Self-aggregation of binary mixtures of alkyltriphenylphosphonium bromides: a critical assessment in favor of more than one kind of micelle formation

The micellization behavior of binary combinations of alkyltriphenylphosphonium bromides (ATPBs) with alkyl chain carbons 10, 12, 14, and 16 has been studied by conductometry and calorimetry. The combinations C(10)-C(12), C(10)-C(14), C(10)-C(16), C(12)-C(14), C(12)-C(16), and C(14)-C(16) were found to form two cmc's by both the methods, with good agreement, except C(14)-C(16)TPB, which has evidenced only a single cmc by calorimetry for all combinations. The combinations C(10)-C(12) (for both cmc(1) and cmc(2)) and C(10)-C(14)TPB (for cmc(2)) formed ideal mixtures, whereas the rest were nonideal. In the nonideal binary mixtures, the ATPB components showed antagonistic interaction with each other. The cmc, interaction parameter (beta), mixed micellar composition, extent of counterion binding, and thermodynamic parameters for the micellization process have been reported and discussed. The enthalpy of mixed micelle formation has been found to have a fair correlation with a Clint-type relation applicable to ideal binary mixtures of surfactants.     

Physicochemical studies on the micellization behavior of cetylpyridinium chloride and triton X-100 binary mixtures in aqueous medium

Physicochemistry of micellization of binary mixtures of cetylpyridinium chloride (CPC) and Triton X-100 (TX-100) have been investigated and the data collected have been analyzed and correlated. Tensiometric, conductometric, spectrophotometric, calorimetric and polarographic methods have been employed in the study. Parameters like critical micellar concentration (CMC), counter-ion binding, energetics of micellization, interfacial surfactant adsorption and minimum area of amphiphile head groups at CMC have been determined. The diffusion coefficients of pure and mixed micelles in solution have been determined by the polarographic method. The regular solution theory of Rubingh has been considered to get information on the micellar composition and their mutual interaction (synergistic for the studied system) in solution. The packing of the monomer in micelle has been estimated to witness spherical geometry for CPC and its mixtures with TX-100, whereas the later has been found to be spheroidal. Polarographic measurements have evidenced comparable diffusion coefficients of CPC and TX-100 micelles whereas their mixed micelles have shown lower values with a minimum, at equimolar composition.     

Micellization and related behavior of binary and ternary surfactant mixtures in aqueous medium: cetyl pyridinium chloride (CPC), cetyl trimethyl ammonium bromide (CTAB), and polyoxyethylene (10) cetyl ether (Brij-56) derived system

Mixed micelles formed with cetyl pyridinium chloride (CPC), cetyl trimethylammonium bromide (CTAB), and polyoxyethylene (10) cetyl ether (Brij-56) mixed in different combinations in aqueous medium have been studied in detail by tensiometric, conductometric, calorimetric, spectrophotometric, and fluorimetric techniques. Different physicochemical properties such as critical micellar concentration (cmc), micellar dissociation, energetic parameters (free energy, enthalpy, and entropy) of micellization, interfacial adsorption, and micellar aggregation number have been determined. The results have been analyzed in terms of the equations of Clint, Motomura, Rosen, Rubingh, Blankschtein et al., and Rubingh and Holland for justification of the experimental cmc, determination of micellar composition parameters, quantification of interaction among the mixed micelle components, and estimation of their activity coefficients.     

Unusual behavior of CMC for binary mixtures of alkyltrimethylammonium bromides: dependence on chain length difference

The critical micelle concentrations (CMC) of binary mixtures of alkyltrimethylammonium bromides (CnTAB) were measured by a conductivity method. The CMCs of C12TAB-C14TAB and C14TAB-C16TAB systems exhibit the usual behavior, namely a monotonic decrease of the CMC with the mole fraction of the longer chain surfactant. However, the CMC behaviors of C10TAB-C16TAB, C11TAB-C16TAB, C12TAB-C16TAB, and C11TAB-C14TAB are unusual. The behaviors of the CMCs with mole fraction for these systems consist of three regions, of which the first is characterized by a very small decrease of the CMC in the range of low mole fraction, followed by a second where there is an abrupt decrease of the CMC, and a third where the CMCs exhibit their usual behavior. The molecular interaction parameter omega is almost equal to zero for mixtures that have the usual CMC behavior, but is small and positive for those systems with unusual CMCs. We infer that for very low mole fractions of C16TAB, the C16TA ion in the C12TAB-C16TAB system penetrates imperfectly into the micelle and its two methylene groups exist outside the micelle.     

Conductometric and spectrofluorimetric characterization of the mixed micelles constituted by dodecyltrimethylammonium bromide and a tricyclic antidepressant drug in aqueous solution

Conductivity and static fluorescence measurements have been carried out at 25 degrees C to study the monomeric and micellar phases of aqueous solutions of mixed micelles constituted by a conventional cationic surfactant, dodecyltrimethylammonium bromide (D(12)TAB), and a tricyclic antidepressant drug, amitriptyline hydrochloride (AMYTP), with aggregation properties. From conductivity data, the total mixed critical micelle concentration and the dissociation degree of the mixed micelle have been obtained, while fluorescence experiments allow for the determination of the total aggregation number, and the micropolarity of micellar inside. Furthermore, the partial contribution of each surfactant to the mixed micellization process, through their critical micelle concentrations and their aggregation numbers have been determined, as well. The solubilization of the drug in the mixed micelles has been also studied through the mass action model, by determining the association constant between the micelles and the drug. From these results, the use of the micelles studied in this work as potential models for vectors of antidepressant drugs of the amitriptyline family has been discussed. The theoretical aspects of the mixed micellization process have been also analyzed.     

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.     

Conductivities, volumes, fluorescence, and aggregation behavior of ionic liquids [C4mim][BF4] and [C(n)mim]Br (n = 4, 6, 8, 10, 12) in aqueous solutions

Densities, conductivities, and polarity indexes of pyrene for aqueous solutions of a series of ionic liquids [C(n)mim]Br (n = 4, 6, 8, 10, 12) and [C4mim][BF4] have been determined at 298.15 K as a function of ionic liquid concentrations. It was shown that possible aggregation appeared for the ionic liquids in aqueous solutions except for [C4mim]Br. The critical aggregation concentration (CAC) of the ionic liquids, the ionization degree of aggregates (beta), the standard Gibbs energy of aggregation (Delta G(m)(o)), the limiting molar conductivity (Lambda(m)(o)), and the standard partial molar volume (V(m)(o)) for the ionic liquids were derived from the experimental data. The dependence of the CAC, Delta G(m)(o), Lambda(m)(o), and V(m)(o) on the length of the alkyl chain of the cations was examined. It was further suggested from volumetric data that a micelle was formed for [C8mim]Br, [C10mim]Br, and [C12mim]Br in aqueous solutions. Their apparent molar volumes at the critical micelle concentration (V Phi,CMC), apparent molar volumes in the micelle phase (V(Phi)(mic)), and the change of their apparent molar volume upon micellization (Delta V Phi,m) were calculated by application of the pseudophase model of micellization. In addition, the average aggregation number of [C(n)mim]Br (n = 8, 10, 12) has been determined by the steady-state fluorescence quenching technique, and predicted from a simple geometrical mode. It is found that the experimental values are in good agreement with the predicted ones.     

Effects of organic solvent addition on the aggregation and micellar growth of cationic dimeric surfactant 12-3-12,2Br-

The micellization and micellar growth of cationic dimeric surfactant propanediyl-alpha-omega-bis(dodecyldimethylammonium) bromide, 12-3-12,2Br-, have been studied in several water-organic solvent mixtures. The organic solvents were ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, acetonitrile, dioxane, formamide, and N,N-dimethylformamide. Results showed that the aggregation process was less favored in the binary mixtures than in pure water, which was explained by considering the influence of the solvophobic effect on micellization. The addition of organic solvents was accompanied by a diminution in the average aggregation number, Nagg, of the dimeric micelles. This diminution was due to the decrease in the interfacial Gibbs energy contribution, Delta G0interfacial, to the Gibbs energy of micellization caused by the decrease in the hydrocarbon/bulk-phase interfacial tension. As a result of the micelle size diminution, the concentration at which the sphere-to-rod transition occurred, C*, was higher in the mixtures than in pure water. Micelle size reduction is accompanied by a decrease in the ionic interactions and in the extra packing contribution to the deformation of the surfactants tails, making the formation of cylindrical micelles less favorable.     

Mixtures of monomeric and dimeric surfactants: hydrophobic chain length and spacer group length effects on non ideality

Critical micelle concentrations of the Cm TAB+12- s-12 (s=3, 4, 5 and m=10, 12, 14, 16) binary systems have been determined, through conductivity and fluorescence measurements, at 298 K. Application of different theoretical approaches to explain mixed micellization shows that non-ideality of the binary systems follows the trend C16TAB+12-3-12相似文献   

Aggregation behavior and interaction of an amphiphilic drug imipramine hydrochloride with cationic surfactant cetyltrimethylammonium bromide: light scattering studies

The aggregation behavior and interaction of an amphiphilic antidepressant drug imipramine (IMP) hydrochloride with the cationic surfactant cetyltrimethylammonium bromide (CTAB) have been studied using light scattering (both static and dynamic) techniques. Due to rigid tricyclic hydrophobic moiety present in the molecule, the drug shows interesting association behavior. The static light scattering measurements show that the self-association of IMP commenced above a well-defined critical micellar concentration (CMC), which decreases with increasing the mole fraction of the CTAB surfactant. Both the excess Gibbs energy (ΔG(ex)) and the Gibbs energy of micellization (ΔG(M)°) are negative, and decrease with increasing mole fraction of the surfactant. The hydrodynamic diameters (d(h)) of the micellar aggregates were also evaluated using the dynamic light scattering measurements. The data indicate formation of larger aggregates by IMP and CTAB due to mixed micellization and subsequent micellar growth. The results have been analyzed using different models (viz., Clint, Motomura, Rosen, Rubingh, etc.) for mixed micelle formation.     

Analysis of interfacial and micellar behavior of sodium dioctyl sulphosuccinate salt (AOT) with zwitterionic surfactants in aqueous media

The interfacial and bulk properties of mixtures of the anionic surfactant (dioctyl sulphosuccinate sodium salt, AOT) with zwitterionic surfactants 3-(N,N-dimethyldodecylammonio) propane sulfonate (DPS), 3-(N,N-dimethyltetradecylammonio) propane sulfonate (TPS), 3-(N,N-dimethylhexadecylammonio) propane sulfonate (HPS) have been studied employing surface tension, fluorescence, and viscometric techniques in aqueous media at 25 °C. It is observed that these mixtures exhibit synergism and these synergistic interactions increase with the enhancement of the hydrocarbon chain of the zwitterionic surfactant. The various physicochemical properties such as critical micelle concentration (cmc), surface excess concentration (Г(max)), minimum area per molecule (A(min)), aggregation number (N(agg)), interaction parameters (β(σ), β(m)), and thermodynamic parameters such as standard Gibbs free energy of adsorption (ΔG(ads)(o)), excess free energy of micellization (ΔG(ex)), and standard Gibbs free energy of micellization (ΔG(m)(o)) have been evaluated. The negative values of ΔG(m)(o) and ΔG(ads)(o) show that the micelle formation and adsorption of surfactant at the air/solution interface is energetically favorable, while a negative value of ΔG(ex) ensures stability of the mixed micelles formed. The Regular Solution Approximation, Motomura and Rosen's approaches have been used to explain and compare the results. The packing parameter (p) ensures the formation of vesicles or bilayers for AOT+DPS/TPS mixtures, which can potentially be used as delivery agents for industrial applications.     

Transport Properties of Aqueous Solutions of Alkyltrimethylammonium Bromide Surfactants at 25 degrees C

Intradiffusion coefficients, D, of n-alkyltrimethylammonium bromides [CH(3)-(CH(2))(n-1)-N(CH(3))(3)Br, C(n)TAB] (n=6, 8, 10, 12) in mixtures with heavy water were measured by the PGSE-NMR technique at 25 degrees C. The experimental data permitted evaluation of the influence of the alkyl chain length on the surfactant self-aggregation process. For all the surfactants considered, the D trend showed a slope change corresponding to the critical micellar composition (cmc). In the premicellar composition range, D decreased linearly with the square root of the surfactant molality. The D values extrapolated at infinite dilution were related to the limiting mutual diffusion coefficients, determined through the Taylor dispersion technique. In the micellar composition range, solubilized tetramethylsilane (TMS) molecules were used to determine the micelle intradiffusion coefficient, D(M), from which the aggregate radii and the aggregation numbers were obtained. The decreasing trend of D(M) with increasing surfactant molality was interpreted in terms of interparticle electrostatic repulsion. D(M) values allowed evaluation of the Gouy-Chapman layer thickness. The solvent intradiffusion coefficient in the heavy water-C(n)TAB mixtures, D(w), was also measured. It decreased with increasing surfactant molality. For n=8, 10, 12 the D(w) trend presented a slope change at the cmc, which could be ascribed to the strong decrease in hydration of surfactant molecules upon micellization. Because of its short hydrophobic tail, C(6)TAB exhibited peculiar aggregation behavior. Its cmc, which is poorly marked, is lower than the value predicted by extrapolating the cmc values obtained for the other terms of the series. The C(6)TAB aggregates do not solubilize TMS molecules; the estimated aggregation number is extremely low ( approximately 3). Finally, no abrupt slope change in the solvent intradiffusion coefficient trend was detected. This evidence suggests that C(6)TAB molecules do not micellize in aqueous solution, but form trimers in which the surfactant hydrophobic tails are not hidden from contact with water molecules. Copyright 2001 Academic Press.     

Role of the solvophobic effect on micellization

Experimental data of amphiphiles aggregation phenomena in water-organic solvent mixtures were considered with the idea of investigating the role of the solvophobic effect on micellization. Changes in the critical micelle concentration, in the micellar ionization degree (for ionic surfactants) and in the aggregation number accompanying variations in the composition of the bulk phase of the micellar solutions were examined with the scope of understanding which properties of the water-organic solvent mixtures are important in the micellization process. Results point out that the cohesive energy density, measured either through the Hildebrand-Hansen solubility parameter or the Gordon parameter, seems to play an important role in determining the contribution of the solvophobic effect on the Gibbs energy of micellization in water-organic solvents mixtures.     

Surfactants with an amide group "spacer": Synthesis of 3-(acylaminopropyl)trimethylammonium chlorides and their aggregation in aqueous solutions

The cationic surfactants RCONH(CH2)3N+(CH3)3Cl-, where RCO = C10, C12, C14, and C16, respectively, have been synthesized by reacting the appropriate carboxylic acids with 3-N,N-dimethylamino-1-propylamine, followed by dehydration of the ammonium salt produced. Reaction of the intermediates obtained (RCONH(CH2)3N(CH3)2) with methyl iodide, followed by chloride/iodide ion-exchange furnished the surfactants. Their adsorption and aggregation in aqueous solutions have been studied by surface tension, conductivity, EMF, static light scattering and FTIR. Additional information on the micellar structure was secured from effects of the medium on the 1H NMR chemical shifts and 2D ROESY spectra. Increasing the length of the acyl moiety increased the micelle aggregation number, and decreased the minimum area/surfactant molecule at the solution/air interface, the critical micelle concentration, and the degree of dissociation of the counter-ion. Gibbs free energies of adsorption at the solution/air interface and of micelle formation were calculated, and compared to those of 2-(acylaminoethyl)trimethylammonium chloride; alkyl trimethylammonium chloride; and benzyl(3-acylaminopropyl)dimethylammonium chloride surfactants. For both processes (adsorption and micellization), contributions of the CH2 groups in the hydrophobic tail and of the head-group to DeltaG0 were calculated. The former contribution was found to be similar to those of other cationic surfactants, whereas the latter one is more negative than those of 2-(acylaminoethyl)trimethylammonium chlorides and trimethylammonium chlorides. This is attributed to a combination of increased hydrophobicity of the head-group, and (direct- or water-mediated) intermolecular hydrogen-bonding of aggregated monomers, via the amide group. FTIR and NMR results indicated that the amide group lies at the micellar interface.     

Interaction Behavior Between an Amino Sulfonate Surfactant and Octylphenol Polyoxyethylene Ether (10) in Aqueous Solution

The micellization of binary mixtures of sodium dodecyl diamino sulfonate (C12AS) and nonionic octylphenol polyoxyethylene ether (10) (OP-10) was investigated in aqueous solution at a pH of about 6.0. Two techniques, UV–Vis spectroscopy using pyrene as a probe and surface tensiometry, were employed in this work to obtain information on the micellization behavior of the mixed C12AS/OP-10 system. The interaction parameters between the two components, activity coefficients in mixed micelles, compositions of mixed micelles, and thermodynamic parameters of micellization (calculated using Clint’s equation, Rubingh’s treatment based on regular solution theory, and Rodenas’s treatment considering the Gibbs–Duhem equation) were evaluated for this mixed surfactant system. The results show that the synergistic effect between C12AS and OP-10 in all mixed systems plays a vital role in the reduction of the overall critical micelle concentration (cmc) value in aqueous solution. In the process of micellization, both the steric effect of the head group and the charge density for C12AS affect the formation and stability of the mixed micelles, and the entry of a small amount of C12AS into the unconsolidated micelle of OP-10 is more favorable to the formation of the mixed micelle by promoting the reduction of the mixed micelle cmc value. Thermodynamic data show that micellization for the mixed C12AS/OP-10 system is both an enthalpy and entropy driven process.     

Study of host–guest interaction between ß-cyclodextrin and alkyltrimethylammonium bromides in water

Cyclodextrins were found to play important roles in self-assembly systems of surfactants. The interactions between host molecule ß-cyclodextrin (CD) and model cationic surfactants, alkyltrimethylammonium bromides with different alkyl chain length: dodecyl-(C₁₂TAB), tetradecyl-(C₁₄TAB) and hexadecyl-(C₁₆TAB) are studied by means of conductivity measurements at 313.2 K. The data obtained indicate that inclusion complexes (CD:S⁺) had formed, and apparent critical micelle concentration (CMC*) is equivalent to the combined concentrations of surfactant monomers complexed with the CD and that of a free dissolved monomer in equilibrium with the micellized surfactant without CD. Inclusion complexes were characterized by an equilibrium binding constant K ₁₁, which value increases as the length of alkyl chains, and consequently the hydrophobicity, increases. From mathematical model the concentrations of the uncomplexed cyclodextrin, uncomplexed surfactant ion, and inclusion complex in the submicellar, as well as in the micellar range were calculated. The competition between the micellization and complexation processes leads to the existence of a significant concentration of free CD in equilibrium with the micellar aggregates. The percentage of uncomplexed cyclodextrin in equilibrium with the micelles is independent on cyclodextrin concentration for a particular ternary system and is 31, 37, and 34 % for C₁₂TAB/water/ß-CD, C₁₄TAB/water/ß-CD and C₁₆TAB/water/ß-CD, respectively. By using standard Gibbs free energy for micellization and surfactant complexation by CD, we can explain the observed behavior.     

Structure of mixed anionic/nonionic surfactant micelles: experimental observations relating to the role of headgroup electrostatic and steric effects and the effects of added electrolyte

The structures of the mixed anionic/nonionic surfactant micelles of SDS/C12E6 and SDS/C12E8 have been measured by small angle neutron scattering (SANS). The variations in the micelle aggregation number and surface charge with composition, measured in D2O and in dilute electrolyte, 0.01 and 0.05 M NaCl, provide data on the relative roles of the surfactant headgroup steric and electrostatic interactions and their contributions to the free energy of micellization. For the SDS/C12E8 mixture, solutions increasingly rich in C12E8 show a modest micellar growth and an increase in the surface charge. The changes with increasing electrolyte concentration are similarly modest. In contrast, for the SDS/C12E6 mixture, solutions rich in C12E6 show a more significant increase in aggregation number. Furthermore, electrolyte has a more substantial effect on the aggregation for the nonionic (C12E6) rich mixtures. The experimental results are discussed in the context of estimates of the steric and electrostatic contributions to the free energy of micellization, calculated from the molecular thermodynamic approach. The variation in micelle surface charge is discussed in the context of the "dressed micelle" theory for micelle ionization, and other related data.     

Blending effects on adsorption and micellization of different membrane protein solubilizers: a thermodynamic study on three mixed systems of CHAPS with MEGA-8, -9 and -10 in pH 7.2 phosphate buffer solution

By means of surface tension measurement (Wilhelmy method), micellization and adsorbed film formation were investigated for three combinations of mixed surfactant systems, all of which are used for solubilizing membrane proteins: a typical zwitterionic surfactant, CHAPS (a derivative of cholic acid) with n-alkyl (octyl, nonyl and decyl)-N-glucamides, MEGA-n (n=8, 9, 10). The data based on plotting of surface tension (gamma) versus logarithmic total molarity (or molality) (Ct or Mt) as a function of mole fraction of surfactant 2 (2 corresponds to MEGA-n's) enabled us to determine critical micellization concentration (CMC), minimum surface tension at CMC (gammaCMC), surface excess (Gamma(t)), mean molecular surface area (Am), the minimum Gibbs energy (Gmin(S)) of adsorbed film of both single and mixed surfactant systems and partial molecular area (PMA) in addition to parameters such as pC20 and CMC/C20 being related to synergism accompanied by blending (mixing) in regard to surface activity as well as micelle forming ability. On the basis of the regular solution theory, the relations of compositions of singly dispersed phase (X2), micellar phase (Y2) and adsorbed film (Z2) were estimated, and then the interaction parameters in micelles (omegaR) and in the adsorbed film phase (omegaA) were also calculated. From both the CMC-X2 and CMC-Y2 curves, it was found for all the combinations to show synergistically enhanced ability of mixed micelle formation as well as surface tension reduction. The resultant synergism coming from blending CHAPS with MEGA-n's was discussed in comparison with different combinations of various types of surfactants including membrane proteins solubilizers.