Aggregation behavior of fluorocarbon and hydrocarbon cationic surfactant mixtures: a study of 1H NMR and 19F NMR

The aggregation behavior and the interaction of four mixed systems for a cationic fluorocarbon surfactant, diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMACl), mixing with cationic hydrocarbon surfactants, alkyltrimethylammonium chloride, CnTACl (n=12, 14, 16, and 18; where n=12 is DTACl, n=14 is TTACl, n=16 is CTACl, and n=18 is OTACl), were studied by 1H and 19F NMR in more detail. The results of 19F NMR measurements strongly indicate that in the three mixed systems of DEFUMACl/DTACl, DEFUMACl/TTACl, and DEFUMACl/CTACl at different molar fractions of fluorocarbon surfactant (alphaF=(cDEFUMACl/cDEFUMACl+cCnTACl)), with an increase of the total concentration of fluorocarbon and hydrocarbon surfactants (cT=cF+cH), the mixed micelles at the first break point and the individual DEFUMACl micelles at the second break point form. However, three different types of micelles were determined in DEFUMACl/OTACl mixtures by 19F NMR measurements, OTACl-rich and DEFUMACl-rich mixed micelles and individual DEFUMACl micelles, respectively. The chemical shifts of proton Deltadelta (1H) for -CH3 in the mixed systems of DEFUMACl/CnTACl (n=12, 14, 16, and 18) have different variation trends from the 19F NMR measurements. For the two systems of DEFUACl/DTACl and DEFUMACl/TTACl, the mixed micelles form at the first break point. At the second break point, for lower alpha F values the DTACl-rich and TTACl-rich mixed micelles form with a strong downfield shift and for higher alpha F values DEFUMACl-rich mixed micelles form with a strong upfield. For the other two systems of DEFUMACl/CTACl and DEFUMAC/OTACl, the chemical shifts of proton Deltadelta (1H) of -CH3 increase with an increase of the total concentration of DEFUMACl/CTACl or OTACl, and mixed CH- and CF-surfactant micelles form. At higher total concentration, the greater effect of fluorinated chains of DEFUMACl on CH-chains was obvious, resulting in the strong upfield chemical shifts. In cationic fluorocarbon and hydrocarbon surfactant mixtures, the different kinds of micelles observed by 19F and 1H NMR measurements could be caused by the increase in alkyl chain length of hydrocarbon surfactants with different critical micelle concentrations. Combining two theoretical models for mixing, for the four different chain-length hydrocarbon surfactants studied, one can conclude that the two components of mixtures interact with each other and form mixed micelles in two completely different ways according to their molecular properties and cmc values in a certain range of total concentrations. One is close to an ideal mixing case with the formation of one type of mixed micelles, such as the DEFUMACl/DTACl and DEFUMACl/TTACl systems. The other is a demixing case with the formation of two types of micelles, i.e., fluorocarbon-rich and hydrocarbon-rich mixed micelles, such as DEFUMACl/CTACl and DEFUMACl/OTACl systems. However, as the total concentrations of the mixed systems are high enough, the four systems tend to demix and to form individual micelles of corresponding components due to the initial respective interaction between fluorocarbon and hydrocarbon chains. That is to say, at high total concentration, the individual DEFUMACl micelles in all four systems could form. These results may be primarily directed toward acquiring an understanding of the mechanism of CF-CH mixtures in aqueous solution and secondarily directed toward providing more detailed information on nonideal mixing.     

阳离子碳氟表面活性剂研究I: 水溶液中的胶束特性及生长

利用动态光散射(Dynamic Light Scattering, DLS)、瞬态电双折射(Transient Electric Birefringence, TEB)和粘度测定方法研究了部分氟代阳离子表面活性剂氟代-2-羟基十一烷基二乙羟基甲基氯化铵(diethanolheptadecafluoro-2-undecanol methylammonium chloride, C₈F₁₇CH₂CH(OH)CH₂NCH₃(C₂H₄OH)₂Cl, DEFUMACl)水溶液的胶束化特性. 结果表明: DEFUMACl的临界胶束浓度cmc为3.8 mmol•L^－1. 稀溶液中随着DEFUMACl浓度的增加或者无机盐NaCl的加入, DEFUMACl胶束由球形向棒状转变, 其转变浓度, 即第二临界胶束浓度(cmc_II)为0.2 mol•L^－1; 电导测定的反离子(Cl^－)结合度为0.72. 利用球形和棒状胶束模型确定的DEFUMACl胶束聚集数分别为45和335.     

pH-responsive surface activity and solubilization with novel pyrrolidone-based Gemini surfactants

A new series of pH-responsive Gemini surfactants with 2-pyrrolidone head groups, N,N'-dialkyl-N,N'-di(ethyl-2-pyrrolidone)ethylenediamine (Di-C(n)P, where n = 6, 8 10, 12), were synthesized and characterized by (1)H NMR, (13)C NMR, ESI-MS, and elemental analysis. The surface activity and micellization behavior at acidic, neutral, and basic conditions were characterized by equilibrium surface tension and fluorescence techniques. It was found that the surface activity of Di-C(n)P depends on the pH of aqueous solutions due to the protonation state of surfactant molecules when pH was varied. The new compounds have lower cmc and γ(cmc) in comparison with that of m-2-m type conventional cationic Gemini surfactants and gluconamide-type nonionic Gemini surfactants. Fluorescence data confirm that micelles are formed when the concentration is above the cmc. Since micellization is of fundamental importance in surfactant applications such as solubilization, microemulsion, and related technologies, the significant difference in cmc at different pH of this new Gemini surfactant is employed to solubilize cyclohexane. The preliminary result indeed shows that the solubilization capacity of Di-C(n)P can be tuned by pH.     

Interaction between β‐Cyclodextrin and Mixed Cationic‐Anionic Surfactants (1): Thermodynamic Study

The interactions between β‐cyclodextrin (β‐CD) and the mixtures of cationic‐anionic surfactants in aqueous solution were investigated by surface tension and ¹H NMR measurements. It was shown that the critical micelle concentration (cmc) increased linearly with the increase of β‐CD concentration. Furthermore, β‐CD formed 1∶1 inclusion complex with both cationic and anionic surfactants in the mixed surfactant systems, and no significant selective inclusion was observed. The thermodynamic parameters of the inclusion process of β‐CD to mixed cationic‐anionic surfactants were calculated by a numerical method based on the surface tension measurements, and it was found that the inclusion process was both enthalpy and entropy favorable.     

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.     

新型阴离子Gemini表面活性剂与非离子表面活性剂C10E6混合溶液的胶团化的研究

研究了烷基苯磺酸盐Gemini表面活性剂Ia与非离子表面活性剂C10E6溶液混合胶团中分子间的相互作用. 通过表面张力法测定了Ia 和C10E6不同比例不同温度下的临界胶束浓度(cmc). 结果表明, 两种表面活性剂以任何比例复配的cmc比单一表面活性剂的cmc都低, 表现出良好的协同效应. 传统型非离子表面活性剂C10E6、Gemini表面活性剂Ia及混合物的cmc都随着温度升高而降低. 而且, 任何配比的混合胶团中两种表面活性剂分子间的相互作用参数β都是负值, 这说明两种表面活性剂在混合胶团中产生了相互吸引的作用. 混合表面活性剂体系的胶团聚集数比单一Ia的大, 但比单一C10E6的小. 向Gemini表面活性剂Ia胶束中加入非离子表面活性剂C10E6会使胶束的微观极性变小.     

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.     

Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

Mixed micellar properties of cationic trimeric-type quaternary ammonium salts and anionic sodium n-octyl sulfate surfactants

The properties of quaternary ammonium salt-type cationic trimeric surfactants (m-2-m-2-m, m represents the carbon atom number in alkyl chain lengths of 8, 10, and 12) and oppositely charged anionic monomeric surfactant, sodium n-octyl sulfate (SOS), were characterized by employing several techniques such as static surface tension, fluorescence spectroscopy, and dynamic light-scattering measurements. The critical micelle concentrations (cmc) of m-2-m-2-m were much lower than those of the corresponding dimeric and monomeric surfactants, and decreased with increasing chain length. The addition of SOS to m-2-m-2-m solutions resulted in a further decrease of the cmc. The mixed surfactants showed higher efficiencies in lowering the surface tension than the individual surfactants. The fluorescence measurements suggested the formation of mixed micelles with a hydrophobic environment in the solutions even at lower concentrations. The dynamic light-scattering study indicated the presence of two different kinds of aggregates with different hydrodynamic diameters. The larger one was attributed to the mixed micelle of m-2-m-2-m and SOS. These results indicated a decline of the electrostatic repulsion between cationic head groups through the incorporation of anionic surfactant into the mixed surfactants.     

Interaction of sodium N-lauroylsarcosinate with N-alkylpyridinium chloride surfactants: spontaneous formation of pH-responsive, stable vesicles in aqueous mixtures

The interaction of sodium N-lauroylsarcosinate (SLS) with N-cetylpyridinium chloride (CPC) and N-dodecylpyridinium chloride (DPC) was investigated in aqueous mixtures. A strong interaction between the anionic and cationic surfactants was observed. The interaction parameter, β was determined for a wide composition range and was found to be negative. The mixed systems were found to have much lower critical micelle concentration (cmc) and surface tension at cmc. The surfactant mixtures exhibit synergism in the range of molar fractions investigated. The self-assembly formation in the mixtures of different compositions and total concentrations were studied using a number of techniques, including surface tension, fluorescence spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), confocal fluorescence microscopy (CFM). Thermodynamically stable unilamellar vesicles were observed to form upon mixing of the anionic and cationic surfactants in a wide range of composition and concentrations in buffered aqueous media. TEM as well as DLS measurements were performed to obtain shape and size of the vesicular structures, respectively. These unilamellar vesicles are stable for periods as long as 3 months and appear to be the equilibrium form of aggregation. Effect of pH, and temperature on the stability was investigated. The vesicular structures were observed to be stable at pH as low as 2.0 and at biological temperature (37°C). In presence of 10 mol% of cholesterol the mixed surfactant vesicles exhibited leakage of the encapsulated calcein dye, showing potential application in pH-triggered drug release.     

Molecular mechanism and thermodynamics study of plasmid DNA and cationic surfactants interactions

The molecular mechanism and thermodynamics of the interactions between plasmid DNA and cationic surfactants were investigated by isothermal titration calorimetry (ITC), dynamic light scattering, surface tension measurements, and UV spectroscopy. The cationic surfactants studied include benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, cetylpyridinium chloride, and cetyltrimethylammonium chloride. The results indicate a critical aggregation concentration (cac) of a surfactant: above the cac the surfactant forms aggregates with plasmid DNA; below the cac, however, there is no detectable interaction between DNA and surfactant. Surfactants with longer hydrocarbon chains have smaller cac, indicating that hydrophobic interaction plays a key role in DNA-surfactant complexation. Moreover, an increase in ionic strength (I) increases the cac but decreases the critical micellization concentration (cmc). These opposite effects lead to a critical ionic strength (I(c)) at which cac = cmc; when I < I(c), cac < cmc; when I > I(c), DNA does not form complexes with surfactant micelles. In the interaction DNA exhibits a pseudophase property as the cac is a constant over a wide range of DNA concentrations. ITC data showed that the reaction is solely driven by entropy because both deltaH(o) (approximately 2-6 kJ mol(-1)) and deltaS(o) (approximately 70-110 J K(-1) mol(-1)) have positive values. In the complex, the molar ratio of DNA phosphate to surfactant is in the range of 0.63-1.05. The reaction forms sub-micrometer-sized primary particles; those aggregate at high surfactant concentrations. Taken together, the results led to an inference that there is no interaction between surfactant monomers and DNA molecules and demonstrated that DNA-cationic surfactant interactions are mediated by the hydrophobic interactions of surfactant molecules and counterion binding of DNA phosphates to the cationic surfactant aggregates.     

Mixed micelles containing sodium oleate: the effect of the chain length and the polar head group

We have investigated the mixing behavior of binary mixtures of the alkylglucosides (CnG) octyl beta-D-glucoside and decyl D-glucoside in combination with sodium oleate (NaOl), and the amine oxide surfactants (AO) N,N-dimethyldodecylamine oxide, N,N-bis (2-hydroxyethyl)dodecylamine oxide, and 3-lauramidopropyl-N,N-dimethylamine oxide in combination with NaOl. From the equilibrium surface tension measurements, the critical micelle concentration (cmc) data were obtained as functions of the composition. Values of the cmc were analyzed according to both the regular solution model developed by Rubingh for mixed micelles and Maeda's formulation for ionic/nonionic mixed micelles. Two interaction parameters, beta and B1, were estimated from the regular solution model and Maeda's formulation, respectively. For NaOl/CnG mixed systems, a decrease in the hydrocarbon chain length of CnG resulted in a stronger interaction with NaOl from both beta and B1 values. For NaOl/AO mixed systems, the bulkiness of a polar head group of AO surfactants influenced the interaction between NaOl and AO. The dynamic surface tension measurements show that all surface tension values of surfactant solutions examined decreased with the time. We found that the time dependence of surface tension values for NaOl mixed systems was greatly influenced by the presence of NaOl rather than the other component.     

Polymerizable cationic gemini surfactant

A polymerizable cationic gemini surfactant, [CH(2)=C(CH(3))COO(CH(2))(11)N(+)CH(3))(2)CH(2)](2).2Br(-), 1 has been synthesized and its basic interfacial properties were investigated (in water and in the presence of 0.05 M NaBr). For comparison, the properties of monomeric surfactant corresponding to 1, CH(2)=C(CH(3))COO(CH(2))(11)N(+)(CH(3))(3).Br(-), 2, were also investigated. Parameters studied include cmc (critical micelle concentration), C(20) (required to reduce the surface tension of the solvent by 20 mN/m), gamma(cmc) (the surface tension at the cmc), Gamma(cmc) (the maximum surface excess concentration at the air/water interface), A(min) (the minimum area per surfactant molecule at the air/water interface), and cmc/C(20) ratio (a measure of the tendency to form micelles relative to adsorb at the air/water interface). For the polymerizable gemini surfactant, 1, the methacryloxy groups at the terminal of each hydrophobic group in a molecule have no contact with the air/water interface in the monolayer, whereas for the corresponding monomeric surfactant, 2, the methacryloxy group contacts at the interface forming a looped configuration like a bolaamphiphile. Polymerized micelles of the gemini surfactant are fairly small monodisperse and spherical particles with a mean diameter of 3 nm.     

Molecular interactions of cationic and anionic surfactants in mixed monolayers and aggregates

The properties of anionic-rich and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry and surface tension measurements and by determining the surfactant NMR self-diffusion coefficients. The critical aggregate concentration (CAC), surface tension reduction effectiveness(gamma(CAC)), surface excess(Gamma(max)), and mean molecular surface area (A(min)) were determined from plots of the surface tension (gamma) as a function of the total surfactant concentration. The compositions of the adsorbed films (Z) and aggregates (chi) were estimated by using regular solution theory, and then the interaction parameters in the aggregates (beta) and the adsorbed film phases (beta(sigma)) were calculated. The results showed that the synergism between the surfactants enhances the formation of mixed aggregates and reduces the surface tension. Further, the nature and strength of the interaction between the surfactants in the mixtures were obtained by calculating the values of the following parameters: the interaction parameter, beta, the size parameter, rho, and the nonrandom mixing parameter, P*. These results indicate that in ionic surfactant mixtures the optimized packing parameter has the highest value and that the size parameter can be used to account for deviations from the predictions of regular solution theory. It was concluded that, for planar air/aqueous interfaces and aggregation systems, this nonideality increases as the temperature increases. This trend is attributed to the increased dehydration of the surfactant head groups that results from increases in temperature. Further, our conductometry measurements show that the counterion binding number of mixed micelles formed in mixtures with a high CTAB content is different to those with a high SDS content. This difference is due to either their different aggregation sizes or the different interactions between the head groups and the counterions.     

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.     

Study of mixtures of n-dodecyl-beta-D-maltoside with anionic, cationic, and nonionic surfactant in aqueous solutions using surface tension and fluorescence techniques

Surfactants of practical interest are invariably mixtures of different types. In this study, mixtures of sugar-based n-dodecyl-beta-D-maltoside with cationic dodecyltrimethylammonium bromide, anionic sodium dodecylsulfate, and nonionic pentaethyleneglycol monododecyl ether in solution, with and without supporting electrolyte, have been studied using surface tension and fluorescence spectroscopic techniques. Interaction parameters and mole fraction of components in mixed micelles were calculated using regular solution theory. The magnitude of interactions between n-dodecyl-beta-D-maltoside and other surfactants followed the order anionic/nonionic > cationic/nonionic > nonionic/nonionic mixtures. Since all surfactants have the same hydrophobic groups, strengths of interactions are attributed to the structures of hydrophilic headgroups. Electrolyte reduced synergism between n-dodecyl-beta-D-maltoside and ionic surfactant due to charge neutralization. Industrial sugar-based surfactant, dodecyl polyglucoside, yielded results similar to that with dodecyl maltoside, implying that tested commercial alkyl polyglucosides are similar to the pure laboratory samples in synergistic interactions with other surfactants. Fluorescence study not only supported the cmc results using tensiometry, but showed that interfaces of all the above mixed micelle/solution interfaces are mildly hydrophobic. Based on these results, an attempt is made to discover the nature of interactions to be a combination of intermolecular potential energies and free energy due to packing of surfactant molecules in micelles.     

Non-surface activity and micellization behavior of cationic amphiphilic block copolymer synthesized by reversible addition-fragmentation chain transfer process

Cationic amphiphilic diblock copolymers of poly(n-butylacrylate)-b-poly(3-(methacryloylamino)propyl)trimethylammonium chloride) (PBA-b-PMAPTAC) with various hydrophobic and hydrophilic chain lengths were synthesized by a reversible addition-fragmentation chain transfer (RAFT) process. Their molecular characteristics such as surface activity/nonactivity were investigated by surface tension measurements and foam formation observation. Their micelle formation behavior and micelle structure were investigated by fluorescence probe technique, static and dynamic light scattering (SLS and DLS), etc., as a function of hydrophilic and hydrophobic chain lengths. The block copolymers were found to be non-surface active because the surface tension of the aqueous solutions did not change with increasing polymer concentration. Critical micelle concentration (cmc) of the polymers could be determined by fluorescence and SLS measurements, which means that these polymers form micelles in bulk solution, although they were non-surface active. Above the cmc, the large blue shift of the emission maximum of N-phenyl-1-naphthylamine (NPN) probe and the low micropolarity value of the pyrene probe in polymer solution indicate the core of the micelle is nonpolar in nature. Also, the high value of the relative intensity of the NPN probe and the fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene (DPH) probe indicated that the core of the micelle is highly viscous in nature. DLS was used to measure the average hydrodynamic radii and size distribution of the copolymer micelles. The copolymer with the longest PBA block had the poorest water solubility and consequently formed micelles with larger size while having a lower cmc. The "non-surface activity" was confirmed for cationic amphiphilic diblock copolymers in addition to anionic ones studied previously, indicating the universality of non-surface activity nature.     

Lidocaine and soyasterole-PEG-16-ether — investigations on the interaction between an amphiphilic drug and a nonionic surfactant in aqueous solution

In order to study the interactions between the surface active local anaesthetic drug lidocaine and the nonionic surfactant soyasterole-PEG-16-ether firstly the self association of the drug in aqueous solution was investigated by different methods. Transmission electron microscopy hinted at micellization and surface tension measurements resulted in a CMC of 12.9% (salt form) and 0.08% (base form), respectively, whereas solubilization experiments, NMR spectroscopy and osmotic pressure measurements obviously disproved the existence of drug micelles. The detected CMC only meant a surface saturation and the TEM pictures probably showed artifacts. In diluted systems containing both drug and surfactant no formation of mixed micelles took place, as pointed out by the tensiometric determination of the CMC of the mixtures showing no minimum in the CMC/% drug-curve. Also, gel permeation chromatography clearly separated surfactant micelles and drug molecules. In contrast to this, evident interactions between the base form of the drug and the surfactant occurred when the drug concentration was increased: the dynamic viscosity of the systems rose distinctly, probably caused by growth of the surfactant associates to a more rodlike form. The salt form had nearly no influence on the viscosity of the preparations.     

Soluble complexes of sodium poly(isoprene-b-methacrylate) micelles with cationic surfactants in aqueous media

Water-soluble complexes between sodium poly(isoprene-b-methacrylate) (NaIMA) amphiphilic block copolymer micelles and two cationic surfactants with different hydrophobic tail lengths, namely, dodecyltrimethylammonium bromide (DTMAB) and octyltrimethylammonium bromide (OTMAB), were prepared by mixing individual aqueous solutions of block copolymers and surfactants. The complexes were characterized in terms of size, overall charge, and micropolarity by dynamic light scattering, zeta-potential measurements, and fluorescence spectroscopy. Properties of the systems were investigated as a function of surfactant concentration and surfactant type and state in the initial solutions, as well as temperature. Experiments reveal surfactant complexation at the coronal sodium poly(methacrylate) (NaMA) chains, followed by an increase in mass and a decrease in size of the micelles. Complexation of individual surfactant micelles was observed when the DTMAB concentration in the starting solutions was higher than the surfactant cmc. The complexes show a temperature dependence of their dimension due to the hydrophobic effect.     

Adsorption and Micellization in Solutions of Dodecylpyridinium Bromide–Nonionic Surfactant Mixtures

Dependences of the surface tension of aqueous solutions of cationic (dodecylpyridinium bromide) and nonionic (Tween 80, Triton X-100) surfactants and their mixtures on total surfactant concentration and solution composition were studied. The values of critical micellization concentration (CMC) and excess free energy of adsorption were determined from tensiometric measurements. Based on Rubingh–Rosen model (approximation of the theory of regular solutions), the compositions of micelles and adsorption layers at the solution–air interface as well as parameters of interaction between the molecules of cationic and nonionic surfactants were calculated for the systems indicated above. It was established that, in the case of surfactant mixtures with considerable difference in the CMCs, the micelles of individual surfactant with lower CMC value are formed. The effect of negative deviation from the ideality during the adsorption of surfactants from mixed solutions at the solution–air interface was disclosed. It was shown that the interaction energy depends significantly on the composition of mixed systems.