Interfacial Tensiometry Research Articles

Interactions of clathrate hydrate promoters sodium dodecyl sulfate and tetrahydrofuran investigated using 1H diffusion nuclear magnetic resonance at hydrate-forming conditions.

Thermodynamic hydrate promoters and kinetic hydrate promoters can be used to reduce the P-T conditions for clathrate hydrate synthesis to decrease the nucleation induction time while increasing growth rates. Two commonly used promoters for hydrate research are tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS), which can increase the overall hydrate promotion when used in tandem as compared to individually. There are several molecular theories regarding how SDS promotes hydrate growth. This study explores the micellular theory, for which hydrate formation depends on surfactant aggregates (micelles) at a critical micelle concentration (CMC) to increase the interfacial surface area. The micellular theory is the most investigated and criticized surfactant hydrate promotion theory. To address questions related to micellar behavior, this study investigates the intermolecular behavior between SDS and THF for the identification of micelles at hydrate-forming conditions. The systems explored contained THF at 3 and 5 wt. % with varying concentrations of SDS below and above the CMC. Several methods including a qualitative visual method, conductivity, interfacial tensiometry, 13C Liquid-state Nuclear Magnetic Resonance (NMR) spectroscopy, and 1H diffusion NMR spectroscopy were evaluated at temperatures below the Krafft point of SDS and above 0 °C. The presence of THF at low concentrations decreased the critical temperature for the formation of SDS micelles, where SDS is solubilized in THF/water solution at hydrate-forming temperatures without precipitation. The CMC of SDS was decreased significantly even at hydrate-forming conditions. Mixed surfactant-cosolvent micellular behavior of SDS in the presence of low concentrations of THF was confirmed at hydrate-forming conditions above 0 °C.

Encapsulation of Nanoparticles with Statistical Copolymers with Different Surface Charges and Analysis of Their Interactions with Proteins and Cells.

Encapsulation with polymers is a well-known strategy to stabilize and functionalize nanomaterials and tune their physicochemical properties. Amphiphilic copolymers are promising in this context, but their structural diversity and complexity also make understanding and predicting their behavior challenging. This is particularly the case in complex media which are relevant for intended applications in medicine and nanobiotechnology. Here, we studied the encapsulation of gold nanoparticles and quantum dots with amphiphilic copolymers differing in their charge and molecular structure. Protein adsorption to the nanoconjugates was studied with fluorescence correlation spectroscopy, and their surface activity was studied with dynamic interfacial tensiometry. Encapsulation of the nanoparticles without affecting their characteristic properties was possible with all tested polymers and provided good stabilization. However, the interaction with proteins and cells significantly depended on structural details. We identified statistical copolymers providing strongly reduced protein adsorption and low unspecific cellular uptake. Interestingly, different zwitterionic amphiphilic copolymers showed substantial differences in their resulting bio-repulsive properties. Among the polymers tested herein, statistical copolymers with sulfobetaine and phosphatidylcholine sidechains performed better than copolymers with carboxylic acid- and dimethylamino-terminated sidechains.

Identification of maximal cyclic pressure with the non-motorized method based on specific refraction

ВACKGROUND: Russian scientists constantly deal with the issues of the engine performance evaluation with non-standard methods, as they are commonly called “express methods”. In many cases, if the initial components retain the relative constancy of their physicochemical properties, the determination of performance indicators can be carried out with simple classical methods of refractometry, magneto-optics, densimetry, interfacial tensiometry or their combination (aggregation).
 AIM: Identification of the maximal cycle pressure of an operating diesel engine with the non-motorized method based on the values of specific refraction for each type of biofuel.
 METHODS: The object of research was the D-245.5S2 turbocharged four-stroke engine with intercooler. Mixtures of DT with ethanol, rapeseed oil and surep oil were prepared for the study. The mass fraction of oils and ethanol in the mixture varied from 0% to 50%. Density d and refractive index were measured for each sample. The measurements were carried out at an ambient temperature of 20˚C. The refractive index of the samples was measured using the IRF – 454b refractometer. The density was determined using the PZh-2-25 pycnometer and the VIBRAAJH-620CE laboratory scales according to GOST 3900-85 “Oil and petroleum products. Methods for determining density”.
 RESULTS: Data analysis showed that there is a strong correlation between the specific refraction sR and the maximal pressure in a cylinder Pz (MPa). Linear regression models for various alternative fuel mixtures have been developed to determine the maximal cycle pressure during diesel operation.
 CONCLUSION: The application of the proposed dependencies makes it possible to identify the maximal cycle pressure of an operating a diesel engine with sufficient accuracy in a non-motorized way.

Clinical evaluation of dynamic interfacial tensiometry in patients with chronic pancreatitis (CP)

Clinical evaluation of dynamic interfacial tensiometry in patients with chronic pancreatitis (CP)

Effect of line tension on domain formation of fluorinated compounds at alkane/water interface

Condensed domain formation of fluorinated compounds (alcohol and ester) in adsorbed films at alkane/water interfaces was investigated by interfacial tensiometry, X-ray reflectometry, and BAM observation. The results obtained are explained by the effects of contact energy and dipole-dipole interaction, which are competitive contributions to the line tension acting at the domain boundary. Estimation of the two contributions indicated that the former is more dominant than the latter for the domain formation. In the adsorbed films of fluorinated alcohol, F8H2OH, at alkane/water interfaces, the domain formation was suppressed with increasing alkane chain length due to an increase in contact energy. The mixing of hybrid alcohol with fluorocarbon and hydrocarbon chains of the same carbon number, F6H6OH, in adsorbed film reduces contact energy. This stabilizes the dispersion of many domains with small size. On the other hand, when F8H2OH molecules are mixed with a cationic surfactant, C12TAB, in the adsorbed film, an attractive dipole-ion interaction between the hydrophilic groups relaxes the repulsive dipole-dipole interaction between F8H2OH molecules, resulting in the formation of domains with smooth boundary and large size. Furthermore, fluorinated ester, FC12Me molecules form flower shaped domains with intricate boundary mainly due to a larger dipole moment of FC12Me than F8H2OH.

Physicochemical properties of blood and urine in patients with alcohol-induced chronic pancreatitis against the background of obesity

In this article, the authors present the results of their studies of the physicochemical properties of blood and urine in patients with chronic alcohol-induced pancreatitis (CAP) combined with obesity.
 110 patients with CAP in the acute stage against the background of obesity were examined. The ages of the examined patients ranged from 23 to 60. There were 77 (70.0%) men and 33 (30.0%) women among the patients. We also examined 30 almost healthy people aged 20 to 60 (the control group).
 There are significant changes in the physicochemical properties of blood and urine in patients with CAP against the background of obesity. Indices of interfacial tensiometry and rheometry of these biological fluids correlate with other clinical, laboratory, and instrumental data in patients with CAP combined with obesity. This allows us to recommend the assessment of dynamic surface tension and rheometric indices of blood and urine for screening and an integral assessment of the functional state of the pancreas in comorbidity. In addition, it is reasonable to use the results of interfacial tensiometry and rheometry for screening the metabolic syndrome in patients with CAP against the background of obesity. In the metabolic syndrome, there is a significant increase in the surface tension 3 of the blood; in the absence of this syndrome, on the contrary, the surface tension 3 of the blood is significantly reduced.
 In patients with biliary sludge and cholelithiasis, the blood viscoelasticity index (E) was significantly lower (23.18±1.07 mN/m), while without concomitant diseases of the biliary tract, the blood E was equal to 27.84±1.08 mN/m (p<0.05). Both with and without changes in the biliary system, blood E in patients with CAP against the background of obesity was significantly lower than in the control group.
 The prospects of research are to study the dynamics of tensiometry and rheometry of biological fluids in CAP combined with obesity under the influence of treatment in order to study the possibility of using these indices in the integrated assessment of the effectiveness of therapy.

Effect of Polar Hydrocarbon Contents on Oil-Water Interfacial Tension and Implications for Recent Observations in Smart Water Flooding Oil Recovery Schemes.

For decades now, low salinity water flooding (LSWF) oil recovery has emerged as an environmentally benign and cost-effective method for improved oil recovery, where research findings have reported pH and interfacial tension effects. Considering the effect of oil chemistry on interfacial tension and the potential of this chemistry to have a direct relationship with LSWF, we measured the interfacial tension of four crude oils with composition varying from those of conventional to unconventional ones. We also characterized the crude oil samples using infrared spectroscopy and a wet chemistry method based on asphaltene precipitation. Our research approach has enabled us to relate the composition of crude oil to the interfacial tension trend at pH encountered in improved oil recovery schemes. Our research methodology, based on an integrated approach to using infrared spectroscopy and interfacial tensiometry, has also enabled us to propose a more robust theoretical explanation for current observations in LSWF related to pH and interfacial tension. In this regard, oil-water interfacial tension depends on the concentration of polar components, such that the higher the concentration of polar groups in crude oil, the higher the interfacial tension at a given pH of aqueous solution. We have also shown that the acid-base behavior of polar groups at the oil-water interface provides a theoretical interpretation of the explicit relationship between oil-water interfacial tension and the electrostatic components of interfacial tension as given by the energy additivity theory.

Enhanced oil recovery performance and mechanism of a wormlike micelles flooding system with zwitterionic-anionic surfactants

Surfactant-based wormlike micelles (WLMs) have been proven to be efficient in improving oil recovery due to their high viscosity and low oil/water interfacial tension (IFT). In this study, a novel WLMs oil displacement system was developed by mixing zwitterionic surfactant (Erucylamido propyl betaine, EAPB) and anionic surfactant (Sodium dodecylsulfate, SDS) at the mass ratio of 1.5:1. The viscosity, IFT and emulsification properties were studied by rheometry, interfacial tensiometry and bottle testing, respectively. The core and etched glass micro-model oil displacement tests were conducted to investigate the oil recovery efficiencies and the related mechanism. The results show that the EAPB-SDS combination system exhibits shear thickening compared to that of sole EAPB system due to the electrostatic attraction between SDS and EAPB. The viscosity is first increased and then decreased with the increase in pH, temperature and salinity. The IFT is decreased with pH, while it is first decreased and then increased with the increase of temperature and salinity. The EAPB-SDS combination system with mass concentration of 0.3% can enhance oil recovery by 25.91% and 19.79% after water flooding in homogeneous and heterogeneous cores, respectively. The high viscosity makes the system to exhibit good mobility control ability, while the low IFT contributes to the peeling and emulsification of residual oil, thereby significantly improving the oil displacement performance.

Адсорбционно-реологические свойства крови при подагрическом артрите

Цель исследования — провести оценку клинико-патогенетической значимости изменений адсорбционно-реологических свойств сыворотки крови (АРСК) у больных с разными формами течения подагрического артрита. С помощью межфазной тензиореометрии крови обследовано 89 больных и 30 практически здоровых людей контрольной группы (преимущественно мужчин). Использовали компьютерные аппараты MPT2-Lauda, ADSA-Toronto и PAT2-Sinterface. Интермиттирующий вариант артрита установлен в 63 % наблюдений, хронический — в 37 %, легкое течение суставного синдрома имело место в 19 % случаев, средней тяжести — в 51 %, тяжелое — в 30 %. Определяли поверхностные вязкость (ПВ), упругость (ПУ), натяжение (ПН), модуль вязко­упругости (ВУ), время релаксации (ВР), угол наклона и фазовый угол (ФУ) тензиограмм, угол реальной вязкоупругости (УРВУ) и интегральный угол вязкоупругости (ИУВУ). Подагрический артрит сопровождается достоверным повышением параметров ВР сыворотки крови на 26 % и ИУВУ — вдвое при уменьшении ПУ на 8 %, ВУ на 26 %, ПН на 4 % и УРВУ на 11 %, что наблюдается соответственно у 45, 39, 36, 48, 44 и 38 % больных, имеет половой диморфизм, зависит от формы (ПУ, ФУ, ИУВУ) и тяжести течения (ПВ, ВР, ПН) артикулярного синдрома, наличия костных тофусов (ПВ, ВР, ФУ, ИУВУ) и рентгеносонографических признаков поражения суставов. Изменения АРСК отражают характер течения подагрического артрита, отдельные показатели участвуют в патогенетических построениях заболевания и могут иметь прогностическую значимость.

Studies into interactions and interfacial characteristics between cellulose nanocrystals and bovine serum albumin

This study investigates the interactions between cellulose nanocrystals (CNCs) and bovine serum albumin (BSA) under different pH conditions. A multiscale technique was employed to characterize the CNCs and BSA at pH 7 and pH 3. ζ-Potential measurement and UV–vis spectroscopy demonstrated strong interactions between CNCs and BSA at pH 3, whereat they have opposite charges. Interfacial tensiometry showed a deficiency in the surface activity of the CNCs and indicated that BSA dominated the interface behavior in their complex. Quartz crystal microbalance with dissipation revealed that the sequential adsorption of BSA and CNCs produced viscoelastic bilayers at pH 3, and the mass adsorbed was ∼ 28 times that adsorbed at pH 7. Molecular dynamics simulations indicated that the key interactions between the two materials were produced between the hydrophobic CNC surface and the BSA domain IIA region. These results provide interesting insights into the design of complex food emulsions and fluid interfaces.

Synergistic and Competitive Adsorption of Hydrophilic Nanoparticles and Oil-Soluble Surfactants at the Oil-Water Interface.

Fundamental insights into the interplay and self-assembly of nanoparticles and surface-active agents at the liquid-liquid interface play a pivotal role in understanding the ubiquitous colloidal systems present in our natural surroundings, including foods and aquatic life, and in the industry for emulsion stabilization, drug delivery, or enhanced oil recovery. Moreover, well-controlled model systems for mixed interfacial adsorption of nanoparticles and surfactants allow unprecedented insights into nonideal or contaminated particle-stabilized emulsions. Here, we investigate such a model system composed of hydrophilic, negatively, and positively charged silica nanoparticles and the oil-soluble cationic lipid octadecyl amine with in situ synchrotron-based X-ray reflectometry, which is analyzed and discussed jointly with dynamic interfacial tensiometry. Our results indicate that negatively charged silica nanoparticles only adsorb if the oil-water interface is covered with the positively charged lipid, indicating synergistic adsorption. Conversely, the positively charged nanoparticles readily adsorb on their own, but compete with octadecyl amine and reversibly desorb with increasing concentrations of the lipid. These results further indicate that with competitive adsorption, an electrostatic exclusion zone exists around the adsorbed particles. This prevents the adsorption of lipid molecules in this area, leading to a decreased surface excess concentration of surfactants and unexpectedly high interfacial tension.

Ibuprofen and the Phosphatidylcholine Bilayer: Membrane Water Permeability in the Presence and Absence of Cholesterol.

The interactions between drugs and cell membranes can modulate the structural and physical properties of membranes. The resultant perturbations of the membrane integrity may affect the conformation of the proteins inserted within the membrane, disturbing the membrane-hosted biological functions. In this study, the droplet interface bilayer (DIB), a model cell membrane, is used to examine the effects of ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID), on transbilayer water permeability, which is a fundamental membrane biophysical property. Our results indicate that the presence of neutral ibuprofen (pH 3) increases the water permeability of the lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). When cholesterol is present with the DOPC, however, the water permeability is not influenced by addition of ibuprofen, regardless of the cholesterol content in DOPC. Given the fact that cholesterol is generally considered to impact packing in the hydrocarbon chain regions, our findings suggest that a potential competition between opposing effects of ibuprofen molecules and cholesterol on the hydrocarbon core environment of the phospholipid assembly may influence the overall water transport phenomena. Results from confocal Raman microspectroscopy and interfacial tensiometry show that ibuprofen molecules induce substantial structural and dynamic changes in the DOPC lipid bilayer. These results, demonstrating that the presence of ibuprofen increases the water permeability of pure DOPC but not that of DOPC-cholesterol mixtures, provide insight into the differential effect of a representative NSAID on heterogeneous biological membranes, depending upon the local composition and structure, results which will signal increased understanding of the gastrointestinal damage and toxicity induced by these molecules.

Surface Freezing of Cetyltrimethylammonium Chloride-Hexadecanol Mixed Adsorbed Film at Dodecane-Water Interface.

The surface freezing transition of a mixed adsorbed film containing cetyltrimethylammonium chloride (CTAC) and n-hexadecanol (C16OH) was utilized at the dodecane-water interface to control the stability of oil-in-water (O/W) emulsions. The corresponding surface frozen and surface liquid mixed adsorbed films were characterized using interfacial tensiometry and X-ray reflectometry. The emulsion samples prepared in the temperature range of the surface frozen and surface liquid phases showed a clear difference in their stability: the emulsion volume decreased continuously right after the emulsification in the surface liquid region, while it remained constant or decreased at a much slower rate in the surface frozen region. Compared to the previously examined CTAC-tetradecane mixed adsorbed film, the surface freezing temperature increased from 9.5 to 25.0 °C due to the better chain matching between CTAC and C16OH and higher surface activity of C16OH. This then renders such systems much more attractive for practical applications.

Diffusion-Controlled Spontaneous Emulsification of Water-Soluble Oils via Micelle Swelling.

Spontaneous emulsification of toluene, xylenes, cyclohexane, and mineral oil in a nonionic nonylphenol polyethoxylate surfactant solution was investigated by visual observations coupled with dynamic light scatting measurements and interfacial tensiometry. For water-soluble oils, nanoscale emulsions formed spontaneously by diffusion of oil molecules into the aqueous surfactant solutions and subsequent swelling of surfactant micelles with oil. Micelle swelling rates were quantified to assess system spontaneity, revealing that oil solubility in water was directly correlated to the spontaneity of the emulsion (toluene > xylenes > cyclohexane). When experiments were intentionally designed to create surfactant concentration gradients, Marangoni flows were found to enhance spontaneity. Despite their spontaneous formation, emulsion stability was limited over the course of 40 days by Ostwald ripening followed by creaming and evaporation. These results provide insights on the likelihood of nanoemulsion formation and persistence in oily wastewater as the components in this study are present in many wastewater systems.

Ferrofluid Microdroplet Splitting for Population-Based Microfluidics and Interfacial Tensiometry.

Ferrofluids exhibit a unique combination of liquid properties and strong magnetic response, which leads to a rich variety of interesting functional properties. Here, the magnetic‐field‐induced splitting of ferrofluid droplets immersed in an immiscible liquid is presented, and related fascinating dynamics and applications are discussed. A magnetic field created by a permanent magnet induces instability on a mother droplet, which divides into two daughter droplets in less than 0.1 s. During the splitting process, the droplet undergoes a Plateau–Rayleigh‐like instability, which is investigated using high‐speed imaging. The dynamics of the resulting satellite droplet formation is shown to depend on the roughness of the supporting surface. Further increasing the field results in additional splitting events and self‐assembly of microdroplet populations, which can be magnetically actuated. The effects of magnetization and interfacial tension are systematically investigated by varying magnetic nanoparticles and surfactant concentrations, and a variety of outcomes from labyrinthine patterns to discrete droplets are observed. As the splitting process depends on interfacial tension, the droplet splitting can be used as a measure for interfacial tension as low as 0.1 mN m−1. Finally, a population‐based digital microfluidics concept based on the self‐assembled microdroplets is presented.

Study Evaluates Hydrate Antiagglomerants

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28578, “Quantitative Ranking and Development of Hydrate Antiagglomerants,” by Shane A. Morrissy, Temiloluwa O. Kuteyi, Mike L. Johns, Eric F. May, SPE, and Zachary M. Aman, SPE, University of Western Australia, and Stuart F. McKay, SPE, Woodside Energy, prepared for the 2018 Offshore Technology Conference Asia, Kuala Lumpur, 20–23 March. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission. A common hydrate-management strategy involves the use of large volumes of thermodynamic inhibitors (THIs) to operate outside the hydrate-stability region. However, this strategy represents significant capital expenditure and operating costs. Low-dosage hydrate inhibitors (LDHIs), in the form of kinetic hydrate inhibitors (KHIs) and antiagglomerants (AAs), present an economical alternative to THIs. In this study, a quantitative micromechanical force (MMF) has been deployed to study the performance of seven industry AAs. The results illustrate that an effective AA is one that lowers the cohesive forces between hydrate particles. Introduction AAs prevent hydrate agglomeration of a steady-state hydrate slurry. Hydratephilic AAs are surfactants that adsorb to the hydrate/oil interface in preference to the water/oil interface. Current operating experience suggests that AAs may be unsuited to the high water cuts that are characteristic of late field life. A successful hydrate AA lowers the cohesive force or surface free energy of hydrate particles to prevent agglomeration. Rocking cells and high-pressure visual autoclaves provide a semiquantitative assessment of hydrate blockage. However, a knowledge gap exists with regard to whether current industry AAs actually lower hydrate interparticle cohesive and surface free energy. Techniques to deconvolute the mechanism of the action of AAs are required to better understand how AAs affect hydrate blockage. Experimental Procedure Micromechanical Hydrate Cohesive Force. A third-generation MMF apparatus was used to measure the cyclopentane hydrate interparticle cohesive force. The MMF uses cyclopentane to create Structure II cyclopentane hydrates, the same hydrate structure present in the field. The cohesive-force-measurement technique was adapted from previous re-search on hydrate cohesion and asphaltene cohesion. Interfacial Tensiometry. An optical interfacial tensiometer was used to measure the interfacial tension (IFT) between water and oil phases at ambient pressure and room temperature. A hooked needle with the AA prepared in paraffin oil was placed in a bulk phase of deionized water. The resolution of this apparatus is typically +- 1 mN/m and the threshold sensitivity is 1 mN/m. Typically, surfactant-free systems will rap-idly reach equilibrium within 1 minute of creating an oil droplet in water. Conversely, the presence of a surfactant may decrease the IFT as a function of time, asymptotically approaching a steady-state value. Because the AAs studied contain surfactant functionality, each IFT was measured for at least 20 minutes, after which point the IFT was not observed to change with time. Each data point represents an average of at least four independent trials.

Solid Film Formation at the Tetradecane/Aqueous Hexadecyltrimethylammonium Bromide Solution Interface Studied by Interfacial Tensiometry and X-ray Reflectometry.

The effect of oil on condensed film formation in the adsorbed film of hexadecyltrimethylammonium bromide (C16TAB) at the tetradecane (C14)/water (W) interface was examined by interfacial tension and X-ray reflectivity measurements. The interfacial tension vs temperature curves have break point due to the expanded?condensed phase transition of the adsorbed film. The partial molar entropy of C16TAB at the interface changes discontinuously, whereas the interfacial density changes almost continuously at the phase transition point. The electron density profile normal to the interface manifested that the condensed film is regarded as a two-dimensional (2D) solid rotator phase in which C16TAB and C14 molecules are densely packed with perpendicular orientation. Combining the interfacial tension and X-ray reflectivity data, the mixing ratio of C16TAB to C14 in the solid film was determined to be 2:3 and thus the film is enriched in oil molecules than surfactant ones. Furthermore, the partial molar entropy change of C14 associated with solid film formation was found to be largely negative and very close to that of surface freezing of liquid alkane, manifesting that C14 molecules are well ordered to form a 2D solid film by mixing with C16TAB molecules at the interface. The solid film formation of the present system is driven by effective vdW interactions between adsorbed C16TAB and intercalated C14 molecules. The morphology of the condensed domain observed during phase transition suggested that the contact energy is more predominant than the dipole repulsion at the domain boundary, which promotes coalescence of small domains into large ones during phase transition.

Molecular Interactions Leading to the Coadsorption of Surfactant Dodecyltrimethylammonium Bromide and Poly(styrenesulfonate) at the Oil/Water Interface.

The strong synergistic adsorption of mixed polymer/surfactant (P/S) systems at the oil/water interface shows promise for applications such as oil remediation and emulsion stabilization, especially with respect to the formation of tunable mesoscopic multilayers. There is some evidence that a combination of dodecyltrimethylammonium bromide (DTAB) and sodium poly(styrenesulfonate) (PSS) exhibits the adsorption of a secondary P/S layer, though the structure of this layer has long eluded researchers. The focus of this study is to determine whether the DTAB-assisted adsorption of PSS at the oil/water interface occurs as a single layer or with subsequent multilayers. The study presented uses vibrational sum-frequency spectroscopy and interfacial tensiometry to determine the degree of PSS adsorption and orientation of its charged groups relative to the interface at three representative concentrations of DTAB. At low and intermediate DTAB concentrations, a single mixed DTAB/PSS monolayer adsorbs at the oil/water interface. No PSS adsorbs above the system critical micelle concentration. The interfacial charge is found to be similar to that of P/S complexes solvated in the aqueous solution. The surface adsorbate and P/S complexes in the bulk both exhibit a charge inversion at around the same DTAB concentration. This study demonstrates the importance of techniques which can differentiate between coadsorbing species and calls into question current models of P/S adsorption at an oil/water interface.

Flow monitoring of underground aquifers by interfacial tensiometry

The aim of this study is online specification of water productivity of crude oil wells based on the multidimensional analysis of the dynamic surface tension (DST) of produced water from underground sub–layers, assuming the impacts of asphaltenes emulsification. The novelties are the discriminant analysis of produced water streams from one aquifer but via different sub–layers, enhancement of tensiometery characteristics to improve the validity and reliability of algorithm, and smoothing the uncertainties and error function or sources. The experimental tests were conducted by the pendant–drop tensiometer via computation of water–air DST of samples obtained from distinct wells exposed to individual sub–layers. DST–partial least squares (PLS) and elasticity–PLS algorithms was computed and the results revealed that the production ratio of L1–L4 sub–layers of aquifer were set in the range of 1–53% (for DST–PLS) and 10–50% (for elasticity–PLS) while the conventional method had reported an equal 25% productivity for each layer. The algorithm of elasticity–PLS was developed to determine the production ratio of four sub–layers as that of DST–PLS; however the validity of this algorithm can be improved to higher frequencies more than 5.0 Hz. Both models of DST–PLS and elasticity–PLS were applied successfully for accurate and fast determination of layers productivity in an oil well exposed to multi layers of aquifer and error limit of DST–PLS was determined to be in the range of 1.0–3.2%.

Assessing Pair Interaction Potentials of Nanoparticles on Liquid Interfaces.

The pair interaction potentials of polymer-grafted silica nanoparticles (NPs) at liquid surfaces were determined by scanning electron microscopy, exploiting the nonvolatility of ionic liquids to stabilize the specimens against microscope vacuum. Even at near contact, individual, two-dimensionally well-dispersed NPs were resolved. The potential of mean force, reduced to the pair interaction potential for dilute NPs, was extracted with good accuracy from the radial distribution function, as both NP diameter and grafted polymer chain length were varied. While NP polydispersity somewhat broadened the core repulsion, the pair potential well-approximated a hard sphere interaction, making these systems suitable for model studies of interfacially bound NPs. For short (5 kDa) poly(ethylene glycol) ligands, a weak (< kB T) long-range attraction was discerned, and for ligands of identical length, pair potentials overlapped for NPs of different diameter; the attraction is suggested to arise from ligand-induced menisci. To understand better the interactions underlying the pair potential, NP surface-binding energies were measured by interfacial tensiometry, and NP contact angles were assessed by atomic force microscopy and transmission electron microscopy.