Synthesis and properties of ionic liquid-type Gemini imidazolium surfactants

A series of ionic liquid-type Gemini imidazolium surfactants with four-methylene spacer groups were synthesized ([C(n)-4-C(n)im]Br(2), n=10, 12, 14). The surface activity and thermodynamic properties of micellization between the Gemini imidazolium surfactants and their corresponding monomers ([C(n)mim]Br, n=10, 12, 14) were compared by means of surface tension and electrical conductivity measurements. The values of cmc, gamma(cmc), pc(20), Gamma(max), and A(min) derived from surface tension measurement at 25 degrees C suggest that the surface activity of [C(n)-4-C(n)im]Br(2) is higher than that of [C(n)mim]Br. While the thermodynamic parameters of micellization (DeltaG(m)(o), DeltaH(m)(o), DeltaS(m)(o)) derived from electrical conductivity indicate that the micellization of [C(n)-4-C(n)im]Br(2) is entropy-driven, aggregation of [C(n)mim]Br is entropy-driven at low temperature but enthalpy-driven at high temperature. Finally, the activation energy of conductance (E(a)) that is associated with the effective charge is also obtained for [C(n)-4-C(n)im]Br(2) and it is constant below the cmc, but it increases above the cmc.     

Gemini imidazolium surfactants: synthesis and their biophysiochemical study

New gemini imidazolium surfactants 9-13 have been synthesized by a regioselective epoxy ring-opening reaction under solvent-free conditions. The surface properties of these new gemini surfactants were evaluated by surface tension and conductivity measurements. These surfactants have been found to have low critical micelle concentration (cmc) values as compared to other categories of gemini cationic surfactants and also showed the tendency to form premicellar aggregates in solution at sufficiently low concentration below their cmc values. The thermal degradation of these surfactants was determined by thermograviometry analysis (TGA). These new cationic surfactants have a good DNA binding capability as determined by agarose gel electrophoresis and ethidium bromide exclusion experiments. They have also been found to have low cytotoxicity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on the C6 glioma cell line.     

Aggregation and thermodynamic properties of ionic liquid-type gemini imidazolium surfactants with different spacer length

The aggregation behavior and thermodynamic properties of micellization for the ionic liquid-type gemini imidazolium surfactants with different spacer length ([C₁₂–s–C₁₂im]Br₂, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence measurements. The values of cmc, γ _cmc, Γ _max, A _min, π _cmc, pc₂₀ and cmc/pc₂₀ suggest that the shorter the spacer, the higher the surface activity of [C₁₂–s–C₁₂im]Br₂ is. The cmc and γ _cmc values are decreased significantly in the presence of sodium halides, and the values decrease in the order NaCl < NaBr < NaI. The thermodynamic parameters of micellization (, , ) indicate that the micellization of [C₁₂–2–C₁₂im]Br₂ and [C₁₂–4–C₁₂im]Br₂ is entropy-driven, whereas aggregation of [C₁₂–6–C₁₂im]Br₂ is enthalpy-driven at lower temperature but entropy-driven at higher temperature. Finally, the fluorescence measurements show that the micropolarity of micelles increases but the aggregation numbers decrease with increasing the spacer length of [C₁₂–s–C₁₂im]Br₂.     

Thermodynamic properties of micellization of Sulfobetaine-type Zwitterionic Gemini Surfactants in aqueous solutions--a free energy perturbation study

In this article, the validity and accuracy of the free energy perturbation (FEP) model used in a previous article for ionic liquid-type Gemini imidazolium surfactants (ILGISs) is further evaluated by using it to model the Enthalpy-entropy compensation of Sulfobetaine-type Zwitterionic Gemini Surfactants (SZGSs), with different carbon atoms of the hydrophobic group or the spacer chain length, in aqueous solutions. In the FEP model, the Gibbs free energy contributions to the driving force for micelle formation are computed using hydration data obtained from molecular dynamics simulations. According to the pseudo-phase separation model, the thermodynamic properties of micellization in aqueous solutions for SZGS were discussed. The results show that the micellization of SZGS in aqueous solutions is a spontaneous and entropy-driven process. It is linearly Enthalpy-entropy compensated and different from the micelle formation of ILGIS but similar to anionic surfactants. The compensation temperature was found to be (302±3)K which was lower than ILGIS. As the temperature rises, the micellization is easy initially but then becomes difficult with the unusual changes of enthalpy values from positive to negative. The contribution of entropy change to the micellization tends to decrease but the contribution of enthalpy change tends to increase. In particular, as the number carbon atoms in the alkyl chains and spacer chains are increased, the thermodynamic favorability and stability of the micelles both increase.     

Solubilities of ionic surfactants in aqueous polymer solutions

Summary Solubility of ionic surfactants in water have been found to increase with added amount of nonionic hydrophilic polymers when both are capable of forming watersoluble complexes. Experiments were carried out with sodium hexadecyl sulfate (SHS) and hexadecyl amine hydrochloride (HAC) below theKrafft points of the respective surfactants. The solubility increment of the surfactants brought about by the polymers depends upon the kind of polymers, their molecular weight, concentration and temperature. The results have been interpreted on the basis of the amount of surfactants bound to the polymers and by the properties of the polymer-surfactant complexes formed. It is noteworthy that the anionic surfactant (SHS) can be bound to polymers much more extensively than the cationic surfactant (HAC).

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Zusammenfassung Die L?slichkeit von ionischen Benetzern in Wasser w?chst mit dem zugefügten Betrag an nicht-ionischen hydrophilen Polymeren, wenn beide zusammen wasserl?sliche Komplexe büden k?nnen. Versuche wurden mit Natrium-hexadecyl-sulfat (SHS) und Hexadecylamin-hydrochlorid (HAC) ausgeführt, und zwar unter denKrafft-Punkten der bezüglichen Benetzer. Das L?slichkeitsinkrement der Benetzer, gegeben durch die Polymeren, h?ngt von der Art des Polymeren, dessen Molekulargewicht, Konzentration und Temperatur ab. Die Ergebnisse werden interpretiert auf der Grundlage des Betrages an Benetzer, der an das Polymere gebunden ist, und durch die Eigenschaften des Komplexes Polymer/Benetzer. Es ist bemerkenswert, da? der anionische Benetzer (SHS) viel st?rker an das Polymere gebunden werden kann als der kationische Benetzer (HAC).

     

Thermodynamics of dilute aqueous solutions of imidazolium based ionic liquids

Experimental measurements of density ρ, speed of sound u, and viscosity η of aqueous solutions of various 1-alkyl-3-methylimidazolium based ionic liquid (IL) solutions have been performed in dilute concentration regime at 298.15 K to get insight into hydration behaviour of ILs. The investigated ILs are based on 1-alkyl-3-methylimidazolium cation, [C_nmim] having $[{\text{BF}}_4{]}^{-}$, [Cl]^?, $[{\text{C}}_1{\text{OSO}}_3{]}^{-}$, and $[{\text{C}}_8{\text{OSO}}_3{]}^{-}$ as anions where n = 4 or 8. Several thermodynamic parameters like apparent molar volume φ_V, isentropic compressibility β_s, and viscosity B-coefficients have been derived from experimental data. Limiting value of apparent molar volume has been discussed in terms of intrinsic molar volume (V_int) molar electrostriction volume (V_elec), molar disordered (V_dis), and cage volume (V_cage). Viscosity B-coefficients have been used to quantify the kosmotropic or chaotropic nature of ILs. Hydration number of ILs obtained using elctrostriction volume, isentropic compressibility, viscosity, and differential scanning calorimetry have been found to be comparative within the experimental error. The hydrophobic hydration has found to play an important role in hydration of ILs as compared to hydration due to hydrogen bonding and electrostriction. Limiting molar properties, hydration numbers, and B-coefficients have been discussed in terms of alkyl chain length of cation or nature of anion.     

Dispersion of carbon nanotubes by carbazole-tailed amphiphilic imidazolium ionic liquids in aqueous solutions

Spectrophotometric, kinetic, and transmission electron microscopic (TEM) data for the formation of Ag-nanoparticles using aspartic acid (Asp) as reductant are reported for the first time. In the formation of transparent silver sols, an alkaline medium is required. The silver nanoparticles are spherical, uniform particle size, and strongly depend on the [Asp]. The apparent rate constant decreases with [Asp] (from 4.0 to 24.0×10(-4)moldm(-3), the rate constants decreased from 2.6×10(-4) to 0.3×10(-4)s(-1)). For a certain reaction time, i.e., 30min, the absorbance of the silver sol first increased until it reached a maximum, and then decreased with [Asp]. Kinetic and TEM results indicate that the size of the Ag-nanoparticles depends on the [Asp]. It is proposed that the oxidation of Asp occurs by the adsorbed Ag(+) ions on the surface of Ag(2)O particles.     

Dynamic surface tension of aqueous solutions of ionic surfactants: role of electrostatics

The adsorption kinetics of the cationic surfactant dodecyltrimethylammonium bromide at the air-water interface has been studied by the maximum bubble pressure method at concentrations below the critical micellar concentration. At short times, the adsorption is diffusion-limited. At longer times, the surface tension shows an intermediate plateau and can no longer be accounted for by a diffusion-limited process. Instead, adsorption appears kinetically controlled and slowed down by an adsorption barrier. A Poisson-Boltzmann theory for the electrostatic repulsion from the surface does not fully account for the observed potential barrier. The possibility of a surface phase transition is expected from the fitted isotherms but has not been observed by Brewster angle microscopy.     

Sodium carbonate as phase promoter in aqueous solutions of imidazolium and pyridinium ionic liquids

Several methylsulfate and chloride anion-based ionic liquids, such as 1-alkyl-3-methyl imidazolium methyl sulfate, C_nMIM CH₃SO₄ (n = 1, 2, and 4), 1-benzyl-3-methyl imidazolium methyl sulfate, BzMIM CH₃SO₄, 1-benzyl, or hexyl-3-methyl imidazolium chloride, XMIM Cl (X = Bz and Hx), and methylpyridinium methylsulfate, Mpy CH₃SO₄, with sodium carbonate, Na₂CO₃, as phase forming salt, have been investigated and discussed for their potential use in separations based on aqueous two-phase systems (ATPS). Phase diagrams have been experimentally ascertained at T = 298.15 K, and Merchuck equation and a variation of this model have been used for correlating the binodal data. The alkyl chain length in the cation and the type of anion and cation have been explored and discussed due to their decisive influence in the ATPS behavior. The consistence of tie-line data was ascertained by applying the Othmer–Tobias and Bancroft equations.     

Gemini阳离子表面活性剂在水溶液中胶团化行为的温度效 应与焓、熵补偿

测定了Cemini阳离子表面活性剂C~m-----s-----C~m·2Br(m=8,10,12,;s=2,6及m=12;s=3,4)水溶液的电导,从电导(k)～表面活性剂浓度(c)曲线的转折点可求得临界胶团浓度cmc.实验发现,Gemini阳离子表面活性剂的胶团化倾向明显强于其“单体分子”)即单离子头基单烷烃链表面活性剂)。根据质量作用模型计算了胶经过程的吉布氏能、焓和熵的改变。结果表明Gemini表面活性剂聚集机理和其对应的“单体分子”类似,主要来自熵驱动。所有的焓/熵补偿图均呈现良好的线性关系,补偿直线在γ轴的截距随s减小而变小,这意味着具有较小s的Gemini表面活性剂倾向于生成稳定的胶团。     

Formation of ionic associates by Phenol Red and their interaction with ionic surfactants in aqueous solutions

Formation of associates between single-or double-charged anions of sulfophthalein dye Phenol Red and single-charged cations of cyanines in aqueous solutions was considered. The association constants were estimated from the spectral data. Geometric and energy characteristics of the associates were calculated. The suitability of the associates formed by Phenol Red for quantitative determination of cationic surfactants in aqueous solutions was examined.     

Sonochemistry of surfactants in aqueous solutions: an EPR spin-trapping study.

The surfactant properties of solutes play an important role in the sonochemistry and sonoluminescence of aqueous solutions. Recently, it has been shown, for relatively low molecular weight surfactants, that these effects can be correlated with the Gibbs surface excess of the solute. In the present study we investigate whether this correlation is valid for relatively high molecular weight surfactants and the mechanisms of surfactant decomposition during sonolysis. Sonolysis of argon-saturated aqueous solutions of nonvolatile surfactants [n-alkanesulfonates, n-alkyl sulfates, n-alkylammoniopropanesulfonates (APS), and poly(oxyethylenes) (POE)] was investigated by EPR and spin-trapping with 3,5-dibromo-4-nitrosobenzenesulfonate. Secondary carbon radicals (-.CH-), formed by abstraction reactions, were observed for all surfactants that were sonicated. The yield of primary carbon (-.CH(2)) and methyl (.CH(3)) radicals that are formed by pyrolysis is greatest for the zwitterionic (i.e., APS) and nonionic surfactants (i.e., POE). The yield of (-.CH-) radicals was measured following sonolysis of n-alkyl anionic surfactants [sodium pentanesulfonate (SPSo), sodium octanesulfonate (SOSo), sodium octyl sulfate (SOS), and sodium dodecyl sulfate (SDS)]. In the concentration range of 0-0.3 mM, the -.CH- radical yield increases in the order SDS approximately equal to SOS approximately equal to SOSo > SPSo. At higher concentrations, a plateau in the maximum (-.CH-) radical yield is reached for each surfactant, which follows the order SPSo > SOS approximately equal to SOSo > SDS; i.e., the radical scavenging efficiency increases with decreasing n-alkyl chain length. A similar trend was observed for the .CH(3) yield following sonolysis of a homologous series of n-alkyl APS surfactants. The results show that the Gibbs surface excess of certain nonvolatile surfactants does not correlate with the extent of decomposition following sonolysis in aqueous solutions. Instead, the decomposition of surfactants depends on their chemical structure and their ability to equilibrate between the bulk solution and the gas/solution interface of cavitation bubbles.     

Cation-anion-water interactions in aqueous mixtures of imidazolium based ionic liquids

We have examined the cation-anion-water interactions in aqueous mixtures of imidazolium ionic liquids (ILs) over the whole composition range using FTIR spectroscopy. Changes in the peak positions or band areas of OH vibrational modes of water and CH vibrational modes of imidazolium cation as a function of IL concentration indicated a diminishing trend in hydrogen-bonding network of water and qualitative changes in solution structures. ¹H NMR chemical shifts of C(2)H, HC(4)C(5)H and alkyl chain protons of imidazolium cation provided useful information about the comparative strength of cation-anion-water interactions.     

Electrical conductivity study on micelle formation of long-chain imidazolium ionic liquids in aqueous solution

Electrical conductivity was measured for aqueous solutions of long-chain imidazolium ionic liquids (IL), 1-alkyl-3-methylimidazolium bromides with C(12)-C(16) alkyl chains. The break points appeared in specific conductivity (kappa) vs concentration (c) plot indicates that the molecular aggregates, i.e., micelles, are formed in aqueous solutions of these IL species. The critical micelle concentration (cmc) determined from the kappa vs c plot is somewhat lower than those for typical cationic surfactants, alkyltrimethylammonium bromides with the same hydrocarbon chain length. The electrical conductivity data were analyzed according to the mixed electrolyte model of micellar solution, and the aggregation number, n, and the degree of counter ion binding, beta, were estimated. The n values of the present ILs are somewhat smaller than those reported for alkyltrimethylammonium bromides, which may be attributed to bulkiness of the cationic head group of the IL species. The thermodynamic parameters for micelle formation of the present ILs were estimated using the values of cmc and beta as a function of temperature. The contribution of entropy term to the micelle formation is superior to that of enthalpy term below about 30 degrees C, and it becomes opposite at higher temperature. This coincides with the picture drawn for the micelle formation of conventional ionic surfactants.     

Thermodynamic study in aqueous solutions of weakly soluble ionic compounds

Any investigation for a better knowledge of precipitation/dissolution problems necessitates the availability of all the beta formation constants of the uncharged soluble species (ion-pair). Several difficulties dealing with solubility measurements are briefly reviewed, especially related to phase structure variations, time-lag or supersaturation phenomena. Thanks to some thermodynamic considerations, the evolution of the uncharged soluble species with hydration and solid phase modifications can give a new explanation about the observed dispersion in literature values for some weakly soluble ionic compounds. When not given elsewhere, the evaluation of thermodynamic data of interest (formation constants, solubility product, etc.) is made possible according to given methods.     

Correlation between surface free energy of quartz and its wettability by aqueous solutions of nonionic, anionic and cationic surfactants

The measurements of the advancing contact angle for water, glycerol, diiodomethane and aqueous solutions of Triton X-100 (TX-100), Triton X-165 (TX-165), sodium dodecyl sulfate (SDDS), sodium hexadecyl sulfonate (SHDS), cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) on quartz surface were carried out. On the basis of the contact angles values obtained for water, glycerol and diiodomethane the values of the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of the surface free energy of quartz were determined. The determined components and parameters of the quartz surface free energy were used for interpretation of the influence of nonionic, anionic and cationic surfactants on the wettability of the quartz. From obtained results it was appeared that the wettability of quartz by nonionic and anionic surfactants practically does not depend on the surfactants concentration in the range corresponding to their unsaturated monolayer at water–air interface and that there is linear dependence between adhesional and surface tension of aqueous solution of these surfactants. This dependence for TX-100, TX-165, SDDS and SHDS can be expressed by lines which slopes are positive. This slope and components of quartz surface free energy indicate that the interaction between the water molecules and quartz surface might be stronger than those between the quartz and surfactants molecules. So, the surface excess of surfactants concentration at the quartz–water interface is probably negative, and the possibility of surfactants to adsorb at the quartz/water film–water interface is higher than at the quartz–water interface. This conclusion is confirmed by the values of the adhesion work of “pure” surfactants, aqueous solutions of surfactants and water to quartz surface. In the case of the cationic surfactants the relationship between adhesional and surface tension is more complicated than that for nonionic and anionic surfactants and indicates that the relationship between the adsorption of the cationic surfactant at water–air and quartz–water interface depends on the concentration of the surfactants in the bulk phase.     

Pulse radiolytic investigation of perfluorinated surfactants in aqueous solutions

Pulse radiolysis studies were performed for aqueous solutions of ammonium perfluorooctanoate, tetraethylammonium perfluorooctyl sulfonate, and an ammonium salt of a carboxylic perfluoropolyether derivative. The protiated system of sodium octanoate was also examined for comparison. The rate constants of hydrated electron (e⁻ _aq) and ^·OH radical reactions with these amphiphiles, and absorption spectra of the intermediate products are reported for the first time. It is demonstrated that the critical micellar concentrations (CMC) can be determined from the kinetic data. The observed differences in e⁻ _aq reactivity towards fluorinated amphiphiles above CMC are rationalized in terms of different charge density at the micellar interface.     

Micellization in aqueous solutions of mixed surfactants containing alkylpolyglucosides

Tensometry is used to find the dependences of critical micelle concentration in aqueous solutions on the composition of mixed systems comprising anionic surfactants (alkyl sulfates and individual sodium soaps) and alkylpolyglucosides. Mixed micellization is revealed and the compositions of micelles and the parameters of intermolecular interaction are calculated. The average hydrodynamic diameter of micelles is measured by dynamic light scattering.     

Transport properties of alkyltrimethylammonium bromide surfactants in aqueous solutions

Differential mutual diffusion coefficients of n-alkyltrimethylammonium bromides [CH₃(CH₂)_n–1N(CH₃)₃Br, C_nTAB] (n=10, 12, 14, 16) have been measured in aqueous solutions at 298.15 K using a conductimetric cell and an automatic apparatus to follow diffusion. The cell is based on an open-ended capillary, and the technique follows the diffusion process by measuring the resistance of a solution inside the capillaries at various times. The electrical conductances of those solutions have also been measured to calculate the critical micellar concentration (cmc). Thermodynamic analysis of the data suggests that the free ion concentration decreases at concentrations above the cmc, in agreement with theoretical predictions. The obtained values of the micellization parameters were used to model the mutual diffusion coefficients of C_nTAB aqueous solutions.