demulsification of W/O crude oil emulsion. In this paper, firstly, three types of HMPAM containing cationic, anionic, and nonionic hydrophobic monomers (abbreviated as P(AM-AANa-N)Cn, P(AM-AANA-S)Cn, and P(AM-AANA-O)Cn, respectively) were synthesized; Then, demulsification experiments and interface behavior experiments (including dynamic interfacial tension, dilatational rheology and dynamic coalescence time measurement) were conducted to investigate the influence of HMPAM on the demulsification performance of a W/O heavy oil emulsion demulsifier D1. The demulsification results showed that HMPAM reduced the dehydration speed of D1, the type of hydrophobic monomer and the length of hydrophobic chain in HMPAM can affect the final water separated of D1. P(AM-AANa-S)Cn, P(AM-AANa-N)Cn with long hydrophobic chain, and P(AM-AANa-O)Cn with short hydrophobic chains had the negative effect on performance of D1. The results of dynamic interfacial tension experiments indirectly showed that HMPAM had the influence on the D1′s conformation and speed of rearrangement at the W/O interface during the water droplet coalescence process, thereby affecting the reduction of elastic modulus (G′) of W/O interface and the coalescence rate of water droplets. When there was HMPAM in water, the coalescence time of water droplets increased, resulting in the decrease of dehydration rate. At the meantime, HMPAM had an impact on the lg(G1′/Gdemulsifier′)/lgG1′, thereby affecting the final water separated of D1.

Role of oil polarity on myofibrillar protein emulsions stability: A multi-scale research

The oil polarity was hypothesized to significantly influence the microscopic conformation of interfacial myofibrillar protein (MP) and thus the mesoscopic interfacial rheology of MP film, which ultimately tuned the macroscopic stability of MP-stabilized emulsions. In this research, the inner mechanism was revealed hierarchically based on emulsions multi-scale properties, by a combination of in vitro interfacial concentration measurement, dynamic interfacial tension measurement and interfacial dilatational rheology (highlighting Lissajous plots). Then, the above conclusion was verified through in silico molecular dynamic simulation. At macroscopic level, the light scattering results showed that emulsion prepared with higher polarity oil exhibited higher physical stability. This could be explained from the mesoscopic perspective that: (1) the adsorption dynamics of MP was faster (though lower diffusion rate, but higher penetration and rearrangement rate) on the higher polarity interface, which decreased interfacial tension more efficiently; (2) adsorption ratio, surface load and desorption ratio indicated that ‘multilayer interfacial film’ was formed by loosely-bound MP on the lower polarity interface, which decreased the effective interfacial coverage to impair emulsions stability; (3) Lissajous plots showed that interfacial structure with higher stability against large deformation was formed on the higher polarity oil interface. Finally, the microscopic molecular mechanism for explaining the above findings was revealed by in silico molecular dynamic simulation: though MP was less unfolded on the higher polarity interface leading to weaker intermolecular hydrophobic interactions, this compact molecular structure with stronger intramolecular rigidity predominantly contributed to steadier interfacial film structure. This multi-scale study provides a deep insight into the inner relationship between oil polarity and emulsions stability.

Evaluating the Emulsifying Capacity of Cellulose Nanofibers Using Inverse Gas Chromatography.

Cellulose nanofibers (CNFs) are attracting increasing attention as emulsifiers owing to their high emulsifying capacity, biocompatibility, and biodegradability. The emulsifying capacity has been experimentally shown to depend not only on the type of oil but also on the chemical structure of the CNF surface. However, the theoretical relationship between these two factors and emulsification remains unclear, and therefore, industrial applications are limited. Here, we assess the desorption energy (DE) of CNFs from the oil surface in o/w emulsion for various CNF/oil combinations to understand the mechanism of emulsification. Two types of surface-carboxylated CNFs having different cationic counterions, namely, sodium and tetrabutylammonium ions, were used as emulsifiers. The surface free energies of the CNFs were evaluated using inverse gas chromatography, and the nonpolar Lifshitz-van der Waals γLW, electron-acceptor γ+, and electron-donor γ- components were obtained from the chromatography profiles based on the van Oss-Chaudhury-Good theory. CNF with tetrabutylammonium ions was found to have a higher γ+ component than CNF with sodium ions. Therefore, the emulsion stability improved with oils having high γ- components owing to the increase in the DE value; this was verified through both theoretical calculations using a fibrous model and experimental dynamic interfacial tension measurements. Our approach is useful for predicting the emulsifying capacity of CNFs, and it should contribute toward the design of novel CNF-based emulsions.

Molecular optimization of castor oil maleate as demulsifier for water-in-crude oil emulsions

The formation of stable water-in-oil emulsions is a frequent problem in the oil industry. In general, the difficulty of processing, unwanted water co-production, and damage to machinery are the main issues. Chemical demulsifying additives are used to destabilize petroleum emulsions. In this context, new environmentally friendly demulsifying components are being developed, preferably those produced from low-cost sources. This work synthesized five chemical surfactants based on castor oil maleate (MACO). These additives were characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR). The demulsification activity was studied through bottle tests on emulsions formulated with two Brazilian oils. A performance scan evaluated different molecular structures and concentrations of the demulsifiers (100 to 5000 ppm) to determine an optimum demulsifier molecular structure. Dynamic interfacial tension measurements were performed to elucidate the demulsification activity at the water-oil interface under the same experimental conditions as the bottle tests. The Ward and Tordai equation was applied according to asymptotic approximations to assess the diffusivity of additives. All results were discussed correlating the demulsifying mechanisms, performance at the interface, and the possibility of applying the additives. All additives showed demulsifying behavior in the form of a water dropper. The demulsifier containing 2.3 mols of maleic anhydride incorporated with 1.0 mol of castor oil showed more significant activity, with a maximum water resolution of 90% for both emulsion systems.

Effect of hydrophobic modification of cellulose nanocrystal (CNC) and salt addition on Pickering emulsions undergoing phase-transition

The charge density of emulsifiers determines the thermodynamics and kinetics adsorption properties at the oil-water interface of an emulsion. This study examines the rupture resistance and stability of the crystallized dispersed phase based on the partitioning capability of cellulose nanocrystals (CNCs) with different surface charges. The charge density of CNC particles was designed through salt addition and hydrophobic modification. The measurement of dynamic interfacial tension confirmed that the reduction of negative charge of CNC particles improves their Pickering stabilizer role. We observed that the interfacial tension displayed a sigmoidal profile with increasing time. The dynamic stability of the emulsion during phase transition of the oil phase was enhanced by increasing the interfacial particle accumulation via the reduction of surface charge of CNC. The results indicated based on the surface charge adjustment, a balance between diffusion rate and kinetic barrier adsorption of particles is required to achieve optimum system stability.

Capillary pressure-based measurement of dynamic interfacial tension in a spontaneous microfluidic sensor

The size of droplets and bubbles, and the properties of emulsions and foams strongly depend on dynamic interfacial tension (γd) - a parameter that is often inaccessible due to the very short time scales for droplet and bubble formation, and the inaccessibility of (e.g., food) production lines. To solve this challenge, we developed a microfluidic tensiometer that can measure γd by monitoring the formation time of both droplets and bubbles. Our tensiometer is a pressure-driven microfluidic device that operates based on the principle of a pressure balance: the formation of a droplet (or a bubble) is initialized when the Laplace pressure of the interface is decreased below the externally applied pressure, and this decrease is caused by a reduction in γd that can be calculated from the applied pressure and the Young-Laplace equation. The decay of γd due to surfactant adsorption can be followed at the characteristic time scale, which is dependent on surfactant type and concentration. For 0.05-1% wt sodium dodecyl sulfate (SDS), we were able to measure γd at time scales down to 1 ms and 0.1 ms for droplet and bubble interfaces, respectively, at increasing applied pressures and SDS concentrations. Our tensiometer proves to be a simple, robust method that inherently allows access to nearly the full range of dynamic interfacial tension at relevant time scales.

Comparison of surfactant mass transfer with drop formation times from dynamic interfacial tension measurements in microchannels

Dynamic interfacial tension was studied experimentally during drop formation in a flow-focusing microchannel. A low viscosity silicone oil (4.6 mPa s) was the continuous phase and a mixture of 48% w/w water and 52% w/w glycerol was the dispersed phase. An anionic (sodium dodecylsulfate, SDS), a cationic (dodecyltrimethylammonium bromide, DTAB) and a non-ionic (Triton™ X-100, TX100) surfactant were added in the dispersed phase, at concentrations below and above the critical micelle concentration (CMC). For SDS and DTAB the drop size against continuous phase flowrate curves initially decreased with surfactant concentration and then collapsed to a single curve at concentrations above CMC. For TX100 the curves only collapsed at surfactant concentrations 8.6 times the CMC. From the collapsed curves a correlation of drop size with capillary number was derived, which was used to calculate the dynamic interfacial tension at times as low as 3 ms. The comparison of the surfactant mass transport and adsorption times to the interface against the drop formation times indicated that surfactant adsorption also contributes to the time required to reach equilibrium interfacial tension. Criteria were proposed for drop formation times to ensure that equilibrium interfacial tension has been reached and does not affect the drop formation.

Measuring and modelling the adsorption kinetics of polydisperse PiBSA-based emulsifiers using dynamic interfacial tension measurements

Adsorption kinetics of industrially relevant emulsifiers typically show complex behaviour that cannot be simply explained by conventional adsorption kinetics models. In this work, we seek to understand the complex adsorption behaviour of PiBSA (polyisobutenyl succinic anhydride) based emulsifiers and SMO (sorbitan monooleate), which have significant industry relevance as they are often used as the stabiliser in emulsion explosive formulations. We attempt to explain the dynamics of multiple adsorbing species in emulsion systems by using PiBSA based emulsifiers and SMO as a model. We measure dynamic interfacial tension at toluene–water and methylated canola oil (mc oil)–water interfaces using pendant drop tensiometry for different concentrations of four industrial-grade emulsifiers that have different head group chemistries. Using our experimental measurements of dynamic interfacial tension, we estimate the dynamic adsorbed amounts of these emulsifiers using the Gibbs isotherm and Langmuir-Szyszkowski equation. The observed adsorption kinetics of these emulsifier molecules deviate from a single-mode adsorption process, likely because of competition between the kinetically versus thermodynamically favoured molecules present in the emulsifier, and the total dynamic adsorbed amount thus depends on the competition between these faster-diffusing (kinetic) and slower-diffusing (thermodynamic) species. We demonstrate that the adsorption kinetics of all the four types of emulsifiers near their equilibrium adsorption states can be well approximated by the ‘two adsorbing species model’ discussed in our previous work (Tripathi and Tabor, 2016).

PH-responsive pickering foam created from self-aggregate polymer using dynamic covalent bond

HypothesisResponsive surfactant systems based on dynamic covalent bond exhibit an unsatisfactory foamability and foam stability, despite their documented functionality in emulsions. As such we anticipate that the foaming performance should be improved by introducing Pickering effect, which is possible when the responsiveness of the dynamic covenant bonds controls not only the hydrophobicity of polymers but also their aggregation behavior (to form nanoparticles). ExperimentsHere we created surface active nanoparticles made from self-aggregated polymers consisting of PAH (polyallylamine hydrochloride)-BA (benzaldehyde). The covalent imine bonds between originally hydrophilic PAH and hydrophobic BA are dynamic in that their formation and breakage is a function of solution pH, confirmed by 1H NMR and dynamic interfacial tension measurement. FindingsAt pH 7.4, a stable foam is achieved in the PAH-BA (amino to aldehyde ratio at 1:0.2) solution; while at pH 2.5, it defoams due to breakage of dynamic bonds corresponding to the measured diminishing surface activity. The reversibility of foaming-defoaming has been demonstrated by alternatively changing pH for multiple cycles, with the foaming performance persistent. The foam stability can be improved by more hydrophobic compounds e.g. at a lower amino to aldehyde ratio or using PAH-cinnamaldehyde (CA). The reversible and responsive foaming demonstrated in a Pickering system provides a new method to create novel foaming systems with properties desirable to many applications.

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. ExperimentalIn 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.

Interplay between interfacial behaviour, cell structure and shear enables biphasic lipid extraction from whole diatom cells (Navicula sp.)

HypothesisBacillariophyceae (i.e., diatoms) are an important class of algae with potential use in the production of proteins and lipids including long-chain ω-3 polyunsaturated fatty acids. Biphasic extraction of microalgae lipids using water-immiscible solvents such as hexane, can avoid the excessive energy required to distil solvents from water, but generally requires energy-intensive rupture of the cells. The unique cell structure and surface chemistry of diatoms compared to other microalgae species might allow biphasic lipid extraction without prior cell rupture. ExperimentsThe kinetics of biphasic lipid extraction from intact Navicula sp. cells was investigated during low-shear and high-shear mixing, and with prior or simultaneous application of ultrasound (20 kHz at 0.57 W/mL). Dynamic interfacial tension measurements and electron microscopic analysis were used to investigate lipid extraction in relation to interfacial behaviour and cell structure. ResultsHigh yields (>80%) of intracellular lipids were extracted from intact cells over the course of hours upon low-shear contacting with hexane. The cells associated with and stabilised the hexane-water interface, allowing hexane to infiltrate pores in the frustule component of the cell walls and access the intracellular lipids. It was shown that mucilaginous extracellular polymeric substances (EPS) bound to the cell walls acted as a barrier to solvent penetration into the cells. This EPS could be removed by prior ultrasonication. Biphasic extraction was greatly accelerated by shear applied by rotor-stator mixing or ultrasound. High-shear could remove mucilaginous EPS from the cell surfaces to facilitate direct contact of the cell surface with hexane and produced smaller emulsion droplets with increased surface area. The combination of high-shear in the presence of hexane resulted in the in-situ rupture of the cells, which greatly accelerated lipid extraction and allowed high yields of neutral lipid (>95%) to be recovered from freshly harvested cells within less than 5 min. The study demonstrated the ability of shear to enable simultaneous cell rupture and lipid extraction from a diatom alga based on its cell structure and interfacial behaviour.

Primary structure of gum arabic and its dynamics at oil/water interface

Gum arabic (GA), an arabinogalactan-based gum, is a well-known powerful emulsifier. However, the poor stability of emulsion has often been pointed out. In order to clarify the origin, the structure-property relationship of GA, especially the interfacial property at oil/water interface, needs to be investigated. Here, we tried to correlate the primary structure with interfacial property at oil/water interface. A series of structural analyses by SEC-MALLS, SAXS, etc. showed that the primary structure of GA was a disk-like star shaped nanoparticle. The dynamic interfacial tension measurement showed that GA molecules adsorb onto oil surface in 2 steps: Firstly, the micron-aggregates of GA approach onto the oil surface, and then the aggregates are dissociated into nano-particles so that they cover the oil surface. Therefore, the emulsification and emulsion stability are controlled not by the property of the primary structure of GA but by the higher-order molecular network structure made of GA molecules.

Determination of dynamic interfacial tension in a pulsed column under mass transfer condition

AbstractInterfacial tension is an essential physical property in two‐phase flow, and it changes due to the mass transfer. The measurement of dynamic interfacial tension (DIFT) in such a condition is a difficult problem. In the previous study (Zhou et al., Chem Eng Sci. 2019; 197:172–183), we presented the quantitative relation between the droplet breakup frequency function (DBFF) and interfacial tension. It is found that the DBFF is highly depended on interfacial tension. Therefore, the DBFF is a suitable parameter to quantitatively characterize the interfacial tension. Based on this concept, the DIFT in the column is determined by regression method after the DBFF under mass transfer condition is measured. It is found that the DIFT is smaller than the static interfacial tension. This result indicates that interphase mass transfer leads to decreasing of the interfacial tension. The decreasing extent of the DIFT has a positive correlation with the mass transfer flux.

Separation of oily wastewater using titanium modified multi-walled carbon nanotubes as demulsifier

Oily wastewater causes a lot of environment problems and draws wide attention. In this paper, titanium modified multi-walled carbon nanotubes (CNTs/TiO2) for the treatment of oily wastewater were synthesized using in situ sol-gel methods. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were employed to characterize the structure and composition of CNTs/TiO2. Also, scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that TiO2 was evenly distributed in carbon nanotubes (CNTs) to induce a good synergistic effect. After the oily wastewater was treated with 400 mg/L of CNTs/TiO2 at room temperature for 30 min, the light transmittance of the aqueous phase was 89.7%. Furthermore, the composites with good interfacial activity could be reused at least five times. The combination of dynamic interfacial tension measurements, interfacial activity, interfacial film assemble and optical microscope was employed to investigate the demulsification mechanism.

Dynamic interfacial tension measurement under electric fields allows detection of charge carriers in nonpolar liquids

HypothesisElectric fields enhance surfactant transport to oil-water interfaces when the surfactant forms charged aggregates in the oil phase. Hence, transport under electric fields could be used to detect charged surfactant aggregates in nonpolar media. ExperimentsTwo surfactants with different architecture were dispersed in Isopar-M. The transport of surfactants to an oil-water interface under a constant electric field was quantified using a custom-built electrified microtensiometer platform. Electrical conductivity of the oil with surfactant concentration was also measured to determine the presence of charge carriers. FindingsThe charging mechanism of the oil phase, and field-enhanced transport was different for the two surfactants. At low concentrations where the electrical conductivity of the surfactants is indistinguishable, dynamic interfacial tension measurements under electric fields can ascertain the presence of charge carriers in Isopar-M. The transport of ionic surfactants in the aqueous phase was unaffected by the field, confirming that the field-enhanced transport of oil-phase surfactants is due to electrophoresis of charge carriers. Moreover, the equilibrium interfacial tension was not found to change under an electric field, suggesting the adsorption isotherm is independent of the field strength. We demonstrate that dynamic interfacial tension measurements under electric fields is a sensitive technique to detect charge carriers in nonpolar fluids.

Evaluation of surface activity of asphaltene and resin fractions of crude oil in the presence of different electrolytes through dynamic interfacial tension measurement

It is generally believed that asphaltenes and resins as the polar components in crude oil can get adsorbed at the oil/water interface and act as a surface active agents. However, due to the complex behavior of asphaltenes and resins, the understanding of their surface properties is challenging. In this work, the effects of addition of six electrolytes: NaCl, KCl, Na2SO4, MgSO4, MgCl2, and CaCl2 have been employed to experimentally evaluate their effect on dynamic interfacial tension of asphaltenic and resinous in oil/water interface. All of the electrolytes had the same ionic strength (0.7 M) and the pedant drop shape method was used for analysis. For this purpose, asphaltene and resin fractions of a crude oil sample with 27 API° are extracted and analyzed with elemental and Fourier-transform infrared spectroscopy (FTIR) analyses. Then, two synthetic oils samples prepared based on dissolution of extracted asphaltene and resin in toluene, their dynamic interfacial tension (IFT) values are measured in the presence of different brines. The adsorption/relaxation reorganization times of asphaltene and resin components at the oil samples/aqueous solution interface are evaluated with exponential decay model. Results suggest that divalent cations, Ca2+ and Mg2+, possess higher affinity toward the polar groups of asphaltene and resin components in the presence of Cl− compared to SO42−. Specially, Ca2+ is more preferred over Mg2+, particularly for resinous oil sample. Due to the higher affinity of the polar functional groups toward the interface in the presence of CaCl2, the lowest adsorption time was obtained for CaCl2, which refers to the time required for coverage and packing of active agents at the interface.