Molecular Dynamics Simulation of Sulfobetaine-Type Zwitterionic Surfactants at the Decane/Water Interface: Structure,Interfacial Properties

Molecular dynamics simulations of interfacial properties of new sulfobetaine-type zwitterionic surfactants were performed using a united atomistic model, and a detailed analysis of hydrophilicity, temperature sensitivity, and salt resistance of surfactants was carried out. The new model was parameterized to reproduce the density and showed good agreement with experimental values. The results showed that the surfactant will not cease to be effective with the increase of the temperature from 300 to 373 K but as it rises, the interfacial tension will have a reduction. This kind of surfactant can be proved to remain an activity at high concentration of monovalent and divalent cations. It has commendable salt tolerance.     

高盐油藏下两性/阴离子表面活性剂协同获得油水超低界面张力

研究了在高盐油藏中, 利用两性/阴离子表面活性剂的协同效应获得油水超低界面张力的方法. 两性表面活性剂十六烷基磺基甜菜碱与高盐矿化水具有很好的相容性, 但在表面活性剂浓度为0.07%-0.39%(质量分数)范围内仅能使油水界面张力达到10^-2 mN·m^-1量级, 加入阴离子表面活性剂十二烷基硫酸钠后则可与原油达到超低界面张力. 通过探讨表面活性剂总浓度、金属离子浓度、复配比例对油水动态界面张力的影响, 发现两性/阴离子表面活性剂混合体系可以在高矿化度、低浓度和0.04%-0.37%的宽浓度范围下获得10^-5 mN·m^-1量级的超低界面张力, 并分析了两性/阴离子表面活性剂间协同获得超低界面张力的机制.     

不同电性Gemini表面活性剂界面扩张性质

利用Langmuir槽法研究了含聚氧乙烯醚链中间链的两性Gemini表面活性剂C8E4NC12、阳离子Gemini表面活性剂C12NE3NC12和阴离子Gemini表面活性剂C8E4C8在空气/水表面和癸烷/水界面上的扩张性质,考察浓度对3种Gemini表面活性剂溶液表、界面扩张性质的影响.结果表明,由于分子间存在库仑引力,两性Gemini分子表现出较高的扩张弹性和粘性,且界面扩张性质类似于表面.对于有相同电荷Gemini分子,C8E4C8分子中的刚性苯环导致其疏水长链在表面上的取向不同于C12NE3NC12分子,两者表现出不同的表面扩张性质;而油分子能改变同电荷Gemini分子中长链烷基的取向,造成其界面扩张弹性和粘性远低于表面.提出了不同电性Gemini分子在界面排布的示意图,并利用弛豫过程的特征参数进行了验证.     

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.     

The Fast Relaxation Process between Hydrophobically Modified Associating Polyacrylamide and Different Surfactants at the Water‐Octane Interface

In our previous work (Macromolecules 2004, 37:2930), we found that the hydrophobic blocks of polyacrylamide modified with 2‐phenoxylethyl acrylate (POEA) and anionic surfactant sodium dodecyl sulfate (SDS) may form mixed associations at octane/water interface. However, the process involving the exchange of surfactant molecules between monomers and mixed associations in interface is so fast that we cannot obtain its characteristic time. In this article, the interfacial dilational viscoelastic properties of another hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2‐ethylhexyl acrylate (EHA) (<1.0 mol%) at the octane‐water interfaces were investigated by means of oscillating barriers method and interfacial tension relaxation method respectively. The influences of anionic surfactant SDS and nonionic surfactant Triton X‐100 on the dilational viscoelastic properties of 7000 ppm polymer solutions were studied. The results showed that the interaction between P(AM/2‐EHA) and SDS was similar to that of P(AM/POEA) and SDS. Moreover, we got the relaxation characteristic time of the fast process involving the exchange of s Triton X‐100 molecules between monomers and mixed associations.

We also found that the interfacial tension response of hydrophobically associating water‐soluble copolymers to the sinusoidal oscillation of interfacial area at low bulk concentration is as same as that of the typical surfactants: the interfacial tension decreases with the decrease of interfacial area because of the increase of interfacial active components. However, the interfacial tension increases with the decrease of interfacial area at 7000 ppm P(AM/2‐EHA), which is believed to be correlative with the structure of absorbed film. The results of another hydrophobically associating polymer P(AM/POEA) and polyelectrolyte polystyrene sulfonate (PSS) enhanced our supposition. The phase difference between area oscillation and tension oscillation has also been discussed considering the apparent negative value.     

Interfacial and micellar properties of binary mixtures of surfactant and phospholipid in an aqueous medium

Mixed micelles formed by zwitterionic surfactant dimethyldodecylammniopropane sulfonate and short-chain phospholipid 1,2-diheptanoyl-sn-glycero-3-phosphocholine in different proportions in an aqueous medium have been studied physicochemically at an air/water interface and in the bulk by using interfacial tension and pyrene fluorescence intensity measurements, respectively. The critical micellar concentration and free energies of micellization and of interfacial adsorption have been determined. The interfacial study reveals that a mixed monolayer is formed at the air/water interface by the adsorption of surfactant and phospholipid monomers. This has been confirmed by evaluating the interfacial parameters; the maximum surface excess, the minimum area per molecule of a surface-active compound, and the Gibbs surface excess related to surface pressure. The nonideality of mixing, expressed in the terms of the regular solution interaction parameter, #, has negative values over the whole mole fraction range. The negative # values indicate the mutual synergism between the surfactant and phospholipid monomers. The equilibrium distribution of components between micelle and monomer phases was evaluated using a theoretical treatment based on excess thermodynamics quantities evaluated by Motomura's formulation.     

Interfacial tension of alkylglucosides in different APG/oil/water systems

The interfacial performance of pure alkylglucosides (C₈G₁, C₁₀G₁ and C₁₂G₁) and of technical grade alkylpolyglucoside (APG) surfactants was investigated in three different water/oil systems (decane, isopropylmyristate and 2-octyldodecanol). From the dependence of the interfacial tension on the surfactant concentration below the CMC the cross-sectional area of the molecules at the decane/water interface was estimated. The plateau values of the interfacial tension at the CMC _c are independent of temperature and almost independent of added electrolyte in the decane/water system. The ability of the surfactants to lower the oil/water interfacial tension is most pronounced for the nonpolar oil. The partition coefficient of the surfactant between oil and water phase (k _c) was estimated from the CMC and the observed break point of the interfacial tension after equilibration of the two phases. In decane/water,k _c is nearly zero for all surfactants studied. For the polar oils,k _c increases with the chain length of the surfactant up tok _c10 for C₁₂G₁ in octyldodecanol/water. The values of _c in the different oil/water systems appear to be correlated withk _c and exhibit a minimum neark _c=1.     

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.     

Effect of Alkyl Chain Length on the Interfacial Dilational Properties of Hydroxy-Substituted Alkyl Benzenesulfonates

Dilational rheological behaviors of adsorption layers of three surfactants, sodium 2-hydroxy-3,5-dioctyl benzene sulfonate (C₈C₈), sodium 2-hydroxy-3-octyl-5-decyl benzene sulfonate (C₈C₁₀), and sodium 2-hydroxy-3-octyl-5-dodecylbenzenesulfonate (C₈C₁₂) formed at air–water and decane–water interfaces, have been investigated as a function of concentration and frequency (0.002–0.1 Hz) by the oscillating bubble/drop method. The experimental results show that the dilational moduli of hydroxy-substituted alkyl benzenesulfonates are obviously higher than those of the common surfactants, because the interfacial interactions between alkyl chains are improved drastically by the unique arrangement of C₈C₈ molecules at the interface. However, the moduli at the decane–water interface are much lower than those at the surfaces because decane molecules will insert into the surfactant molecules adsorbed at the interface and destroy the interactions between alkyl chains. With an increase in the number of carbon atom of 5-alkyl, the surface dilational modulus decreases because the orientation of the surfactant molecules at the surface varies from parallel to tilt. On the other hand, the diffusion-exchange process dominates the interfacial behavior and the interfacial modulus improves with the increase in the length of the alkyl chain.     

Effect of Molecular Weight on the Interfacial Dilational Viscoelasticity of Anionic Polyelectrolyte/Surfactant Systems

In this article, the effect of molecular weight on the interfacial tension and interfacial dilational viscoelasticity of polystyrene sulfonate/surfactant adsorption films at the water-octane interface have been studied by spinning drop method and oscillating barriers method respectively. The experimental results show that different interfacial behaviors can be observed in different type of polyelectrolyte/surfactant systems. PSS/cationic surfactant CTAB systems show the classical behavior of oppositely charged polyelectrolyte/surfactant systems and can be well explained by electrostatic interaction. Molecular weight of PSS plays a crucial role in the nature of adsorption film. The complex formed by CTAB and higher molecular weight PSS, which has larger dimension and stronger interaction, results in higher dilational modulus at lower surfactant bulk concentration. In the case of PSS/anionic surfactant SDS systems, the co-adsorption of PSS at interface through hydrophobic interaction with alkyl chain of SDS leads to the increase of interfacial tension and the decrease of dilational modulus at lower surfactant bulk concentration. For PSS/nonionic surfactant T × 100 systems, PSS may form a sublayer contiguous to the aqueous phase, which has little effect on interfacial tension but slightly decreases dilational modulus.     

聚丙烯酰胺对烷基苯磺酸盐界面吸附膜扩张流变性质的影响

采用小幅低频振荡和界面张力弛豫技术, 研究了部分水解聚丙烯酰胺(Mo-4000)和阴离子表面活性剂2-丙基-4,5-二庚基苯磺酸钠(377)体系在癸烷/水界面上的扩张黏弹性质, 并考察了电解质对体系界面流变性质的影响. 研究结果发现, 低表面活性剂浓度时, 聚合物的加入大大降低了扩张模量; 而高表面活性剂浓度时, 聚合物的存在导致了界面膜更接近弹性膜. 一方面电解质压缩双电层, 增加界面膜的紧密程度, 造成高频条件下扩张模量增大; 另一方面, 电解质增强表面活性剂分子在界面与体相间的扩散交换作用, 增大了扩张模量的频率依赖性, 造成低频条件下扩张模量降低.     

Effect of Cationic and Zwitterionic Surfactants on Contact Angle of Quartz–Water–Crude Oil System

The influences of four cationic surfactants hexadecyl glycidyl ether ammonium chloride and four zwitterionic surfactants hexadecyl glycidyl ether glycine Betaine solutions on contact angle of crude oil on a quartz surface were investigated using a captive drop method. The effects of surfactant type, structure, and concentration on contact angle were expounded. From obtained results it appears that the adsorbed surfactant at oil–water interface reduces the interfacial tension and the adsorption at quartz–water interface improves interfacial free energy, which results in reducing the stable value of contact angle and weakening dynamic behavior. At high concentration, the zwitterionic surfactant with branched-chain may form semi-micelle at quartz surface. As a result, the stable value of contact angle passes through a sharp minimum with the increasing concentration.     

Synthesis of Surfactants from Alkali Lignin for Enhanced Oil Recovery

With the cheap and abundant resource of alkali lignin as feedstock, surfactants for enhanced oil recovery were synthesized by amination and alkylation reaction of lignosulfonate. The effects of amination conditions, including the ratio of raw materials, amination reagent, temperature, and reaction time, on nitrogen contents and surface tension of the surfactants were investigated. The results showed that ethylenediamine was more suitable for amination, and the molar ratio of alkali lignin, ethylenediamine, and formaldehyde was 1:2:1.5 at 80°C for 5 hours. The structure of synthesized products was characterized by Fourier transform infrared spectrometry. The HLB value of synthesized product was 10. The interfacial tension between Daqing crude oil and synthetic water could be decreased to 10^?2 mN/m with synthesized surfactant and NaOH at 45°C. Moreover, the effects of molecular weight of surfactants on interfacial tension were also studied. The synthesized surfactant (M_w > 10,000) showed a better interfacial activity on Daqing crude oil.     

Impact of imidazolium-based ionic liquid surfactant additions on dilational rheology properties of different protein adsorption layer

The interfacial behavior of β-casein and BSA solutions have been investigated in the presence of imidazolium-based ionic liquid surfactant ([C₁₄mim]Br) at the decane/water interface with the oscillating the drop and interfacial tension relaxation measurements. Both the electrostatic and the hydrophobic interaction between protein and [C₁₄mim]Br played crucial roles as [C₁₄mim]Br concentration increases. Furthermore, it was found that the dilational rheology parameters provided information of the adsorbed layers structure, and the dynamics properties of the adsorbed layers depend on the bulk [C₁₄mim]Br concentration. Moreover, with the concentration of [C₁₄mim]Br increasing, β-casein in the interfacial layer was subject to conformational changes where it gave space to [C₁₄mim]Br molecules in the form of co-adsorb; for BSA/[C₁₄mim]Br solutions, the globule protein BSA deformed and then co-adsorb with [C₁₄mim]Br molecules at the decane/water interface. These results will contribute to elucidation of the influence of the surfactant on the different structure proteins and the wide applications of protein/surfactant systems in practice.     

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

Various experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (～2.0?×?10^?3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50?=?25.04?µm) and was well emulsified with crude oil after the mechanical oscillation (D50?=?4.27?µm).     

The Wettability Alteration and the Effect of Initial Rock Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes

Wettablity alteration of rock surface is an important mechanism for surfactant-based enhanced oil recovery (EOR) processes. Two salt and temperature-tolerant surfactant formulations were developed based on the conditions of high temperature (97–120°C) and high salinity (20 × 10⁴ mg/L) reservoirs where a surfactant-based EOR process is attempted. Both the two sufactant formulations can achieve ultralow interfacial tension level (≤10^?3 mN/m) with crude oil after aging for 125 days at reservoir conditions. Wettability alteration of core slices induced by the two surfactant formulations was evalutated by measuring contact angles. Core flooding experiments were carried out to study the influence of initial rock wettabilities on oil recovery in the crude oil/surfactant/formation water/rock system. The results indicated that the two formulations could turn oil-wet core slices into water-wet at 90–120°C and 20 × 10⁴ mg/L salinity, while the water-wet core slices retained their hydrophilic nature. The core flooding experiments showed that the water-wet cores could yield higher oil recovery compared with the oil-wet cores in water flooding, surfactant, and subsequent water flooding process. The two surfactant formulations could successfully yield additional oil recovery in both oil-wet and water-wet cores.     

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.     

Interactions between Hydrophobically Modified Associating Polyacrylamide and Cationic Surfactant at the Water‐Octane Interface: Interfacial Dilational Viscoelasticity and Relaxation Processes

The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2‐ethylhexyl acrylate (EHA) (<1.0 mol%) with a hydrolyzed degree of about 1.5–2.0% at the octane‐water interfaces were investigated by means of two methods: the interfacial tension response to sinusoidal area variations (oscillating barriers method) and the relaxation of an applied stress (interfacial tension relaxation method) respectively. The influence of cationic surfactant cetyl trimethylammonium bromide (CTAB) on the dilational viscoelastic properties was studied. The results obtained by oscillating barriers method showed that dilational modulus decreased moderately with the increase of CTAB concentration. The results obtained by interfacial tension relaxation measurements showed that two main relaxation processes exist in the interface at 7,000 ppm polymer concentration: one is the fast process involving the exchange of hydrophobic blocks between the proximal region and distal region in the interface; the other is the slow relaxation process involving conformational changes of polymer chain in the interface. By adding CTAB, the slow process changed obviously due to the strong electrostatic interaction between oppositely charged surfactant and hydrolyzed part of polymer chain. Only when the CTAB concentration was close to the “equal charge point,” the associations formed mainly by the hydrophobic interaction like that in SDS/polymer system appeared and the characteristic time of fast process decreased obviously. The information of relaxation processes obtained from interfacial tension relaxation measurements can explain the results from dilational viscoelasticity measurements very well.     

Studies of Interfacial Activities of Four Kinds of Surfactants at Oil/Water Interface

This article aims to compare the interfacial activities of different kinds of surfactants in the same oil/water system. The anionic surfactants of alkylbenzene sulfonates, the polyoxyethylenated nonionic surfactants, the cationic surfactants of alkyl trimethyl ammonium chlorides, and the zwitterionic surfactants of alkyl hydroxyl sulfobetaines were used, and the interfacial tensions of the surfactant solutions against kerosene at different NaCl concentrations were measured. It is found that the interfacial activities of the alkylbenzene sulfonates are high and ultralow interfacial tensions (<0.01 mN/m) can be obtained at proper salinities. While, the nonionic surfactants have relatively low interfacial activities and the minimum tensions are around 0.01 mN/ms. The salinity scanning curves of the alkylbenzene sulfonates and nonionic surfactants decrease first, then increase, showing their interfacial activities can be changed by the salinity effectively. The cationic and zwitterionic surfactants have very low interfacial activities, of which all the tensions are higher than 0.1 mN/ms and are hard to be changed by the salinity. The experimental results may have important reference values for enhanced oil recovery.     

十二烷基硫酸钠对两性咪唑类离子液体表面活性剂1-磺丙基-3-十二烷基咪唑内盐界面聚集行为的影响

利用界面扩张流变技术,研究了两性咪唑类离子液体表面活性剂1-磺丙基-3-十二烷基咪唑内盐(C₁₂imSP)的界面聚集行为,探讨传统表面活性剂十二烷基硫酸钠(SDS)对C₁₂imSP界面聚集行为的影响机制。 结果表明,少量SDS的加入可以填补界面上疏松的C₁₂imSP分子间的空位,界面上形成表面活性剂混合吸附膜,界面张力显著降低;提高SDS的浓度,其分子从体相向界面层的扩散交换占优势,界面层分子逐渐达到饱和吸附,此后体系中有混合胶束形成。 体相胶束中富集的SDS分子对C₁₂imSP分子的“收纳”作用及进一步的“挽留”作用,加之C₁₂imSP分子本身相对较大的空间位阻效应导致界面上的C₁₂imSP分子一旦通过扩散作用被交换至体相,其很难再回复到表面层,即界面膜以SDS分子为主。 通过调节体系中SDS的含量,可以实现对混合体系SDS/C₁₂imSP/NaCl(0.1 mol/L)界面聚集行为的调控,进而实现对界面膜性质的调控。