支状嵌段聚醚的界面聚集行为及对原油乳状液的破乳作用

合成了三种不同聚氧丙烯/聚氧乙烯(PPO/PEO)比例的含苯环支状嵌段聚醚, 通过界面张力、界面流变、表面压以及对原油乳状液的破乳脱水效果的测定, 考察了其界面聚集行为和破乳作用对PEO含量和分子量的依赖性, 并且对比研究了三种支状聚醚分子交联前后的破乳性能. 结果表明, PEO含量高且分子量大者,其单分子界面占据面积大, 在油/水界面达到吸附平衡的时间短, 其油/水界面扩张模量及扩张弹性均高于PEO含量较少者. 但是对原油乳状液的破乳脱水效果则是PEO含量居中的聚醚最好. 温度影响和交联与否的研究表明, 交联并不能提高分子量较大的聚醚对原油乳状液的破乳效果, 温度对聚醚分子交联前后的破乳效果有不同的影响规律. 本研究可为原油集输过程中化学品的选择与应用提供一定的依据.     

Study on Influencing Factors of Chemical Flooding for Heavy Oil

Alkali and alkali/surfactant displacing agents are designed for two kinds of heavy oil. Results of emulsifying capacity, dynamic interfacial tension (IFT) and water-wet core flooding tests show that, although alkaline/surfactant systems exhibit better capacity in emulsification and IFT reduction, oil recovery values of alkaline/surfactant flooding are lower than those of alkaline flooding. Glass-etched micromodel tests further demonstrate that, when alkaline solution penetrates into the oil phase, water streams break into ganglia coating oil film. Water ganglia may be entrapped by narrow throats, consequently presenting a water-oil alternating slug flow. Similar water ganglia also appears in alkaline/surfactant flooding, however, water channeling along the pore surface occurs subsequently, resulting in its relatively lower oil recovery.     

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

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

Partition and water/oil adsorption of some surfactants

Adsorption isotherms have been determined at the water/oil interface for five biphasic systems involving surfactants (non-ionic and ionic) present in both phases at partition equilibrium. The systems studied were polyoxyethylene(23)lauryl ether (Brij35) in water/hexane and four ionic surfactants, hexadecyltrimethylammonium bromide (CTAB), and a series of three tetraalkylammonium dodecylsulfate (TEADS, TPADS, and TBADS) in water/CH 2Cl 2. Interfacial tension measurements performed at the water/air and water/oil interfaces provided all the necessary information for the determination of the adsorption parameters by taking partition into account. These measurements also allowed the comparison of the adsorption properties at both interfaces which showed an increase of the adsorption equilibrium constant and a decrease of the maximum surface concentration at the water/oil interface compared to water/air. The values of the critical aggregation concentration showed, in all cases, that only the surfactant dissolved in the aqueous phase contribute to the decrease of the water/oil interfacial tension. In the case of the four ionic surfactants, the critical aggregation concentration obtained in biphasic conditions were lowered because of the formation of mixed surfactant-CH 2Cl 2 aggregates.     

The influence of pH on phosphatidylcholine monolayer at the air/aqueous solution interface

The measurements of the interfacial tension at the air/aqueous subphase interface as the function of pH were performed. The interfacial tension of the air–aqueous subphase interface was divided into contributions of individuals. A simple model of the influence of pH on the phosphatidylcholine monolayer at the air/hydrophobic chains of phosphatidylcholine is presented. The contributions of additive phosphatidylcholine forms (both interfacial tension values and molecular area values) depend on pH. The interfacial tension values and the molecular areas values for LH⁺, LOH⁻ forms of phosphatidylcholine were calculated. The assumed model was verified experimentally.     

Interfacial dilational behaviour of adsorbed β-lactoglobulin layers at the different fluid interfaces

β-Lactoglobulin adsorption layers at the interfaces solution/air, /tetradecan and /sunflower oil were characterised by dynamic interfacial tension measurements and harmonic drop oscillation experiments in a time scale of some seconds. Axialsymmetric drop shape analysis (ADSA) was used to calculate drop volume, area and interfacial tension. Within a definite range of drop volume amplitude, the oscillation of the surface tension is harmonic and interfacial dilation parameters can be determined. Dependence of the dilational parameters on the amplitude and frequency of drop volume oscillation were determined and methodical demands are given for this special kind of ADSA application. The concentration of interfacial saturation is minimal at the interface with sunflower oil. Interfacial dilational elasticities, and viscosities are maximal at the saturation concentration of all systems investigated. The dilational viscosities are maximal in the frequency range 0.007–0.011 Hz and characterise molecular rearrangement processes in the adsorption layer. Interfacial dilational elasticity and viscosity are the largest at the interface with air. They are the smallest at the interface with sunflower oil. Similarities and differences of the systems investigated are discussed by taking into account the adsorption behaviour and the solvatation of different apolar and polar parts of the protein molecules in the neighbouring phase.     

Spreading of oil from protein stabilised emulsions at air/water interfaces

Spreading of a drop of an emulsion made with milk proteins on air/water interfaces was studied. From an unheated emulsion, all oil molecules could spread onto the air/water interface, indicating that the protein layers around the oil globules in the emulsion droplet were not coherent enough to withstand the forces involved in spreading. Heat treatment (90 °C) of emulsions made with whey protein concentrate (WPC) or skim milk powder reduced the spreadability, probably because polymerisation of whey protein at the oil/water interface increased the coherence of the protein layer. Heat treatment of emulsions made with WPC and monoglycerides did not reduce spreadability, presumably because the presence of the monoglycerides at the oil/water interface prevented a substantial increase of coherence of the protein layer. Heat treatment of caseinate-stabilised emulsions had no effect on the spreadability. If proteins were already present at the air/water interface, oil did not spread if the surface tension (γ) was <60 mN/m. We introduced a new method to measure the rate at which oil molecules spread from the oil globules in the emulsion droplet by monitoring changes in γ at various positions in a ‘trough’. The spreading rates observed for the various systems agree very well with the values predicted by the theory. Spreading from oil globules in a drop of emulsion was faster than spreading from a single oil drop, possibly due to the greater surface tension gradient between the oil globule and the air/water interface or to the increased oil surface area. Heat treatment of an emulsion made with WPC did not affect the spreading rate. The method was not suitable for measuring the spreading rate at interfaces where surface active material is already present, because changes in γ then were caused by compression of the interfacial layer rather than by the spreading oil.     

Effect of pH on the adsorption kinetics of egg yolk at the triacylglycerol–water interface and viscoelastic properties of interfacial egg yolk films: a dynamic drop tensiometry study

Interfacial properties of normal egg yolk (EY), as well as stabilized, i.e. enzymatically modified with phospholipase A2, egg yolk (SEY) at the triacylglyceride (TAG) oil–water interface have been investigated with the use of the dynamic drop tensiometry (DDT) technique in the wide interval of pH values of aqueous EY solutions. We found that for both EY and SEY pH values of their aqueous solutions affect absolute values of interfacial tension at the TAG oil–water interface. In the presence of EY this effect was more pronounced, with minimum of interfacial tension values at pH nearly equal to the isoelectric point of EY proteins. For SEY solutions no clear trend was noticed, although a reduction of interfacial tension near pH 6 was also observed. Moreover, the pH-dependence of nearly steady values of interfacial tension in the presence of EY was substantially less pronounced than it has been reported previously. It was also found that there is a difference in the interfacial viscoelasticity of SEY and EY films formed at the TAG oil–water interface. Although the dependence of dilational modulus, ∣ε∣, versus surface pressure for SEY solutions goes through a maximum, absolute values of ∣ε∣ increase for EY solutions in a wide pH range. At the same time, no visible effect of pH on the viscoelasticity of EY and SEY interfacial films was noticed. It became clear from the dilational modulus versus surface pressure curves for both EY and SEY that adsorption of their surface-active components at the TAG oil–water interface occurs in a step-wise manner. We found also that the phase angle values for the adsorbed EY layers were lower that those observed in the presence of SEY, indicating an increasing viscous contribution to the dilational modulus in the SEY-containing system.     

Stability of emulsions of water in mineral oils containing asphaltenes

Emulsions of water in mineral oils are stable if the oil phase contains asphaltenes which are near the condition of incipient flocculation. This condition is determined by the composition of the oil phase and by the nature of the asphaltenes. High aromaticity of the oil phase and the presence of deflocculants prevent flocculation of asphaltenes; the deflocculants may be interfacially active agents or asphaltene-like compounds with better solubility in the oil phase. Conditions of incipient flocculation of asphaltenes correlate very well with a considerable increase of rheological resistance of the interface between the oil phase and distilled water, determined according to the torsion oscillation method. Stabilization of the water-in-oil emulsions is therefore caused by the build-up of a coherent layer of asphaltenes in the water-oil interface in these cases. Deflocculants of asphaltenes in the oil phase destroy their stabilizing effect; however, the deflocculants themselves may stabilize the water-in-oil emulsions by adsorption on the water-oil interface and then the correlation between the condition of asphaltenes and emulsion stability does not hold, nor is the interfacial viscosity perceptibly increased. Under borderline conditions of emulsion stability a few percent of sodium chloride in the water phase counteracts the build-up of a stabilizing layer of asphaltenes in the water-oil interface and so do higher p_H values of a buffered water phase. At low p_H-values emulsion stability does not correlate with interfacial resistance. It can be concluded that asphaltenes stabilize water-in-oil emulsions if they accumulate on the water-oil interface. This interfacial layer may show a coherence, which is an indication of the presence of asphaltenes rather than a condition for stability of the emulsions.     

Interfacial and self-assembly properties of bolaamphiphilic compounds derived from a multifunctional oil

The self-assembly characteristics in aqueous solutions of cationic bolaamphiphiles with systematic changes in their chemical structure is described with respect to their interfacial properties within water and at the air/water interface. Six cationic bolaamphiphiles were synthesized from multifunctional vernonia oil with the following variations: (a) two different alkyl chain lengths connecting the head groups, (b) polar ester or hydrogen bonding amide groups within the hydrophobic domain, and (c) an acetylcholine cationic head group with different conjugation sites to the alkyl chain. Surface tension measurements were used for determining critical aggregation concentration (CAC) values and air/water interfacial parameters such as 'effectiveness', surface excess concentration and area occupied by one molecule in the air/water interface. Fluorescent studies with pyrene were used to characterize CAC properties within the aqueous volume and transmission electron microscopy (TEM) for determining the aggregate structure's size, homogeneity and morphology. A bolaamphiphile molecular structure vs. interfacial property relationship was derived from this data which could be used to determine the molecular structure properties needed to generate interfacial forces to form either spherical vesicles or fibrous networks. The effects of the aliphatic chain length, head group orientation and functional groups within the hydrophobic domain on CAC, surface tension properties and self-aggregate morphology are described. Most bolaamphiphiles studied had CAC values in the 10-190 μM range, while two out of the six were found to assemble into MLM spherical vesicles with diameters ranging up to 120 nm suitable for drug delivery applications. Others formed a gelatinous network of fibers or multi-lamellar vesicles.     

Asphaltene self-association and water-in-hydrocarbon emulsions

The configuration of asphaltenes on the water-oil interface was evaluated from a combination of molar mass, interfacial tension, drop size distribution, and gravimetric measurements of model emulsions consisting of asphaltenes, toluene, heptane, and water. Molar mass measurements were required because asphaltenes self-associate and the level of self-association varies with asphaltene concentration, the resin content, solvent type, and temperature. Plots of interfacial tension versus the log of asphaltene molar concentration were employed to determine the average interfacial area of asphaltene molecules on the interface. The moles of asphaltenes per area of emulsion interface were determined from the molar mass data as well as drop size distributions and gravimetric measurements of the model emulsions. The results indicate that asphaltenes form monolayers on the interface even at concentrations as high as 40 kg/m(3). As well, large aggregates with molar masses exceeding approximately 10,000 g/mol did not appear to adsorb at the interface. The area occupied by the asphaltenes on the interface was constant indicating that self-associated asphaltenes simply extend further into the continuous phase than nonassociated asphaltenes. The thickness of the monolayer ranged from 2 to 9 nm.     

Demulsification and Interfacial Properties of Crosslinking Phenol-Amine Resin Block Polyether Demulsifiers

Six novel crosslinking phenol-amine resin block polyether demulsifiers were synthesized for demulsification of surfactant-polymer flooding emulsion. The demulsification performances of these demulsifiers were investigated by conventional graduated bottle test. Their interfacial behaviors at water-oil interface were explored by dynamic interfacial tension and interfacial dilational viscoelasticity measurements. The results show that the demulsification efficiency is dependant on the hydrophilic-hydrophobic balance (HLB) value of these demulsifiers. It was also correlated to the interfacial activity and the dilational elasticity at the water-oil interface. The higher the HLB value of demulsifiers, the better the demulsification efficiency is.     

Influence of pH and cationic surfactant on stability and interfacial properties of Algerian bitumen emulsion

The influence of water pH and cationic surfactant content on the interfacial properties and stability of an Algerian bitumen aqueous emulsion were investigated. While the stability was quantified by both the test-bottle method and size distribution measurements, the interfacial properties of the water-bitumen interface were assessed using interfacial tension measurements. Optical microscopy was also used to visualise the dispersed water droplets in the oil phase. The results showed that addition of the cationic surfactant at a concentration of 25 mmol L^?1 in acidic water (pH 2) improves the bitumen emulsion stability and effectively decreases the interfacial tension.     

Interfacial tension and wetting behavior of air/oil/ionic liquid systems

We measured the interfacial tension and the density of air/n-hexane, n-decane, 1-perfluorohexane/1-hexyl-3-methyl-imidazolium hexafluorophosphate systems as a function of temperature. From the air/ionic liquid surface tension values, it was suggested that Coulombic interaction between imidazolium cations and counter anions are not so much different between the surface and bulk. The density values indicated that the decrease of surface tension by saturating organics was closely correlated to the mutual solubility between ionic liquid and organics. Interfacial tension at the oil/ionic liquid interfaces suggested that ionic liquid molecules were more ordered at the oil/ionic liquid interfaces compared to the air/ionic liquid interfaces, but the decrease of the entropy due to the interfacial orientation of ionic liquid was compensated by the increase of the entropy due to the contact of different chemical species. The initial spreading coefficients and the Hamaker constants indicated that all the oil phases spread at the air/ionic liquid interfaces spontaneously, and form the complete wetting films.     

Behavior of polymer chains grafted from latex particles at soft interfaces

We have studied the behaviors of a poly(methyl methacrylate) (PMMA) chains anchored to polystyrene particles at air/water and oil/water interfaces to recognize the roles of oil molecules in the PMMA property at the interfaces. Through the comparison of π-A isotherms we found two aspects of unique structural and rheological characteristics observed in PMMA-grafted polystyrene latex (PSL-PMMA) monolayer system in common. (1) The π-A isotherms showed surface pressure increase at larger occupied area compared to the PSL-PMMA size in solution at three different types of interfaces in most cases. (2) Compressional modulus, C _s ^?1, obtained by π-A isotherm analysis for PSL-PMMA at interfaces, showed the tendency to decrease with molecular weight of PMMA. This is opposite to that of PMMA homopolymer at interfaces. The effect of oil molecules on PSL-PMMA system at interfaces are found both in the difference of occupied area and C _s ^?1. The occupied areas were larger for the isotherms at the oil/water interfaces than those at the air/water interface in most cases, which suggested the reduced attractive interactions between anchored polymers by oil molecules. On the other hand, C _s ^?1 of PMMA monolayers is strongly dependent on the constituents of the interface and the order of C _s ^?1 is air/water?>?decane/water?>?dibutyl ether/water interfaces. The difference between oil species was not explained only by PMMA/oil interaction in bulk, but we suggested that interfacial tension of oil/water interface affects the miscibility of oil molecules with PMMA to cause higher miscibility between PMMA and dibutyl ether at the oil/water interfaces.     

Poly(styrene-b-2-vinylpyridine-1-oxide) diblock copolymers: 3. Microemulsions in water/propan-2-ol/toluene mixtures

Pseudo-ternary phase diagrams have been constructed for the three-component solvent system (toluene+water+propan-2-ol) containing diblock copolymers of poly(styrene-b-2-vinylpyridine-1-oxide). Microemulsions have been shown to form on the water-rich side of the phase diagram, in the region of the phase boundary without polymer. Dynamic light-scattering experiments have led to droplet size values in the region of 100 nm, with the size depending strongly on the propan-2-ol/water concentration, as well as the amount of solubilised toluene in the core. Viscometry experiments have been carried out to measure polymer aggregation numbers in the microemulsion droplets, and interfacial tension measurements have shown that in the absence of propan-2-ol (effectively a cosurfactant) the limiting value of the oil/water interfacial tension, even an saturation adsorption of the copolymer is 20 mNm^–1. However, addition of propan-2-ol reduces the interfacial tension to the very low values generall commensurate with microemulsion formation.     

界面张力弛豫法研究芳香侧链酰基牛磺酸钠的界面相互作用

采用界面张力弛豫方法研究了表面活性剂N-(α-苯氧基)十四酸牛磺酸钠(12+B-T),N-(α-乙基苯氧基)十四酸牛磺酸钠(12 +2B-T)和N-(α-己基苯氧基)十四酸牛磺酸钠(12+6B-T)在空气-水表面和癸烷-水界面上的扩张流变性质,考察了芳环支链链长变化对分子界面行为的影响,获得了表面活性剂结构对极限扩张弹...     

Adsorption of Alkyltrimethylammonium Bromides at the Various Interfaces

The adsorption of alkyltrimethylammonium bromide homologues has been studied at oil/water and air/water interfaces. Dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and hexadecyltrimethylammomium bromide were used. As an oil phase the aliphatic hydrocarbons of the same chain length as that of surfactants molecules were used. The interfacial tension was measured by the drop volume method and the equilibrium values were received. The surface tension was measured by the drop weight method. The values of surface excess Gamma were calculated from the Gibbs equation. The experimental results were tested by the Langmuir isotherm as well as by the isotherm developed by E. Blomgren and J. O'M. Bockris (J. Phys. Chem. 63, 1475 (1959)). Copyright 2000 Academic Press.     

Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

The time dependence of the interfacial tension between water–acidic crude oil and water–synthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20°C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.     

Determination of the interfacial characteristics of a series of bolaamphiphilic poly(fluorooxetane) surfactants through molecular dynamics simulation

Constant surface tension (NgammaT) and constant volume (NVT) molecular dynamics simulations have been conducted on a series of bolaamphiphilic alpha,varpi-(diammonium disulfato)poly(fluorooxetane)s and on a typical "long-chain" anionic fluorosurfactant used to improve the flow-and-leveling characteristics of aqueous coatings, to compare their behavior at a water/air interface. Recent research has shown that the poly(fluorooxetane) surfactants considered in this paper could serve as an effective substitute for traditional fluorosurfactants used in flow-and-leveling applications.(1) From molecular dynamics simulation, we have determined the saturated interfacial area per surfactant, interfacial area per surfactant as a function of surface tension, density profiles, the degree of hydration for various atoms in each surfactant, the degree of counterion binding, and order parameters. Our results for saturated interfacial area per surfactant molecule are greater than what has been obtained by other researchers through parametric fitting of interfacial area from experimental surface tension data using the Davies isotherm. Possible explanations for this difference are discussed. The low interfacial areas occupied by each poly(fluorooxetane) at the water/air interface are the result of their ability to adopt a "looped" conformation, in which the carbon and oxygen backbone of each surfactant and the attached perfluoroalkyl chains are forced into the air phase. A geometrically defined penetration parameter was calculated from the density profiles, which reveals that each poly(fluorooxetane) surfactant is more effective at separating the air and water phases than the "long-chain" anionic fluorosurfactant. The degree of hydration measured for different atoms in poly(fluorooxetane) during simulation confirms that a "looped" conformation is adopted in which the surfactant backbone and the perfluoroalkyl chains are lifted away from the water surface. Calculation of order parameters revealed a much lower degree of ordering for the perfluoroalkyl side chains in each bolaamphiphile than in the "long chain" anionic fluorosurfactant. When viewed in the context of the penetration parameter analysis, the density profiles and hydration data suggest why each poly(fluorooxetane) is capable of significantly reducing surface tension when other fluorosurfactants with similarly short perfluoroalkyl moieties provide inadequate surface tension reduction for practical flow-and-leveling applications.