Micellization and Interfacial Interaction Behaviors of Gemini Cationic Surfactants–CTAB Mixed Surfactant Systems

The interfacial and micellization behaviors of binary mixtures of two gemini cationic surfactants and conventional the cetyl trimethyl ammonium bromide surfactant were studied at various molar ratios. From the equilibrium surface tension measurements, the critical micelle concentrations (CMC) data were obtained as functions of the composition. Values of the CMC were analyzed according to the regular solution model developed by Rubingh for mixed micelles. Two interaction parameters were obtained for each system, the interaction at the interface, and in the micellar phase. The results showed that micellization and adsorption properties of the studied mixed systems depend on the spacer chain lengths of the gemini surfactants and their ratio in the mixed systems.     

SYNERGISTIC EFFECTS OF ANIONIC SURFACTANT AND NONIONIC POLYMER ADDITIVES ON DRAG REDUCTION

Turbulent drag reduction (DR) behavior of mixed nonionic polymer and anionic surfactant solutions in water was studied in a pipeline set up to explore the synergic effects of mixed additives on DR. The concentration of polymer polyethylene oxide (PEO) was varied from 0 to 2000 ppm and the concentration of surfactant sodium dodecyl sulfate (SDS) was varied from 0 to 5000 ppm. The critical aggregation concentration (CAC), where the interaction between the polymer and the surfactant begins, and the polymer saturation point (PSP), where the polymer molecules become saturated with the surfactant, were determined using electrical conductivity and surface tension measurements. As the polymer concentration was increased the CAC decreased but the PSP increased. The relative viscosity showed a remarkable increase upon the addition of surfactant to the polymer solution due to extension of polymer chains caused by the formation of micelles on the backbone of the polymer molecules. The data exhibited a considerable increase in DR in the case of mixed polymer/surfactant systems. The percent reduction in friction factor was as high as 79 when 3000 ppm or more surfactant was added to the 500 ppm polymer solution. Furthermore, the drag reduction behavior of the polymer solution changed from so-called Type A to Type B. In Type A drag reduction, a transition from laminar to turbulent regime is observed with a clear-cut onset point. In Type B drag reduction, no transition or onset point is observed; the data fall on a gradual extension of the laminar line.     

Zinc Corrosion in Acidic Solutions Containing Single and Mixed Surfactants

The influence of surfactant synergism on Zn corrosion inhibition in 0.1-M HCl aqueous solutions has been determined at room temperature. Solutions of single and mixed surfactants consisting of sodium dodecylsulfate (SDS) and N,N-dimethyldodecan-1-amine oxide (DDAO) in water and in 0.1-M HCl were also prepared at room temperature. Critical micelle concentration (CMC) data were obtained through surface tension measurements as a function of mixing composition. A regular solution model was considered to analyze CMC values. The interaction parameter (β), the composition of mixed micelles (x) and the activity coefficients (f) were estimated by a regular solution model for all amphoteric–anionic mixed systems. β Vvalues showed synergism for the binary mixtures of these solutions in the absence and presence of 0.1-M HCl at all investigated compositions. Zinc corrosion in single and binary SDS/DDAO mixed solutions at 5-mM total surfactant concentrations in the presence of 0.1-M HCl was also investigated at static and dynamic conditions. The weight loss data revealed corrosion inhibition activity obeyed the following order: binary (0.75 DDAO + 0.25 SDS) > binary (0.50 DDAO + 0.50 SDS) > single DDAO > single SDS, suggesting an enhancement in the corrosion inhibition activity of DDAO in the presence of a proper amount of SDS. Conductivity time measurements show a similar trend as that obtained by a weight loss method at (0.50 DDAO + 0.50 SDS). The results were illustrated on the basis of synergistic interaction between the mixed surfactants.     

Influence of breakup and reformation of micelles on surfactant diffusion in pure and mixed micellar systems

Pulsed field gradient (PFG) NMR technique was used to study diffusion of surfactant ions in the following two micellar systems: (i) aqueous solution of an anionic surfactant sodium dodecyl sulfate (SDS), and (ii) aqueous solution of a mixture of SDS and a small amount of the cationic surfactant N-dodecyltrimethylammonium bromide (C₁₂TAB). PFG NMR measurements provided separate sets of data on diffusion of SDS and C₁₂TAB surfactant ions for a broad range of diffusion times. For each type of surfactants at least two components with different effective diffusivities were observed at sufficiently small diffusion times. The faster component was assigned to the surfactants that experience breakup or reformation of micelles during the diffusion time of the PFG NMR measurement, while the slower component was assigned to the surfactants that did not participate in such events during the diffusion time. The observed changes of the fractions and diffusivities of these components with increasing diffusion time were found to be in a qualitative agreement with such assignment. Fundamental understanding of surfactant diffusion in micellar system is important due to an increasing use of such systems for synthesis of porous materials where micelles are used as templates as well as for many other applications.     

Hydrophobic hydration of cationic mixed micelles by alkoxyethanols in aqueous media

The conductances of hexadecylpyridinium chloride (HPyCl) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyCl (α_HPyCl) were measured in aqueous binary mixtures of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether containing 10 to 30 wt% additive in their respective binary mixtures at 30°C. Each conductivity curve showed a single break over the whole mole fraction range of HPyCl + TTAB mixtures. From the break in the conductivity curve, various micellar parameters were calculated and the results were discussed on the basis of alkoxyethanol's hydrophobic hydration of the mixed micelle. The micellar parameters of HPyCl, TTAB, and of their mixtures showed a strong dependence both on the amount and on the number of repeating units of ethylene and diethylene glycol derivatives. The hydrophobic hydration was considerably higher in the case of diethylene glycol derivatives owing to the presence of an extra ether oxygen. An evaluation of the non-ideality in the HPyCl + TTAB mixtures in the presence of additives revealed that alkoxyethanols reduce the unlike surfactant monomer interactions in order to form the mixed micelles in comparison to those in pure water. It has also been observed that such interactions systematically decrease with an increase in the number of repeating units from monomethyl ether to monobutyl ether, both in the case of ethylene and diethylene glycol derivatives.     

Mixed micelles of hexadecylpyridinium bromide + tetradecyltrimethylammonium bromide in aqueous glycol oligomers

Conductances of hexadecylpyridinium bromide (HPyBr) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyBr (α_HPyBr) were measured in pure water as well as in the presence of various aqueous ethylene glycol oligomers containing 10 and 30 wt% of each additive in their respective binary mixtures at 30°C. Each conductivity curve shows two breaks corresponding to two critical micelle concentrations (cmc; C₁ and C₂ over the whole mole fraction range of HPyBr + TTAB mixtures except in the presence of pure HPyBr and TTAB, where a single break was observed. From the conductivity data, various micellar paramelers in the absence and presence of glycol additives were computed. A variation in the micellar parameters in the presence of additive showed that additive introduction mainly influence the medium properties and therefore the micellar properties. However, no significant micelle-glycol interactions were observed even with an increase in the number of repeating units from ethylene glycol to polyethylene glycol 600. The mixing behavior of HPyBr + TTAB is close to nonideal and is identical in pure water and in the presence of various glycols. This has been attributed to the presence of synergistic interactions between unlike monomers at C₁ that are not influenced even by the presence of additives. The appearance of the second cmc is mainly attributed to structural transitions of the mixed micelles at C₁ with a further increase in surfactant concentration.     

Packing of polyethylene oxide chains in a mixed micelle

The effects of an anionic surfactant, sodium dodecyl sulfate (SDS), on the micellar properties of a nonionic surfactant such as homogeneous heptaethylene glycol n-dodecyl ether (7ED) have been studied by the charge transfer solubilization of 7,7,8,8-tetracyanoquinodimethane, pNa, and electric conductivity measurements. Attention has been paid to changes in packing of polyethylene oxide chains in the mixed micelle and to binding of the counterions onto the micelle surface. All measurements were made on solutions ranging in 7ED concentration from 1 × 10⁻⁶ to 1×10⁻¹ M, while the SDS concentration was maintained constant. It has been shown that the binding of Na⁺ ions to the mixed micelle occurs in the 7ED concentration region where the packing of polyethylene oxide chains in the micelle is loose, while release of Na⁺ ions is observed when the packing is compact. The results of electric conductivity correspond well with those mentioned above. However, in the region of high 7ED concentration, the decreasing mobility of the mixed micelles affects the electric conductivity more than the increasing degree of ionic dissociation of the micelle.     

Synergistic Behavior Between Zwitterionic Surfactant α-Decylbetaine and Anionic Surfactant Sodium Dodecyl Sulfate

Here, we present experimental surface tension isotherms of mixed solutions of a zwitterionic surfactant α-decylbetaine (DB) and an anionic surfactant sodium dodecyl sulfate (SDS) in different molar ratios. These mixed solutions show a composition dependency with respect to both surface tension effectiveness and critical micelle concentration. The pseudo-regular solution theory has been used to evaluate the interaction parameters in the micelle, β ^m and at the surface, β ^s. The results revealed that the mixed solutions of DB/SDS behave synergistically in both surface tension reduction effectiveness and mixed micelle formation at all mole fractions investigated. The values of adsorption area per surfactant molecule at air/solution interface were estimated, which provides some useful information on evaluating the interaction between DB and SDS in mixed adsorbed monolayers. The solubilization behaviors of toluene in DB/SDS mixed solutions were also investigated to help in understanding the structure of mixed micelles of DB and SDS.     

Mixed Micellization Properties of Nonionic Fluorocarbon/Cationic Hydrocarbon Surfactants

The physico-chemical properties of mixed surfactant aqueous solutions at various proportions of dodecyltrimethyl ammonium bromide DTAB and undecafluoro n-pentyl decaoxyethylene ether C5F11EO10 have been investigated at 25 °C using surface tension and conductivity measurements. The critical micelle concentration and superficial minimum tension have been experimentally estimated for different DTAB molar fractions. The micellar composition and mutual interaction parameters have been deduced on the basis the theoretical treatments proposed by Clint, Rubingh, and Motomura. The results show a significant synergism effect at about equimolarity of DTAB/C5F11EO10 system probably due to the efficient electrostatic self-repulsion reduction between DTAB cationic head groups related to the presence of the nonionic surfactant in the mixed micelles.     

Properties of aqueous solutions for two binary mixed systems between two kinds of bile salts and nonionic surfactants

The micellar properties of aqueous binary mixed solutions for two systems consisting of sodium cholate (NaC)-octaoxyethylene glycol mono n-decyl ether (C₁₀E₈) and sodium glycocholate (NaGC)-C₁₀E₈ have been studied on the basis of surface tensions, polarity of the micelle interior and the mean aggregation number. Application of two theoretical treatments, based on regular solution and excess thermodynamic quantities for critical micellar concentration (CMC) data from surface tension curves of two mixed systems showed that the mole fraction of each bile salt in the mixed micelles near the CMC is lower than that of the corresponding prepared mole fraction in the mixed solution. The polarity of the interior suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of bile salt in the mixed solution and that the mixed micelles become dramatically more hydrophobic at a mole fraction of 0.68 for NaGC−C₁₀E₈ system and 0.75 for NaC−C₁₀E₈ system, respectively. This implies that the micelles become richer in the bile salt molecules and the tendency appears strongly for NaGC−C₁₀E₈ system due to the strong cohesion between the conjugated glycines in the NaGC molecules. The decrease of aggregation number with the increase of the mole fraction of bile salts shows that the micelles approach those of the single system of each bile salt. This supports the previously mentioned facts.     

Importance of micellar relaxation time on detergent properties

As we enter the new millennium, manufacturers of laundry detergents would like to provide new products for the twenty-first century. With the goal of achieving new and better performance characteristics, design strategies for research and development should be defined. This paper highlights the importance of micellar relaxation kinetics in processes involved in detergency. Earlier Shah and coworkers showed that the stability of sodium dodecyl sulfate (SDS) micelles plays an important role in various technological processes. The slow relaxation time (τ₂) of SDS micelles, as measured by the pressure-jump technique, was in the range of 10⁻⁴ to 10¹ s, depending on the surfactant concentration. A maximal relaxation time and thus a maximal micellar stability was found at 200 mM SDS (5 s), corresponding to the least-foaming, largest bubble size, longest wetting time of textile, largest emulsion droplet size, and the most rapid solubilization of oil. These results are explained in terms of the flux of surfactant monomers from the bulk to the interface, which determines the dynamic surface tension. More stable micelles lead to less monomer flux and hence to a higher dynamic surface tension. The relaxation time for nonionic surfactants (as measured by the stopped-flow technique) was much longer than for ionic surfactants because of the absence of ionic repulsion between the head groups. The τ₂ was related to dynamic surface-tension experiments. Stability of SDS micelles can be greatly enhanced by the addition of long-chain alcohols or cationic surfactants. In summary, relaxation time data of surfactant solutions enable us to predict the performance of a given surfactant solution. Moreover, results suggest that one can design appropriate micelles with specific stability, or τ₂, by controlling surfactant structure, concentration, and physicochemical conditions, as well as by mixing anionic/cationic or ionic/nonionic surfactants for a desired technological application, e.g., detergency.     

Physicochemical Studies on the Interfacial and Micellization Behavior of CTAB in Aqueous Polyethylene Glycol Media

Interfacial and micellization behavior of cetyltrimethylammonium bromide (CTAB) have been studied in aqueous polyethylene glycol (PEG) mixed solvent systems of varying concentrations and molar mass. Interfacial behavior of CTAB was investigated by the equilibrium surface tension method. Conductance studies of surfactant solutions under different condition helped in determining the critical micelle concentration (CMC) and degree of dissociation of CTAB micelles. In addition, the limiting molar conductivity of surfactant and micellar species were evaluated from the differential plots. The CMC of CTAB was found to increase with increasing PEG concentration as well as its molar mass, although, the process of interfacial adsorption and micellization was found to be spontaneous, as evidenced by negative free energy change. The viscosity of CTAB micelles in aqueous-PEG mixtures was found to increase with the increase in PEG concentration and molar mass. Dynamic light scattering measurements revealed a size enhancement effect contributed by the PEG oligomers. An increase in the CMC of CTAB and the subsequent presence of a higher number of ionic species in their dissociated form was further established by an overall increase in the zeta potential value in the presence of PEG oligomers. It is proposed that the PEG could wrap around the micelles through their conformational changes. Results also suggest that PEG oligomers could give solvophobic effect which enhances the CMC of CTAB compared to that in pure water.     

Interaction Between an Anionic and an Amphoteric Surfactant. Part I: Monomer–Micelle Equilibrium

A mixture of anionic and amphoteric surfactants is composed of three components at intermediate pH levels: anionic, cationic (protonated amphoteric), and zwitterionic (unprotonated amphoteric). Knowledge of the composition of each surfactant in both monomer and micellar forms (monomer–micelle equilibrium) is important in applications using this mixture. Hydrogen ion titration of the mixed surfactant solution as a function of surfactant composition is combined with the pseudophase separation model and regular solution theory for the three-surfactant mixture to calculate the concentration of each surfactant in monomer and in micelle forms at different pH levels. The specific systems studied here contain sodium dodecyl sulfate (SDS) and dimethyldodecylamine oxide (DDAO), which are used in a wide range of consumer products. The degree of protonation of monomeric DDAO is not affected by the presence of SDS, indicating an insignificant formation of ion pairs between these monomers. However, the presence of SDS in micelles shifts the micellar pK _a of DDAO protonation significantly and the method used here allows the quantification of partial fugacities of each individual surfactant in micelle form. The composition in the monomer phase at each pH will aid in understanding and predicting solution compositions corresponding to anionic/amphoteric surfactant precipitation boundaries, which is the focus of the subsequent paper in this series.

Alcohols Effect on Critic Micelle Concentration of Polysorbate 20 and Cetyl Trimethyl Ammonium Bromine Mixed Solutions

In this research, the micellar behavior of a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) and an nonionic surfactant, polysorbate 20 (Polyoxyethylene (20) sorbitan monolaurate) in different alcohol solutions media was investigated over the temperature range 293.15–313.15 K. The interaction between two surfactants in binary systems can be determined by calculating the values of their β parameters. The critical micelle concentrations (CMC) of the micelles were determined from the surface tension, the conductivity at different temperatures. The CMC behavior of CTAB and polysorbate 20 was analyzed in terms of the effect of temperature and the increase in the alcohol carbon chain. Changes in the critical micelle concentration of mixed surfactant systems of different alcohol solutions were measured. The CMC decreased sharply as the hydrocarbon chain length of the alcohols becomes larger. This shows that the more hydrophobic alcohols are, the more marked a decrease in CMC is observed.     

Synergisms in Binary Mixtures of Anionic and pH‐Insensitive Zwitterionic Surfactants and Their Precipitation Behavior with Calcium Ions

This work aims to investigate synergy in anionic and zwitterionic surfactant mixtures, as they result in better interfacial properties and micellization behavior. Various mixtures of the pH‐insensitive zwitterionic surfactant 3‐(decyldimethylammonio) propanesulfonate (Zwittergent 3–10) and sodium dodecylsulfate (SDS) were prepared in aqueous solution at a range of pH values between 2 and 13. The thermodynamic parameters during mixed surfactant adsorption at the air/water interface are obtained and the results show the mixed surfactant systems having superior properties to the constituent surfactants. Experimentally, the mixed surfactant solutions clearly improve the surface activities by lowering the critical micelle concentration (CMC) and lowering the surface tension at the air/water interface. The synergisms are investigated through the interaction parameters estimated from regular solution theory that is used to quantitatively describe the nonideality of surfactant mixtures. High negative interaction parameters are obtained from these surfactant mixtures. Experimental precipitation phase boundaries of SDS in the presence of CaCl₂ were also investigated in mixtures containing pH‐insensitive zwitterionic surfactant at different pH levels from 2 to 13 and SDS mole fractions of 0.25, 0.50, 0.75, and 1.00. Changes in the precipitation phase boundaries are due to the changes in the speciation or activities of the major components both below and above the CMC. As a result, the precipitation phase boundaries are pH dependent. In addition, mixed micellization and counterion binding to the micelle also change the precipitation phase boundary above the CMC. The activity‐based solubility product of calcium dodecylsulfate is also determined from the precipitation phase boundaries below the CMC. X‐ray diffraction patterns and SEM images confirm that only calcium dodecylsulfate precipitates in the soap scum for all pH and surfactant compositions studied.     

Mixed Micelles of Trisiloxane Based Silicone and Hydrocarbon Surfactants Systems in Aqueous Media: Dilute Aqueous Solution Phase Diagrams, Surface Tension Isotherms, Dilute Solution Viscosities, Critical Micelle Concentrations and Application of Regular Solution Theory

Mixtures of trisiloxane type nonionic silicone surfactant (SS) with sodium dodecylsulfate, tetradecyltrimethylammonium bromide or tert-octylphenol ethoxylated with 9.5 ethylene oxide groups were studied in water at 30 °C by dilute aqueous solution phase diagrams, surface tension and dilute solution viscosity methods. The cloud points for the silicone surfactant aqueous solutions increased upon addition of hydrocarbon surfactants indicating the formation of hydrophilic complexes in mixture solutions. The scrutiny of the surface tension isotherms plotted as a function of SS concentration revealed that competitive adsorption effects are the characteristic features in these mixtures depending upon the SS concentration. Otherwise the isotherms exhibited two break points and the difference of concentration between the two break points increased with the increase in SS concentration indicating the cooperative nature of interactions. The micellar mole fractions of individual surfactants were determined by Rublingh's regular solution theory; interaction parameters and activity coefficients were evaluated and interpreted in terms of synergistic type interactions in these mixtures. The surface active parameters in mixture solutions were estimated and their analysis shows that the molecular species in the mixture solutions have a preferential tendency for adsorption at the air/water interface than in association form in the bulk solution. The effect of hydrocarbon surfactants on the intrinsic viscosity of SS micelles was monitored and related to the enhanced hydration in mixed micelles.     

二元表面活性剂体系微乳液的相行为及热力学研究

用表面张力法研究了苯乙烯基酚聚氧乙烯聚氧丙烯醚嵌段型非离子表面活性剂(PEP)分别与十二烷基硫酸钠(SDS)、十二烷基三甲基溴化铵(CTAB)复配体系分子间的相互作用,并根据测定的临界胶束浓度(CMC)及正规溶液理论计算了复配体系分子间相互作用参数及分子交换能,考察了表面活性剂、助表面活性剂、温度等因素对复配表面活性剂体系微乳液形成过程的相行为及热力学性质的影响。结果表明,二元组分(PEP+SDS)及(PEP+CTAB)复配体系在胶束中和表面吸附层中的都存在较强的增效作用,体系的能量降低,且前者的增效作用大于后者。(PEP+SDS)/正己醇/正庚烷/水微乳液的W/O微乳区域面积最大,温度对该微乳液的相行为影响很小。在此微乳液形成的过程中,助表面活性剂醇从连续油相进入微乳液界面层的标准自由能变化ΔGs0;标准焓变-ΔHs=0,为无热效应过程,ΔGs是由醇分子的混乱度熵变ΔSs决定的。     

SDS/正丁醇/正庚烷/水微乳液稳定性分析及应用

研究了十二烷基硫酸钠(SDS)/正丁醇/正庚烷/水(或氯化镁与硝酸铝混合水溶液或氢氧化钠溶液)四组分形成稳定微乳液的条件。考察了表面活性剂与助表面活性剂的质量比、温度、pH值、盐浓度对该体系稳定性的影响及水与表面活性剂的摩尔比(ωo)对水核粒径的影响。结果表明,m(SDS)∶m(正丁醇)=4∶6时,反相微乳液最稳定,对温度变化不敏感,pH值为7～13时,具有较好的稳定性,随着镁铝混合盐溶液浓度的增加,反相微乳区域急剧缩小,水核粒径随着ωo增大而增大,在稳定微乳液区域内制备了分布较均匀,尺寸范围30～70 nm的粒状纳米颗粒。     

R12TAB/苯甲醇/水体系混合胶束的微观结构研究

绘制了3-十二烷氧基-2-羟丙基三甲基溴化铵（R12TAB）／苯甲醇／水体系的三元相图，采用。HNMR方法研究了该体系胶束的微观结构，与电导法对照确定了W／O型胶束、O／W型胶束和油水双连续结构存在的区域，通过。HNMR谱图分析了苯甲醇在各胶束中的增溶位置。结果发现：苯甲醇主要增溶在胶束的栅栏层中，极性头靠近胶束界面，但由于不同胶束所处的微环境不同，苯甲醇沿烃链的分布也不相同。     

Micellar and Interfacial Behavior of Cationic Benzalkonium Chloride and Nonionic Polyoxyethylene Alkyl Ether Based Mixed Surfactant Systems

Micellar and interfacial properties of mixed surfactant systems comprising benzalkonium chloride, a cationic surfactant and nonionic polyoxyethylene alkyl ether surfactants (POE: C₁₀E₇, C₁₀E₈, C₁₀E₉, C₁₀E₁₀) have been investigated by surface tension, fluorescence and dynamic light scattering techniques. Critical micelle concentration (CMC) for different mixing mole fractions has been investigated by surface tension and fluorescence measurements. Ideal CMC, mixed micellar composition (X ₁ ^m , X ₁ ^σ ), interaction parameters for mixed micelles (β ^m) and adsorption monolayer (β ^σ ), surface excess concentration (Г_max), minimum area per molecule (A _min) and related thermodynamic properties have also been determined. Lowering of the CMC and negative interaction parameter values indicate synergism in the mixed micelle and monolayer formed, whereas, thermodynamic parameters evaluated for the proposed mixed systems indicate stability of the resulting micelles and monolayer. Micellar aggregation number (N _agg) and hydrodynamic diameter (D _h) computed from fluorescence and dynamic light scattering measurements respectively illustrate micellar growth in the mixed state. Results obtained for the proposed mixed systems can be helpful in designing smart materials for industrial surfactant based formulations.