Mixed micelles of polyethylene glycol (23) lauryl ether with ionic surfactants studied by proton 1D and 2D NMR

(1)H NMR chemical shift, spin-lattice relaxation time, spin-spin relaxation time, self-diffusion coefficient, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the nonionic-ionic surfactant mixed micelles. Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the ionic surfactants and polyethylene glycol (23) lauryl ether (Brij-35) as the nonionic surfactant. The two systems are both with varying molar ratios of CTAB/Brij-35 (C/B) and SDS/Brij-35 (S/B) ranging from 0.5 to 2, respectively, at a constant concentration of 6 mM for Brij-35 in aqueous solutions. Results give information about the relative arrangement of the surfactant molecules in the mixed micelles. In the former system, the trimethyl groups attached to the polar heads of the CTAB molecules are located between the first oxy-ethylene groups next to the hydrophobic chains of Brij-35 molecules. These oxy-ethylene groups gradually move outward from the hydrophobic core of the mixed micelle with an increase in C/B in the mixed solution. In contrast to the case of the CTAB/Triton X-100 system, the long flexible hydrophilic poly oxy-ethylene chains, which are in the exterior part of the mixed micelles, remain coiled, but looser, surrounding the hydrophobic core. There is almost no variation in conformation of the hydrophilic chains of Brij-35 molecules in the mixed micelles of the SDS/Brij-35 system as the S/B increases. The hydrophobic chains of both CTAB and SDS are co-aggregated with Brij-35, respectively, in their mixed micellar cores.     

Micellization and related behavior of binary and ternary surfactant mixtures in aqueous medium: cetyl pyridinium chloride (CPC), cetyl trimethyl ammonium bromide (CTAB), and polyoxyethylene (10) cetyl ether (Brij-56) derived system

Mixed micelles formed with cetyl pyridinium chloride (CPC), cetyl trimethylammonium bromide (CTAB), and polyoxyethylene (10) cetyl ether (Brij-56) mixed in different combinations in aqueous medium have been studied in detail by tensiometric, conductometric, calorimetric, spectrophotometric, and fluorimetric techniques. Different physicochemical properties such as critical micellar concentration (cmc), micellar dissociation, energetic parameters (free energy, enthalpy, and entropy) of micellization, interfacial adsorption, and micellar aggregation number have been determined. The results have been analyzed in terms of the equations of Clint, Motomura, Rosen, Rubingh, Blankschtein et al., and Rubingh and Holland for justification of the experimental cmc, determination of micellar composition parameters, quantification of interaction among the mixed micelle components, and estimation of their activity coefficients.     

表面活性剂胶束形状随浓度转变的核磁共振研究

运用核磁共振一维氢谱和自扩散实验方法研究了聚乙烯乙二醇异辛酚醚(TX-100)、十二烷基苯磺酸钠(SDBS)和十四烷基三甲基溴化铵(TTAB)三种不同类型的表面活性剂在重水溶液中的胶束形状转变, 发现它们在临界胶束浓度以上的各自相应浓度都有胶束形状的变化(由球状转变为椭球状或棒状). 在常温常压和没有其他添加剂的情况下, 表面活性剂溶液浓度高于其临界胶束浓度时, 球状胶束开始形成. 核磁共振一维氢谱和自扩散实验的结果显示, 当溶液浓度继续增加到一定程度时, 溶液中表面活性剂分子的化学位移和自扩散系数的变化速率都有明显的转折, 这说明溶液中球状胶束开始发生转变. 进一步通过仔细分析对比核磁共振一维氢谱中各基团谱峰, 发现表面活性剂胶束亲水表面上的质子的化学位移变化速率要远高于其疏水内核中的质子, 据此推测胶束形状很可能由球状转变为椭球状或棒状.     

Mechanism of surfactant micelle formation

The mechanism of micelle formation of surfactants sodium dodecyl sulfate (SDS), n-hexyldecyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) in heavy water solutions was studied by 1H NMR (chemical shift and line shape) and NMR self-diffusion experiments. 1H NMR and self-diffusion experiments of these three surfactants show that their chemical shifts (delta) begin to change and resonance peaks begins to broaden with the increase in concentration significantly below their critical micelle concentrations (cmc's). At the same time, self-diffusion coefficients ( D) of the surfactant molecules decrease simultaneously as their concentrations increase. These indicate that when the concentrations are near and lower than their cmc's, there are oligomers (premicelles) formed in these three surfactant systems. Carefully examining the dependence of chemical shift and self-diffusion coefficient on concentration in the region just slightly above their cmc's, one finds that the pseudophase transition model is not applicable to the variation of physical properties (chemical shift and self-diffusion coefficient) with concentration of these systems. This indicates that premicelles still exist in this concentration region along with the formation of micelles. The curved dependence of chemical shift and self-diffusion coefficient on the increase in concentration suggests that the premicelles grow as the concentration increases until a definite value when the size of the premicelle reaches that of the micelle, i.e., the system is likely dominated by the monomers and micelles. Additionally, the approximate values of premicelle coming forth concentration (pmc) and cmc were obtained by again fitting chemical shifts to reciprocals of concentrations at a different perspective, and are in good accordant with experimental results and literature values and prove the former conclusion.     

阳离子表面活性剂混合胶团对2,4-二硝基氯苯水解反应的 催化作用

研究了阳离子表面活性剂混合胶团对2,4-二硝基氯苯(DNCB)碱性水解反应的催化作用。结果表明：(1)在十六烷基三甲基溴化铵(CTAB)和十六烷基溴化吡啶(CPB)混合溶液中DNCB水解一级速率常数k1与混合胶团中CTAB或CPB的摩尔分数有直线关系,表面活性剂形成理想的混合胶团。(2)辛基三甲基省化铵(OTAB)与CTAB,CPB的cmc值相差很大,在它们的混合胶团中OTAB含量极少,DNCB水解k1与CPB/OTAB混合胶团中CPB摩尔分数的关系与直线呈负偏差。(3)在CTAB(或CPB)与OTAB混合体系中OTAB起溴盐作用,使催化活性降低。用假相离子交换(PIE)模型对所得结果给出了定量的处理和解释。     

Investigation on the mixed micellar systems of cationic surfactants with propylene glycol and its oligomers

The effects of the addition of several propylene glycol oligomer additives on the micellar properties of the cationic mixed micelle system of cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) were investigated. Through conductivity studies, the critical micelle concentration (cmc) and counter-ion binding values were observed in the presence of the additives. A regular solution approach was employed to determine the effects of the additives on the interactions between the two surfactants to form the mixed micelles. The effects of the additives on the interaction parameter and the composition of the mixed micelles were evaluated. Excess Gibbs energy of mixing and the values of activity coefficients were also calculated and described in terms of non-ideality of the system.     

Micellization and catalytic activity of the cetyltrimethylammonium bromide-Brij 97-water mixed micellar system

Surface tension measurements and the kinetic study of the basic hydrolysis of ethyl p-nitrophenyl chloromethyl phosphonate were used to examine the structural behavior and catalytic activity of the cethyltrimethylammonium bromide (CTAB)-polyoxyethylene (10) oleyl ether, C(18)H(35)(OCH(2)CH(2))(10)OH (Brij 97)-water mixed micellar system. Application of the regular solution model to the experimental data yields the value of the interaction parameter beta as -4.6, which indicates an attractive interaction of the surfactants in the mixed micelle and reflects synergistic solution behavior of the mixture. The mixed micellar composition is found to be enriched in the surfactant with the lower critical micelle concentration (cmc). In the kinetic study a nonmonotonic change in the pseudo-first-order rate constant of basic hydrolysis of the substrate is observed with increasing mole fraction of nonionic surfactant. The pseudophase micellar model reveals that the concentration factor mainly contributes to the catalytic effect, while the microenvironmental factor plays a negative role.     

Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

Abnormal micellar growth in sugar-based and ethoxylated nonionic surfactants and their mixtures in dilute regimes using analytical ultracentrifugation

To develop structure-property relationships for surfactants that control their adsorption, solubilization, and micellization behavior in mixed systems and to develop predictive models based on such relationships, it is necessary to acquire quantitative information on various species present in these complex systems. The analytical ultracentrifugation technique is selected for the first time to characterize the species present in mixed micellar solutions due to its powerful ability to separate particles on the basis of their size and shape. Two nonionic surfactants, n-dodecyl-beta-D-maltoside (DM) and nonyl phenol ethoxylated decyl ether (NP-10), and their 1:1 molar ratio mixture were investigated in this study. Micelles of the nonionic surfactants and their mixture are asymmetrical in shape at the critical micelle concentration (cmc). Interestingly, unlike ionic surfactants, the micellar growths of the nonionic surfactants were found to occur at concentrations immediately above the cmc. The results from both sedimentation velocity and sedimentation equilibrium experiments suggest coexistence of two types of micelles in nonyl phenol ethoxylated decyl ether solutions and in its mixture with n-dodecyl-beta-D-maltoside, while only one micellar species is present in n-dodecyl-beta-D-maltoside solutions. Type 1 micelles were primary micelles at the cmc, while type 2 micelles were elongated micelles. The differences in the micellar shapes of n-dodecyl-beta-D-maltoside and nonyl phenol ethoxylated decyl ether are attributed to packing parameters detected by their molecular structures.     

Conformation and dynamics of polyoxyethylene lauryl ether (Brij-35) chains in aqueous micellar solution studied by 2D NOESY and 1H NMR relaxation

Spin-lattice relaxation time, spin-spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY) experiments of polyoxyethylene lauryl ether (Brij-35) micelles in aqueous solutions at a concentration of 100 times the critical micellar concentration (cmc) give direct evidence that the hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, are coiled, bent and aligned around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. 1H NMR relaxation time measurements show that the first oxyethylene group next to the alkyl chain participates in the formation of the surface area of the micellar core. The motion of the hydrophilic polyoxyethylene chains is less restricted as compared with the hy-drophobic alkyl chains.     

Inclusion complexes between beta-cyclodextrin and a Gemini surfactant in aqueous solution: an NMR study

(1)H NMR spectra, diffusion-ordered NMR (DOSY), and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY) experiments for aqueous solutions at 298 K containing the gemini surfactant, bis (dodecyl dimethylammonium)diethyl ether dibromide (12-EO(1)-12), in the absence and presence of beta-cyclodextrin (beta-CD) were used to characterize the surfactant and to determine the effects of the complexation in the micellization. For the binary system, the critical micelle concentration (cmc), the aggregation number, the stepwise micellization constant, and the size of the monomer have been obtained by studying the dependence of the chemical shifts and the self-diffusion coefficients with the concentration of surfactant. For the ternary system, the analysis of the (1)H NMR spectra and the self-diffusion coefficients reveal the formation of complexes of 1:1 and 2:1 stoichiometry (beta-CD:gemini), with a calculated stability constant for the second binding step higher than that of the first. The values of the hydrodynamic radii of the complexes were obtained from the calculated diffusion coefficients. The presence of beta-CD modifies the cmc in an extension that indicates mainly the formation of a 2:1 complex. The analysis of the chemical shifts of the surfactant indicates the nonparticipation of the complexes into the micelles. ROE enhancements depend substantially on the amount of the macrocycle added and therefore on the stoichiometry; at low concentrations of beta-CD, one of the hydrocarbon chains binds favorably with the cavity whereas the other interacts with the outer face. By contrast, at higher concentrations of beta-CD, the two hydrocarbon tails are included in two different macrocycles.     

Diffusion Coefficients of Three Organic Solutes in Aqueous Sodium Dodecyl Sulfate Solutions

Tracer diffusion coefficients of phenol, toluene, and benzoic acid in aqueous solutions of sodium dodecyl sulfate (SDS) were measured by the Taylor dispersion technique. In addition, the viscosities and densities of the SDS solutions were measured. For phenol and toluene, the effect of micelle formation on the diffusion coefficient is pronounced. When the SDS concentration is below the critical micelle concentration (cmc), the diffusion coefficients are almost independent of the SDS concentration. However, above the cmc there is a rapid decrease in the diffusion coefficients, and the apparent diffusion coefficients of the two solutes are the weighted average of free solute diffusion and the micelle diffusion. A model is presented to describe the diffusion behavior of the two solutes in aqueous micellar solutions of SDS. The interaction between the two solutes and the micelles has been investigated and the fraction of each solute that is solubilized by the micelles is estimated from the measured apparent diffusion coefficient. For benzoic acid, the diffusion coefficient is dependent on the joint contribution of the benzoic acid molecules that are solubilized by the micelles as well as the corresponding benzoate ions. The effect of micelle formation on the diffusion coefficient of benzoic acid is not as pronounced as for phenol and toluene. Copyright 2000 Academic Press.     

Interfacial and aggregation properties of the binary mixture of decanoyl-N-methyl-glucamide and hexadecyltriphenylphosphonium bromide

The interfacial and aggregation behavior of the nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) with the cationic surfactant hexadecyltriphenylphosphonium bromide (HTPB) have been studied using interfacial tension measurements and fluorescence techniques. From interfacial tension measurements, the critical micellar concentrations (cmc) and various interfacial thermodynamic parameters have been evaluated. The experimental results were analyzed in the context of the pseudophase separation model, the regular solution theory, and the Maeda’s approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTPB+Mega-10 were obtained. It was found that that the aggregation number decreases with increasing mole fraction of HTPB. This behavior is attributed to the presence of the bulky head group of HTPB, which creates steric head group incompatibility and/or electrostatic repulsion. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio. It was observed that the increasing participation of HTPB induces the formation of micelles with a hydrated structure. The polarization of the fluorescent probe Rhodamine B was monitored in micellar medium and found to increase with the increase of ionic content. This behavior suggests the formation of mixed micelles with a more ordered or rigid structure.     

头孢唑酮对CTAB胶束结构特性的影响

应用电导法和荧光法测定了头孢唑酮对阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）胶束第一cmc1、第二cmc2、胶束聚集数及体系粘度的影响,测定了头孢唑酮在CTAB胶束中的分配系数.结果表明,头孢唑酮的加入使得CTAB胶束的第一cmc和第二cmc均上升,胶束的聚集数和体系的粘度降低.上述结果与头孢唑酮和CTAB分子的相互作用及其在CTAB胶束相和水连续相的分配有关.     

Conformation and dynamics of polyoxyethylene lauryl ether (Brij- 35) chains in aqueous micellar solution studied by 2D NOESY and <Superscript>1</Superscript>H NMR relaxation

Spin-lattice relaxation time, spin-spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY) experiments of polyoxyethylene lauryl ether (Brij-35) micelles in aqueous solutions at a concentration of 100 times the critical micellar concentration (cmc) give direct evidence that the hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, are coiled, bent and aligned around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. ¹H NMR relaxation time measurements show that the first oxyethylene group next to the alkyl chain participates in the formation of the surface area of the micellar core. The motion of the hydrophilic polyoxyethylene chains is less restricted as compared with the hydrophobic alkyl chains.     

Conductometric and fluorometric investigations on the mixed micellar systems of cationic surfactants in aqueous media

Micellar properties of binary mixtures of hexadecyldiethylethanolammonium bromide surfactant with tetradecyldimethylammonium, trimethylammonium, triphenylphosphonium, diethylethanolammonium, and pyridinium bromide surfactants have been characterized employing conductometric and fluorescence techniques. The critical micelle concentration (cmc*) and the degree of counter-ion binding values (delta) of the binary systems were determined from the conductivity measurements. The results were analyzed in light of various existing theories to calculate micellar composition, activity coefficients, and the interaction parameter (beta). Partial contribution of each surfactant, cmc1*, cmc2*, to the overall cmc* value was also evaluated. Aggregation numbers and micropolarity of the mixed micelles were determined from fluorescence measurements. The results were discussed in terms of synergetic interactions in these systems on the basis of the head group/head group and tail/tail interactions and the counter-ion binding.     

Self-assembly of symmetrical and dissymmetrical dicationic surfactants in the solid phase and in solution

The effect of the spacer structure (linear, cyclic, bicyclic) and dissymmetry of alkyl fragment in a series of dicationic gemini surfactants on the ability to form thermotropic liquid crystals and on the micellar properties was studied. Transitions crystal-thermotropic liquid crystals-isotropic solution were studied using differential scanning calorimetry and optical microscopy. The self-diffusion coefficients of micelles and monomers of the dicationic dialkyl derivatives of 1,4-diazabicyclo[2.2.2]octane in water were determined by pulsed field gradient NMR spectroscopy. The effect of the surfactant structure on the values of critical micelle concentrations, hydrodynamic radii, and aggregation numbers of micelles was analyzed.     

Interactions Between the Cationic Surfactants Bearing Different Polar Head Groups: Interfacial,Conductivity, NMR,and Fluorescence Studies

Interfacial tension (γ), conductivity (κ), nuclear magnetic resonance (NMR), and fluorescence measurements have been carried out to study the mixed interfacial and micellar behavior of cationic surfactants cetyltributylphosphonium bromide (CTBB) and the cetyltrimethylammonium bromide (CTAB). From the γ versus log C _s plots, the values of critical micellar concentration (cmc) and various interfacial parameters were computed. From κ measurements, the equivalent conductivities of the monomers (Λ _mon), the micelles (Λ _mic) states and the degree of counterion dissociation (δ) have been evaluated. The cmc values have been analyzed in the context of the pseudophase separation model and regular solution theory. The interaction parameters, β^m and β^σ, in the mixed micelle as well as in the mixed monolayer, respectively, also have been computed. The self‐diffusion coefficients for the micelles have been evaluated by using NMR spectroscopy. From the fluorescence quenching method, the mean micellar aggregation number (N _agg) of the pure and mixed micelles has been obtained from the slope of the ratio of fluorescence intensities in the absence and in the presence of quencher (ln (I _1,0/I ₁) versus [Q] plots. It was found that the incorporation of CTBB into the mixed micelle decreases the N _agg. The microviscosity of the fluorescence probe Rhodamine (RB) was monitored by using fluorescence polarization measurements. The values of fluorescence anisotropies (r) indicate that the penetration of CTBB monomer into CTAB micelles produced less rigid mixed micelles.     

Interaction in Binary Mixtures of Gemini Surfactant G12-6-12 and CTAB by NMR

The interaction between N, N′-bis（dimethyldodecyl）-1,6-hexanediammoniumdibromide （G12-6-12） and cetyltrimethylammonium bromide （CTAB） in D20 aqueous medium has been investigated by NMR at 298 K. The G12-6-12 and CTAB are about 0.773 and measured critical micelle concentration （cmc） of 0.668 mmol/L, respectively. The cmc^＊ （cmc of mixture） values are less than CMC^＊ （cmc of ideally mixed solution） in the mixed system, and the interaction parameter βM〈0 at different molar fractions α of G12-6-12 in the mixed systems, but just when α≤0.3, cmc^＊ values are much smaller than CMC^＊, and βM satisfies the relation of ｜βM｜〉｜ln（cmc1/cmc2）｜ （cmcl： cmc of pure G12-6-12 and cmc2： cmc Of pure CTAB）. The results indicate that there exists synergism between G12-6-12 and CTAB, and they can form mixed micelles, which is further proven by 2D NOESY and self-diffusion coefficient D experiments. There are intermolecular cross peaks between G12-6-12 and CTAB in 2D NOESY, and the radius of micelles in mixed solution is bigger than that in G12-6-12 pure solution in D experiments, indicating there are mixed micelles. However, when α〉0.3, we find that cmc^＊≈CMC^＊, βM≈0, obviously, the two surfactants are almost ideal mixing fitting the pseudo-phase separation model and regular solution theory.     

Micellisation behaviour of mixtures of sodium dodecylsulphate and sodium lauroylsarcosinate in water

The critical micelle concentrations of binary mixtures of sodium dodecylsulphate (SDS) and sodium lauroylsarcosinate (SLAS) have been determined in water by conductivity measurements at different mole fractions for each of the components. The critical micelle concentrations were slightly lower than that predicted from ideal mixing theory indicating positive synergistic interactions in mixed micelle formation. The results of the mixed systems were analysed using the Regular Solution Theory and the approach based on the Gibbs–Duhem equation which allowed for the determination of the composition of the mixed micelle, the activity coefficients and the pair-wise molecular interaction parameter β. The β values were all negative at all mole fractions investigated, showing a slight deviation from ideality, with an average value of –0.27. The excess free energy of the mixed systems was also calculated and the values were all negative for the mixed systems studied, an indication that the mixed micelles are thermodynamically stable relative to the individual component. This thermodynamic parameter also exhibits symmetrical behaviour with respect to micellar composition suggestive of a regular solution behaviour of the mixed surfactant system.