Sodium Hexadecyl Sulfonate Research Articles

Water-Based Bi2S3 Nano-Inks Obtained with Surfactant-Assisted Liquid Phase Exfoliation and Their Direct Processing into Thin Films

Bi2S3 has gained considerable attention as a semiconductor for its versatile functional properties, finding application across various fields, and liquid phase exfoliation (LPE) serves as a straightforward method to produce it in nano-form. Till now, the commonly used solvent for LPE has been N-Methyl-2-pyrrolidone, which is expensive, toxic and has a high boiling point. These limitations drive the search for more sustainable alternatives, with water being a promising option. Nonetheless, surfactants are necessary for LPE in water due to the hydrophobic nature of Bi2S3, and organic molecules with amphoteric characteristics are identified as suitable surfactants. However, systematic studies on the use of ionic surfactants in the LPE of Bi2S3 have remained scarce until now. In this work, we used sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS) and sodium hexadecyl sulfonate (SHS) as representative species and we present a comprehensive investigation into their effects on the LPE of Bi2S3. Through characterizations of the resulting products, we find that all surfactants effectively exfoliate Bi2S3 into few-layer species. Notably, SDBS demonstrates superior stabilization of the 2D layers compared to the other surfactants, while SHS becomes the most promising surfactant for obtaining products with high yield. Moreover, the resulting nano-inks are used for fabricating films using spray-coating, reaching a fine tuning of band gap by controlling the number of cycles, and paving the way for the utilization of 2D Bi2S3 in optoelectronic devices.

Systematic Investigation on the Surfactant‐Assisted Liquid‐Phase Exfoliation of MoS2 and WS2 in Water for Sustainable 2D Material Inks

MoS2 and WS2 have gathered significant attention due to their tunable properties and wide range of applications. Liquid‐phase exfoliation (LPE) is a facile method to prepare 2D MoS2 and WS2. Currently, the principally employed solvents for LPE of MoS2 and WS2 are expensive and toxic, and have high boiling points. These drawbacks encourage to find more sustainable alternatives to the liquid medium used for the preparation of 2D material inks. Water is the best option, but surfactants are necessary for LPE in water, since MoS2 and WS2 are hydrophobic. Organic molecules with amphoteric character such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium hexadecyl sulfonate (SHS) are selected as suitable candidates for the role. However, the study of these surfactants used in LPE is barely systematically reported. In this work, a detailed investigation is presented on their impact on the LPE of MoS2 and WS2, which are representatives of transition‐metal dichalcogenides. By characterizing and qualifying the products from average number of layers, it is found that all the surfactants work efficiently to exfoliate MoS2 and WS2 into few layers, and SHS stabilizes the 2D layers better than the other two. However, in terms of yield and relative surfactant concentration, a real trade‐off is not identified between maximized quantity of exfoliated materials and minimized surfactant concentration, which prompts to select the colloidal ink based on the specific further needs for processing.

Research and application of microfoam selective water plugging agent in shallow low-temperature reservoirs

There exists a large interlayer pressure difference in the oil wells of the Fuyu oilfield, and the high-pressure layer has a relatively high liquid production. The low-pressure layer is characterized by a relatively low liquid production, and water shut-off is urgently needed. Selective plugging technology is designed to temporarily block the oil layer before plugging the water layer, which is suitable for low-temperature shallow reservoirs. The foaming comprehensive exponent is considered to optimize the formula of the temporary plugging agent, consisting of 200 mL clean water, 0.25% sodium hexadecyl sulfonate, 0.8% sodium carboxymethyl cellulose, and 0.8% soluble starch. In addition, the formula of the multicomponent gel plugging agent is designed via extremum difference analysis, and the formula is 5% acrylamide (AM), 5% acrylic acid (AA), 0.8% PVA, 0.3% N,N-methylenebisacrylamide, 0.1% ammonium persulfate, and 0.2% sodium hydroxide. The selective plugging performance and permeability recovery characteristics of the system are evaluated. The experimental results show that the microfoam temporary blocking agent is more suitable for a core permeability ranging from 100–200 × 10−3 μm2, and the plugging agent can quickly gel at low temperatures. Field tests in a typical well show that the breakthrough pressure gradient of the temporary plugging layer reaches 3.5 MPa/m, thereby effectively protecting the low-pressure layer, and the fluid production of the high-pressure layer is reduced from 13.7 m3/d to 0.6 m3/d, thus realizing the purpose of plugging the high-pressure layer.

Spectrophotometric investigation of the interactions between cationic porphyrazine and different anionic surfactants

Interactions between tetrakis(N, N � ,N �� ,N ��� -tetramethyl tetra-2,3-pridino)porphyrazine copper(II) (Cu(tmtppa)) with anionic surfactants: sodium dodecyl sulfate (SDS), sodium tetradecyl sulfonate (STS) and sodium hexadecyl sulfonate (SHS) were investigated in aqueous submicellar solutions using spectrophotometric method at 298.15, 303.15, 313.15, 318.15 and 323.15 K. Binding constants between the submicellar solutions of surfactants and Cu(tmtppa) system were calculated from the changes in absorbance values at different temperatures. The results showed that increasing alkyl chain length of surfactants caused a stronger interaction indicating the importance of hydrophobic forces. It was found that the values of binding constant increased with increasing temperature. Thermodynamic parameters (ΔG ◦ , ΔH ◦ and ΔS ◦ ) were determined for the binding processes of porphyrazine-surfactant system. It was concluded from ΔG ◦ and ΔH ◦ values that the binding process occurred

Wettability, adhesion, adsorption and interface tension in the polymer/surfactant aqueous solution system: II. Work of adhesion and adsorption of surfactant at polymer–solution and solution–air interfaces

The values of the surface tension of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethyethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide and those of contact angle measured in the polytetrafluoroethylene (polymethyl methacrylate, nylon 6)–solution–air system were applied for the studies of correlation between the adsorption of surfactants at the solution–air and polymer–solution interfaces, critical surface tension of polymer wetting and work of adhesion of aqueous solutions of these surfactants to the above mentioned polymer surfaces. On the basis of the surface tension of aqueous solutions of surfactants studied and polymer–solution interface tension the Gibbs surface excess concentration at the polymer–solution interface was calculated and compared to that at the solution–air one. Using the Gibbs surface excess concentration data the molar fraction of surfactants at the polymer–solution interface was determined and compared to that at the solution–air one. The values of the activity of surfactants at the polymer–solution interface obtained from the Sprow and Prausnitz equation were also compared to those at the solution–air one and next used for calculations of the work of adhesion of solution to the polymer surface. The obtained values were compared to those determined from the Young–Dupree equation.

Wettability, adhesion, adsorption and interface tension in the polymer/surfactant aqueous solution system. I. Critical surface tension of polymer wetting and its surface tension

The contact angle of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethyethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide on polytetrafluoroethylene, polymethyl methacrylate and nylon 6 was studied. The contact angle values were used in the Young equation for the polymer–solution interface tension calculation and for the determination of the critical surface tension of polymer wetting. The critical surface tension of polymer wetting was obtained on the basis of the relationship between the cosine of contact angle and/or the adhesion tension as a function of the surface tension of aqueous solution of studied surfactants and then was discussed in relation to the Lifshitz–van der Waals components and electron-acceptor and electron-donor parameters of polytetrafluoroethylene, polymethyl methacrylate and nylon 6 surface tension. The role of the parameter of interfacial interactions in the relationship between the critical surface tension of polymer wetting and the surface tension was also considered. This parameter was calculated by using the polymer–solution interface tension as well as the polymer and aqueous solutions of surfactant surface tension.

Critical micelle concentration of some surfactants and thermodynamic parameters of their micellization

Measurements of density, viscosity, conductivity and light scattering of aqueous solutions of sodium dodecylsulfate (SDDS), sodium hexadecylsulfonate (SHS), sodium N-lauryl sarcosinate (SDSa), cetyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPyB), dodecyldimethyethylammonium bromide (DDEAB), tetradecyltrimethylammonium bromide (TTAB), benzyldimethyldodecylammonium bromide (BDDAB) and Triton X-100 (TX-100), Triton X-114 (TX-114), Triton X-165 (TX-165) were carried out at different temperatures. On the basis of the results obtained from these measurements critical micelle concentration, aggregation number, apparent and partial molar volume, standard Gibbs energy, enthalpy and entropy were calculated. In the case of ionic surfactants the degree of surfactant dissociation in micelle was taken into account. There was also determined the standard Gibbs energy of micellization using hydrophobic tail-water, hydrophilic head-water interfacial free energy and electrostatic intermolecular interactions. Then the results were compared with those obtained by other methods and the literature data. The presence of micelles at the concentration of aqueous surfactant solutions determined by the above mentioned methods was confirmed by the light scattering measurements.

Activity and thermodynamic parameters of some surfactants adsorption at the water–air interface

Measurements of the surface tension of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethylethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide were made at different temperatures. On the basis of the obtained results the activity of the surfactants at the water–air interface was determined and discussed based on the intermolecular interactions. The surfactant activity at the water–air interface was taken into account for determination of thermodynamic parameters of surfactant adsorption using the Langmuir method and the Szyszkowski equation. The thermodynamic parameters were also determined by means of the Rosen and Aronson, Gamboa and Olea methods as well that based on the changes of tail–water interface tension to that of tail–air.

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.

Behavior of Anionic Surfactants and Short Chain Alcohols Mixtures in the Monolayer at the Water–Air Interface

AbstractMeasurements of the surface tension of aqueous solution of mixtures of sodium dodecyl sulfate (SDDS) with methanol and ethanol in SDDS concentration range from 10−5 to 10−2 M and mixtures of sodium hexadecyl sulfonate (SHS) with methanol and ethanol at SHS concentration from 10−5 to 8 × 10−4 M and for methanol and ethanol from 0 to 21.1 and, 11.97 M, respectively, were carried out at 293 K. Moreover, the surface tension of aqueous solution mixtures of SDDS with propanol in the concentration range from 0 to 6.67 M taken from the literature was also considered. The results obtained indicate that it is possible to describe the relationship between the surface tension and molar concentration or molar fraction of alcohol by Szyszkowski and Connors equations. However, the Fainerman and Miller equation allows us to predict the isotherm of the surfactant tension at constant anionic surfactants concentration at which their molecules are present in the solution in the monomeric form if the molar area of surfactants and alcohols can be determined. Based on the surface tension isotherms, the Gibbs surface excess of anionic surfactants and alcohols concentration at water–air interface was determined and then recalculated for Guggenheim‐Adam surface excess concentration of these substrates, and next the molar fraction of alcohols and surfactants in the surface layer was determined. These molar fractions were discussed with regard to surfactant and alcohol standard free energy of adsorption at the water–air interface determined from Langmuir and Aronson and Rosen equations. The standard free energy of adsorption determined in these ways was compared to that deduced on the basis of pC20 and Lifshitz van der Waals‐components of the anionic surfactant and alcohol tails.

The relationship between the adhesion work, the wettability and composition of the surface layer in the systems polymer/aqueous solution of anionic surfactants and alcohol mixtures

Measurements of advancing contact angle ( θ) were carried out on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) for aqueous solution of sodium dodecyl sulfate (SDDS) mixtures with methanol, ethanol and propanol in the range of SDDS concentration from 10 −5 to 10 −2 M, and for sodium hexadecyl sulfonate (SHS) with the same alcohols at the SHS concentration ranging from 10 −5 to 8 × 10 −4 M at 293 K. The concentration of methanol, ethanol and propanol used for measurements varied from 0 to 21.1, 11.97 and 6.67 M, respectively. On the basis of the contact angles the critical surface tension of PTFE and PMMA wetting was determined by using for this purpose the relationship between the adhesion and the surface tension and cos θ and surface tension both at constant alcohol and surfactant concentration, respectively. The obtained contact angles were also used in the Young Dupre’ equation for calculations of the adhesion work of aqueous solution of mixtures of anionic surfactants and short chain alcohols to PTFE and PMMA surface. The adhesion work calculated in this way was compared to that of the particular components of aqueous solution to these surfaces determined on the basis of the surface tension components and parameters of the surface tension of the surface active agents, water, PTFE and PMMA from van Oss et al. equation. The calculated adhesion work was discussed in the light of the concentration of surface active agents at polymer–water and water–air interface determined from Lucassen-Reynders, Gibbs and Guggenheim-Adam equations.

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.

Molecular dynamics investigation into the adsorption of oil–water–surfactant mixture on quartz

Molecular dynamics (MD) simulations have been carried out to investigate the adsorption behavior of different surfactants–water–oil mixture on quartz surfaces. The effects of rhamnolipid, sodium dodecyl benzene sulfonate and sodium hexadecyl sulfonate on binding energy and radial distribution function (RDF) of oil–quartz are calculated at molecular level. The study shows that these surfactants can reduce binding energy between oil molecules and quartz surface, which plays a role of oil-displacing agent.

Molecular dynamics simulation of adsorption of an oil-water-surfactant mixture on calcite surface

An interface super molecular structure model for oil-water-surfactant mixture and calcite was established. By using a molecular dynamics method, the effects of rhamnolipid, sodium dodecyl benzene sulfonate and sodium hexadecyl sulfonate on the interface adsorption behavior of oil molecules were investigated. It was found that these three surfactants could reduce oil-calcite interface binding energy, and play a role of oil-displacing agent.

Wettability of polytetrafluoroethylene by aqueous solutions of two anionic surfactant mixtures

Advancing contact angle ( θ) measurements were carried out on mixtures of aqueous solutions of sodium dodecyl sulfate (SDDS) and sodium hexadecyl sulfonate (SHDSs) on polytetrafluoroethylene (PTFE). The obtained results indicate that there were only small contact angle changes over the range of surfactant concentrations in the solution, corresponding to the unsaturated surfactant layer at the aqueous solution–air interface. However, when saturation of the surfactant layer was achieved a considerable decrease in the contact angle (increase in cos θ) as a function of concentration was observed. The dependence of cos θ on the monomer mole fraction of SHDSs in the mixture of the surfactants ( α) for aqueous solutions of mixtures at concentrations corresponding to the critical micelle concentration (CMC) had a maximum at α=0.2. From the results of these measurements and application of the Gibbs and Young equations the ratio of the excess concentration of surfactants at the solid–aqueous solution interface to the excess of their concentration at the aqueous solution–air interface was calculated. On the basis of the measurements and calculations it was found that there was a straight linear relationship between the adhesion tension and surface tension of aqueous solutions of surfactant mixtures at a given α, and that the slope of the obtained straight lines was equal to −1, which suggests that the surface excess of the surfactant concentrations at the PTFE–solution interface is the same as that at the solution–air interface for a given bulk concentration of the surfactant mixtures. The dependence of the surface concentration excess at the PTFE–solution interface on the monomer mole fraction of SHDSs in the mixture of the surfactants for the concentration region of the mixture of aqueous solutions, corresponding to a saturated monolayer, had a maximum at α=0.4, probably resulting from increased degree of binding between adsorbed surface-active ions and counterions. It was also found that the critical surface tension of PTFE wetting by aqueous solutions of two anionic surfactant mixtures was equal to 23.35 mN/m, which was higher than the critical surface tension of wetting determined from straight linear dependence between cos θ and surface tension of alkanes (19.94 mN/m). This suggests that polar interaction at PTFE–aqueous solutions of surfactant mixtures can probably take place.

Flow injection determination of anionic surfactants with cationic dyes in water bodies of central India

A new, simple and specific flow injection analysis (FIA) procedure for the determination of anionic surfactants, viz., sodium lauryl sulfate (SLS), sodium dodecyl sulfonate, sodium hexadecyl sulfonate and sodium dodecyl benzenesulfonate, with cationic dyes, viz., Brilliant Green (BG), Malachite Green, Methylene Blue, Ethyl Violet and Crystal Violet, in water bodies, viz., ponds, tube wells, rivers and municipal wastes, of central India (east Madhya Pradesh) is described. It is based on the precipitation of the cationic dyes with the anionic surfactant due to formation of an ion-associate species within the pH range 5.5–8.0. The apparent molar absorptivity of the ion-associate species formed with various anionic surfactants and cationic dyes is in the range (0.60–1.50) × 104 l mol–1 cm–1 at λmax 590–665 nm. Among them, the pair BG+–LS– was selected for detailed investigation. The detection limit (amount causing absorbance >3s) of the method with BG is 100 ppb SLS and the sample throughput is 50 h–1. Optimization of FIA and the analytical variables in the precipitation and determination of SLS with BG is described. The method is free from interferences from almost all ions which are commonly present with the surfactant. The proposed method was applied to the mapping of SLS pollution levels in the various water bodies. All surface waters and municipal waste waters and some ground waters lying near the sources were found to be contaminated with SLS beyond permissible limits.

Determination of Association Constants for Cyclodextrin–Surfactant Inclusion Complexes: A Numerical Method Based on Surface Tension Measurements

Inclusion complexes of β-cyclodextrin (β-CD) with sodium octyl sulfonate (C8As), sodium dodecyl sulfonate (C12As), and sodium hexadecyl sulfonate (C16As) in aqueous solutions are studied by surface tension measurement at the air/water interface at different temperatures. At fixed concentrations of the surfactants, the surface tension increases with an increase in β-CD concentration to a maximum value, at which it holds. The surface tension curves of the surfactants in the presence of β-CD are higher than those in the absence of β-CD. The curves rise higher with the increase in β-CD concentration for each surfactant. The apparent critical micelle concentrations (CMC*) of the surfactants vary linearly with β-CD concentration. The CMC* and surface tension values (including those after the CMC*) for the same system decrease with increase in temperature. A numerical method based on surface tension measurements is developed to determine the association constants for 1:1 inclusion complexes. This method is very reliable and easy to perform. The results demonstrate that the longer the hydrophobic tail of the surfactant, the greater the association constant with β-CD, and that for the same surfactant the association constant is higher at lower temperatures.

FLUORESCENCE PROBE STUDIES ON THE SECOND CRITICAL MICELLE CONCENTRATION OF SEVERAL KINDS OF SURFACTANTS

ABSTRACT The fluorescence intenstiy ratios (F2/F1) of excimer (F2) to monomer (F1) of probe (pyrene) were measured as a function of the concentration of the surfactant in several systems, which consist of sodium hexadecyl sulfonate (C16As)-anionic surfactant, cetyltrimethylammonium bromide (CTAB)-cationic surfactant and pentaoxyethylene decyl ether (C10E5)-nonionic surfactant. The second CMC values were obtained according to F2/F1 ~ surfactant concentration curve break. In addition, we also studied the variation of second CMC vs NaCl concentration. It was found that the second CMC values of C16A5 and CTAB decreased with the increase of NaCl concentration. But the present of NaCl had no influence on the second CMC value of C10E5. Results showed that sphere-shaped micelles turn into rod-like micelle at the second CMC. The results were interpreted in terms of diffusion of pyrene molecules and the distribution of pyrene among micelles.

Fluorescence-probe study of anionic/cationic surfactant systems 2. Alkylsulfonate/alkyltrimethylammonium bromide

Steady state fluorescence and time-resolved fluorescence techniques have been used to study the properties of two kinds of anionic surfactant systems and four kinds of mixed anionic/cationic surfactant systems. The two anionic surfactant systems are sodium dodecyl sulfate and sodium dodecylsulfonate (C 12As) aqueous solutions. The four alkylsulfonate/alkyltrimethylammonium bromide systems consist of C 12As/cetyltrimethylammonium bromide (CTAB), sodium octylsulfonate (C 8As)/CTAB, sodium hexadecylsulfonate (C 16As)/CTAB and C 12As/dodecyltrimethylammonium bromide (DTAB). We discuss mainly the variation of the micellar aggregation number of these systems with the NaCl concentration and temperature. Both the addition of anionic surfactant to cationic surfactant and of cationic surfactant to anionic surfactant result in a large increase in the micellar aggregation number. In addition, by a steady state fluorescence technique, the critical micelle concentration (CMC) for the C 8As/CTAB and C 12As/DTAB systems and the second CMC for the C 12As, C 12As/CTAB and C 12As/DTAB systems at which the micelles changed from spherical to rod shaped were determined. At the same time, the solubilization position of the fluorescence probe (pyrene) and the polarity of the probe microenvironment in the mixed anionic/cationic micelles were studied.