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.     

X型与线型嵌段聚醚在空气/水和正庚烷/水界面上聚集行为的比较研究

通过阴离子聚合方法合成了环氧乙烷(EO)含量和分子量均相同的线型聚氧丙烯(PEO)-聚氧乙烯(PPO) (LPE)和X型聚氧丙烯-聚氧乙烯(TPE)嵌段聚醚,考察了它们在空气/水及正庚烷/水界面上聚集行为的差异. 界面活性的研究结果表明,TPE降低水、正庚烷界面张力的效率和效能均低于LPE的. 聚醚分子在正庚烷/水界面达到吸附平衡的时间比在空气/水表面短. 由于正庚烷分子插入到聚醚吸附层中,聚醚分子可以在正庚烷/水界面上采取更为直立的状态,因此聚醚分子在正庚烷/水界面扩散较快. 聚醚在正庚烷/水界面的扩张弹性高于空气/水表面的.     

X型与线型嵌段聚醚在空气/水和正庚烷/水界面上聚集行为的比较研究

通过阴离子聚合方法合成了环氧乙烷(EO)含量和分子量均相同的线型聚氧丙烯(PEO)-聚氧乙烯(PPO)(LPE)和X型聚氧丙烯-聚氧乙烯(TPE)嵌段聚醚,考察了它们在空气/水及正庚烷/水界面上聚集行为的差异.界面活性的研究结果表明,TPE降低水、正庚烷界面张力的效率和效能均低于LPE的.聚醚分子在正庚烷/水界面达到吸附平衡的时间比在空气/水表面短.由于正庚烷分子插入到聚醚吸附层中,聚醚分子可以在正庚烷/水界面上采取更为直立的状态,因此聚醚分子在正庚烷/水界面扩散较快.聚醚在正庚烷/水界面的扩张弹性高于空气/水表面的.     

铒在HBTMPTP-正庚烷/水溶液间的传质动力学

在(30±0.5)℃下,用层流恒界面池研究了铒在HBTMPTP-正庚烷-0.2mol/L(H,Na)Ac萃取体系中的传质动力学.测定了该体系的界面张力,考察了水相酸度、萃取剂浓度、氯离子浓度、温度和比界面对萃取速率的影响.实验表明,在本实验条件下,萃取过程属于扩散控制过程.Cyanex302中的杂质具有动力学的协萃作用.     

碳氟表面活性剂与碳氢表面活性剂混合水溶液的表面吸附和胶团形成——Ⅱ.全氟辛酸钠-十烷基硫酸钠体系

测定了不同摩尔比的全氟辛酸钠(7CFNa)-十烷基硫酸钠(C_(10)SNa)混合水溶液(加NaCl,恒定离子强度μ=0.1m)的表面张力和界面张力(正庚烷-水溶液界面张力)。由表(界)面张力-浓度关系求出混合体系的表(界)面吸附和临界胶团浓度(cmc)。结果表明:(1)7CFNa和C_(10)SNa在μ=0.1m的溶液中,cmc相近,两者表面活性相近;但7CFNa降低水表面张力的能力较强,在cmc时的表面张力可低达～23mNm~(-1)。因此,在混合溶液的表面上,7CFNa的表面活性较高,优先吸附于表面。对于各种摩尔比的混合溶液,7CF~-在表面层中的比例皆大于在溶液内部的比例。(2)正庚烷-水溶液界面上的吸附与表面吸附截然不同。7CF~-在界面吸附层中的比例低于溶液内部,表明其吸附能力比C_(10)S~-为弱。这是由于界面一边的正庚烷与C_(10)SNa碳氢链之间的作用大于与7CFNa碳氟链之间的作用。亦即碳氟链与碳氢链“互憎”作用在界面上的表现。(3)在不同摩尔比的混合溶液中,各组分的cmc接近一恒值,进一步说明混合溶液中存在碳氟链与碳氢链间的互憎作用,以致两种表面活性剂在混合溶液中(有过量无机盐时)基本上各自形成胶团。     

支化十六烷基甲苯磺酸钠的油水界面张力

研究了自制的3种十六烷基甲苯磺酸钠,在正构烷烃/水体系的界面性能. 分别考察了磺酸盐脂肪链支化程度及浓度等以及外加助剂脂肪醇类型和无机盐浓度对磺酸盐最小烷烃碳数nmin和界面张力值的影响. 结果表明,磺酸盐支化程度增加,其nmin变大,最低界面张力值变小;随着磺酸盐浓度的增加,界面张力值先下降后上升;随着助剂脂肪醇碳链长度的增加,其nmin逐渐变大;无机盐的影响则表现为随着盐浓度的增加界面张力值先下降后上升,超低界面张力值出现在一个适宜的盐浓度范围内.     

十六烷基甲苯磺酸钠的界面性能研究

用自制的3种十六烷基甲苯磺酸钠,研究了其正构烷烃/水体系的界面性能。分别考察了磺酸盐支化程度及浓度等内部因素以及外加助剂脂肪醇类型和无机盐浓度等外界因素对磺酸盐最小烷烃碳数n_min以及界面张力值的影响。结果表明,磺酸盐支化程度增加,其n_min变大,最低界面张力值变小;而随着磺酸盐浓度的增加,界面张力值先下降后上升;随着助剂脂肪醇碳链长度的增加,其n_min逐渐变大;无机盐的影响则表现为随着盐浓度的增加界面张力值先下降后上升,超低界面张力值出现在一个适宜的盐浓度范围内。     

氨基化氧化石墨烯和脂肪酸在水-油界面的共吸附动力学北大核心CSCD

合成了氨基化氧化石墨烯(NH_(2)-PEG-GO),利用界面张力仪研究了脂肪酸质量浓度、NH_(2)-PEG-GO质量浓度以及脂肪酸链长度对于NH_(2)-PEG-GO与脂肪酸在水-油界面共吸附行为的影响。结果表明,当NH_(2)-PEG-GO与脂肪酸共同存在于液相且质量浓度较低时,此时的水-油界面张力值要明显低于体系中只添加NH_(2)-PEG-GO或脂肪酸时的张力值。脂肪酸的链长越长,NH_(2)-PEG-GO与脂肪酸共吸附降低界面张力能力越强。由于相对于NH_(2)-PEG-GO,脂肪酸尺寸较小,所以初期的界面张力降低由脂肪酸吸附引起,而且,脂肪酸在水-油界面的吸附能够吸引NH_(2)-PEG-GO向界面扩散,表现出吸附的协同效应。而在吸附后期,界面张力降低现象由NH_(2)-PEG-GO主导,NH_(2)-PEG-GO与脂肪酸之间存在竞争吸附。     

疏水改性pH响应型智能水凝胶P(HEMA-NaAA-DiAC16)的制备及其溶胀性能

以二烯丙基胺和1-溴代十六烷为原料合成了疏水单体N,N-二烯丙基正十六烷胺(DiAC16),用FTIR、1H NMR 和元素分析对其进行了表征。 以2-羟基甲基丙烯酸乙酯(HEMA)、丙烯酸(AA)和N,N-二烯丙基正十六烷胺为共聚单体,N,N′-亚甲基双丙烯酰胺(BIS)为交联剂,十二烷基硫酸钠(SDS)为表面活性剂,过硫酸铵-四甲基乙二胺(TMEDA)为引发体系,制得的疏水改性智能水凝胶P(HEMA-NaAA-DiAC16)具有pH敏感特性。 研究了DiAC16、NaAA、BIS用量及pH值和离子强度等因素对水凝胶P(HEMA-NaAA-DiAC16)溶胀性能的影响。 结果表明,凝胶在水中的平衡溶胀率(为78.9～163.91),随DiAC16、BIS用量的增加和NaAA用量的减少而减少,n值(一般在0.5~1.0之间)随DiAC16、NaAA和BIS用量的增加而增加,为非Fickian扩散。 水凝胶的吸水溶胀是放热过程,ΔHm在-2.09～-3.64 kJ/mol,ΔHm的绝对值随DiAC16用量的减少、NaAA用量和BIS用量的增加而增大,聚合物与水的亲和力逐渐增强。 随离子强度的增强,平衡溶胀率下降。     

表面活性剂分子间弱相互作用的直接能量表征——高灵敏等温滴定量热法

分子间弱相互作用热力学研究的直接实验方法就是利用量热手段测定相互作用的能量参数. 本文对TAM III-ITC 纳焦级量热计进行了电标定实验和标准反应热测量, 结果显示本量热计的精密度为±0.09%; 量热用基准物质三羟甲基氨基甲烷(Tris)与盐酸的反应热((-47.48±0.12) kJ·mol^-1)与文献值一致. 采用此量热计,对典型的头-尾链型阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)测量得到了与文献报导值很好吻合的临界胶束浓度(cmc)和胶束化焓, 而且对具有亲水-疏水面式刚性结构的生物表面活性剂胆酸钠(NaC)也获得了可靠的结果. 进一步地, 对于相反电荷的混合表面活性剂体系(DTAB/NaC), 分别研究了在富NaC区和富DTAB区体系混合胶束的形成. 结果说明DTAB/NaC混合表面活性剂体系在富NaC区有较强的协同效应, 而在富DTAB区的协同效应较弱. 本文结合电导率测定结果, 对DTAB/NaC混合体系在水溶液中的分子自组装热力学行为进行了有价值的讨论.     

Effect of surfactants on temperature-dependent self-assembling property of copolyethylenimine/cinnamic acid aqueous mixture

The transmittance of polyethylenimine (PEI)/cinnamic acid (CA) aqueous mixture was close to zero at 20–40°C, and it began to increase around 40°C due to the disassembling of the self-assembly of the PEI/CA conjugate. As the concentration of sodium dodecyl sulfate (SDS) increased, the increasing rate of the transmittance decreased and the onset temperature increased, indicating that the self-assembly of the PEI/CA conjugate became more stable against heat with the aid of SDS. Tween 20 could also suppress the thermally induced disassembling of the self-assembly, possibly because poly(ethylene oxide) chains of the surfactant could be entangled with the PEI chains. Dodecyltrimethyl ammonium bromide (DTAB) did not have an effect on the temperature-dependent self-assembling phenomena as much as SDS and Tween 20 did. The interfacial tension of the PEI/CA/SDS aqueous mixture and that of the PEI/CA/Tween 20 aqueous mixture at 70°C were lower than the respective tensions observed at 25°C. On the contrary, the interfacial tension of the PEI/CA/DTAB aqueous mixture at 70°C was higher than that observed at 25°C, possibly because the PEI/CA conjugate could lose its surface activity at the higher temperature due to the adsorption of DTAB on CA molecules.     

Gemini阴离子表面活性剂水溶液的界面活性

Gemini阴离子表面活性剂水溶液的界面活性;Gemini阴离子表面活性剂;表面张力;CMC;C20;界面张力     

CORRELATION BETWEEN INTERFACIAL TENSIONS AND MICELLAR STRUCTURES

It is shown that results of surface and interfacial tension measurements can be used to predict the type of micelles and of liquid crystalline phases which are formed in binary and ternary surfactant solutions. In particular it is possible to predict the position of l.c. cubic phases in ternary systems consisting of surfactant, hydrocarbon and water. Data to demonstrate the conclusions were obtained on the surfactants Alkyltrimethylammoniumbromides, Alkyldimethylaminoxides and Alkyldimethylphosphinoxides. It was found that the interfacial tension of a dilute micellar solution against a reference hydrocarbon is a most sensitive and indicative parameter for the prediction of the different structures. Large changes of the interfacial tension were observed for the three systems having the same hydrocarbon chainlength. The value of the interfacial tension directly reflects also the amount of hydrocarbon which can be solubilized in the micellar solution. Interfacial tensions larger than 1mN/m are indicative of globular micelles while interfacial tensions between 0.1 and 1 mN/m indicate the formation of rods. Values below 0.1 mN/m indicate disclike micelles or lamellar phases.

The interfacial tension depends somewhat on the kind of hydrocarbon which is used for the measurements. It is observed that for several surfactant solutions the interfacial tension passes through a shallow minimum when the chainlength of the hydrocarbon is increased from six to sixteen.     

Effects of Charged Surfactants on Interfacial Water Structure and Macroscopic Properties of the Air-Water Interface

Surfactants are used to control the macroscopic properties of the air-water interface. However, the link between the surfactant molecular structure and the macroscopic properties remains unclear. Using sum-frequency generation spectroscopy and molecular dynamics simulations, two ionic surfactants (dodecyl trimethylammonium bromide, DTAB, and sodium dodecyl sulphate, SDS) with the same carbon chain lengths and charge magnitude (but different signs) of head groups interact and reorient interfacial water molecules differently. DTAB forms a thicker but sparser interfacial layer than SDS. It is due to the deep penetration into the adsorption zone of Br⁻ counterions compared to smaller Na⁺ ones, and also due to the flip-flop orientation of water molecules. SDS alters two distinctive interfacial water layers into a layer where H⁺ points to the air, forming strong hydrogen bonding with the sulphate headgroup. In contrast, only weaker dipole-dipole interactions with the DTAB headgroup are formed as they reorient water molecules with H⁺ point down to the aqueous phase. Hence, with more molecules adsorbed at the interface, SDS builds up a higher interfacial pressure than DTAB, producing lower surface tension and higher foam stability at a similar bulk concentration. Our findings offer improved knowledge for understanding various processes in the industry and nature.     

Interfacial Tension of Aqueous Three‐Phase Systems Formed by Triton X‐100/PEG/Dextran

A novel aqueous three‐phase system was formed spontaneously when a nonionic surfactant (Triton X‐100) and two polymers (PEG and dextran) were mixed. The interfacial tension between the phases was measured by the spinning drop method. It was shown that the values of interfacial tension were extremely small. The interfacial tensions of the top/middle phases were much lower than those of the middle/bottom phases. The interfacial tension was affected by component concentrations, temperature, added salts, and the density difference between two phases. Temperature exhibited a special effect on interfacial tension: with the increase of temperature, interfacial tension increases significantly.     

Interfacial Tension Measurements Between Oil Fractions of a Crude Oil and Aqueous Solutions with Different Ionic Composition and pH

Dynamic and equilibrium interfacial tensions between crude oil fractions and aqueous solutions of various compositions and pH were measured. The basic oil components seemed to determine the interfacial tensions at pH 2, while the non-dissociated and dissociated acidic components governed the interfacial tension at the natural pH and pH 9, respectively. The ionic composition of the aqueous phase influenced the degree of dissociation of the acidic components at pH 9: Na⁺ ions in the aqueous phase promoted dissociation of the interfacial acidic components (compared to pure water), while Ca²⁺ ions resulted in complexation with the dissociated acids and most likely formation of stable interfacial films. The amount of Ca²⁺ determined which of these phenomena that dominated when both ions were present in sea water solutions. Generally, the interfacial tensions of the oil fractions were lower when measured against the high salinity aqueous solutions than against the corresponding low salinity solutions.      

Effect of Neck Formation on the Measurement of Dynamic Interfacial Tension in a Drop Volume Tensiometer

Dynamic interfacial tension values obtained by drop volume tensiometry will be affected under certain experimental conditions by the formation of a neck between the drop and the capillary tip. This phenomenon must be accounted for to obtain accurate values of interfacial tension. In this work, neck formation for a water–mineral oil system is studied under conditions where hydrodynamic effects can be neglected. A model originally developed for the determination of the surface tension of a suspended drop is modified for application to dynamic interfacial tensions of surfactant-containing liquids. The model relates apparent values of interfacial tension calculated from drops possessing necks to actual values. Experiments with Span 80 (sorbitan monooleate) and sodium dodecyl sulfate (SDS) surfactants in a mineral oil–water system are used to test the validity of the developed model. For the small tip diameter used, good agreement is obtained for Span 80 up to the critical micelle concentration, and for low concentrations of SDS, when the surfactant adsorption is diffusion-limited. In both cases, the neck diameter of the growing drop can be considered constant over the range of dynamic interfacial tensions tested.     

Aqueous surfactant solutions which exhibit ultra-low tensions at the oil-water interface

Ultra-low values of the tension at an oil-aqueous electrolyte solution interface can be developed by the addition of water-soluble surfactants of the petroleum sulfonate type. Interfacial tensions in the range of 10⁻³ dyne/cm or lower are readily achieved with surfactant concentrations of the order of 0.1 wt%. For a given oil and aqueous solution, the minimum interfacial tension resulting from the addition of a petroleum sulfonate depends markedly on the average equivalent weight of the sulfonate. Sulfonates having average equivalent weights higher and lower than a previously determined optimum weight, when mixed so as to yield this particular average weight, will also produce ultra-low interfacial tensions. For a given oil, additional control of this unusual type of interfacial activity is accomplished by adjustment of the electrolyte concentration of the aqueous phase.     

The life of an anise-flavored alcoholic beverage: does its stability cloud or confirm theory?

The well-known alcoholic beverage Pastis becomes turbid when mixed with water due to the poor solubility of trans-anethol, the anise-flavored component of Pastis in the water solution formed. This destabilization appears as the formation of micrometer-sized droplets that only very slowly grow in size, thus expanding the life of the anise-flavored beverage. The slow growth has been attributed to an extremely low interfacial tension of the droplets. Fitting experimental droplet growth rates to an Ostwald ripening model, interfacial tensions were deduced in the past. Direct determination of the interfacial tensions was not yet reported on these systems. We have measured the interfacial tensions and used these data to predict droplet growth rates using an Ostwald ripening model and a model for creaming of the droplets. The interfacial tension was measured to be about 11 mN/m for a 30/70 w/w % ethanol/water mixture, and it decreases slightly to a value of 1.4 mN/m in the case of a 70/30 w/w % ethanol/water mixture. These values are not as low as those deduced in the past. The theoretical predictions for both the Ostwald ripening rates and the creaming rates, using the directly measured interfacial tensions, are found to contradict with the experimental results on Ostwald ripening and creaming. While the experiments on Ostwald ripening show an increase in stability with increasing ethanol concentration, the results based on our interfacial tension measurements in combination with the same Ostwald ripening model show a decrease in stability with an increase in ethanol concentration. Further research is needed to understand fully which parameters play a role in both droplet growth and the stability of these three-component emulsions to elucidate the current discrepancy between model and experiment. This could be useful for a better control of "spontaneous emulsification" processes.