Pulsed field gradient NMR investigation of solubilization equilibria in amino acid and dipeptide terminated micellar and polymeric surfactant solutions

Pulsed field gradient NMR spectroscopy was used to investigate the association of toluene, chlorobenzene and benzyl alcohol with amino acid and dipeptide terminated polymerized surfactants (PS). The diffusion coefficient for each probe was measured in the presence and absence of the polymers and the mole fraction of bound probe molecules, f_b, was calculated. For all solutions investigated, the probes associated more strongly with unpolymerized surfactant micelles than with corresponding PS. For example, the toluene f_b values for association with sodium undecanoyl valinate micelles and the PS poly(sodium undecanoyl valinate) were 0.88 and 0.15, respectively. The relatively weak probe–polymer association was attributed to the polarity and fluidity of the polymers' hydrocarbon cores and to the fact that these PS have smaller aggregation numbers than the corresponding unpolymerized surfactant micelles. Copyright © 2002 John Wiley & Sons, Ltd.     

Role of alcohol in microemulsions as determined from volume and heat capacity data for the water-sodium dodecylsulfate -n-butanol system at 25°C

Densities and heat capacities of the ternary system water-sodium dodecylsulfate — n-butanol were measured at 25°C over the complete alcohol mole-fraction or solubility range. Apparent and partial molar volumes and heat capacities of n-butanol were derived and have been analyzed as a function of the concentration of both the surfactant and the alcohol. Characteristic changes suggest that, at low concentrations, n-butanol is partially solubilized in mixed micelles but, in concentrated alcohol solutions, n-butanol largely exists in the form of microaggregates stabilized by the surfactant. Results would also suggest that at low concentrations of n-butanol another transition zone occurs in the micellar structure around 0.2–0.3 mol-kg^–1 in sodium dodecylsulfate.     

Ultrafiltration of sodium dodecylsulfate solutions

The present paper is devoted to ultrafiltration (UF) of aqueous solutions containing micellized sodium dodecylsulfate (NaDS) through zircon membranes, following permeation data of cetyltrimethylammonium bromide (CTABr), which we have reported recently.The experimental results are analyzed using the same model of diffusion in the membrane matrix based on the thermodynamics of irreversible processes (TIP). A comparison with the classical model of resistances in series leads to a new analysis of the measured resistances in terms of membrane–permeant and permeant–permeant interactions. NaDS micelles being able to cross the membrane as permeants, in contrast with CTABr micelles, the comparison of the behaviors of anionic and cationic surfactants is worthwhile. The resistance of the membrane strongly depends on the composition of the feed. The TIP approach allows us to relate the membrane resistance to the concentrations of all the species present in the feed, namely free ions, spherical micelles and rod-like aggregates. It is shown that the resistance is highly influenced by free ions (dodecylsulfate (DS⁻) and sodium (Na⁺)), very slightly by negatively charged spherical micelles, and weakly by rod-like aggregates, also negatively charged.     

Effect of Temperature on the Binding and Distribution Characteristics of Thionine in Sodium Dodecylsulfate Micelles

The interaction between thionine (a cationic thiazine dye) and anionic surfactant sodium dodecylsulfate in aqueous solution at different temperatures has been studied spectrophotometrically. The absorption spectra were used to quantify the dye/surfactant binding constants and surfactant/water partition coefficients of the dye by applying mathematical models that consider partitioning of the dye between the micellar and aqueous pseudo-phases. The Benesi-Hildebrand equation was applied to calculate the binding constants of thionine to sodium dodecylsulfate micelles over a temperature range of 293 to 333 K. To evaluate the thermodynamic aspects of the interaction of thionine with sodium dodecylsulfate micelles, Gibbs energy, enthalpy and entropy changes were determined. The effect of temperature on the critical micelle concentration of sodium dodecylsulfate in the presence of thionine was also studied and discussed. The binding affinity of thionine to the sodium dodecylsulfate micelles significantly decreased with increasing temperature because of the thermal agitation.     

Triton X-100/n-C~4H~9OH/H~2O体系的扩散系数与结构特性

在无外加探针条件下用循环伏安法测定了不同形状TritonX-100胶束的扩散系数,得到第一cmc(临界胶束浓度)为3.1×10^-^4mol.L^-^1,第二cmc为1.3×10^-^3mol.L^-^1,并给出了TritonX-100的电化学反应机理。随正丁醇含量的增加,TritonX-100球形胶束的扩散系数迅速增加,正丁醇的增溶分数略有降低,但胶束内微极性却降低较多;棒状胶束转变为球形胶束,正丁醇的增溶分数基本不变,但胶束内微极性降低。随温度升高,TritonX-100分子与胶束的扩散系数均增加。正丁醇含量<1.5%时,扩散活化能E~D随正丁醇含量增加而迅速增加;但正丁醇含量>1.5%时,E~D增加变缓。     

Aggregation number of aqueous sodium cholate micelles from mutual diffusion measurements

With reported values ranging from about 3 to 16, the aggregation number of aqueous sodium cholate micelles is not well established. To provide new information on the aggregation of a bile salt, Taylor dispersion is used to measure the binary mutual diffusion coefficientD of aqueous sodium cholate at concentrations from 0.001 to 0.100 mol-dm^-3 at 25°C. The results are compared with calculatedD values based on the association equilibrium nCholate^- + βnNa⁺ ⇋ (NaβCholate) _n ^(β-1)n wheren is the aggregation number and β is the degree of sodium counterion binding. Fitting the association model to the diffusion data givesn = 3.9±0.6 and β = 0.21 ±0.08. In contrast to the drop inD with increasing concentration of sodium cholate, the diffusion coefficients of sodium dodecylsulfate and other long-chain ionic surfactants increase above the critical micelle region. The ent diffusion behavior of the surfactants is related to changes in the driving forces and mobilities caused by ion association.     

Microemulsions studies: Correlation between viscosity,electrical conductivity and electrochemical and fluorescent probe measurements

Microemulsion systems involving brine and dodecane, and stabilized by sodium dodecylsulfate and both pentanol and heptanol have been investigated. Results of various experiments including conductivity and viscosity measurements, electrochemical diffusion coefficients and fluorescent probe studies have been gathered and compared in order to gain additional understanding of the microemulsion structure. The diffusion coefficients of hydrophilic hydroquinone and hydrophobic ferrocene obtained from the Levich equation at the rotating disc electrode, vary as the self-diffusion coefficients of water and dodecane, respectively; the results are consistent with those obtained by other workers from tracer or NMR self-diffusion studies. The fluorescence analysis of the polarity sensed by pyrene and the microviscosity felt by dipyrenylpropane suggests that the progressive addition of pentanol and dodecane to SDS micelles leads to solubilizate the probes more in the droplet interior where they experience a more hydrophobic environment. The systematic study of the two microemulsion systems provides insight into the microscopic properties of the oil domains in which the fluorescent probes are assumed to be located. In the system stabilized by n-heptanol as cosurfactant, the microviscosity sensed by P(CH₂)₃P is shown to be much lower than the bulk viscosity of the microemulsion. All the results evidence the well-known structural transitions: water continuous, bicontinuous and oil continuous in the single monophasic area of the brine/ SDS/n-pentanol/dodecane system; premicellar aggregates and water swollen micelles in the W/O area of the brine/SDS/n-heptanol/dodecane system.     

Micelle and Solvent Relaxation in Aqueous Sodium Dodecylsulfate Solutions

Dielectric spectra have been measured for aqueous sodium dodecylsulfate (SDS) solutions up to 0.1 mol L^?1 at 25 °C over the frequency range 0.005≤ν GHz^?1≤89. The spectra exhibit two relaxation processes at approximately 0.03 GHz and 0.2 GHz associated with the presence of micelles in addition to the dominant solvent relaxation process at approximately 18 GHz and a small contribution at approximately 1.8 GHz due to H₂O molecules hydrating the micelles. Detailed analysis reveals that the micelles bind 20 water molecules per SDS unit, but not as strongly as trimethylalkylammonium halide surfactants do. The relaxation times and amplitudes of both micelle relaxation processes can be simultaneously analysed with the theory of Grosse, yielding the effective volume of a SDS unit in the micelle and the lateral diffusion coefficient of the bound counterions. The findings of this investigation fully corroborate recent molecular dynamics simulations on structure and dynamics of SDS micelles.     

Effect of NaOH and NaCl on the disodiumn-decane phosphonate micellar aggregation number

The diffusion coefficient of disodiumn-decane phosphonate micelles was studied by polarography at 25°C in NaCl and in NaOH solutions, and the size and aggregation number of the micelles was computed as a function of Na⁺ concentration. All other conditions being equal, the addition of NaCl produces micelles with an aggregation number one order of magnitude larger than the NaOH addition. This is due to the increase of the effective charge per micellized head group produced by the reaction of OH- with the hydrolized head groups which are mainly present as-PO₃H- in the micellar Stern layer.     

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.     

Electrostatic contribution to the interaction of α, β poly (N-hydroxyethyl)-DL-aspartamide with sodium dodecylsulfate micelles

The enthalpic effect due to the interaction between α, β poly(N-hydroxyethyl)-DL-aspartamide (PHEA) and sodium dodecylsulfate (SDS) in aqueous solutions as a function of the surfactant concentration was measured by the calorimetric technique at various NaCl concentrations. A marked influence of the added electrolyte on the PHEA-SDS interaction was observed. An analysis of the experimental enthalpies allows to estimate the electrostatic and the hydrophobic contributions to the enthalpy of interaction between PHEA and SDS micelles. The results were rationalized in terms of effects due to the screening of the charges residing on PHEA and SDS micelles.     

Fluorescence in microemulsions and reversed micelles : A Review and New Results

The use of fluorescence to study physicochemical structures of alcohol/surfactant/water systems, microemulsions and reversed micelles is reviewed, and the application of these media in analytical fluorescence spectroscopy is discussed. The sodium dodecylsulfate/1-pentanol/heptane/ water system is studied by using pseudo-ternary diagrams. Wide areas of existence of thermodynamically stable and optically clear phases (Winsor IV and two liquid crystals) were found both in the absence and presence of sodium sulfate (0.2 M). The influence of the composition of media on the fluorescence characteristics of pyrene, benzo [e]pyrene, 2-naphthol and p-amino-benzoic acid is studied.     

Solubilization of methane,ethane, propane andn-butane in aqueous solutions of sodium dodecylsulfate

The solubilities of methane, ethane, propane, and n-butane were measured in aqueous solutions of sodium dodecylsulfate (NaDS) (0–0.1M) from 15 to 27°C. From these measurements the standard Gibbs energies, entropies, and enthalpies for the process of transferring the solute molecules from the gaseous phase into the solutions were calculated. An approximate relationship was found relating the volume fraction of the micelles to NaDS concentration.     

Tracer diffusion in fluctuating block copolymer melts

We present a theoretical investigation of the tracer diffusion of diblock copolymers and homopolymers in a thermally fluctuating block copolymer melt above the order-disorder transition (ODT) temperature. Entanglement effects and differences in monomeric friction coefficients are ignored; hence, the theory should be most applicable to short copolymers with rheologically similar blocks. Overall, we find that the diffusion rates of both tracer block copolymers and homopolymers in a block copolymer melt are suppressed when compared with diffusivities in a strictly homogeneous medium with the same average composition. This mobility suppression is due to thermally excited composition fluctuations in block copolymer melts near the ODT; the latter result in transient potential barriers to diffusion. We explore the dependence of the tracer diffusion coefficient on molecular weights and compositions of both matrix and tracer, as well as temperature. A comparison of our theoretical predictions to recent experiments by T. Lodge and coworkers shows qualitative agreement. © 1996 John Wiley & Sons, Inc.     

Counter ion condensation on mixed cationic/nonionic micellar systems: Bjerrum's electrostatic condition

The association of counter-ions with mixed ionic/nonionic micelles has been investigated in the case of dodecyl/tetradecyl/ and hexadecyl-trimethylammonium bromide with two nonionic surfactants: dodecylpolyoxyethylene 23 and Triton X-100. The degree of association has been measured by potentiometry using a Bromide ion-selective electrode. Previous results with sodium and copper dodecylsulfate suggesting that in the nonionic-rich composition domain, bare mixed micelles are formed without associated counter-ions have been confirmed. These results are in agreement with the prediction of Bjerrum's condition for ion association. The effect of copper dodecylsulfate on the cloud point of Triton X-100 has also been determined as a means of investigating mixed micelles with multivalent counter-ions. The dramatic cloud point increase observed, even larger than with sodium dodecylsulfate, has been discussed as evidence of the solvation of divalent ions by ether groups, a factor which complicates the analysis of multivalent counterion condensation on mixed micelles.     

Monomer exchange kinetics, radial diffusion, and hydrocarbon chain isomerization of sodium dodecylsulfate micelles in water

Molecular relaxation properties of sodium dodecylsulfate in aqueous solutions with surfactant concentrations between 0.009 and 0.4 mol/L have been studied using broadband ultrasonic spectrometry in the frequency range 0.1-2000 MHz. Ultrasonic excess attenuation characteristics were found that could be well represented by a sum of three relaxation terms, each one characterized by a discrete relaxation time. The low-frequency term with concentration-dependent relaxation time, tau1, between 0.06 and 3.5 micros is discussed in terms of the surfactant monomer exchange. The noticeable effect from the incomplete dissociation of the surfactant counter ions and the variation of the monomer concentration following thereby is discussed. The second relaxation term (0.9 相似文献   

Preconcentration and fluorimetric determination of polycyclic aromatic hydrocarbons based on the acid-induced cloud-point extraction with sodium dodecylsulfate

The acid-induced cloud-point extraction (CPE) technique based on sodium dodecylsulfate (SDS) micelles has been used for preconcentration of ten representatives of polycyclic aromatic hydrocarbons (PAHs) for the following fluorescence determination. The effect of the acidity of solution, SDS and electrolyte concentrations, centrifugation time and rate on the two-phase separation process and extraction percentages of PAHs have systematically been examined. Extraction percentages have been obtained for all PAHs after CPE ranged from 67 to 93%. Pyrene was used as a fluorescent probe to monitor the micropolarity of the surfactant-rich phase compared with SDS micelles and this allows one to conclude that water content in micellar phase after CPE is reduced. The spectral, metrological and analytical characteristics of PAH fluorimetric determination after acid-based CPE with sodium dodecylsulfate are presented. Advantages provided by using CPE in combination with fluorimetric determination of PAHs are discussed. The determination of benz[a]pyrene in tap water is presented as an example.     

Partition equilibria of phenols between water and anionic micelles : Correlation with the Octanol/Water System

The partition equilibria of a series of thirty substituted phenols bearing different chemical groups between aqueous solutions and sodium dodecylsulfate micelles was investigated by using micellar high-performance liquid chromatography and by studying the variation of the acidity constant. The contribution of each substituent to the free energy of transfer from water to micelles was estimated. The group contribution approach is shown to be valid for polysubstituted compounds under well defined conditions. A comparison with partition coefficients obtained in classical two-phase system (1-octanol/water), frequently used as biochemical model systems, is discussed     

Tracer diffusion properties of core–shell latex films studied by photoinduced grating relaxation

This article reports the application of the Photo‐Induced Grating Relaxation technique (also known as Forced Rayleigh Scattering) to investigate the dynamics of films prepared from structured core–shell latex particles via the transport property of the photochromic tracer molecule Aberchrome 540®. The core–shell particles were prepared with a fluoropolymer core (immiscible and impenetrable to the tracer) and a poly(butyl methacrylate) shell. The incompletely dried films (with residual water) manifest their spatial heterogeneity via non‐Fickian behavior (spatial scale‐ dependent apparent diffusion coefficient). The diffusion data was interpreted using the two‐state diffusion model, previously developed to describe the tracer diffusion in latex films without any core–shell structure. In contrast to dry latex films made from homogeneous particles, where one observes Fickian diffusion indicative of a homogeneous polymer film, we find that the lattice of fluoropolymer cores leads to a length scale dependent diffusion coefficient for the tracer. This effect can be interpreted as microscopic evidence for a strain hardening effect due to the presence of a hardened layer of matrix polymer (= shell) surrounding the core, which act as nanofillers. This strain hardening effect could be quantified within the two‐state diffusion model in terms of tracer diffusion coefficients and root mean squared displacements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2823–2834, 2007