Spacer effects in dimeric cationic surfactants

A series of dimeric cationic surfactants (gemini surfactants), which have spacer groups of varying length and flexibility, was synthesized. The series is derived from the parent compounds dodecyltrimethylammonium chloride or benzyldodecyldimethylammonium chloride. Characteristic surfactant properties of the dimeric ammonium compounds such as surface activity, micellization, viscosity effects, foaming, and solubilization, were studied with respect to the influence of the spacer group on the surfactant. For all properties, the influence of the length of the spacer group was predominant though the chemical nature of the spacer cannot be neglected.     

Dimeric and oligomeric surfactants. Behavior at interfaces and in aqueous solution: a review

Dimeric and oligomeric surfactants are novel surfactants that are presently attracting considerable interest in the academic and industrial communities working on surfactants. This paper first presents a number of chemical structures that have been reported for ionic, amphoteric and nonionic dimeric and oligomeric surfactants. The following aspects of these surfactants are then successively reviewed the state of dimeric and oligomeric surfactants in aqueous solutions at concentration below the critical micellization concentration (cmc); their behavior at the air/solution and solid/solution interfaces; their solubility in water, cmc and thermodynamics of micellization; the properties of the aqueous micelles of dimeric and oligomeric surfactants (ionization degree, size, shape, micropolarity and microviscosity, solution microstructure, solution rheology, micelle dynamics, micellar solubilization, interaction between dimeric surfactants and water-soluble polymers); the mixed micellization of dimeric surfactants with various conventional surfactants; the phase behavior of dimeric surfactants and the applications of these novel surfactants.     

Aggregation numbers of cationic oligomeric surfactants: a time-resolved fluorescence quenching study

The micelle aggregation numbers (N(agg)) of several series of cationic oligomeric surfactants were determined by time-resolved fluorescence quenching (TRFQ) experiments, using advantageously 9,10-dimethylanthracene as fluorophore. The study comprises six dimeric ("gemini"), three trimeric, and two tetrameric surfactants, which are quaternary ammonium chlorides, with medium length spacer groups (C(3)-C(6)) separating the individual surfactant fragments. Two standard cationic surfactants served as references. The number of hydrophobic chains making up a micellar core is relatively low for the oligomeric surfactants, the spacer length playing an important role. For the dimers, the number decreases from 32 to 21 with increasing spacer length. These numbers decrease further with increasing degree of oligomerization down to values of about 15. As for many conventional ionic surfactants, the micelles of all oligomers studied grow only slightly with the concentration, and they remain in the regime of small micelles up to concentrations of at least 3 wt %.     

Analysis of the Interactions of Polyvinylpyrrolidone with Conventional Anionic and Dimeric Anionic Surfactant

Classical physical method has been applied in the present study of interaction between water soluble polymer with anionic dimeric and conventional anionic surfactants. Micellization activity of carboxylate-based anionic dimeric (CAD) as well as sodium dodecyl sulfate (SDS) surfactants in the presence of nonionic polymer, that is, polyvinylpyrrolidone (PVP), has been studied through conductometric and surface tensiometric measurements. From these methods the critical aggregation concentrations (CACs), critical micelle concentrations (CMCs), and the effective degree of counterion binding (β) were determined. For the evaluation of behavior of CAD toward the PVP various thermodynamic properties viz. standard Gibbs energy of micellization, standard enthalpy, and entropy of micellization of CAD/PVP mixed system have also been estimated and discussed. The results exhibit that anionic dimeric surfactant interacts strongly with PVP as compared to conventional surfactant.     

Dimeric (gemini) surfactants: effect of the spacer group on the association behavior in aqueous solution

Dimeric (gemini) surfactants are made up of two amphiphilic moieties connected at the level of, or very close to, the head groups by a spacer group of varying nature: hydrophilic or hydrophobic, rigid or flexible. These surfactants represent a new class of surfactants that is finding its way into surfactant-based formulations. The nature of the spacer group (length, flexibility, chemical structure) has been shown to be of the utmost importance in determining the solution properties of aqueous dimeric surfactants. This paper reviews the effect of the nature of the spacer on some of these properties. The behavior of dimeric surfactants in the submicellar range of concentration, at interfaces, in dilute solution (solubility in water, Krafft temperature, critical micellization concentration, thermodynamics of micelle formation, micelle ionization degree, size, polydispersity, micropolarity and microviscosity, microstructure and rheology of the solutions, solubilization, micelle dynamics, and interaction with polymers) and in concentrated solution (phase behavior) are successively reviewed. Selected results concerning trimeric and tetrameric surfactants are also reviewed.     

Synthesis and physicochemical characterization of alkanedyil-α-ω-bis(dimethyldodecylammonium) bromide, 12-s-12,2Br(-), surfactants with s=7, 9, 11 in aqueous medium

In this work, three didodecyl dicationic dibromide dimeric surfactants 12-s-12,2Br(-), with different methylene spacer lengths (s=7, 9, and 11) were prepared and characterized and their properties compared to those of 12-s-12,2Br(-) surfactants with s=2, 3, 4, 5, 6, 8, 10, and 12. Information about the critical micelle concentration, the micellar ionization degree, the average aggregation number and the polarity of the interfacial region, and microviscosity of the micellar interior was obtained by using different techniques. Their surface activity was investigated by means of surface tension measurements. Micellization was also studied by using (1)H NMR and diffusion NMR (DOSY) spectroscopy as well as isothermal titration calorimetry. The values of the thermodynamic parameters show that the dimeric surfactants micellization is exothermic and driven by entropy. The occurrence of morphological transitions upon increasing surfactant concentration was studied, and the results indicate that the spacer length, s, plays a key role in the micellar growth of 12-s-12,2Br(-) aggregates. The value of s not only control the magnitude of C(*), the surfactant concentration above which the morphological transition from spherical micelles into elongated ones occurs, but also the sign of the enthalpy change accompanying the sphere-to-rod transition.     

New anionic gemini surfactant based on EDTA accessible by convenient synthesis

A straightforward, broadly applicable synthetic strategy to anionic dimeric (“gemini”) surfactants is demonstrated, reacting ethylenediamine tetraacetic acid (EDTA) dianhydride with fatty amines. Characteristic surfactant properties in water are examined for the model compound based on N-methyldodecylamine. The new dimeric surfactant exhibits a low value for the critical micellization concentration (cmc < 10⁻⁴ mM), low surface tension at the cmc, and an enhanced solubilization capacity in comparison with a monomeric reference surfactant, sodium laurate. In particular, solutions of the gemini surfactant are remarkably stable in hard water, compared to conventional carboxylate surfactants.     

Synthesis of New Dimeric Amphiphiles. Influence of Anomeric Configuration and Spacer Functionality on Interfacial Properties

ABSTRACT

The synthesis of new dimeric carbohydrate-based surfactants was performed connecting two butyl glucopyranosides with a spacer through ester and ether linkages. Critical micellar concentrations were determined to study the influence of anomeric configuration and spacer functionality on surfactant properties.     

Unique Micellization and CMC Aspects of Gemini Surfactant: An Overview

Critical micelle concentration (CMC) is an essential fundamental property of surfactant molecules, as the CMC value provides significant information regarding the surfactant for industrial use. The industrial efficacy of surfactant molecules totally depends on its CMC value. Without a complete perceptive approach of CMC, it is impractical to employ surfactant molecules efficiently. This article provides an elaborate discussion of dimeric gemini surfactant and pays particular attention to the aggregation behavior, that is, micelle formation, CMC, and thermodynamics of micellization. Micelles structures, packing parameters, and properties of the micelles are summarized. The principles and techniques involved in the determination of CMC are discussed. Thermodynamics of micellization of dimeric surfactants including free energy, enthalpy, and entropy is successively reviewed. Superiority of gemini surfactant in respect of their CMC values is interpreted.     

Linear solvation energy relationships of anionic dimeric surfactants in micellar electrokinetic chromatography I. Effect of the length of a hydrophobic spacer

The influence of the length of a flexible hydrophobic spacer on the selectivity of anionic dimeric surfactants was investigated. Disodium 1,omega-bis(decyloxymethyl)-dioxa alkane-1,omega disulfates with a spacer containing an ethylene, butylene, hexylene, octylene, decylene or dodecylene group were synthesized, and four of these were evaluated for use in micellar electrokinetic chromatography (MEKC) via linear solvation energy relationships (LSERs). There were no significant differences in the system constants of these surfactants, indicating that their micelles all have a very similar interface with the aqueous phase, regardless of the length of the hydrophobic spacer. Compared to sodium dodecylsulfate (SDS), these dimeric surfactants are slightly more cohesive, interact better with polarizable compounds, and are somewhat better hydrogen bond acceptors and worse hydrogen bond donors, while there is no difference in dipolarity. The critical micelle concentrations (CMCs) of these surfactants were in the order of 1mM, except for the dimeric surfactant with a spacer containing an ethylene group, which had a CMC <0.03 mM.     

Effect of the nature of the spacer on the aggregation properties of gemini surfactants in an aqueous solution

The aggregation properties of three dicationic quaternary ammonium gemini surfactants with the same structure, except the spacer group, diethyl ether, six methylene, and p-xylyl, have been studied using electrical conductivity and fluorescence. The critical micelle concentration (cmc) and the micelle aggregation number (N) were determined, and the micropolarity and the microviscosity of the micelle were characterized. The micelle ionization degree (alpha) was obtained by a combination of the electrical conductivity data and the micelle aggregation number. Furthermore, the Gibbs free energy of micellization (deltaGmic) was studied. These results have shown that the nature of the spacer has an important effect on the aggregation properties of gemini surfactants in an aqueous solution. A hydrophilic, flexible spacer prompts micelle formation, which leads to a smaller cmc, smaller alpha, larger N, and more negative deltaGmic. Meanwhile, the microviscosity study indicates that the gemini surfactant with a hydrophilic, flexible spacer forms a more closely packed micelle structure than the one with a hydrophobic, rigid spacer.     

易水解类表面活性剂的表面与胶团性质

对直链烷基羧酸盐与烷基氯化伯铵两类易水解型表面活性剂进行了较系统的研究,发现pH 值、温度、 盐浓度的变化对体系表面性质及胶团形成有较明显的影响.二类体系中相应水解产物的存在均可较大幅度地提高体系的表面活性,但pH 值在碱性范围内的变化仍对羧酸钠的表面性质与胶团形成有明显影响,而烷基氯化铵的表面性质与聚集能力在酸性条件下则主要受盐浓度的影响,而不受pH 值影响.表明这两类易水解体系产生的极性有机物对各自体系的表面性质和聚集能力影响力度不同.考察了温度对易水解类表面活性剂的影响,并利用相分离模型对相应体系的胶团形成热力学参数进行了计算与讨论.     

Synthesis and dilute aqueous solution properties of ester functionalized cationic gemini surfactants having different ethylene oxide units as spacer

New series of ester functionalized quaternary ammonium gemini surfactants having different ethylene oxide units as spacer have been synthesized and investigated for their aggregation behavior and thermodynamic properties of micellization by surface tension, conductivity, and fluorescence methods. The critical micelle concentration (cmc) of these gemini surfactants increases with the increase in the length of polar hydrophilic ethylene oxide spacer. The micellization process has been found to be entropy-driven and dependent on both the tendency of the hydrophobic group of the surfactants to transfer from aqueous environment to interior of micelle as well as the rearrangement of flexible ester-linked ethylene oxide units (hydrophilic spacer) into aqueous phase. The polar ester functional groups and pairs of nonbonding electrons on oxygen atom of ethylene oxide spacer form hydrogen bonding with water molecules enhancing their solubility in aqueous system.     

Linear solvation energy relationships of anionic dimeric surfactants in micellar electrokinetic chromatography II. Effect of the length of a hydrophilic spacer

Anionic dimeric surfactants with hydrophilic spacers containing two to six oxygen atoms were synthesized and applied as pseudostationary phases in micellar electrokinetic chromatography. Their selectivity was determined via linear solvation energy relationships. There were no differences in cohesiveness, polarizability or dipolarity with increasing spacer length, but there was a clear trend in increasing hydrogen bond accepting ability, and a concomitant decrease in hydrogen bond donating ability. The different selectivity of these dimeric surfactants compared to sodium dodecylsulfate can be useful for optimizing separations of mixtures of solutes for which these types of interactions are important. Their critical micelle concentrations were in the range of 0.2-0.3mM, except for the surfactant with the shortest spacer (<0.03 mM), and are much lower than those of conventional surfactants used in micellar electrokinetic chromatography.     

壬基酚聚氧乙烯醚二聚和三聚表面活性剂的合成及表面性质

合成了系列壬基酚聚氧乙烯醚二聚表面活性剂(DNP)和三聚表面活性剂(TNP), 用核磁共振、红外光谱和元素分析等手段对其结构进行了表征, 并用表面张力法和稳态荧光法对DNP和TNP的表面性能进行了研究. 结果表明, 随着氧乙烯(EO)单元数的增长, DNP和TNP的临界胶束浓度(cmc)值逐渐增大; DNP和TNP的cmc值较相应的单体壬基酚聚氧乙烯醚表面活性剂(NP)明显降低, 显示了较高的表面活性、吸附能力和润湿能力.     

Surface properties, aggregation behavior and micellization thermodynamics of a class of gemini surfactants with ethyl ammonium headgroups

Cationic gemini surfactant homologues alkanediyl-α,ω-bis(dodecyldiethylammonium bromide), [C(12)H(25)(CH(3)CH(2))(2)N(CH(2))(S)N(CH(2)CH(3))(2)C(12)H(25)]Br(2) (where S=2, 4, 6, 8, 10, 12, 16, 20), referred to as C(12)C(S)C(12)(Et) were synthesized systematically. This paper focused on various properties of the above gemini surfactants in order to give a full understanding of this series of surfactants. The following points are covered: (1) surface properties, which include (i) effect of the spacer carbon number on the general properties and (ii) the effect of added NaBr on the general surface properties; (2) aggregation behavior in bulk solution, including (i) morphologies of above gemini surfactants classed as having short spacers, middle-length spacers and long spacers and (ii) superior vesicle stability against high NaBr concentration for the long spacer gemini surfactants; (3) thermodynamic properties during micellization and the effect of spacer carbon number on them; and (4) perspectives for the further use and application of these compounds.     

甲酰胺与正负离子表面活性剂有序溶液的研究

对羧酸钠与烷基三甲基溴化铵1：1混合体系的研究表明：常温下各体系在不同比例甲酰胺（FA）／水混合溶剂中，表面张力随浓度变化均有明显的转折点，显示了混合体系中胶团的存在．实验中发现随混合溶剂中FA比例增加，各体系的临界胶团浓度（cmc）增大．在较高温度下发现在甲酰胺中亦存在着因胶团形成而产生的表面张力-浓度对数（γ－logc）曲线的转折点，利用相分离模型对体系胶团热力学参数进行了计算．并探讨了FA对正负离子表面活性剂囊泡的影响．     

Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants 9. Effect of the spacer carbon number and temperature on the enthalpy of micellization

The enthalpies of dilution of micellar solutions of several 12-s-12 dimeric surfactants of the alkanediyl-alpha,omega-bis(dodecyldi-methylammonium bromide) type, differing by the carbon number s of the alkanediyl spacer, and of dodecyltrimethylammonium bromide (DTAB) have been measured calorimetrically, in a range of concentrations extending from well below to well above the critical micelle concentration (cmc). The results permitted the determination of the enthalpy of micellization, DeltaH degrees (M), of the investigated surfactants at 25 and 35 degrees C. The values of DeltaH degrees (M) were always negative and became more negative as the temperature was increased. The plot of -DeltaH degrees (M) against s showed a shallow minimum at about s=5 and a large decrease of -DeltaH degrees (M) going from 12-2-12 to 12- 4-12. This effect has been attributed to the contribution to DeltaH degrees (M) of the hindered rotation of the dodecyl chains around the spacer C-C bond for 12-2-12. This hindrance is shown to rapidly disappear when s is increased from 2 to above 4. The specific heats of micellization, the free energies of micellization, and the entropies of micellization (DeltaS degrees (M)) have been calculated using the DeltaH degrees (M) values and the reported cmc and micelle ionization degree data for 12-s-12 surfactants and DTAB. For all surfactants the results show that TDeltaS degrees (M)>-DeltaH degrees (M), indicating an entropy-driven micellization.     

Micellization and adsorption of zwitterionic surfactants at the air/water interface

Zwitterionic surfactants are formally neutral but with headgroups containing both a positive charge center and a negative charge center separated from each other by a spacer group, with a long hydrophobic tail attached to one of the charge centers, usually but not always the positive charge center. The micellization and adsorption properties of zwitterionic surfactants depend on specifics of the surfactant structure such as the length m of the hydrophobic alkyl chain, the length n of the intercharge spacer and the nature of the headgroup charge centers. Micellization is favored by an increase in the hydrophobic tail length m, but goes through a maximum for interchange spacings of n = 3–4 methylene groups. There are additional effects from the presence of additional hydrophilic substituent groups in the spacer. Specific binding of anions and the cation valence of added electrolyte are factors that also modulate the micellization and adsorption properties of zwitterionic surfactants in the presence of added electrolyte. Anions in particular bind preferentially to zwitterionic micelles independent of the relative order of the charge centers in the headgroup. The anion binding affinities follow a Hofmeister series and impart a net negative charge to the micelles. Micellization is temperature-dependent and exhibits enthalpy-entropy compensation, with entropy dominant at lower temperatures and enthalpy more important at higher temperatures. The judicious manipulation of these factors permits control of the interfacial properties of zwitterionic surfactants, responsible for a wide range of applications in chromatography, electrophoresis, cloud point extraction, solubilization, stabilization of biomolecules and nanomaterials and catalysis.     

Micellization of dissymmetric cationic gemini surfactants and their interaction with dimyristoylphosphatidylcholine vesicles

The micellization process of a series of dissymmetric cationic gemini surfactants [CmH2m+1(CH3)2N(CH2)6N(CH3)2C6H13]Br2 (designated as m-6-6 with m = 12, 14, and 16) and their interaction with dimyristoylphosphatidylcholine (DMPC) vesicles have been investigated. In the micellization process of these gemini surfactants themselves, critical micelle concentration (cmc), micelle ionization degree, and enthalpies of micellization (DeltaHmic) were determined, from which Gibbs free energies of micellization (DeltaGmic) and entropy of micellization (DeltaSmic) were derived. These properties were found to be influenced significantly by the dissymmetry in the surfactant structures. The phase diagrams for the solubilization of DMPC vesicles by the gemini surfactants were constructed from calorimetric results combining with the results of turbidity and dynamic light scattering. The effective surfactant to lipid ratios in the mixed aggregates at saturation (Resat) and solubilization (Resol) were derived. For the solubilization of DMPC vesicles, symmetric 12-6-12 is more effective than corresponding single-chain surfactant DTAB, whereas the dissymmetric m-6-6 series are more effective than symmetric 12-6-12, and 16-6-6 is the most effective. The chain length mismatch between DMPC and the gemini surfactants may be responsible for the different Re values. The transfer enthalpy per mole of surfactant within the coexistence range may be associated with the total hydrophobicity of the alkyl chains of gemini surfactants. The transfer enthalpies of surfactant from micelles to bilayers are always endothermic due to the dehydration of headgroups and the disordering of lipid acyl chain packing during the vesicle solubilization.