Interfacial properties of cationic and anionic Gemini surfactant mixtures

The possibility and the prospect of cationic/anionic (“catanionic”) surfactant mixtures based on sulfonate Gemini surfactant (SGS) and bisquaternary ammonium salt (BQAS) in the field of enhanced oil recovery was investigated. The critical micelle concentration (CMC) of SGS/BQAS surfactant mixtures was 5.0 × 10⁻⁶ mol/L, 1–2 orders of magnitude lower than neat BQAS or SGS. A solution of either neat SGS or BQAS, could not reach an ultra-low interfacial tension (IFT); but 1:1 mol/mol mixtures of SGS/BQAS reduced the IFT to 1.0 × 10⁻³ mN/m at 100 mg/L. For the studied surfactant concentrations, all mixtures exhibited the lowest IFT when the molar fraction of SGS among the surfactant equaled 0.5, indicating optimal conditions for interfacial activity. The IFT between the 1:1 mol/mol SGS/BQAS mixtures and crude oil decreased and then increased with the NaCl and CaCl₂ concentrations. When the total surfactant concentration was above 50 mg/L, the IFT of SGS/BQAS mixtures was below 0.01 mN/m at the studied NaCl concentrations. Adding inorganic salt reduced the charges of hydrophilic head groups, thereby making the interfacial arrangement more compact. At the NaCl concentration was above 40,000 mg/L, surfactant molecules moved from the liquid–liquid interface to the oil phase, thus resulting in low interfacial activity. In addition, inorganic salts decreased the attractive interactions of the SGS/BQAS micelles that form in water, decreasing the apparent hydrodynamic radius (D_{H, app}) of surfactant aggregates. When the total concentration of surfactants was above 50 mg/L, the IFT between the SGS/BQAS mixtures and crude oil decreased first and then increased with time. At different surfactant concentrations, the IFT of the SGS/BQAS mixtures attained the lowest values at different times. A high surfactant concentration helped surfactant molecules diffuse from the water phase to the interfacial layer, rapidly reducing the IFT. In conclusion, the cationic-anionic Gemini surfactant mixtures exhibit superior interfacial activity, which may promote the application of Gemini surfactant.     

盐对阴阳离子表面活性剂水溶液相行为的影响

以阴阳离子表面活性剂混合体系为研究对象,通过测定体系在不同种类盐溶液中的三元相行为,探索了盐对体系相行为中的双水相区位置及相区宽度的影响规律.研究发现,阴离子双水相区的位置与宽度主要受盐阳离子的影响,盐阳离子半径越大,极化率越高,阴离子双水相区向阴离子表面活性剂方向移动的趋势越大,相区越宽;而盐的阴离子是影响阳离子双水相区位置与宽度的主要因素.     

Surfactant mixtures: A short review

Every commercial formulation that contains surfactant contains a mixture of surfactants. This chapter is a short review on surfactant mixtures in water focusing on important concepts that differ from single-component systems. The chapter assumes a basic understanding of surfactants. Topics include micelles; adsorption at the air–water, oil–water, and water–solid interfaces; and phase behavior/precipitation. Mixtures of surfactant types that are important in applications are emphasized. In addition, those molecular aspects that affect macroscopic behavior, especially macroscopic behavior that is important for applications of surfactants, are emphasized.     

微乳液最佳中相醇用量和增溶能力与油相等效烷基碳数的定量关系

主要考察了十八烷基三甲基氯化铵(OTAC)和十二烷基硫酸钠(SDS)对油相的增溶规律。通过不同烃类混合,包括两种烃类的混合和4种烃类混合,调整混合油相的等效烷基碳数(EACN),探索最佳中相醇用量(A*)、最佳增溶量(SP*)与EACN的关系。A*、SP*与EACN在两类表面活性剂条件下都呈现二次函数的关系,且在同一表面活性剂体系中,控制其他组分含量恒定的情况下,函数关系与所用的烃无关。     

双尾表面活性剂/盐水溶液/正辛烷三元体系相态特性的研究

研究了在不加助表面活性剂的情况下,双尾表面活性剂盐水溶液和正辛烷组成的三元体系中能否形成中相微乳液及其相关的相态特性。结果表明,在不加助表面活性剂的情况下,双尾表面活性剂CmGA(EO)nS(m=12,14,16;n=0,1,3,4,8)中,只有C14GA(EO)nS(n=1,3,4)可与盐水及正辛烷形成中相微乳液;以适宜的增溶参数、低界面张力值以及相体积图为基础所确定的形成中相微乳液的最佳含盐量三者一致性较好;随着C14GA(EO)nS(n=1,3,4)中EO基团数增加,形成中相微乳液的最佳盐度和增溶参数皆随之增加,而最佳界面张力值则降低。     

Surface activity of mixtures of dodecyl trimethyl ammonium bromide with sodium perfluorooctanoate and sodium octanoate

In this study, the surface tension of mixtures of cationic surfactant dodecyl trimethylammonium bromide (DTAB) and anionic surfactant sodium perfluorooctanoate (SPFO) was evaluated as a function of DTAB-SPFO composition and total surfactant concentration, with and without added electrolyte. It was found that the critical micelle concentration (CMC) of these mixtures was reduced by more than two orders of magnitude when compared to the CMC of SPFO and DTAB alone. The surface tension, after CMC, of the mixtures was close to that of SPFO with added electrolyte and even lower than that of SPFO without added electrolyte. Using the appropriate, combination of SPFO and DTAB, surface tensions near 18 mJ/m² were obtained using a concentration 1/500 of that required for SPFO alone. When these results were compared to those obtained for DTAB-sodium octanoate (SOCT) mixtures, it was evident that the DTAB-SPFO system shows a larger degree of synergism than the DTAB-SOCT system. Contact angle measurements on Teflon^® surfaces corroborates that the lower surface tension of DTAB-SPFO mixtures improves wetting on these hydrophobic surfaces. Using the regular solution theory to interpret the data of CMC and C45mJ/m² (monolayer formation) versus DTAB-SPFO composition, it was concluded that even when small concentrations of SPFO are introduced in the mixture, the composition of the micelles (at the CMC) and monolayer adsorbed at the air-water interface tends to be equimolar in SPFO and DTAB.     

油水比对阴离子型微乳液相行为的影响

微乳液由水、油、盐、表面活性剂及助表面活性剂组成,其相行为及增溶情况受各组分的影响。研究发现,在SDBS（SDS、SLS）/航空煤油/水/正丁醇/氯化钠体系中,随着NaCl含量的不断增多,微乳液体系发生Winsor Ⅰ型→Winsor Ⅲ型→Winsor Ⅱ型的相态转变。固定水的用量,通过油扫实验不断改变体系中的油水比,利用相图研究油水比对微乳液相行为的影响,并通过冷冻电镜对不同相态下微乳液的微观形貌进行了表征。随着油水比的增加,在低盐度下,体系由胶团溶液转变为Winsor Ⅰ型;而在高盐度下,体系发生由胶团溶液→Winsor Ⅱ型→Winsor Ⅲ型→Winsor Ⅰ型的相态转变。盐度一定时,微乳液的中相形成及消失所需的油量会随着表面活性剂浓度的增多而增多,且三种表面活性剂中,表面活性剂的增溶能力的大小顺序为SDBS>SDS>SLS,对煤油的敏感程度顺序为SLS>SDS>SDBS。     

Polymorphic behavior of gondoic acid and phase behavior of its binary mixtures with asclepic acid and oleic acid

Molecular properties of polymorphic forms of gondoic acid [cis-C_20:1Δ11ω9 (GOA)] have been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), optical microscopy, and Raman scattering, in comparison to those of six principal unsaturated fatty acids: oleic acid [cis-C_18:1Δ9ω9 (OA)], erucic acid [cis-C_22:1Δ13ω9 (ERA)], petroselinic acid [cis-C_18:1Δ6ω12 (PSA)], asclepic acid [cis-C_18:1Δ11ω7 (APA)], palmitoleic acid [cis-C_16:1Δ9ω7 (POA)], and elaidic acid [trans-C_18:1Δ9ω9 (ELA)]. In addition, phase behavior of binary mixtures of GOA and APA and OA was examined by XRD and DSC. The polymorphic structures of GOA are quite similar to those of APA, ERA, POA, and partly to OA. In particular, DSC and Raman scattering studies have shown that gondoic acid exhibits conformational disordering on heating at the ω-chain, a chain segment between the double bond and CH₃ group, as a transition from all-trans (γ form) to gauche-rich (α form) conformations. A miscible mixing phase was observed in the mixture of GOA and APA, yet eutectic phases were observed in the GOA and OA mixtures. This is a remarkable contrast because the binary mixture systems of varying combinations of cis-unsaturated fatty acids examined so far exhibited either eutectic nature or molecular compound formation. It is expected that specific molecular interactions between GOA and APA that originate from the equivalence of the length of the Δ-chain, the chain segment between the cis-double bond and COOH group, and also from the presence of the γ-α order-disorder transformation would be operating to form the miscible mixing phase.     

Micellar solubilization of binary organic liquid mixtures for surfactant enhanced aquifer remediation

Although non-aqueous phase liquids (NAPLs) are typically released to the environment as complex mixtures, most investigations of subsurface remediation focus on single contaminants and ignore the potential effects of co-constituents on mass recovery and groundwater plume evolution. In this study, we investigate the dissolution and micellar solubilization of binary NAPL mixtures in completely mixed batch reactors and heterogeneous aquifer cells using a commercially-available nonionic surfactant, Tween® 80. Micellar solubilization of trichloroethene (TCE), tetrachloroethene (PCE), decane, and dodecane measured in batch studies containing binary mixtures of TCE/PCE or decane/dodecane exhibited nonideal behavior that could not be predicted using Raoult's law. For a mixed PCE/decane NAPL, micellar solubilization of PCE was approximately 40% less than predicted, while decane was over 100% greater, which was attributed to expansion of the micelle core. In two aquifer cells containing different size fractions of quartz sand and low-permeability lenses, the initial NAPL (1:1 TCE:PCE) saturation distributions resulted in “pool” fractions (PFs) of 0.88 and 0.36. During the initial water flood, the greater aqueous solubility of TCE relative to PCE resulted in preferential removal of TCE from the source zone. However, when a 4% (wt) solution of Tween® 80 was introduced, preferential micellar solubilization of PCE relative to TCE resulted in enhanced removal of PCE, with TCE mass discharge reduced from 97% and 90% and PCE mass discharge reduced from 79% and 53%. The observed relationships between mass discharge and mass removal indicating that plume evolution is strongly influenced by the initial NAPL saturation distribution, changes in the mole fraction of NAPL constituents, and regions of high NAPL saturation that persist over time.     

Effect of Ethylene Oxide Group in the Anionic–Nonionic Mixed Surfactant System on Microemulsion Phase Behavior

The phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12-14 alcohol ethoxylate (C_{12 − 14}E_j) that contains an ethylene oxide (E_j) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C_{12 − 14}E_j systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C_{12 − 14}E₁ was more lipophilic, while SDHS − C_{12 − 14}E₉ was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C_{12 − 14}E₅ system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.     

表面活性剂水溶液相行为研究进展

综述了关于表面活性剂溶液相行为研究的几种常用的方法和手段;介绍了表面活性剂几种复配体系相行为的研究进展;讨论了温度、盐和有机物种类等因素对表面活性剂溶液相行为的影响。     

Synchrotron radiation X-ray diffraction study on phase behavior of PPP-POP binary mixtures

The phase behavior of thesn-1,3-dipalmitoyl-2-oleoylglycerol (PPP-POP) binary mixture system was studied by powder X-ray diffraction with synchrotron radiation and by differential scanning calorimetry. The results showed that the immiscible phases were observed in metastable and in the most stable forms. In particular, synchrotron X-ray diffraction enabled us to reveal the monotectic nature of α as a kinetic phase behavior. The equilibrium phase diagram of the PPP-POP mixture is divided into two regions. In POP concentration ratios below 40%, solid-state transformation from α to β was observed, indicating that the α-β transition of PPP was promoted in the presence of POP. By contrast, the polymorphic transition proceeds from α to β through the occurrence of the intermediate β′ form at POP concentration ratios above 50%.     

Phase behavior of fatty acid/oil/water systems: Effect of the alkyl length chain acid

The phase behavior of different fatty acids (FA) in pseudo-ternary mixtures [(water)/(FA) + (alcohol)/(oil)] was studied. The Winsor I-III-II transitions of ionized compounds were attained by varying the FA composition through the formulation scan. The middle-phase volume, the pH of the optimum system, and the partition coefficient increased with the chain length of FA. Conversely, the acid partition coefficient allows calculation of the Gibbs free energy of transfer of a CH₂ group from oil to water, which is found to be +0.87 J/mol.     

Effect of solvents on closed-loop phase behavior of block copolymers

We studied the effect of solvent selectivity on the closed-loop phase behavior of a polystyrene-block-poly(n-pentyl methacrylate) copolymer. It was found that the lower disorder-to-order transition temperature (LDOT) and upper order-to-disorder transition temperature (UODT) consisting of the closed-loop were very sensitive to the selectivity of the solvent. With the addition of very small amounts of non-selective solvents such as di-n-octyl phthalate and dimethyl phthalate, the LDOT increased rapidly, whereas the UODT decreased dramatically; thus, the immiscibility loop was shrunk greatly. On the other hand, both the LDOT and UODT decreased with increasing amount of dodecanol, a highly selective solvent to poly(n-pentyl methacrylate) block. However, the decrease in the LDOT was greater than that of the UODT, leading to an increased immiscibility loop.     

Preferential Adsorption Phenomena in Polyelectrolytes in Methanol/Water Solution: Effect of the Counterion

The preferential adsorption behaviour of nitrate and chloride salts of poly(N,N-dimethyl-N-(2-hydroxypropyl)ammonium) in solutions of methanol/ water mixtures is analysed. At low methanol content both polyions show an adsorption of methanol which is 2·5 times larger for chloride polyion than that for nitrate salt. In the former case, the amount of methanol adsorption is enough to produce an important change in the average distances between charges. This change induces an anomalous behaviour of the conductimetric interaction parameter with solvent composition. This effect is not observed in the case of nitrate polyion and the trend of the conductimetric interaction parameter correlates well with the nature of the medium. This effect is attributed to the low methanol adsorption in this case. © of SCI.     

Effect of Electrolytes on Octanol‐Water Partition Coefficients: Calculations with COSMO‐RS

In this work, the possibility of the a priori predictive model COSMO‐RS to describe partitioning of pharmaceutically active compounds in the octanol‐water system (P_OW) in the presence of electrolytes is investigated. It is shown that the calculated values of P_OW depend on the pH and the ionic strength of the solution for both dissociated and non‐dissociated solutes. Whereas the partitioning of the non‐dissociated form in the presence of salts or buffers can be explicitly described by COSMO‐RS, the partitioning of the ionized pharmaceuticals is taken into account by their dissociation constants. Overall, reasonable agreement with experimental values is achieved. Principally, these types of calculations can be extended to other two‐phase systems used for extraction and formulations of pharmaceuticals and further organic solutes.     

Generalized Flory–Huggins model for heat‐of‐mixing and phase‐behavior calculations of polymer–polymer mixtures

An extended and generalized Flory–Huggins model for calculating the heats of mixing and predicting the phase stability and spinodal diagrams of binary polymer–polymer mixtures is presented. In this model, the interaction parameter is considered to be a function of both temperature and composition. It is qualitatively shown that the proposed model can calculate the heats‐of‐mixing curves containing exothermic, endothermic, and S‐shaped or sigmoidal types and predict the spinodals, including the upper and lower critical solution temperatures, and closed‐loop miscibility regions. Using experimental results of analog calorimetry for four polymer mixtures of polystyrene/poly(vinyl chloride) (PS/PVC), polycarbonate (PC)/poly(ethylene adipate) (PEA), polystyrene/poly(vinyl acetate) (PS/PVAc), and ethylene vinyl acetate copolymer (EVA Co)/chlorinated polyethylene (CPE), the capabilities of the proposed functionality for the interaction parameter was studied. It is shown that this function can be used satisfactorily for the heat‐of‐mixing calculations and phase‐behavior predictions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1328–1340, 2000     

The production of graphene by direct liquid phase exfoliation of graphite at moderate sonication power by using low boiling liquid media: The effect of liquid media on yield and optimization

There are many production methods for graphene production. One of the most successful production methods in terms of scale-up is liquid phase exfoliation (LPE) method. In this study, after optimizing the sonication time and sonication power that are effective in the production to increase the efficiency of the LPE method, the experiments were continued at moderate sonication powers and the effect of liquid media, another important parameter, was examined. In this study, hexagonal graphite powders were subjected to direct liquid phase exfoliation process by using different liquid media (N-Methyl-2-Pyrrolidone (NMP), N,N-Dimethylformamide (DMF), ethanol, 2-propanol, acetone, methanesulfonic acid, ethanol + Sodium dodecyl sulphate (SDS), 2-propanol + SDS) and the obtained samples were characterized. As a result of the characterization, the liquid media with the highest efficiency was determined to be NMP. Besides, it was observed that a new hybrid solvent obtained by adding a surfactant such as SDS into low-cost and environmentally friendly liquid media such as ethanol and 2-propanol showed a higher efficiency than NMP. It was observed that 3–5 layer graphene ranged between 15 and 19 wt% in either graphene produced by using hybrid solvents containing NMP or SDS. The amount of double or single-layer graphene was negligibly small. The production with the lowest efficiency was observed in the use of acetone. The produced graphenes were dispersed in the liquid and their sedimentation time was observed. The sedimentation time of graphenes, produced using NMP and SDS-doped hybrid solvents, in liquid was more than 120 days. The sedimentation time of graphene produced using acetone was less than 20 days. In the use of graphene as a reinforcing material or adsorbent, large amounts of graphene are needed. In such applications, mass production of graphene is important rather than the number or quality of sheets of graphene. Therefore, optimization of production parameters of LPE method, which is suitable for mass production, is significance.