Studies of synergism/antagonism for lowering dynamic interfacial tensions in surfactant/alkali/acidic oil systems. 1. Synergism/Antagonism in surfactant/model oil systems

Experimental studies are conducted in order to elucidate the mechanisms responsible for synergism/antagonism for lowering dynamic interfacial tension in model oil/surfactant/brine systems. A well-defined model oil is selected for controlled design of experiments, thus enhancing verification of known and unknown mechanisms. The systems examined contain model oils and two petroleum sulfonate solutions. The influence of additives in oil phase, such as carboxylic acids with different chain length, n-octadecanol, and oil soluble surfactant SP-60, on the equivalent alkane carbon number (EACN) values has been examined. The interfacial tensions of different model oils with different EACN values against surfactant solutions with different n(min) values have also been obtained. We find that antagonism has been observed when EACN/n(min) value is far from unity by adding organic components, while synergism has been observed when EACN/n(min) value is close to unity. The results present here suggest that organic additives in oil phase controlled interfacial tension by changing the partition of surfactants in oil phase, aqueous phase, and interface.     

Studies of synergism/antagonism for lowering dynamic interfacial tension in surfactant/alkali/acidic oil systems. 3. Synergism/antagonism in surfactant/alkali/acidic model oil systems

Experimental studies have been conducted to elucidate the mechanisms responsible for synergism/antagonism for lowering dynamic interfacial tension (IFT) in surfactant/alkali/hydrocarbon and surfactant/alkali/acidic model oil systems. Dynamic IFTs between hydrocarbon/acidic model oil and alkali/surfactant solutions were measured. We learned from our experimental results that alkali has the function of decreasing n(min) values of surfactant solutions. The synergism/antagonism for lowering the stable values of dynamic IFTs in surfactant/alkali/hydrocarbon and surfactant/alkali/acidic model oil systems depends on factors that can change the EACN/n(min) value, such as the oleic acid in the oil phase and the n(min) values of surfactant and alkali. A new explanation with respect to EACN/n(min) values is provided.     

Studies of synergism for lowering dynamic interfacial tension in sodium alpha-(n-alkyl) naphthalene sulfonate/alkali/acidic oil systems

Alkylnaphthalene sulfonates with high purity were selected as model components to research synergism for lowering interfacial tension (IFT) in surfactant/alkali/acidic oil systems. The dynamic IFTs between alkylnaphthalene sulfonates with different alkyl chain length and n-decane, oleic acid model oil, or Shengli crude oil were measured. The results showed that the alkylnaphthalene sulfonates with different alkyl chain lengths had different synergism with different acidic components and their ionized acids under the same conditions. The synergism for lowering dynamic IFT in alkylnaphthalene sulfonate/alkali/acidic oil systems was controlled by alkylnaphthalene sulfonate concentration, alkyl chain length, alkali concentration, alkali type, and oleic acid concentration: optimal physicochemical conditions were necessary to the best synergism. This indicates that the synergism among added surfactant acidic components in crude oil and their ionized acids is controlled by the ratio of their interfacial concentrations.     

Studies of Synergism/Antagonism in Sodium Alkyl Benzene Sulfonate/Methyl Oleate Model Oil Systems

Experimental studies are conducted in order to elucidate the mechanisms responsible for synergism/antagonism for lowering interfacial tension in alkyl benzene sulfonate/brine/methyl oleate model oil and alkyl benzene sulfonate/alkali/methyl oleate model oil systems. We found that different mechanisms exist in above two systems. In alkyl benzene sulfonate/brine/methyl oleate model oil systems, methyl oleate influences the partition of added surfactants between oil and aqueous phase by changing equivalent alkane carbon number (EACN) value of model oil. In alkyl benzene sulfonate/alkali/methyl oleate model oil systems, methyl oleate in oil phase has two functions: on the one hand, it influences the partition of surfactant between oil and aqueous phase; on the other hand, it directly affects IFT by displacing surfactant molecule or forming mixed film with surfactant molecule at the interface.     

Studies of Synergism in Binary Alkylbenzene Sulfonate Mixtures for Producing Low Interfacial Tensions at Oil/Water Interface

In order to study the synergism between alkybenzene sulfonate and alkybenzene sulfonate, five di-n-alkylbenzene sulfonates were used and the interfacial tensions of single sulfonates and their binary mixtures against a series of alkane homologues were measured. The effects of hydrophilic-lipophilic abilities of sulfonates and mixing ratio on synergism were discussed. It is revealed that the synergistic mechanism derives from the amelioration of the hydrophilic-lipophilic ability of the surfactant system, and the method to achieve synergism is adding the hydrophilic alkybenzene sulfonate to the lipophilic alkylbenzene sulfonate, and ultralow interfacial tensions can be obtained in proper mixing ratios. The results are useful for enhanced oil recovery.      

Tunable synergism/antagonism in a mixed nonionic/anionic surfactant layer at the solid/liquid interface

The use of mixed surfactants for modification of solid surfaces is important for many applications, since beneficial synergism often occurs depending on the surfactant type and mixing conditions. Systematical information on the properties of surfactant mixtures at the solid/liquid interface can be helpful for optimizing the interactions between the surfactants and then their corresponding performance. In this work, a nonionic/anionic surfactant combination, n-dodecyl beta-d-maltoside (DM) and sodium dodecyl sulfonate (SDS), was selected for the study of adsorption on an oxide solid, alumina. Interestingly, the mixture of the two surfactants with opposite pH-dependence of adsorption on alumina exhibits some unique synergistic or antagonistic features that were found to be tunable in the region of pH 4-10. In addition, the DM/SDS molar ratio in the adsorbed layer was found to decrease with concentration in the saturated region at all the pH and mixing ratios tested. The decrease is attributed to the monomer concentration changes in solution due to the difference in surface activities of the two surfactants. The tunable features of this mixture at the solid/liquid interface provide a way to optimize the properties by changing the mixing conditions. This can be valuable in many applications, such as enhanced oil recovery, flotation, and solubilization.     

The ultralow interfacial tensions between crude oils and gemini surfactant solutions

In this paper, the interfacial tension between crude oil and solution of cationic gemini surfactant has been studied. It is found that the interfacial tension between crude oil and water is closely related to the nature of a gemini surfactant and oil; meanwhile, in the case without additives, some gemini surfactants or mixtures of some gemini surfactants can reduce the interfacial tension between crude oil and water to an ultralow value.     

系列烷基苯磺酸盐对烷烃的动态界面性能研究

从表面活性剂分子量、表面活性剂浓度、电解质浓度、 烷烃碳数等方面考察了系列烷基苯磺酸盐异构体纯化合物的油水动态界面张力行为。研究表明,表面活性剂分子量越大和电解质浓度增加使界面张力动态变化越慢,达到平衡所需时间越长;表面活性剂浓度增加和烷烃碳数增加使界面张力动态变化加快,达到平衡所需时间减少。     

三元复合驱碱/表面活性剂/聚合物模拟原油乳状液稳定动力学特性

基于两相分离的乳状液稳定模型,研究了三元复合驱模拟原油乳状液稳定动力学特性;通过液膜强度和油水界面张力探讨了碱/表面活性剂/聚合物对模拟原油乳状液稳定动力学特性的影响机理。 结果表明,乳状液稳定模型可以很好的评价乳状液的稳定性,并得到乳状液的稳定动力学特性;碱浓度小于900 mg/L有利于乳状液的稳定,碱浓度大于900 mg/L不利于乳状液的稳定;表面活性剂和聚合物浓度的增加使得形成的模拟原油乳状液更加稳定;模拟原油乳状液的稳定作用主要是通过碱、表面活性剂降低油水界面张力并增加油水界面膜强度,聚合物通过提高界面膜强度实现的,三者存在协同效应。     

Interfacial tension in phase-separated aqueous cationic/anionic surfactant mixtures

Interfacial tensions in two aqueous phase-separated cationic/anionic surfactant mixtures, CTAB/AS and 12-3-12/AS, without and with NaBr added were determined by the spinning drop method at 318.15 K. CTAB, 12-3-12 and AS are the abbreviations for cetyltrimethylammonium bromide, 1,3-propanediyl-bis(dodecyldimethylammonium bromide) and sodium dodecyl sulfonate, respectively. The interfacial tension sigma was found to be in the range of 0.06-21 microNm(-1). Toward a better understanding of the influence of the concentration difference between the separated phases in aqueous two-phase systems (ATPS) to interfacial tension, compositions of equilibrium phases were determined by elemental analysis coupled with material balance and electroneutrality. The investigation indicates that the concentration differences of surfactant ions between the separated phases and the adsorption of surfactant ions at the interface are the decisive factors determining the magnitude of interfacial tension.     

Linker molecules in surfactant mixtures

Linker molecules are amphiphiles that segregate near the microemulsion membrane either near the surfactant tail (lipophilic linkers) or the surfactant head group (hydrophilic linkers). The idea of the lipophilic linkers was introduced a decade ago as a way to increase the surfactant–oil interaction and the oil solubilization capacity. Long chain (>9 tail carbons) alcohols were first used as lipophilic linkers. Later it was found that the solubilization enhancement plateaus (saturates) above a certain lipophilic linker concentration. Hydrophilic linkers have been recently introduced as a way to compensate for the saturation effect observed for lipophilic linkers. Hydrophilic linkers are surfactant-like molecules with 6–9 tail carbons that coadsorb with the surfactant at the oil/water interface, thereby increasing the surfactant–water interaction, but have a poor interaction with the oil phase due to their short tail. A special synergism emerges when combining hydrophilic and lipophilic linkers, which further increases the solubilization enhancement over lipophilic linkers alone. We will discuss the profound impact of linker molecules on interfacial properties such as characteristic length, interfacial rigidity and dynamics (coalescence, solubilization and relaxation experiments) of the interface. We also demonstrate how these properties affect the performance of cleaning formulations designed around linker molecules. We describe linker-based formulations for a wide range of oils, including highly hydrophobic oils (e.g. hexadecane) that have proven very hard to clean. We also report on the use of ‘extended’ surfactants as an alternative to self-assembled linker systems.     

Experimental Study of the Effect of Strong Alkali on Lowering the Interfacial Tension of Oil/Heavy Alkylbenzene Sulfonates System

Experimental studies were conducted to explore the fundamental mechanisms of alkali to lower the interfacial tension of oil/heavy alkylbenzene sulfonates (HABS) system. Sodium hydroxide was used as the strong alkali chemical to investigate the interfacial tension (IFT) of oil/HABS system. The influences of salt and alkali on the interfacial activity were studied by the measurement of interfacial tension and partition coefficient. Moreover, the alkali/surfactant solutions were measured by dynamic laser scattering. The results showed that compared with the salt, the function of alkali to lower the interfacial tension and improve partition coefficient is more significant. The micelles formed by surfactants could be disaggregated because of adding alkali, so the size of micelles decreases and the number of mono‐surfactants increases, then more surfactant molecules move to the interface of oil/surfactant system and the adsorption of surfactants at oil‐water interfaces increases, which can lead to the decrease of IFT.     

Effects of additional salts on the interfacial tension of crude oil/zwitterionic gemini surfactant solutions

Zwitterionic gemini surfactants, which have the advantages of both zwitterionic and gemini surfactants, have been widely used in various disciplines. Sulfobetaine-type zwitterionic gemini surfactants consisting of 1,2-bis[N-methyl-N-(3-sulfopropyl)-alkylammonium]ethane (2C_nSb with 6, 8 and 10 carbon atoms) were evaluated for their interfacial activities at the water/crude oil interface. The 2C₁₀Sb molecules showed a remarkable ability to decrease the interface tension (IFT) of water/crude oil, and the degree of decrease was much greater than those in either zwitterionic or gemini surfactant systems by at least two orders of magnitude. Furthermore, the effects of salts (NaCl, CaCl₂, and MgCl₂) on the IFT of the 2C₁₀Sb system were thoroughly investigated. Interestingly, the delicate balance between the effects of additional cations and the intramolecular interactions of 2C₁₀Sb molecules played crucial roles in the interfacial arrangements of 2C₁₀Sb molecules, which were mainly dependent on the bonding abilities of the cations. Moreover, a zwitterionic surfactant and a cationic gemini surfactant were employed in control experiments to verify the proposed mechanisms.     

烷基苯磺酸盐在油水界面行为的介观模拟

采用耗散颗粒动力学(DPD)方法在介观层次上模拟了表面活性剂烷基苯磺酸盐在油/水界面的排布行为, 考察了分子结构、浓度、盐度、油相等因素对表面活性剂界面密度和界面效率的影响, 并探讨了利用表面活性剂复配协同效应提高界面活性的理论机制. 分子模拟给出的分子水平的微观信息为强化采油技术中配方筛选和表面活性剂的有效应用提供指导.     

Triton X-100/甲苯/水三元体系界面张力的耗散颗粒动力学模拟

采用耗散颗粒动力学方法在介观层次上模拟了非离子表面活性剂Triton X-100 在油/水界面上的分布行为, 并把用于油/水二元体系界面张力的计算方法拓展到含表面活性剂的三元体系. 利用该方法可以得到与实验数值吻合的界面张力数据. 另外, 模拟结果直观展示了表面活性剂界面张力与界面密度的关系, 为表面活性剂复配增效理论提供了依据. 该模拟方法给出的微观信息可以为驱油体系配方筛选和表面活性剂有效应用提供指导.     

Influence of pH on the stability of oil-in-water emulsions stabilized by a splittable surfactant

A laboratory study was conducted to evaluate the effect of pH on the stability of oil-in-water emulsions stabilized by a commercial splittable surfactant Triton SP-190 by comparison with the results obtained by a common surfactant Triton X-100. The emulsion stability was explored by measuring the volume of oil phase separated and the size of the dispersed droplets. It was found that the addition of inorganic acids did not significantly affect the stability of emulsions stabilized by Triton X-100, but had a profound influence on the stability of emulsions stabilized by Triton SP-190. Moreover, the droplet size of a Triton X-100-stabilized emulsion and its dynamic interfacial activity were insensitive to acids. However, at lower pH the droplet size of the emulsions stabilized by Triton SP-190 was considerably increased. From the dynamic interfacial tension measurements the dynamic interfacial activity of Triton SP-190 at the oil/water interface was found to be strongly inhibited by the addition of acids, resulting in a slower decreasing rate of dynamic interfacial tension. The results demonstrate that the dramatic destabilization of Triton SP-190-stabilized emulsions could be realized by the use of acids, which evidently changed the interfacial properties of the surfactant and resulted in a higher coalescence rate of oil droplets.     

Properties of surfactant monolayers in relation to microemulsion phase behaviour

The relationship between the properties of surfactant monolayers at oil-water interfaces and the phase behaviour in bulk of mixtures of oil + water + surfactant is discussed. Such monolayer properties include the spontaneous curvature, c_o the interfacial tension, I γ, the elasticity K (or rigidity) associated with the mean curvature, and the elasticity K associated with the Gaussian curvature. The model system chosen for investigation is the anionic surfactant AOT + aqueous NaCl + n-alkane at 20°C. In such systems, inversion of microemulsion type from oil-in-water (o/w) to water-in-oil (w/o) is possible with increasing electrolyte concentration. The tension, γ, passes through an ultralow minimum value at conditions corresponding to the formation of three phases. Using small angle neutron scattering, we have determined the structure of surfactant-rich third phases (c_o ~ 0) formed with the different alkanes. Lamellar phases consisting of surfactant monolayers separated alternately by oil and water appear with short alkanes, whereas L₃ and bicontinuous phases form in systems containing longer alkanes. The bending elasticity K has been measured for planar monolayers at the oil-water interface by ellipsometry. K is independent of salt concentration but depends markedly on alkane chain length N, falling from ~ 1 k_BT for N < 11 to ~0.1 k_BT for N = 14. This is discussed in terms of the differing extents of oil penetration into the surfactant chains. Higher rigidities favouring lamellar phases and lower rigidities favouring bicontinuous microemulsions are in line with the theoretical predictions of de Gennes and Taupin. Estimates of the constant K have been obtained in droplet microemulsions (w/o) from a knowledge of their size, K and γ. The sign of the constant is in agreement with the geometry of the phases formed in three phase systems. Finally, the ideas and concepts developed in the oil-water systems described above are used to explain the wetting behaviour by alkanes of AOT monolayers at the air-water surface.     

Formulating Middle Phase Microemulsions Using Extended Anionic Surfactant Combined with Cationic Hydrotrope

The phase behavior of systems containing sodium alkyl polypropylene oxide sulfate with equimolar ratio of polypropylene oxide ammonium chloride was determined as a function of salt concentration and alkane carbon number at ambient temperature. Visual inspection as well as cross polarizers were used to detect anisotropy. Solubilization ratios for oil and brine in the middle phases were measured and used to calculate the interfacial tension (IFT) between the microemulsion and oil or brine. The fish diagram is presented showing a minimum amount of 0.20 wt% surfactant needed to form the middle phase. Swelling increases with decreasing the alkane carbon number of the oil. Ultra low IFT values were predicted for the systems investigated.     

Synergistic interaction in emulsions stabilized by a mixture of silica nanoparticles and cationic surfactant

Using a range of complementary experiments, a detailed investigation into the behavior of dodecane-water emulsions stabilized by a mixture of silica nanoparticles and pure cationic surfactant has been made. Both emulsifiers prefer to stabilize o/w emulsions. At high pH, particles are ineffective emulsifiers, whereas surfactant-stabilized emulsions become increasingly stable to coalescence with concentration. In mixtures, no emulsion phase inversion occurs although synergism between the emulsifiers leads to enhanced stability at either fixed surfactant concentration or fixed particle concentration. Emulsions are most stable under conditions where particles have negligible charge and are most flocculated. Freeze fracture scanning electron microscopy confirms the presence of particle flocs at drop interfaces. At low pH, particles and surfactant are good emulsifiers alone. Synergism is also displayed in these mixtures, with the extent of creaming being minimum when particles are most flocculated. Experiments have been undertaken in order to offer an explanation for the latter synergy. By determining the adsorption isotherm of surfactant on particles in water, we show that surfactant addition initially leads to particle flocculation followed by re-dispersion. Using suitable contact angle measurements at oil-water-solid interfaces, we show that silica surfaces initially become increasingly hydrophobic upon surfactant addition, as well as surfactant adsorption lowering the oil-water interfacial tension. A competition exists between the influence of surfactant on the contact angle and the tension in the attachment energy of a particle to the interface.     

阴离子表面活性剂在水/正烷烃界面的分子动力学模拟(英文)

利用分子动力学模拟方法研究了阴离子表面活性剂在水/正烷烃(壬烷,癸烷和十一碳烷)界面的结构和动力学特点.十六烷基苯磺酸钠作为研究对象,其中苯磺酸基团在十六碳烷的第4号碳原子上,记作4-C16.分析了不同油相和特定盐度条件下正烷烃-表面活性剂-水体系的界面特点(如密度剖面图、界面张力和径向分布函数).模拟结果表明平衡模型体系展现了一个很好的水/正烷烃界面.当加氯化钠到水溶液中,正烷烃-表面活性剂-水体系的界面张力有微小的变化,有趣的是表面活性剂二面角的反式结构分数的变化联系着界面张力的微小变化.可见,表面活性剂在界面处的结构对降低界面张力起到重要的作用.此外,还发现表面活性剂的极性头与钠离子和水分子存在较强的相互作用.