Enthalpy of solution of phenoxyalcohols solubilized in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solutions

The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems.     

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.     

Binding constants and partial molar volumes of primary alcohols in sodium dodecylsulfate micelles

The densities of methanol, ethanol, 1-propanol, 1-butanol and 1-hexanol were measured in aqueous solutions of sodium dodecylsulfate at 25°C. The partial molar volumes of the alcohols at infinite dilution in the aqueous surfactants solutions were calculated and discussed using a mass-action model for the alcohol distribution between the aqueous and the micellar phase. The partial molar volumes of the alcohols in the aqueous and in the micellar phases, and the ratios between the binding constant and the aggregation number, were calculated. The partial molar volume for all the alcohols in micellar phase is 10 cm³-mol^–1 smaller than that in octane. This can be related to the strong hydrophilic interaction between the head groups of the alcohol and the micellized surfactant. From the extrapolated values of the distribution constant and the partial molar volumes in the aqueous and micellar phases, the standard partial molar volume of heptanol in micellar solutions was found to decrease with increasing surfactant concentration. The standard free energy of transfer of alcohols from water to micelles was rationalized in terms of hydrophilic and hydrophobic contributions. A model is proposed in which the empty space around each solute is assumed to be the same in the gas and liquid phases, and is used to explain the behavior of micelles in the presence of amphiphilic solutes.     

The influence of composition and structure of water-in-oil microemulsions on activities of Iraqi Turnip peroxidase

The activity of the enzyme Iraqi Turnip peroxidase (ITP) is studied in a reverse microemulsion composed of chloroform, aqueous buffer, sodium dodecylsulfate (SDS) and alcohols of the homologous series 1-propanol to 1-hexanol through the measurements of absorbancy of the product of oxidation at the wavelength of 470 nm in the course of reactions. The ITP catalyzed reaction is the oxidation of guaiacol by hydrogen peroxide. Maximum enzyme activity was obtained at ω₀ (molar ratio of water to surfactant) = 8. It was found that the oxidation reaction obeyed Michaelis–Menten kinetics in the investigated concentration rang (0.08–0.8 mM) of the substrate, and the Michaelis constant K_m and maximal reaction rate V_m were determined. The enzyme inhibition caused by the alcohols in microemulsions is a consequence of both the solubility of the alcohols in the buffer and the flexibility of the interfacial film.     

Adsorption of sodium dodecylsulfate on chrysotile

Adsorption of sodium dodecylsulfate (SDS) onto chrysotile from aqueous solutions was investigated along with varying temperature, ionic strength and surface treatments. Commercial chrysotile fibers were treated by sonication or extensive washings. The ratio of adsorbed SDS per gram of chrysotile is approximately constant with varying chrysotile masses. A steady state is reached after about 2 h of contact between SDS and chrysotile. In general, less surfactant is adsorbed on the sonicated chrysotile than on the extensively washed chrysotile. For the sonicated chrysotile, isotherms presented an adsorption maximum in the region of the surfactant critical micelle concentration, when the experiments were carried out without ionic strength control. The adsorption maximum is due to the presence of magnesium ions in the solution, which can form complexes with dodecylsulfate ions. For the extensively washed chrysotile, the isotherm behavior is similar to that obtained with sonicated chrysotile in the presence of an inert electrolyte. No significant difference in adsorption of SDS on the extensively washed chrysotile was observed when varying temperature or ionic strength. The adsorption of SDS was found to be dependent on the prior surface treatment.     

Thermodynamic properties of ibuprofen sodium salt in aqueous/urea micellar solutions at 298.15 K

Thermodynamic, surface and micellar properties of anti-inflammatory drug sodium 2-(4-isobutylphenyl) propionate (sodium salt of ibuprofen (NaIBF)) in aqueous/urea solution were studied by surface tension measurements at 298.15 K in the presence of anionic surfactant sodium dodecylsulfate (SDS). Critical micelle concentration (cmc), surface tension at cmc (γcmc), maximum Gibbs surface excess (Γ_max), minimum surface area per surfactant molecule at the air/water interface (A _min) etc. were determined in pure water as well as in aqueous urea solution. The theories of Clint, Rosen and Rubingh have been applied to describe the interactions between these amphiphiles at the interface and in the micellar solution. Various thermodynamic parameters have been calculated and discussed in detail.     

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.     

Mass action model for solute distribution between water and micelles. Partial molar volumes of butanol and pentanol in dodecyl surfactant solutions

The densities of 1-butanol and 1-pentanol were measured in aqueous solutions of dodecyltrimethylammonium bromide and dodecyldimethylamine oxide and the partial molar volumes at infinite dilution of the alcohols in aqueous surfactants solutions were obtained. The observed trends of this quantity as a function of the surfactant concentration were rationalized using a mass-action model for the alcohol distribution between the aqueous and the micellar phase. At the same time, the model was revised to account for the alcohol effect on the surfactant micellization equilibrium. The partial molar volume of alcohols in the aqueous and in the micellar phases and the ratios between the binding constant and the aggregation number were calculated. These thermodynamic quantities are nearly the same in the two surfactants analyzed in this paper but differ appreciably from those in sodium dodecylsulfate. The apparent molar volume of surfactants in some hydroalcoholic solutions at fixed alcohol concentration were also calculated. In the micellization region the trend of this quantity as a function of the surfactant concentration shows a hump, which depends on the alcohol concentration and on the alcohol alkyl chain length. The alcohol extraction from the aqueous to the micellar phase due to the addition of the surfactant can account for the observed trends.     

The effect of triethylenetetraamine (Trien) on the ion flotation of Cu(2+) and Ni(2+)

Ion flotation is a separation process involving the adsorption of a surfactant and counterions at an air/aqueous solution interface. It shows promise for removing toxic heavy metal ions from dilute aqueous solutions. Here we report the effect of a neutral chelating ligand, triethylenetetraamine (Trien), on the ion flotation of cations with dodecylsulfate, DS(-), introduced as sodium dodecylsulfate, SDS. Ion flotation in the aqueous SD-Cu(II)-Ca(II)-Trien system gave strongly preferential removal of Cu(II) over Ca(II), which is a reversal of the order of selectivity seen in the SDS-Cu(II)-Ca(II) system containing no Trien. The removal rates of Cu(2+) and Ni(2+) with DS(-) were much faster in the presence of Trien than for simple aquo ions, and the final metal concentration was significantly lower. Surface tension measurements showed that Trien enhanced the surface activity and adsorption density for SDS-Cu(II) and SDS-Ni(II) solutions. The overall change in the Gibbs free energy for adsorption resulting from complexation was -3.60 kJ/mol for Cu(II) and -3.50 kJ/mol for Ni(II). This included the effects of hydrophobic interactions between the metal-Trien complexes at the air/solution interface, along with changes in the amount of dehydration associated with cosorption of the metal-Trien complex with DS(-) at the air/solution interface.     

Influence of size and functionality of polymeric nanoparticles on the adsorption behavior of sodium dodecyl sulfate as detected by isothermal titration calorimetry

Isothermal titration calorimetry was used to monitor the adsorption of the surfactant sodium dodecylsulfate (SDS) on different sized pure and carboxy functionalized polystyrene nanoparticles prepared by the mini-emulsion process. The ITC experiment gives, additionally to the CMC values, information about the interaction of the surfactant molecules to the particle’s surface due to the particle surface properties. The adsorption heat depends on the chemical composition of the polymer as well on the particle size. It also provides information about the surface coverage with surfactant and the number of additional adsorbed molecules per particle until full coverage by surfactant is obtained. The surfactant adsorption increases from 0.3 molecules per nm² for 50 nm to 8.5 molecules per nm² for carboxy functionalized particles with diameters larger than 160 nm. The area A _Surf-dens after the adsorption process gives information about the packing density of surfactant molecules on the particles in dependence of carboxy groups: an increasing number of carboxylic groups decreases the area occupied per SDS molecule. The adsorption process was also monitored by zeta potential measurements, where an increasing potential during the adsorption was detected.     

Photophysical Behavior of a New Gemini Surfactant in Neat Solvents and in Micellar Environments

A novel fluorescent gemini surfactant, 1,4-bis-(2'-(N-dodecyl pyridinio-4"-yl)ethenyl)benzene dibromide, abbreviated BDPEBB, has been synthesized and its photophysical properties have been studied in different environments. BDPEBB has a limited solubility in alcohols where it is found in aggregate form at concentrations>/=1 mM. In other solvents, e.g., water, it is only found in aggregate form, even at much lower concentrations. Solvent polarity has a small and insignificant solvatochromic effect but alcohols give a specific interaction with BDPEBB, causing a significant hypsochromic shift in absorption maxima and a large increase in relative fluorescence efficiency. Pyrene fluorescence is effectively quenched by BDPEBB. Pyrene also forms associative complexes with BDPEBB in water. These complexes are partly dissociated in the presence of surfactant micelles. Triton X-100 micelles provide a favorable environment for BDPEBB solubilization well distinguished from the behavior of ionic surfactants. Small quantities of BDPEBB have a large influence on the behavior of aqueous sodium dodecylsulfate (SDS) and sodium decylsulfate (SDeS) micelles, inducing the formation of large aggregates, visible by the naked eye. These large aggregates are most probably microcrystals of BDPEBB(2+)/2DS(-) or BDPEBB(2+)/2DeS(-). The aggregation number of SDS and SDeS micelles in the absence and in the presence of BDPEBB has been calculated by exploitation of the static luminescence quenching kinetics of Ru(bpy)(3)(2+) by 9-methylanthracene, both solubilized in the micellar phase. It has been observed that Ru(bpy)(3)(2+) inhibits the precipitation of SDeS micelles in the presence of BDPEBB. Our results suggest that double-chain surfactant chromophores should be employed with particular care if they are to be used as probes of the micellar phase. Copyright 2000 Academic Press.     

The structure and adsorption properties of colloidal silica used in toothpastes

The dispersity, specific surface area, porosity, and pore size distribution are determined for samples of colloidal silica and calcium o-phosphate, toothpaste constituents. The results obtained show that adsorbents have the developed mesoporous structure. It was found that the adsorption of sodium lauryl sulfate and a nonionic surfactant, glyceryl monocaprylate, at the aqueous surfactant solution-colloidal silica interface is small and has the unusual character. The reasons for a low adsorption of surfactants and their mixtures on the surface of the studied adsorbents are discussed.     

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.     

Effects of electrolyte and nonelectrolyte additives on adsorption and surface rheological characteristics of humic acid salt solutions

The du Noüy and oscillating droplet shape methods are employed to study the effects of the ionic strength and pH of a medium, as well as the addition of nonelectrolytes (lower alcohols and acetone), on the adsorption and surface rheological characteristics of aqueous solutions of humic acid salts (sodium humates) at the liquid-air interface. When added in concentrations at which the aggregation of humic substances is not yet observed, strong electrolytes (NaCl and HCl) decrease the equilibrium surface tension and increase the dilatational viscoelastic modulus of aqueous sodium humate solutions. The aggregation of humic substances enhances the surface tension and reduces the viscoelastic modulus of surface layers. Nonelectrolyte additives decrease the surface tension and dilatational modulus of aqueous humic acid salt solutions. The equilibrium surface tension of sodium humate-nonelectrolyte mixed solutions is described in terms of two different models, namely, a relatively exact model of polyelectrolyte-nonionic surfactant adsorption and a simple additive model. It is shown that the additive model may be used to predict the equilibrium surface tension for the mixtures of high- and low-molecular-mass surfactants.     

Excess enthalpies of solution of some primary and secondary alcohols in sodium dodecylsulfate micellar solutions

The exces enthalpies of solution of some primary and secondary alcohols in aqueous sodium dodecylsulfate micellar solutions were measured and the results were explained by considering the distribution of alcohols between aqueous and micellar phases. The distribution constant and the enthalpy of transfer (and the standard free energy and entropy of transfer) were obtained. The thermodynamic parameters for the transfer of secondary alcohols from the aqueous to the sodium dodecylsulfate (NaDS) micellar phase differ slightly from those of the corresponding primary alcohols. For both series of alcohols the additivity rule holds for free energies of transfer whereas enthalpies and entropies display convex curves. The present data are compared to those for the transfer of the same solutes from the aqueous to the dodecyldimethylamine oxide (DDAO) and dodecyltrimethylammonium bromide (DTAB) micellar phases. The role of the hydrophilic interactions between the OH group and the micelles' head groups is formulated. The thermodynamics of the branched methyl group were determined. Furthermore, the thermodynamics of solvation of primary alcohols in water, in NaDS micelles, and in octane have been calculated using reference states based on the assumption that the empty space around alcohols in the initial and final states is the same. It is shown that the solvation of alcohols in NaDS micellar phase is enthalpy driven and that the thermodynamic properties of solvation vs. the length of the alcohol tail is the same for water and NaDS micelles whereas it is different for octane. A possible explanation for this difference is that the alkyl chain of alcohols folds in octane.     

Alterations in phospholipid bilayers caused by sodium dodecyl sulphate/triton X-100 mixed systems

The mechanisms governing the subsolubilizing and solubilizing interaction of sodium dodecyl sulphate (SDS)/Triton X-100 mixtures and phosphatidylcholine liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxy-fluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light-scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system a) resulted in 50% of CF release (Re _50%CF); b) saturated the liposomes (Re _SAT;c) led to a complete solubilization of these structures (Re _SOL). From these parameters the corresponding surfactant partition coefficientsK _50%CF,K _SAT andK _SOL were determined. The free surfactant concentrationsS _W were lower than the mixed surfactant CMCs at subsolubilizing level, whereas they remained similar to these values during saturation and solubilization of bilayers in all cases. Although theRe increased as the mole fraction of the SDS rose (X _SDS), theK parameters showed a maximum atX _SDS values of about 0.6, 0.4 and 0.2 forK _50%CF,K _SAT andK _SOL respectively. Thus, the higher the surfactant contribution in surfactant/lipid system, the lower theX _SDS at which a maximum bilayer/water partitioning of mixed surfactant systems added took place and, consequently, the lower the influence of the SDS in this maximum bilayer/water partitioning.Abbreviations PC Phosphatidylcholine - PIPES piperazine-1,4 bis (2-ethanesulphonic acid) - SDS sodium dodecyl sulphate - X _SDS mole fraction of sodium dodecyl sulphate in the mixed system - CF 5(6)-carboxyfluorescein - Re effective surfactant/lipid molar ratio - Re _50%CF effective surfactant/lipid molar ratio for 50% CF release - Re _SAT effective surfactant/lipid molar ratio for bilayer saturation - Re _SOL effective surfactant/lipid molar ratio for bilayer solubilization - S _W surfactant concentration in the aqueous medium - S _{W, 50%CF} surfactant concentration in the aqueous medium for 50% CF release - S _{W, SAT} surfactant concentration in the aqueous medium for bilayer saturation - S _{W, SOL} surfactant concentration in the aqueous medium for bilayer solubilization - S _B surfactant concentration in the bilayers - K bilayer/aqueous phase surfactant partition coefficient - K _50%CF bilayer/aqueous phase surfactant partition coefficient for 50% CF release - K _SAT bilayer/aqueous phase surfactant partition coefficient for bilayer saturation - K _SOL bilayer/aqueous phase surfactant partition coefficient for bilayer solubilization - PL phospholipid TLC-FID, thin-layer chromatography/flame ionization detection system - PI polydispersity index - CMC critical micellar concentration - r ² regression coefficient     

Molecular screening of alcohol and polyol adsorption onto MFI-type zeolites

Configurational-bias grand canonical Monte Carlo (CB-GCMC) simulations and expanded ensemble (EE)-CB-GCMC simulations were performed to obtain adsorption isotherms of alcohols and polyols onto MFI-type zeolites from the gas phase and aqueous solution. In adsorption from both phases, Henry's constants and heats of adsorption at infinite dilution for straight-chain alcohols, diols, and triols in silicalite-1 are found to increase, and the saturation loadings decrease with increasing carbon number. Adsorption of straight-chain alcohols is more favorable than that of branched-chain alcohols. Henry's constants increase with increasing number of hydroxyl groups for gas-phase adsorption but decrease for adsorption from aqueous solution due to the strong hydrophilic solvent effect of water. The location of the hydroxyls does not affect significantly the adsorption from aqueous solution but does so in gas-phase adsorption. The saturation pressures for gas-phase adsorption decrease by orders of magnitude from the alcohols to the triols. Nonframework cations increase the adsorption of the small alcohols by an order magnitude at low concentrations (<1 mg/mL), but result in only a factor of 2 increase for larger alcohols like butanol at low concentrations (<0.03 mg/mL), and then decrease the adsorption at higher concentrations. Overall, the simulated results are in reasonable agreement with available experimental data.     

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.     

Microcalorimetric determination of effect of the antioxidant (Quercetin) on polymer/surfactant interactions

Isothermal titration calorimetry (ITC) and batch calorimetry techniques have been used to evaluate the effect of added antioxidant (Quercetin, QN) on the binding between a polymer/surfactant complex, namely the sodium salt of polystyrene sulfonate (PSS) and typical anionic surfactant sodium dodecylsulfate (SDS). An indirect isotherm approximation method and the Satake–Yang model have been used to evaluate the binding parameter (Ku), adsorption cooperativity (u), and the Gibbs free energy of cooperative and non-cooperative binding (ΔG _C and ΔG _N) from the ITC data. The enthalpy of dissolution of QN into various PSS/water and PSS/SDS/water solutions has been evaluated from batch calorimetry to study the energetics of the polymer/surfactant binding in the presence of QN.     

表面活性剂控制的硒纳米线的室温生长

以表面活性剂十二烷基硫酸钠(SDS)为形貌导向剂,利用Na₂Se在室温碱性水溶液中的自发氧化,成功制备了Se纳米线。用TEM、SEM、EDX、XRD、HRTEM、SEAD等手段表征了Se纳米线的组成和结构。结果表明,合成的Se纳米线是沿六方相Se的[001]轴方向生长,具有良好的晶型结构。使用TEM对不同时间Se纳米结构的生长过程的形貌进行了跟踪,探讨了Se纳米线的形成机理,发现其形成与生长过程符合“solid-solution-solid”机理。同时,选择了具有特异官能团(如-OH,-COOH,-CONH₂)的3种表面活性剂,研究它们在纳米硒的取向性生长中的导向作用,只有SDS能引导合成出高质量的Se纳米线。