Effects of Spacer Chain Length and Additives on Solution Properties of Cationic Gemini Surfactant

The critical micelle concentration (CMC) has been determined for the gemini surfactant trimethylene-1,3-bis(dodecyldimethyl ammonium bromide)12-s-12,2Br^?1 by means of electricity conductivity measurements. For the same number of carbon atoms in the hydrophobic chain per hydrophilic head group, geminis have CMC values well below those of conventional single-chain cationic surfactants. The CMC of 12-3-12 reduces with the addition of n-alcohol except ethanol and with the increase of n-alcohol chain length as well as increase of concentration of n-butanol and sodium chloride. Steady-state fluorescence quenching technology has been employed to study the aggregation number of micelle, which increases with increase in the length of n-alcohol. The Kraft temperature measurements also indicate that the stability of solid surfactant hydrate decreases along with the improvement of concentration of n-butanol and sodium chloride.     

Effect of counterion on thermodynamic micellar properties of tetradecylpyridinium in aqueous solutions

Electrical conductivity of aqueous solutions of tetradecylpyridinium bromide and chloride has been measured as a function of surfactant molal concentration and temperature. From the molal dependence of conductivity, the critical micelle concentration and the micellar ionization degree were estimated. The temperature dependence of these parameters has been used for calculating the thermodynamic parameters related with the micellization process by using the classical charged pseudophase separation model. The effect of the counterion on the conventional thermodynamic potentials of micellization such as standard Gibbs free energy, enthalpy and entropy has also been a matter of study. Finally, the occurrence of the enthalpy–entropy compensation phenomenon was verified and the relevant parameters discussed.     

Effects of Fructose and Temperature on the Micellization of a Cationic Gemini Surfactant,Pentanediyl-1,5-bis(dimethylcetylammonium) Bromide in Aqueous Solutions

By the conductivity measurements the effects of fructose and temperature (293–308 K) on the micellization of a cationic gemini surfactant (GS), pentanediyl-1,5-bis(dimethylcetylammonium) bromide in aqueous solutions have been investigated. The critical micelle concentration (CMC) of GS was measured at the different temperatures and fructose concentrations. An increasing trend of the CMC values is with addition of fructose. With increasing temperature, the CMC values are in a similar increasing trend. The CMC of GS by dye solubilization method at room temperature have been determined. The standard Gibbs energy, enthalpy and entropy of GS micellization have been evaluated. From these thermodynamic parameters, it was found that in presence of fructose, the stability of the GS aqueous solutions decreases.     

Effect of (chloride salt) electrolytes on the mixed micellization of (equimolar) a cationic gemini (dimeric) surfactant and a cationic conventional (monomeric) surfactant

Herein we report the effect of (chloride salt) electrolytes on the mixed micellization of (equimolar) a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide) (16-6-16), and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB) in aqueous solutions. In absence and presence of (chloride salt) MCl (where M?Li, Na, and K) electrolytes, the critical micelle concentration (CMC) of mixed (16-6-16 + CTAB) surfactants was measured by surface tension measurements. With increasing the concentration of electrolyte, the CMCs were increasing. The surface properties and the thermodynamic parameters of the mixed micellar systems were also evaluated. From these evaluated thermodynamic parameters, it was found that in presence of electrolyte the stability of the mixed micellar system is more.     

Conductometric studies of hexadecyltrimethylammonium bromide in aqueous solutions of ethanol and ethylene glycol

The effect of cosolvent on micellization of hexadecyltrimethyl ammonium bromide (CTAB) in aqueous solutions was studied. The conductivity of a mixture (cosolvent + water) as function of CTAB concentration was measured at different temperatures. Ethylene glycol and ethanol were used as a cosolvent. The conductivity data were used to determine the critical micelle concentration (CMC) and the effective degree of counterion dissociation of micelle in the temperature range 303.2 to 313.2 K. In all the cases studied, a linear relationship between log([CMC]_mix/mol dm⁻³) and the mass fraction of cosolvent in solvent mixture has been observed. The free energy (ΔG _mic ⁰ ), enthalpy (ΔH _mic ⁰ ), and entropy (ΔS _mic ⁰ ) of micellization were determined using the temperature dependence of CMC. The dependence of these thermodynamic parameters on solvent composition was determined. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the cosolvent content increases. The enthalpy and entropy of micellization are independent of temperature in pure water, while ΔH _mic ⁰ and ΔS _mic ⁰ decrease dramatically with temperature in mixed cosolvents. Furthermore, the entropic contribution is larger than the enthalpic one in pure water, while in the mixed solvents, the enthalpic contribution predominates. The text was submitted by the authors in English.     

Characterization of Surfactant-Diblock Copolymer Interactions and Its Thermodynamic Studies

The interaction of nonionic diblock copolymer poly(ethylene oxide butylene oxide) (E₆₂B₂₂) with a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) were studied using surface tension, conductivity, and dynamic laser light scattering techniques. Surface tension measurements were used to determine critical micelle concentration and thereby its free energy of adsorption (ΔG_ads), free energy of micellization (ΔG_m), surface excess concentration (Γ), and minimum area per molecule (A). Conductivity measurements were used to determine critical micelle concentration (CMC) critical aggregation concentration (CAC) at different temperatures, enthalpy of micellization (ΔH_m), free energy of micellization and entropy of micellization (ΔS_m). Changes in physicochemical properties of the micellized block copolymer were studied by using dynamic laser light scattering. The effect of surfactant on the size and properties of block copolymer has also been discussed.     

Micelle formation of N-(1,1-dihydroperfluorooctyl)- and N-(1,1-dihydroperfluorononyl)-N,N,N-trimethylammonium chlorides

Micelle formation of N-(1,1-dihydroperfluorooctyl)-N,N,N- and N-(1,1-dihydroperfluorononyl)-N,N,N-trimethylammonium chloride was investigated by analyzing the concentration dependence of the electric conductivity and of the activity of the counterion (Cl(-)) of the solution. The three micellization parameters for ionic surfactants, the micellization constant K(n), the micelle aggregation number n, and the number of counterions per micelle m, were determined by combination of electric conductivity and counterion concentration. The present analysis employed two slopes of the plots of specific conductivity against surfactant concentration below and above the critical micelle concentration and the mass action model of micelle formation. The aggregation numbers thus obtained were relatively small, while the degrees of counterion binding to the micelle (m/n) were found to be quite large, much larger than expected from the small aggregation numbers. Thermodynamical parameters of the micellization were evaluated from the temperature dependence of the three parameters, and the micellization of the fluorinated surfactant was found to be enthalpy-driven. A CF(2) group in the perfluorocarbon chain was found to be 1.44 times larger in hydrophobicity for micellization than a CH(2) group in the hydrocarbon chain.     

Thermodynamic and micellization studies of a cationic gemini surfactant 16-6-16: Influence of ascorbic acid and temperature

Herein, we report the study of the influence of ascorbic acid and temperature on the micellization of a cationic gemini surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide), 16-6-16. The critical micelle concentration (CMC) of 16-6-16 was measured by the conductivity method and dye solubilisation technique. A tendency of the CMC values to increase with temperature and upon the adding of ascorbic acid was found. The standard Gibbs energy, standard enthalpy, and standard entropy of micellization of 16-6-16 were evaluated. The results of calculations suggest the decrease of the stability of the 16-6-16 micellar solution in the presence of ascorbic acid.     

Thermodynamics of micellization of tetradecyltrimethylammonium bromide in ethylene glycol–water binary mixtures

The aggregation behaviour of tetradecyltrimethylammonium bromide in ethylene glycol–water mixtures across a range of temperatures has been investigated by electrical conductivity measurements. The critical micelle concentration (cmc) and the degree of counterion dissociation of micelles were obtained at each temperature from plots of differential conductivity, (κ/c) _{T , P} , versus the square root of the total concentration of the surfactant. This procedure not only enables us to determine the cmc values more precisely than the conventional method, based on plots of conductivity against total concentration of surfactant, but also allows straightforward determination of the limiting molar conductance and the molar conductance of micellar species. The equilibrium model of micelle formation was applied to obtain the thermodynamics parameters of micellization. Only small differences have been observed in the standard molar Gibbs free energies of micellization over the temperature range investigated. The enthalpy of micellization was found to be negative in all cases, and it showed a strong dependence on temperature in the ethylene glycol poor solvent system. An enthalpy–entropy compensation effect was observed for all the systems, but whereas the micellization of the surfactant in the solvent system with 20 wt% ethylene glycol seems to occur under the same structural conditions as in pure water, in ethylene glycol rich mixtures the results suggest that the lower aggregation of the surfactant is due to the minor cohesive energy of the solvent system in relation to water. Received: 13 December 1998 Accepted in revised form: 25 February 1999     

Study on the adsorption and aggregation of dilute gemini surfactant solutions

As a function of temperature in aqueous solutions, the adsorption and aggregation of N,N’-bis (tetradecyl dimethyl)-1,2-dibromide-ethanediyl ammonium salt (GS14-2-14) and N,N’-bis (hexadecyl dimethyl)-1,2-dibromide-ethanediyl ammonium salt (GS16-2-16), were researched with drop-volume technique and conductometry, respectively. The results of surface tension measurements, which were analyzed by originally developed thermodynamic equations, illustrate that GS14-2-14 has a better surface activity and arranges more tightly in the adsorbed film than GS16-2-16. The data of conductivity were used to find critical micelle concentration (cmc) and counterion binding degree of micelle (β). Thermodynamic parameters of micellization were also obtained from the temperature dependence of cmc values. From the study, it is discovered that the micellization process is spontaneous and exothermic in nature and it is mainly driven by entropy.     

Effects of Short‐Chain Alcohol on the Micellization of Gemini Surfactant C16‐6‐16 · 2Br in Aqueous Solution

The effects of ethanol, n‐butanol, and n‐hexanol on the micellization of cationic Gemini surfactant C16‐6‐16 · 2Br have been investigated using conductance and steady fluorescence measurements. The results show that the critical micelle concentration (CMC) increases with the addition of ethanol, but decreases with n‐butano1 or n‐hexanol. With the addition of the above alcohols, both the micelle ionization degree and the mole fraction of alcohol in the micelle increase, however, the micelle aggregation number decreases at a fixed concentration of surfactant. When given a special concentration of alcohol, the micelle aggregation number increases as the increase of the surfactant concentration.     

Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution

The aggregation behavior of metal dodecyl sulfates (MDS), [Na¹⁺, Mg²⁺, Mn²⁺, Co²⁺, and Ni²⁺] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (ΔG_m ⁰), enthalpy (ΔH_m ⁰), and entropy (ΔS_m ⁰) were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc) _T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion.     

Interaction of Quercus Infectoria Natural Dye with Cationic and Anionic Surfactants: Adsorption/Micellization of Dye

The interaction of Indian natural dye, that is, Himalaya (Quercus infectoria) with cationic surfactant (cetyl trimethyl ammonium bromide) and anionic surfactant (sodium lauryl sulphate) has been studied. The spectrophotometric data showed an interaction between the natural dye and surfactants. Critical micelle concentration (CMC) of the surfactants, determined by measurement of specific conductance and surface tension methods, was found to be increase in case of anionic surfactant while that was found to decrease in case of cationic surfactant. Thermodynamic and surface parameters showed domination of micellization of dye in case of cetyl trimethyl ammonium bromide and domination of adsorption of dye in case of sodium lauryl sulphate.     

Micellization and mixed micellization of cationic gemini (dimeric) surfactants and cationic conventional (monomeric) surfactants: Conductometric,dye solubilization,and surface tension studies

In the present study, we have investigated the self-association, mixed micellization, and thermodynamic studies of a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide (16-6-16)) and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of pure (16-6-16 and CTAB) and mixed (16-6-16+CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), A_min (the minimum area per surfactant molecule at the air/water interface), etc.) of micellar (16-6-16 or CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were evaluated. The thermodynamic parameters of the micellar (16-6-16 and CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were also evaluated.     

Influence of Glycerol and Temperature on the Phase Behavior and Micellization of CTAB and SDS in Aqueous Solutions

In this work the micellization of sodium dodecylsulfate (SDS) and cetyltrimethyammonium bromide (CTAB) in water-glycerol mixed solvent have been investigated at 25, 35, and 45°C, respectively. The micellization of both surfactants in pure water at different temperatures has also been studied. The phase diagrams of the surfactants in water-glycerol mixed solvent were also established. From the conductivity measurements, the critical micelle concentration (CMC) and the degree of counterion dissociation (β) were obtained as a function of glycerol-water ratio and temperature. Standard free energy of micellization (ΔG°_mic) as a function of glycerol contents and temperature was calculated and discussed. It has been found that the micellization of the two surfactant in solutions with glycerol at 25°C and in pure water at higher temperatures are not the same although they have equal dielectric constants values.     

Characterization of Binary Surfactant Mixtures (Cetylpyridinium Chloride and Tween 60) in an Aqueous Medium

Abstract

Micellar properties of the binary surfactant mixtures of cetylpyridinium chloride (CPC) and polyoxyethylene (20) sorbitan monostearate (Tween‐60) have been investigated in detail using tensiometric, conductometric, spectrophotometric, and fluorimetric techniques. The critical micelle concentration (CMC), counterion binding, interfacial adsorption, energetics of micellization, and micellar dielectric constant have been evaluated. The theories of Clint, Motomura, Rubingh, and Sarmoria, Puvvada and Blankschtein have been followed to understand the CMC, composition, activity coefficients, and synergism of the binary surfactant systems.     

Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Activation parameters, ΔE _a, ΔH ^#, ΔS ^#, ΔG ^≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ_max), minimum area per surfactant molecule (A _min), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π_max), Gibb’s energy of micellization (ΔG _M°), Gibb’s energy of adsorption (ΔG _ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.     

The physicochemical and thermophysical properties of sodium dodecyl sulfate: The influence of p-toluene sulfonyl chloride and temperature

In the present study, we report on the interaction between a hydrotrope, p-toluene sulfonyl chloride (p-TSC), and an anionic surfactant, sodium dodecyl sulfate (SDS) which has been performed using electrical conductivity, Fourier transform infrared (FTIR), ¹H NMR, density, dynamic viscosity, and kinematic viscosity measurements. The effect of p-TSC on the micellization of SDS in non-aqueous (ethanol) medium at various temperatures (viz., 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K) was investigated using the electrical conductivity method. The results show that the CMC value increases as the concentration of the hydrotrope is increased. It is noteworthy that at higher concentrations of hydrotrope, the trend of micelle formation is reversed (i.e., reverse micelles are formed). The thermodynamic parameters in micellization have also been evaluated. The FTIR and ¹H NMR data reveal the physicochemical properties of the pure and mixed systems and confirm no covalent bond formation takes place. Density, dynamic viscosity, and kinematic viscosity of the pure as well as mixed systems at various temperatures were also reported.     

Micelle–monomer equilibria in solutions of ionic surfactants and in ionic–nonionic mixtures: A generalized phase separation model

On the basis of a detailed physicochemical model, a complete system of equations is formulated that describes the equilibrium between micelles and monomers in solutions of ionic surfactants and their mixtures with nonionic surfactants. The equations of the system express mass balances, chemical and mechanical equilibria. Each nonionic surfactant is characterized by a single thermodynamic parameter — its micellization constant. Each ionic surfactant is characterized by three parameters, including the Stern constant that quantifies the counterion binding. In the case of mixed micelles, each pair of surfactants is characterized with an interaction parameter, β, in terms of the regular solution theory. The comparison of the model with experimental data for surfactant binary mixtures shows that β is constant — independent of the micelle composition and electrolyte concentration. The solution of the system of equations gives the concentrations of all monomeric species, the micelle composition, ionization degree, surface potential and mean area per head group. Upon additional assumptions for the micelle shape, the mean aggregation number can be also estimated. The model gives quantitative theoretical interpretation of the dependence of the critical micellization concentration (CMC) of ionic surfactants on the ionic strength; of the CMC of mixed surfactant solutions, and of the electrolytic conductivity of micellar solutions. It turns out, that in the absence of added salt the conductivity is completely dominated by the contribution of the small ions: monomers and counterions. The theoretical predictions are in good agreement with experimental data.     

Aggregation behavior of hexadecyltrimethylammonium surfactants with various counterions in aqueous solution

Both thermodynamic and microenvironmental properties of the micelles for a series of cationic surfactants hexadecyltrimethylammonium (C16TAX) with different counterions, F-, Cl-, Br-, NO3-, and (1/2)SO4(2-), have been studied. Critical micelle concentration (CMC), degree of micelle ionization (alpha), and enthalpy of micellization (DeltaH(mic)) have been obtained by conductivity measurements and isothermal titration microcalorimetry. Both the CMC and the alpha increase in the order SO4(2-) < NO3- < Br- < Cl- < F-, consistent with a decrease in binding of counterion, except for the divalent anion sulfate. DeltaH(mic) becomes less negative through the sequence NO3- < Br- < Cl- < F- < SO4(2-), and even becomes positive for the divalent sulfate. The special behavior of sulfate is associated with both its divalency and its degree of dehydration. Gibbs free energies of micellization (DeltaG(mic)) and entropies of micellization (DeltaS(mic)) have been calculated from the values of DeltaH(mic), CMC, and alpha and can be rationalized in terms of the Hofmeister series. The variations in DeltaH(mic) and DeltaS(mic) have been compared with those for the corresponding series of gemini surfactants. Electron spin resonance has been used to assess the micropolarity and the microviscosity of the micelles. The results show that the microenvironment of the spin probe in the C16TAX surfactant micelles depends strongly on the binding of the counterion.