Mixed micelle behavior of poly(ethylene glycol) alkyl ethers with series of monomeric cationic, phosphonium cationic, and zwitterionic surfactant

The steady state fluorescence measurements have been carried out for the binary mixtures of poly(ethylene glycol) alkyl ethers (C _i E _j ) with series of monomeric cationic (MC), zwitterionic (ZI), and phosphonium cationic (PC) surfactants over the whole mole fraction range by using pyrene as fluorescence probe. The cmc values for all the binary mixtures, thus, determined have been further evaluated by using the regular solution theory. The various micellar parameters such as regular solution interaction parameter (β), micropolarity (I ₁/I ₃), and mean micelle aggregation number (N _agg) have been determined. A strong influence of hydrophobicity of both nonionic as well as cosurfactant (CS) components has been observed on the nature of mixed micelles. The presence of bulky head groups of PC surfactants significantly contributes towards the unfavorable mixing.     

Interaction and Stability of Mixed Micelle and Monolayer of Nonionic and Cationic Surfactant Mixtures

Interaction and stability of binary mixtures of cationic surfactants hexadecyltrimethylammonium bromide (HTAB) or hexadecylpyridinium bromide (HPyBr) with nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) have been studied at different mole fraction of cationic surfactants by using interfacial tension measurements and fluorescence probe techniques. From interfacial tension measurements, the critical micellar concentration and various interfacial thermodynamic parameters have been evaluated. The experimental cmc's were analyzed with the pseudophase separation model, the regular solution theory, and the Maeda's approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTAB + Mega-10 were obtained. It has been observed that the aggregation number of mixed micelles deviates negatively from the ideal behavior. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio and found to be increase with the increase of ionic content. The polarization of fluorescence probe Rhodamine B was monitored at different mole fraction of cationic surfactants.     

Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants

The mixed micellar properties of a triblock copolymer, Pluronic L64, (EO)13(PO)30(EO)13, and a nonionic surfactant, Triton X-100, in aqueous solution with conventional alkyl ammonium bromides and their dimeric homologues were investigated with the help of fluorescence and cloud point measurements. The composition of mixed micelles and the interaction parameter, beta, evaluated from the critical micelle concentration (cmc) data for different mixtures using Rubingh's and Motomura's theories are discussed. It has been observed that the mixed micelle formation between monomeric/dimeric alkyl ammonium bromides and L64 was due to synergistic interactions which increase with the increase in hydrophobicity of the cationic component. On the other hand, synergistic mixing was observed in the mixed micelles of Triton X-100 and monomeric cationic surfactants, the magnitude of which decreases slightly with the increase in hydrophobicity of the cationic component. Antagonistic interactions were observed in the case of Triton X-100 and dimeric cationic surfactants.     

Antagonistic mixing behavior of cationic gemini surfactants and triblock polymers in mixed micelles

Conductance (kappa), pyrene fluorescence (I1/I3), cloud point (C(P)), and Krafft temperature (K(T)) measurements have been carried out for various dimethylene bis(alkyldimethylammonium bromide) (gemini) surfactants with different poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock polymers (TBP). From the kappa and I1/I3 studies, the critical micelle concentrations of mixed micelle formation between the gemini and TBP have been determined using regular solution theory. It has been observed that mixed micelle formation in all the binary mixtures of gemini+TBP occurs due to the unfavorable mixing, the magnitude of which decreases with increased hydrophobicity of the gemini component. The results are further supported by evaluating the mean micelle aggregation number and enthalpy of fusion from fluorescence and Krafft temperature measurements, respectively.     

Studies of mixed micelle formation between cationic gemini and cationic conventional surfactants

Mixed micellization of dimeric cationic surfactants tetramethylene-1,4-bis(hexadecyldimethylammonium bromide)(16-4-16), hexamethylene-1,6-bis(hexadecyldimethylammonium bromide) (16-6-16) with monomeric cationic surfactants hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC), and tetradecyltrimethylammonium bromide (TTAB) have been studied by conductivity and steady-state fluorescence quenching techniques. The behavior of mixed systems, their compositions, and activities of the components have been analyzed in the light of Rubingh's regular solution theory. The results indicate synergism in the binary mixtures. Ideal and experimental critical micelle concentrations (i.e., cmc(*) and cmc) show nonideality, which is confirmed by beta values and activity coefficients. The micelle aggregation numbers (N(agg)), evaluated using steady-state fluorescence quenching at a total concentration of 2 mM for CTAB/16-4-16 or 16-6-16 and 5 mM for TTAB/16-4-16 or 16-6-16 systems, indicate that the contribution of conventional surfactants was always more than that of the geminis. The micropolarity, dielectric constant and binding constants (K(sv)) of mixed systems have also been evaluated from the ratios of respective peak intensities (I(1)/I(3) or I(0)/I(1)).     

Mixed micelle formation and solubilization behavior toward polycyclic aromatic hydrocarbons of binary and ternary cationic-nonionic surfactant mixtures

Water solubility enhancements of polycyclic aromatic hydrocarbons (PAHs), viz., naphthalene, anthracene and pyrene, by micellar solutions at 25 degrees C using two series of surfactants, each involving two cationic and one nonionic surfactant in their single as well as equimolar binary and ternary mixed states, were measured and compared. The first series was composed of three surfactants, benzylhexadecyldimethylammonium chloride (C16BzCl), hexadecyltrimethylammonium bromide (C16Br), and polyoxyethylene(20)mono-n-hexadecyl ether (Brij-58) with a 16-carbon (C16) hydrophobic chain; the second series consisted of dodecyltrimethylammonium bromide (C12Br), dodecylethyldimethylammonium bromide (C12EBr), and polyoxyethylene(4)mono-n-dodecyl ether (Brij-30) with a 12-carbon (C12) chain. Solubilization capacity has been quantified in terms of the molar solubilization ratio, the micelle-water partition coefficient, the first stepwise association constant between solubilizate monomer and vacant micelle, and the average number of solubilizate molecules per micelle, determined employing spectrophoto-, tensio-, and flourimetric techniques. Cationic surfactants exhibited lesser solubilization capacity than nonionics in each series of surfactants with higher efficiency in the C16 series compared to the C12 series. Increase in hydrophobicity of head groups of cationics by incorporation of ethyl or benzyl groups enhanced their solubilization capacity. The mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of the regular solution approximation (RSA). Cationic-nonionic binary combinations showed better solubilization capacity than pure cationics, nonionics, or cationic-cationic mixtures, which, in general, showed increase with increased hydrophobicity of PAHs. Equimolar cationic-cationic-nonionic ternary surfactant systems showed lower solubilization efficiency than their binary cationic-nonionic counterparts but higher than cationic-cationic ones. In addition, use of RSA has been extended, with fair success, to predict partition coefficients of ternary surfactant systems using data of binary surfactants systems. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.     

Spectrophotometric studies of anionic dye-cationic surfactant interactions in mixture of cationic and nonionic surfactants

The interaction between an anionic dye C.I. Reactive Orange 16 (RO16) and a cationic surfactant dodecylpyridinium chloride (DPC) in mixtures of DPC and nonionic surfactants poly(oxyethylene)ethers (C(m)POE(n); m = 12, 16 and 18, n = 4, 10 and 23) are investigated spectrophotometrically in a certain micellar concentration range. The spectrophotometric measurements of dye-surfactant systems are carried out as function of mole fraction of surfactant at four different temperatures. For this reason, a typical system was occurred at 1.0 x 10(-2) mol l(-1) for surfactants and at 1.0 x 10(-4) mol l(-1) for dye concentrations. The formation of DPC-RO16 complex in the C(m)POE(n) solutions of different mole fractions in its micellar concentration range have been determined and compared to those obtained in the binary mixtures. From the spectrophotometric measurements has been observed that the addition of nonionic surfactant in to the mixture of DPC-RO16, causes a significant increase of the value of absorbance. This increase explains that the stability of DPC-RO16 complex is reduced in the presence of nonionic surfactant micelles. It can be seen from results; in mixed surfactant solutions, there are DPC-C(m)POE(n) and RO16-C(m)POE(n) interactions in addition to DPC-RO16 interaction. Since the solubilizaton of the DPC-RO16 complex has been appeared in the C(m)POE(n) solution, our results support the conclusion that adding C(m)POE(n) influences the hydrophobic-hydrophilic balance of the studied complex. Furthermore effect of the alkyl chain length and the number of poly(oxyethylene) in nonionic surfactant on values of absorbance have been investigated.     

Properties of aqueous solution of sodium glycocholate and a nonionic surfactant,and their mixtures

The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C₁₀E₈, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C₁₀E₈. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution.     

Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: the pH and spacer effect

Mixed micelle formation of binary cationic gemini (12-s-12, s=4, 6) and zwitterionic (N-dodecyl-N,N-dimethylglycine, EBB) surfactants has been investigated by measuring the surface tension of aqueous solution as a function of total concentration at various pH values from acidic to basic, under conditions of 298.15 K and atmospheric pressure. The results were analyzed by applying regular solution theory (RST), and Motomura's theory, which allows for the calculation of the excess Gibbs energy of micellization purely on the basis of thermodynamic equations. The synergistic interactions of all the investigated cationic gemini + zwitterionic surfactants mixtures were found to be dependent upon the pH of the solution and the length of hydrophobic spacer of gemini surfactant. The evaluated excess Gibbs free energy is negative for all the systems.     

Mixed Micellization Behavior of 12-2-12 Gemini Surfactant with Some Alkyltrimetyl Ammonium Bromide Surfactants

Mixed micellization behavior of dimeric cationic surfactant ethanediyl-1,2-bis (dimethyldodecylammonium bromide) (12-2-12) with a series of monomeric cationic surfactants dodecyltrimethyl ammonium bromide (DTAB), tetradecyltrimethyl ammonium bromide (TTAB), and cetyltrimethyl ammonium bromide (CTAB) has been studied in aqueous and aqueous polyvinylpyrrolidone (PVP) solutions at 298.15, 308.15, and 318.15 K, respectively, using conductometric method. Various thermodynamic parameters like mixed micelle concentration (C_m), micelle mole fraction (X₁), interaction parameter (β), and free energy of mixing (ΔG_ex) of the mixed systems have been determined and analyzed using Rubingh's regular solution theory. The results indicate that in aqueous solutions the binary mixtures of 12-2-12 with DTAB/TTAB behave nonideally with mutual synergism whereas that with CTAB shows almost ideal behavior at 298.15 K. At 318.15 K, all these binary mixtures exhibit antagonistic behavior. The effect of variation in chain length of alkyltrimethyl ammonium bromide surfactants on the interactions with 12-2-12 have also been evaluated and discussed.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: fluorescence and Krafft temperature studies

Pyrene fluorescence and Krafft temperature measurements have been carried out for various combinations of cationic gemini (m-2-m) with zwitterionic surfactants by changing the length of the hydrophobic tail over the whole mixing range. The results have been evaluated by using the regular solution theory. All the mixtures of cationic gemini+zwitterionic surfactants indicate the presence of synergistic interactions which largely decrease at higher hydrophobicity of both components. A greater amount of gemini component in the mixed micelles induces stronger synergism which reduces with the increase in the length of hydrophobic tail of the gemini component. The Krafft temperature measurements also indicate the presence of strong synergistic interactions, which decrease with increase in the length of hydrophobic tail of both components.     

Thermodynamics of micellization of multiheaded single-chain cationic surfactants

The energetics of micelle formation of three single-chain cationic surfactants bearing single (h = 1), double (h = 2), and triple (h = 3) trimethylammonium [(+)N(CH(3))(3)] headgroups have been investigated by microcalorimetry. The results were compared with the microcalorimetric data obtained from well-known cationic surfactant, cetyl trimethylammonium bromide (CTAB), bearing a single chain and single headgroup. The critical micellar concentrations (cmc's) and the degrees of counterion dissociation (alpha) of micelles of these surfactants were also determined by conductometry. The cmc and the alpha values increased with the increase in the number of headgroups of the surfactant. The relationship between the cmc of the surfactant in solution and its free energy of micellization (DeltaG(m)) was derived for each surfactant. Exothermic enthalpies of micellization (DeltaH(m)) and positive entropies of micellization (DeltaS(m)) were observed for all the surfactants. Negative DeltaH(m) values increased from CTAB to h = 1 to h = 2 and decreased for h = 3 whereas DeltaS(m) values decreased with increase in the number of headgroups. The DeltaG(m) values progressively became less negative with the increase in the number of headgroups. This implies that micelle formation becomes progressively less favorable as more headgroups are incorporated in the surfactant. From the steady-state fluorescence measurements using pyrene as a probe, the micropolarities sensed by the probe inside various micelles were determined. These studies suggest that the micelles are more hydrated with multiheaded surfactants and the micropolarity of micelles increases with the increase in the number of headgroups.     

A disjoining pressure study of foam films stabilized by mixtures of nonionic and ionic surfactants

Studying the disjoining pressure Pi as a function of the film thickness h (Pi-h curves) of foam films stabilized by ionic and nonionic surfactants, one finds that the surface charge density q0 of films stabilized by ionic surfactants increases with increasing surfactant concentration, while the opposite holds true for nonionic surfactants. Thus, it should be possible to tune the surface charge density with mixtures of nonionic and ionic surfactants. To address this question, we studied foam films stabilized by aqueous solutions of surfactant mixtures. The mixtures consisted of the nonionic beta-dodecylmaltoside (beta-C12G2) and the cationic dodecyl trimethylammonium bromide (C12TAB) with mixing ratios of beta-C12G2/C12TAB = 1:0, 50:1, 1:1, 1:50, 0:1. The addition of small amounts of C12TAB to beta-C12G2 first neutralizes the negative surface charge of the beta-C12G2 films and finally leads to a charge reversal from negatively to positively charged surfaces. On the other hand, by adding small amounts of beta-C12G2 to C12TAB, one observes the formation of stable CBFs which was also observed for the pure C12TAB. However, in contrast to the pure C12TAB, the resulting Pi-h curves for the mixtures cannot be described with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; the slope of the curves is too steep, and it barely changes with changing electrolyte concentration. A possible explanation for this observation will be given and discussed.     

Properties of binary surfactant systems of nonionic surfactants C12E10, C12E23, and C12E42 with a cationic gemini surfactant in aqueous solutions

Properties of binary surfactant systems of nonionic surfactants poly(ethylene oxide) (PEO) lauryl ethers (C(12)E(10), C(12)E(23), C(12)E(42)) with a cationic gemini surfactant, butanediyl-α,ω-bis(tetradecyldimethylammonium bromide) (14-4-14), have been investigated by Steady-state Fluorescence (FL), zeta potential, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Cryogenic Transmission Electron Microscopy (CryoTEM), and X-ray Diffraction (XRD). Through FL measurements, critical micelle concentration (CMC) of the three binary systems for different mixing mole fractions is determined and the values fall between those of pure constituent surfactants. Ideal CMC (CMC(ideal)), mole fraction in aggregates (X), interaction parameter (β), activity coefficients (f(1) and f(2)), and excess free energy of mixing (ΔG(ex)) have been calculated. All these parameters indicate nonideal behavior and synergistic interactions between the constituent surfactants, which is explained in terms of electrostatic attraction between headgroups of constituent surfactants and reduction of electrostatic repulsion between headgroups of 14-4-14 due to the presence of nonionic surfactants. DLS, TEM and CryoTEM results show that nonionic surfactants facilitate the formation of larger aggregates. Micelles and vesicles in larger size compared with those of 14-4-14 coexist in the mixed solutions. Both surfactant composition and PEO chain length are found to play a strong effect on the properties of the binary systems.     

Conductometric and fluorometric investigations on the mixed micellar systems of cationic surfactants in aqueous media

Micellar properties of binary mixtures of hexadecyldiethylethanolammonium bromide surfactant with tetradecyldimethylammonium, trimethylammonium, triphenylphosphonium, diethylethanolammonium, and pyridinium bromide surfactants have been characterized employing conductometric and fluorescence techniques. The critical micelle concentration (cmc*) and the degree of counter-ion binding values (delta) of the binary systems were determined from the conductivity measurements. The results were analyzed in light of various existing theories to calculate micellar composition, activity coefficients, and the interaction parameter (beta). Partial contribution of each surfactant, cmc1*, cmc2*, to the overall cmc* value was also evaluated. Aggregation numbers and micropolarity of the mixed micelles were determined from fluorescence measurements. The results were discussed in terms of synergetic interactions in these systems on the basis of the head group/head group and tail/tail interactions and the counter-ion binding.     

Mixed Micellization of Dimeric (Gemini) Surfactants and Conventional Surfactants

The aqueous solutions of mixtures of various conventional surfactants and dimeric anionic and cationic surfactants have been investigated by electrical conductivity, spectrofluorometry, and time-resolved fluorescence quenching to determine the critical micelle concentrations and the micelle aggregation numbers in these mixtures. The following systems have been investigated: 12-2-12/DTAB, 12-2-12/C(12)E(6), 12-2-12/C(12)E(8), 12-3-12/C(12)E(8), Dim3/C(12)E(8), and Dim4/C(12)E(8) (12-2-12 and 12-3-12=dimethylene-1,2- and trimethylene-1,3-bis(dodecyldimethylammonium bromide), respectively; C(12)E(6) and C(12)E(8)=hexa- and octaethyleneglycol monododecylethers, respectively; Dim3 and Dim4=anionic dimeric surfactants of the disodium sulfonate type, Scheme 1; DTAB=dodecyltrimethylammonium bromide). For the sake of comparison the conventional surfactant mixtures DTAB/C(12)E(8) and SDS/C(12)E(8) (SDS=sodium dodecylsulfate) have also been investigated (reference systems). Synergism in micelle formation (presence of a minimum in the cmc vs composition plot) has been observed for the Dim4/C(12)E(8) mixture but not for other dimeric surfactant/nonionic surfactant mixtures investigated. The aggregation numbers of the mixed reference systems DTAB/C(12)E(8) and SDS/C(12)E(8) vary monotonously with composition from the value of the aggregation number of the pure C(12)E(8) to that of the pure ionic component. In contrast, the aggregation number of the dimeric surfactant/C(12)E(8) mixtures goes through a minimum at a low value of the dimeric surfactant mole fraction. This minimum does not appear to be correlated to the existence of synergism in micelle formation. The initial decrease of the aggregation number of the nonionic surfactant upon addition of ionic surfactant, up to a mole fraction of ionic surfactant of about 0.2 (in equivalent per total equivalent), depends little on the nature the surfactant, whether conventional or dimeric. The results also show that the microviscosity of the systems containing dimeric surfactants is larger than that of the reference systems. Copyright 2001 Academic Press.     

Physicochemical studies of pyridinium gemini surfactants with promethazine hydrochloride in aqueous solution

The mixed micellization and interfacial behavior of pyridinium gemini surfactants, 1,1'-(1,1'-(ethane-1,2-diylbis-(sulfanediyl))bis(alkane-2,1-diyl))dipyridinium bromide, i.e., [12-(S-2-S)-12], [14-(S-2-S)-14], [16-(S-2-S)-16] with a phenothiazine tranquilizer drug, promethazine hydrochloride (PMT), has been investigated by conductivity, surface tension and steady state fluorescence measurements. Different spectroscopic techniques like fluorescence, UV-visible and NMR were also employed to understand the nature of interactions between the pyridinium gemini surfactants and PMT. The various micellar, interfacial and associated thermodynamic parameters for different mole fractions of PMT-pyridinium gemini surfactant mixtures have been evaluated. Synergism was observed in the mixed micelle as well as the monolayer formed by these mixtures. The fluorescence quenching experiment indicates that the interactions between PMT and surfactants are hydrophobic in nature. The UV-visible measurements reveal the distinct formation of a drug-surfactant complex. The detailed mechanism for the type of interactions was further studied by NMR titrations which show cation-π interactions between PMT and pyridinium gemini surfactant molecules.     

Molecular interaction of Congo Red with conventional and cationic gemini surfactants

Interaction of tetradecyltrimethylammonium bromide (TTAB), octylophenylpolyoxyethylene ether (TX-100), sodium dodecylsulfate (SDS), N,N′-ditetradecyl-N,N,N′,N′-tetramethyl-N,N′-butanediyl-diammonium dibromide (14,4,14) and N,N′-didodecyl-N,N,N′,N′-tetramethyl-N,N′-butanediyl-diammonium dibromide (12,4,12) with an anionic diazo dye, Congo Red, was investigated using conductometry, spectroscopy, tensiometry, and pulsed field gradient NMR (PFG-NMR). The formation of dye-surfactant ion pairs, their small mixed aggregates (below the critical micelle concentration (CMC) of these surfactants) and surfactant micelles were detected successfully. Above the CMC, the dye reverted to its monomeric state and solubilized in the micelles. Job's method was used to determine the stoichiometric ratio of dye and surfactant in ion pairs and revealed the formation of more hydrophile ion pairs for geminis compared to their conventional analogs. Quantitative results obtained from tensiometry indicated the existence of considerable synergism for cationic surfactants and antagonism for anionic SDS. In addition, the synergism observed for TX-100 revealed the effect of π-π stacking and hydrophobic forces on ion pair and mixed micelle formation. The increase of dye-surfactant interactions by increasing the electrical charge and chain length of cationic surfactants confirmed the importance of both electrostatic and hydrophobic forces in binary dye/surfactant systems. The hydrodynamic radii of the micelles were determined by self-diffusion coefficient measurements. The average size of the cationic and nonionic micelles increased in the presence of CR molecules.     

Self-assembly of cationic surfactants that contain thioether groups in the hydrophobic tails

Self-assembly in aqueous solutions of cationic surfactants that carry thioether groups in their hydrophobic tails has been investigated. Of particular interest was the identification of possible changes in the aggregate structure due to the presence of sulfur atoms. Solutions of four different compounds [CH(3)CH(2)S(CH(2))(10)N(CH(3))(3)(+)Br(-) (2-10), CH(3)(CH(2))(5)S(CH(2))(6)N(CH(3))(3)(+)Br(-) (6-6), CH(3)(CH(2))(7)S(CH(2))(6)N(CH(3))(3)(+)Br(-) (8-6), and CH(3)(CH(2))(7)S(CH(2))(8)N(CH(3))(3)(+)Br(-) (8-8)] were characterized by (1)H NMR, (13)C NMR, NMR diffusometry, and conductivity measurements. In addition to investigating aqueous solutions containing each of the thioethers present as the sole solute, mixtures of 2-10 or 6-6 with dodecyltrimethylammonium bromide (DTAB) were studied. The addition of a sulfide group to the hydrophobic tail causes an increase in the critical micelle concentration but has a limited effect on the aggregate structure. Micelles are formed at a well-defined concentration for all of the investigated surfactants and surfactant mixtures. However, a comparison of the behavior of concentrated solutions of 8-8 to that of solutions of hexadecyltrimethylammonium bromide (CTAB) of similar concentrations suggests that the presence of a sulfur atom decreases the tendency for micellar growth. This may be a consequence of a slightly higher preference for the micellar surface of a sulfur atom as compared to that of a methylene group in a similar position, an idea that is also supported by results for the surfactant mixtures.