Study on cloud points of Triton X-100-cationic gemini surfactants mixtures: A spectroscopic approach

This study investigates the effects of various cationic surfactants on the cloud point (CP) of the nonionic surfactant Triton X-100 (TX-100) in aqueous solutions. Instead of visual observation, a spectrophotometer was used for measurement of the cloud point temperatures. The values of CPs for Triton X-100 can be measured directly because TX-100 has an average number of oxyethylene units per molecule of p ≈ 9.5 and a CP = 66.0 °C. Quaternary ammonium dimeric surfactants (m-s-m, m = 10, 12, and 16, and s = 2, 6, and 10) were synthesized and used. The melting temperature T_M and the Krafft temperature T_K were measured for 1 wt% aqueous solutions of these synthesized surfactants. The melting temperature of the solid gemini surfactants increased with the carbon number of the alkyl chain. The results showed that additions of the gemini surfactants (which are infinitely miscible with water) to Triton X-100 increased the cloud point of the TX-100 solutions. All salts tested in these studies had a large effect on the CPs of nonionic surfactants due to their effect on water structure and their hydrophilicity. The effect of the alkyl chain length of the gemini surfactant on the CP of Triton X-100 is therefore more important than the spacer chain length.     

Phase equilibria in ternary (carbon dioxide + tetrahydrofuran + water) system in hydrate-forming region: Effects of carbon dioxide concentration and the occurrence of pseudo-retrograde hydrate phenomenon

In the present work, the three- and four-phase hydrate equilibria of (carbon dioxide (CO₂) + tetrahydrofuran (THF) + water) system are measured by using Cailletet equipment in the temperature and pressure range of (272 to 292) K and (1.0 to 7.5) MPa, respectively, at different CO₂ concentration. Throughout the study, the concentration of THF is kept constant at 5 mol% in the aqueous solution. In addition, the fluid phase transitions of L_W–L_V–V → L_W–L_V (bubble point) and L_W–L_V–V → L_W–V (dew point) are determined when they are present in the ternary system. For comparison, the three-phase hydrate equilibria of binary (CO₂ + H₂O) are also measured. Experimental measurements show that the addition of THF as a hydrate promoter extends hydrate stability region by elevating the hydrate equilibrium temperature at a specified pressure. The three-phase equilibrium line H–L_W–V is found to be independent of the overall concentration of CO₂. Contradictory, at higher pressure, the phase equilibria of the systems are significantly influenced by the overall concentration of CO₂ in the systems. A liquid–liquid phase split is observed at overall concentration of CO₂ as low as 3 mol% at elevated pressure. The region is bounded by the bubble-points line (L_W–L_V–V → L_W–L_V), dew points line (L_W–L_V–V → L_W + V) and the four-phase equilibrium line (H + L_W + L_V + V). At higher overall concentration of CO₂ in the ternary system, experimental measurements show that pseudo-retrograde behaviour exists at pressure between (2.5 and 5) MPa at temperature of 290.8 K.     

Glass transition behaviour of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H2O mixed solutions

Here, we have measured the glass transition temperature (T_g) of the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H₂O mixed solutions as a function of H₂O concentration (x mol% H₂O). The glass-forming composition region was also determined. Contrary to the results of the quaternary ammonium type of ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate–H₂O mixed solutions, we did not observed the multiple glass transition behaviour. We also measured the glassy Raman spectra of the solutions at T = 77 K. We find that the “nearly free” hydrogen bonded Raman band of water molecules in the aqueous [bmim][BF₄] solution exists up to around x = 60 mol% H₂O, even at T = 77 K.     

High-pressure (vapour + liquid) equilibria for ternary systems composed by {(E)-2-hexenal or hexanal + carbon dioxide + water}: Partition coefficient measurement

A new apparatus based on a static–analytic method assembled in this work was utilised to perform high-pressure (vapour + liquid) equilibria measurements of aqueous ternary systems. This work includes values of isothermal partition coefficients between CO₂ and water of two apple aroma constituents, (E)-2-hexenal and hexanal. Additionally, this work reports new experimental (vapour + liquid) equilibria measurements for the ternary systems (CO₂ + (E)-2-hexenal + water) and (CO₂ + hexanal + water), at fixed liquid phase composition (600 mg · kg⁻¹), at temperatures of (313, 323 and 333) K and at pressures from (8 to 19) MPa. Vapour liquid interphase was checked and monitored visually for all the systems studied in this work. No liquid immiscibility was observed at the composition, temperatures and pressures studied. In order to suggest reasonable operation conditions for fractionation of aromas with dense carbon dioxide, partition coefficients of the aroma compounds between CO₂ and water along with their separation factors from water were calculated. Partition coefficients of (E)-2-hexenal between CO₂ and water were in the range of (6 to 91) and where found to be near six times higher than those of hexanal (9 to 17). Very high separation factors from water were observed (∼10⁴) especially for (E)-2-hexenal. The highest separation factor, for both compounds, was found at a temperature of 313 K and pressures from (12 to 14) MPa.     

Molecular interaction of organic dyes in bulk and confined media

Molecular interactions of five thiazine dyes with increasing alkyl substitution have been studied in aqueous and microemulsion media at 303 K within a concentration range of (1.35–7.00) × 10^?4 M. The dimerization constant (K_d) values for the five dyes are ranged between 1.761 and 6.258 × 10³ l mol^?1 in bulk water media, where as in microemulsion media, K_d's are ranged between 1.760 and 4.110 × 10³ l mol^?1. Thionine (with no methyl substitution) and azure A (with two methyl substitution) displayed slightly larger K_d values in microemulsion water pools compared to bulk water while other dyes recorded significant drop in K_d values. The influence of microemulsion media on the molecular interaction of dyes has been explained in terms of electrostatic and hydrophobic factors. The monomer and the dimer spectra are explained in terms of molecular exciton model and the optical absorption parameters of both the species are reported in bulk and confined media.     

Hydrate phase equilibrium in the system of (carbon dioxide + 2,2-dimethylbutane + water) at temperatures below freezing point of water

The four-phase equilibrium conditions of (vapor + liquid + hydrate + ice) were measured in the system of (CO₂ + 2,2-dimethylbutane + water). The measurements were performed within the temperature range (254.2 to 270.2) K and pressure range (0.490 to 0.847) MPa using an isochoric method. Phase equilibrium conditions of hydrate formed in this study were measured to be at higher temperatures and lower pressures than those of structure I CO₂ simple hydrate. The largest difference in the equilibrium pressures of structure I CO₂ hydrate and the hydrate formed in the present study was 0.057 MPa at T = 258.3 K. On the basis of the four-phase equilibrium data obtained, the quintuple point for the (ice + structure I hydrate + structure H hydrate + liquid + vapor) was also determined to be T = 266.4 K and 0.864 MPa. The results indicate that structure H hydrate formed with CO₂ and 2,2-dimethylbutane is stable exclusively at the temperatures below the quintuple temperature.     

Formation of chiral ionic liquids and imidazol-2-ylidene metal complexes from the proteinogenic aminoacid l-histidine

Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-propyl)₂-OMe⁺Br⁻]. It features a melting point of 39 °C and may serve as a useful readily available optically active ionic liquid. Its subsequent treatment with silver oxide gave the corresponding l-histidine derived chiral N-heterocyclic carbene complex [“(carbene)₂Ag · AgBr₂”]. Transmetallation by treatment with Pd(CH₃CN)₂Cl₂ or [Rh(cod)Cl]₂ led to the formation of the respective chiral late metal imidazol-2-ylidene complexes [“(carbene)₂PdCl₂”] and [“(carbene)RhCl(cod)”], respectively. Four diastereomers of the square planar palladium system were observed. Due to the additional chirality center in the l-histidine-derived “Arduengo-carbene ligand” two diastereomers of the rhodium carbene complex were formed.     

Separation of benzene from alkanes using 1-ethyl-3-methylpyridinium ethylsulfate ionic liquid at several temperatures and atmospheric pressure: Effect of the size of the aliphatic hydrocarbons

The ionic liquid 1-ethyl-3-methylpyridinium ethylsulfate, [EMpy][ESO₄], was studied for the separation of benzene from aliphatic hydrocarbons (octane or nonane) by solvent extraction through the determination of the (liquid + liquid) equilibrium (LLE) of the ternary systems: {octane (1) + benzene (2) + [EMpy][ESO₄] (3)} and {nonane (1) + benzene (2) + [EMpy][ESO₄] (3)} at T = (283.15 and 298.15) K and atmospheric pressure. Binodal curves were determined using the “cloud point” method, and tie-line compositions were obtained by density measurements. The values of selectivity and distribution coefficient, derived from the tie-line data, were used to decide if this ionic liquid can be used as potential solvent for the separation of benzene from aliphatic hydrocarbons using liquid extraction. These results were analyzed and compared to those previously reported for the systems {hexane + benzene + [EMpy][ESO₄]} and {heptane + benzene + [EMpy][ESO₄]}. The experimental results show that this ionic liquid is suitable for the extraction of benzene from mixtures containing octane and nonane. The consistency of tie-line data was ascertained by applying the Othmer–Tobias and Hand equations. The experimental results for the ternary systems were well correlated with the NRTL model. No literature data were found for the mixtures discussed in this paper.     

Platinum-like oxidation of nickel surfaces by rapidly switching voltage to generate highly active bifunctional catalysts

Recently the importance of catalyzing the water splitting step of the hydrogen evolution reaction (HER) was highlighted. We demonstrate here a treatment to modify a nickel surface into a highly effective bifunctional HER catalyst (i₀ = 0.18 A/m², Tafel Slope = 106 mV/dec) that has a good distribution of both water splitting sites and H_ads combination sites. The resulting surface is characterized electrochemically, and with SEM, EDX, XPS and AFM. The data is found to be consistent with the treatment oxidizing the Ni surface in a novel way creating the hypothesized “Ni(OH)_x” structure (x between 0 and 2).     

Phase behaviour of mixed-gas hydrate systems containing carbon dioxide

We describe a new apparatus suitable for measurements of the phase behaviour and phase properties of fluid mixtures under conditions of high-pressure. We propose a synthetic method for the determination of gas solubility, and present results for the system (CO₂ + H₂O). In addition, we report new measurements of the hydrate equilibrium curves in aqueous systems containing either pure carbon dioxide or mixed gases including CO₂. For hydrates formed in the (CO₂ + H₂O) system, we find an enthalpy of dissociation of 77 kJ · mol^?1. This value was unchanged by the addition of mass fraction 0.043 of NaCl to the water. Compared with pure CO₂, mixtures of CO₂ with air exhibited markedly different dissociation pressures at given temperature, but were characterised by the same enthalpy of dissociation. However, two mixtures containing either nitrogen or methane and hydrogen both exhibited a higher enthalpy of dissociation, 106 kJ · mol^?1, consistent with these systems forming structure II hydrates.     

Synthesis of gold nanorods using concentrated aerosol OT in hexane and its application as catalyst for the reduction of eosin

The microemulsion method for the preparation of nanoparticles is well known. We have used the aqueous core of highly concentrated aerosol OT in hexane solution to synthesize gold nanorod by utilizing the aqueous core of surfactant aggregates as host nanoreactor. The shape and size of the aqueous core as well as the particles formed inside the core can be controlled by changing the parameter W₀ (water to surfactant ratio), concentration of gold salt and the concentration of surfactant. When the concentration of the surfactant is very high the shape of the aqueous droplet does not remain spherical but take the shape of prolate. In our study we have made gold nanorods by the reduction of gold chloride with sodium borohydride in the aqueous core of 1 M AOT hexane at a W₀ of 10. The rods are highly monodispersed with a diameter of about 20 nm and a length of 200 nm with an aspect ratio of 10. The absorption spectra of the gold nanorods show two different peaks one at 535 nm and the other at 965 nm. The particles were used as a catalyst for the reduction of eosin with sodium borohydride. The rate constant comes out be very large in comparison with that of uncatalysed reaction. The reaction was carried out at various temperatures between 20 and 60 °C and the activation energy of the reaction was calculated using Arrhenius plot between–ln k and 1/T. The activation energy of the gold nanorods catalysed reaction comes out to be more than two times as compared to uncatalysed reaction.     

Zirconia-based amperometric sensor using ZnO sensing-electrode for selective detection of propene

The sensing characteristics to propene (C₃H₆) were examined at 600 °C under wet condition for the amperometric sensor using a yttria-stabilized zirconia (YSZ) tube and ZnO (+8.5 wt%Pt) sensing-electrode (SE). In order to improve the sensitivity to C₃H₆, the “pulsed-potential method” was adopted here. It was found that the current response varied almost linearly with C₃H₆ concentration in the range of 0–200 ppm when SE was polarized at +1.0 V (vs. Pt/air reference electrode) for a period of 0.3 s. By using the present “pulsed-potential method”, the sensitivity to 100 ppm C₃H₆ was increased about 1000 times, compared with the normal “constant-potential method”. The excellent selectivity to C₃H₆ was also obtained for the present sensor without influence of other hydrocarbons, NO_x, CO, H₂, etc.     

Measuring solubility of carbon dioxide in aqueous blends of N-methyldiethanolamine and 2-((2-aminoethyl)amino)ethanol at low CO2 loadings and modelling by electrolyte SAFT-HR EoS

In this work, new solubility values for CO₂ absorption in aqueous solutions of N-methyldiethanolamine (MDEA) in the presence of different mole ratios of 2-((2-aminoethyl)amino)ethanol (AEEA) at low pressures are obtained. The total molar amine concentration of all the solutions has been fixed equal to 3.360 mol · L⁻¹ (5.370 mol amine · kg⁻¹ water). The mole ratio of AEEA/MDEA was set to 0.12500, 0.10000 and 0.05000. The experimental total pressure varied from (7.3 to 386.6) kPa and the experimental temperature was set to (313.15, 328.15, 343.15 and 358.15) K. The electrolyte SAFT-HR (eSAFT-HR) equation of state (EoS) (Najafloo et al., 2014) has been successfully applied to model the solubility of CO₂ in aqueous mixtures of AEEA and MDEA. The overall average absolute relative per cent deviation (AAD%) in calculating the total pressure as a function of CO₂ loading is 7.74 for (AEEA + MDEA + CO₂ + H₂O) quaternary system at the four values of temperature. To verify the predictive ability of the model, the eSAFT-HR EoS was extrapolated to the Zoghi and Feyzi (2013) solubility results of the same quaternary system that were obtained at higher pressures or higher CO₂ loadings at the same temperatures. The AAD of the present model is 11.39% lower.     

Phase equilibrium for surfactant Ls-54 in liquid CO(2) with water and solubility estimation using the Peng-Robinson equation of state

It is known that the commercial surfactant Dehypon^® Ls-54 is soluble in supercritical CO₂ and that it enables formation of water-in-CO₂ microemulsions. In this work we observed phase equilibrium for the Ls-54/CO₂ and Ls-54/water/CO₂ systems in the liquid CO₂ region, from 278.15 to 298.15 K. In addition, the Peng–Robinson equation of state (PREOS) was used to model the phase behavior of Ls-54/CO₂ binary system as well as to estimate water solubilities in CO₂. Ls-54 in CO₂ can have solubilities as high as 0.086 M at 278.15 K and 15.2 MPa. The stability of the microemulsion decreases with increasing concentration of water, and lower temperatures favor increased solubility of water into the one-phase microemulsion. The PREOS model showed satisfactory agreement with the experimental data for both Ls-54/CO₂ and water/CO₂ systems.     

Measurement and prediction of phase behaviour for 1-alkyl-3-methylimidazolium tetrafluoroborate and carbon dioxide: Effect of alkyl chain length in imidazolium cation

The high-pressure phase behaviour of the binary system {1-ethyl-methylimidazolium tetrafluoroborate ([EMIM][BF₄]) + CO₂} was determined over the temperature range of (293.2 to 323.2) K at intervals of 5.0 K with the CO₂ mole fraction ranging from 0.153 to 0.578 by using a high-pressure variable-volume view cell. Further, the (vapour + liquid) equilibrium of the binary system {1-hexyl-methylimidazolium tetrafluoroborate ([HMIM][BF₄]) + CO₂} was measured over the temperature range of (303.2 to 328.2) K with the CO₂ mole fraction ranging from 0.314 to 0.593. The Peng–Robinson equation of state along with two-parameter mixing rules has been employed to correlate the experimental results. In case of the ([EMIM][BF₄] + CO₂) system, the (vapour + liquid + liquid) equilibrium and (vapour + liquid) equilibrium have been observed at a high CO₂ mole fraction. The experimental values obtained in this study were compared with the available phase behaviour data of the binary system (1-alkyl-3-methylimidazolium tetrafluoroborate + CO₂) in order to investigate the effect of the alkyl chain length in the imidazolium cation on the phase behaviour of such systems.     

The critical behavior of {water + AOT + decane} microemulsion with various molar ratios of water to AOT

To examine the critical behavior of the microemulsion, we have determined the coexistence curves for two ternary microemulsion systems of {water + sodium di(2-ethylhexyl) sulfosuccinate (AOT) + n-decane} with the molar ratios ω = (45.2 and 50.0) of water to AOT, respectively, by measuring refractive index at a constant pressure in the critical region. The critical exponent β and the critical amplitude B have been deduced from the coexistence curves. It was found that the values of β for both systems were consistent with the 3D-Ising exponent in a critical region. By increasing ω, i.e. the droplet size, the critical temperature and, to a lesser extent, the critical concentration decrease. The region of coexisting two phases was drastically reduced by an increase in the droplet size.     

On the phase behaviour of polyethoxylated sorbitan (Tween) surfactants in the presence of potassium inorganic salts

The salting out potential of potassium-based inorganic salts was assessed in aqueous solutions of two non-ionic surfactants from the Tween family. New solubility data of the systems {surfactant (Tween 20/Tween 80) + inorganic salt (K₃PO₄/K₂CO₃/K₂HPO₄/K₂S₂O₃/K₂SO₃) + H₂O} were experimentally ascertained at T = 298.15 K and these data were correlated by means of several three and four parameters empirical equations. Tie-line data were determined for the aqueous ternary systems and Ohtmer-Tobias and Bancroft equations have been proposed to correlate these data. The phase segregation effect of the proposed salts was investigated and compared with the sequence indicated by the Hofmeister series and the molar Gibbs energy of hydration (Δ_hydG) data.     

Measurement and modeling of high-pressure (vapour + liquid) equilibria of (CO2 + alcohol) binary systems

An apparatus based on a static-analytic method assembled in this work was utilized to perform high pressure (vapour + liquid) equilibria measurements with uncertainties estimated at <5%. Complementary isothermal (vapour + liquid) equilibria results are reported for the (CO₂ + 1-propanol), (CO₂ + 2-methyl-1-propanol), (CO₂ + 3-methyl-1-butanol), and (CO₂ + 1-pentanol) binary systems at temperatures of (313, 323, and 333) K, and at pressure range of (2 to 12) MPa. For all the (CO₂ + alcohol) systems, it was visually monitored to insure that there was no liquid immiscibility at the temperatures and pressures studied. The experimental results were correlated with the Peng–Robinson equation of state using the quadratic mixing rules of van der Waals with two adjustable parameters. The calculated (vapour + liquid) equilibria compositions were found to be in good agreement with the experimental values with deviations for the mol fractions <0.12 and <0.05 for the liquid and vapour phase, respectively.     

High monomer content batch microemulsion polymerization of butyl acrylate initiated with gamma ray

Radiation polymerization of butyl acrylate was performed in a microemulsion stabilized with a mixture of sodium of 12-acryloxy-9-octadecenoic acid and sodium dodecyl sulfate in a weight ratio of 2 at room temperature. BA content in microemulsion can be successfully improved up to 40 wt% with low surfactant concentration (lower than 10 wt%). The resulted stable, translucent microlatex contain particles with average diameter from 28.1 to 38.1 nm with different monomer content. Particle size depends on the dose rate and surfactant concentration. Effects of monomer content and dose rate on the maximum polymerization rate are discussed.     

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the ν_as(CH₂), (∼2930–2920 cm⁻¹), ν_s(CH₂) (∼2860–2850 cm⁻¹), 2ν_as(CH₂) (∼5810–5785 cm⁻¹), (ν + δ)_as(CH₂) (∼4340–4330 cm⁻¹) and (ν + δ)_s(CH₂) (∼4270–4250 cm⁻¹) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2ν_as(CH₂) (28 cm⁻¹) than for ν_as(CH₂) (8 cm⁻¹) or ν_s(CH₂) (10 cm⁻¹), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH₂ bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.