Mixed Critical Micelle Concentration Research Articles

Effect of alcohol on synergistic interaction between amino sulfonate amphoteric surfactant and zwitterionic cocamidopropyl hydroxysultaine in aqueous solution

Micellization behavior for quasi-binary mixtures of an amino sulfonate amphoteric surfactant, sodium 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (DES), with a zwitterionic surfactant cocamidopropyl hydroxysultaine (CAHS) both in water-glycerol and in water-glycol and the effect of alcohol were investigated using both the tensiometry and the conductometry. In the framework of regular solution theory and based on the pseudophase separation model, the Rubingh’s model, the Rodenas’ model and the Clint’s model were adopted to successfully estimate the related micellar and thermodynamic parameters. The synergistic interaction between DES and CAHS along with the nonideal mixing are observed in the entire range of mixing. Besides the hydrophobic effect, the compatibility in molecular conformation, the steric hindrance, the feeble electrostatic repulsion, the interaction between dipoles and the formation of hydrogen bond can account for the dependence of the mixed critical micelle concentration and the micellar composition on the content in bulk solution. In comparison with the case of glycerol, the presence of glycol partly disfavors the micellization process. Thermodynamic parameters show that the entropy makes an overwhelming contribution to the spontaneous micellization process, the release of mixing heat promotes the formation of stably mixed micelle, the greater share of entropy in the presence of glycol than in the presence of glycerol displays the disadvantage in the micellization process as well as the dependence of both the free energy change and the share of entropy on the mixing ratio in bulk solution is approximately symmetric with respect to about 0.500.

Interaction and micellar behavior of ternary mixture of amphoteric amino sulfonate surfactant with traditional anionic and nonionic surfactants: Effect of hydrophilicity

The micellization and the molecular interaction behaviors for two ternary mixtures constituted by an amphoteric sodium 3-(n-dodecyl ethylenediamino)-2-hydroxypropyl sulfonate (C12AS), an anionic sodium dodecylbenzene sulfonate (SDBS) and a nonionic octylphenol polyoxyethylated ether with the number (n) of oxyethylene glycol ethers OP-n (n = 10 or 7) in aqueous solution were investigated using the tensiometry and the effect of hydrophilicity on them was also discussed. In the framework of pseudophase separation model and based on the regular solution theory, the related micellization parameters including the mixed critical micelle concentration (cmc) values in the ideal and real cases, the activity coefficients and the compositions in mixed micelle, etc. and thermodynamic parameters were estimated by the Clint’s model and the Rubingh’ model. The mixed cmc value is dependent on the composition in aqueous solution and influenced by the hydrophilicity of nonionic surfactant. With increasing the nonionic in ternary mixture, the mixed cmc value is initially decreased and then slightly rise. An increasing in the hydrophilicity of nonionic will make the minimum value of mixed cmc be increased from 1.299 mM to 1.705 mM. The resulting phenomena can be explained reasonably by the electrostatic effect, the steric hindrance, the hydrogen bonding, etc. Thermodynamic data indicate that the contribution of entropy or enthalpy plays a vital role on the spontaneous process of micellization and the share of entropy or enthalpy in free energy change is dependent largely on the amount of nonionic surfactant and the hydrophilicity. In ternary mixtures of C12AS/SDBS/OP-10, an increase in an amount of OP-10 will induce the change from the enthalpy-driven micellization process to the entropically favorable process. Once an abundant amount of OP-7 is added, while, the enthalpy will make a main contribution on the micellization process, which can be described by the drop in the share of entropy at the composition (0.6970/0.0000/0.3030) of ternary mixture from 0.6478 to 0.4901. These findings will help with understanding the molecular interaction behavior for the ternary surfactant mixture and the effect of the addition of nonionic surfactant and its hydrophilicity.

Molecular interaction between sodium dodecylbenzene sulfonate and octylphenol polyoxyethylene ether and effect of hydrophilic chain

The micellization behavior of two binary mixtures of an anionic sodium dodecylbenzene sulfonate with a nonionic surfactant octylphenol polyethoxylated ether (including OP-10 or OP-7) was investigated in aqueous solution at 298.15 K using the tensiometry, and the effect of hydrophilic chain of nonionic surfactant was discussed. In the framework of pseudophase separation model and based on the regular solution theory, the related micellization parameters and thermodynamic parameters were estimated by some models including Clint’s model, Rubingh’s model, etc. The two mixtures exist some differences in the micellization behavior. The synergistic effect, the antagonism, nonideal mixing and ideal mixing are observed in the two mixtures. The dependence of the mixed critical micelle concentration, the composition in mixed micelle, the interaction parameter between molecules on the composition in aqueous solution is explained by the electrostatic interaction, the steric effect and the shell structure of mixed micelle, etc. Thermodynamic parameters are adopted to account for the difference in energy and verify the micellization behavior. The two binary mixtures show different contributions of energy to the process of micellization. These findings help with understanding the nature on the interaction between two surfactants and the effect of the length of hydrophilic chain of nonionic surfactant so as to obtain some information in theoretical and practical investigations.

Molecular interaction for quasi-binary mixture of N-acyl amino sulfonate amphoteric surfactant from castor oil and stearyltrimethyl ammonium bromide

The micellization behavior and the molecular interaction of quasi-binary mixture constituted by an amphoteric sodium N-acyl amino sulfonate based on castor oil (AAS-CO) with a cationic stearyltrimethyl ammonium bromide (STAB) in aqueous solution at 298.15 K were investigated using both the tensiometry and the conductometry and the two techniques were adopted to determine the mixed critical micelle concentration (cmc). Based on the regular solution theory and in the framework of the pseudophase separation model, Rubingh’s model and Clint’s model were adopted to estimate the mole fractions and the activity coefficients in mixed micelle, the interaction parameters between quasi-one AAS-CO and STAB. Also, thermodynamic parameters were obtained by thermodynamic models. Synergistic interaction between surfactants and non-ideal mixing were observed in the entire range of composition in this investigation. The addition of quasi-one AAS-CO into aqueous solution can induce the alteration of interaction behavior between surfactants, which can be explained rationally by the shielding effect, the electrostatic repulsion and the steric hindrance. Thermodynamic parameters imply that it appears an enthalpically spontaneous behavior in the process of micellization and there exists a largest negative deviation of free energy change of micellization from the ideal case at the optimum composition in which a maximum synergism happens. These findings will help with understanding the molecular interaction between quasi-one component and other one in surfactant mixtures.

Unusual Maximum in the Adsorption of Aqueous Surfactant Mixtures: Neutron Reflectometry of Mixtures of Zwitterionic and Ionic Surfactants at the Silica-Aqueous Interface.

The adsorption of two zwitterionic surfactants, dodecyldimethylammonium propanesulfonate (C12PS) and dodecyldimethylammonium carboxybetaine (C12CB), and of their mixtures with the cationic dodecyltrimethylammonium bromide (C12TAB) and the anionic sodium dodecylsulfate (SDS) at the silica-water interface has been studied by neutron reflection (NR). The total adsorption, the composition of the adsorbed layer, and some structural information have been obtained over a range of concentrations from below the critical micelle concentration (CMC) to about 30× the mixed CMC. The adsorption behavior has been considered in relation to the previously measured micellar equilibrium of these mixtures in their bulk solutions and their adsorption at the air-water interface. C12CB adsorbs cooperatively close to its CMC to form an almost complete bilayer on its own, whereas C12PS adsorbs more weakly in a fragmented bilayer structure. Although SDS does not normally adsorb at the silica-water interface, SDS adsorbs strongly and cooperatively with C12PS at fractional SDS compositions up to about 0.5. This cooperativity is lost when the adsorbed fraction of SDS rises above about 0.5. At this point, adsorption drops sharply, creating an unusual maximum in the variation of adsorption with a total concentration above the mixed CMC. Neither the increase in cooperativity nor the subsequent decline in adsorption results directly from variations of the independently determined monomer concentrations in the bulk solution. The adsorption maximum is predominantly the effect of strong cooperative interaction, possibly accompanied by partial segregation of SDS within the layer, followed by charge repulsion from the surface. Although the solution aggregation and adsorption at the A-W interface are similar for SDS with C12CB, the addition of SDS to C12CB at the silica-water interface promotes the opposite behavior to that of SDS with C12PS, and SDS simply disrupts the cooperative binding of C12CB. Unlike SDS, the cationic surfactant C12TAB adsorbs on silica. It therefore coadsorbs at the SiO2-W interface with either C12CB or C12PS. However, in neither case is there any pronounced cooperativity and, even though the presence of C12TAB might be expected to favor adsorption, the adsorption is generally unexpectedly low.

Studying on the properties of Mixed Surfactant Systems

The Anionic-nonionic Gemini Surfactant oxalamide polyoxyethylene lauryl ether (7) succinate sodium sulfonate (OPLES-7) was synthesized. It was mixed with the dodecyl glucoside in different ratios to enhance application performance. The mixed critical micelle concentration (CMC) of the binary surfactant systems was determined by surface tension measurement. Critical micelle concentration of mixed system is 0.141mmol ⋅ L−1 when the molar fraction of OPLES-7 to dodecyl glucoside 1:1. The influence of NaCl on surface properties of the mixed system was also studied. The surface activity was enhanced with the increase of NaCl concentration.

Mixing Natural and Synthetic Surfactants: Co-Adsorption of Triterpenoid Saponins and Sodium Dodecyl Sulfate at the Air-Water Interface.

Saponins are highly surface active glycosides, derived from a wide range of plant species. Their ability to produce stable foams and emulsions has stimulated their applications in beverages, foods, and cosmetics. To explore a wider range of potential applications, their surface mixing properties with conventional surfactants have been investigated. The competitive adsorption of the triterpenoid saponin escin with an anionic surfactant sodium dodecyl sulfate, SDS, at the air-water interface has been studied by neutron reflectivity, NR, and surface tension. The NR measurements, at concentrations above the mixed critical micelle concentration, demonstrate the impact of the relative surface activities of the two components. The surface mixing is highly nonideal and can be described quantitatively by the pseudophase approximation with the inclusion of the quadratic and cubic terms in the excess free energy of mixing. Hence, the surface mixing is highly asymmetrical and reflects both the electrostatic and steric contributions to the intermolecular interactions. The relative importance of the steric contribution is reinforced by the observation that the micelle mixing is even more nonideal than the surface mixing. The mixing properties result in the surface adsorption being largely dominated by the SDS over the composition and concentration range explored. The results and their interpretation provide an important insight into the wider potential for mixing saponins with more conventional surfactants.

Micellar and Interfacial Behavior of Mixed Systems Containing Anionic-nonionic Gemini Surfactant

The Anionic-nonionic Gemini Surfactant oxalamide polyoxyethylene lauryl ether(9)succinate sodium sulfonate(OPLES-9) was synthesized. It was mixed with the anionic surfactant sodium lauryl sulfate(SDS) and the nonionic surfactant dodecanol polyoxyethylene(9) ether (AEO9) respectively in different ratios to enhance application performance. The experimental results showed that the surface performance of the mixed systems was more superior to the relevant single surfactants. The mixed critical micelle concentration (CMC) of the binary surfactant systems was determined by surface tension measurement. Critical micelle concentration of mixed system reached the minimum 0.146mmol·L−1 when the molar fraction of OPLES-9 to SDS was 1:1. Critical micelle concentration of OPLES-9/AEO9 mixed system reached the minimum 0.259mmol·L−1 when the molar fraction of OPLES-9 to AEO9 was 0.9:1.

Study of aggregation behavior between N-lauryl sarcosine sodium and Dodecyltrimethylammonium bromide in aqueous solution, using conductometric and spectrophotometric techniques

The micellization behavior of N-Lauryl sarcosine sodium (NLS, an anionic surfactant) and Dodecyltrimethylammonium bromide (DOTAB, a cationic surfactant) in aqueous solution is investigated by UV–vis spectrophotometric and conductometric methods at 298.15 K. A critical micelle concentration (CMC) were obtained for pure NLS and DOTAB as well as mixed micelles [NLS(1) + DOTAB(2)]. The CMC values of the studied system at different mole fractions (yi) are much less than that of individual surfactants (due to the strong electrostatic attraction between components after mixing). In this work, the tautomers of 1-phenyl-1, 3-butadione (or benzoylacetone) were used to obtain the mixed CMC of anionic surfactant systems by UV–Vis technique. The deviations of critical micelle concentration (CMC) from the ideal values show the interaction between NLS and DOTAB. The micellar mole fraction values (X1m and X2m) according to Rubingh approach were calculated and the results obtained reveal the same composition in the mixed micellization at most mole fraction(y1) even when the initial mixing ratio is far from equimolar. The activity coefficients of components were less than unity (f1m < < 1 and f2m < < 1) and the values of the interaction parameter (βm) are negative in all compositions, which indicate the strong synergistic interaction between NLS and DOTAB. The Gibbs free energy of micellization (ΔGmic0) and the excess free energy of micellization (GmicE) values are found to be negative in this system demonstrated the stability of the mixture. All of the evaluated results imply a strong synergism between components.

Mixed micellization of binary mixture of amino sulfonate amphoteric surfactant with octadecyltrimethyl ammonium bromide in water/isopropanol solution: Comparison with that in aqueous solution

The micellization behavior of the mixed system of amphoteric sodium 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) and cationic octadecyltrimethyl ammonium bromide (OTAB) in water/isopropanol (abbr. IPA, 20 g·L−1) solution at 40 °C was investigated using both the tensiometry and the conductometry. According to the regular solution theory, pseudophase separation model and other thermodynamic models (including the Rubingh’s model, the Rodenas’s model, Lange’s model, etc.), some parameters were estimated to achieve a full understanding of their aggregation behaviors. For all the mixtures of C12AS/OTAB, the mixed critical micelle concentration and the composition of C12AS in mixed micelle have deviations from their ideal cases, indicating a non-ideal mixing. The presence of cosolvent IPA produces the changes in the composition in mixed micelle and the optimum mixing ratio which can obtain a maximum synergism. The interaction parameter indicates an attractive interaction between two surfactants. Thermodynamic parameters show that the mixed micellization is an entropically spontaneous process and the presence of IPA seemingly reduces the entropy contribution to the formation of mixed micelle. The above behaviors can be explained rationally by the hydrophobic effect, the steric effect and the attractive interaction between two surfactants. These findings are useful for optimizing the composition of mixed surfactant systems and understanding the interaction behavior between surfactant molecules to further achieve more effective and economical formulations.

Micellization and interaction for ternary mixtures of amino sulfonate surfactant and nonionic octylphenol polyoxyethylene ethers in aqueous solution: 2 blending with nonionic surfactant with a longer or shorter hydrophilic chain

The micellization behavior of the ternary mixture of an amphoteric sodium 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) with two nonionic surfactants, octylphenol polyoxyethylene ether (OP-n, where n is the number of hydrophilic unit oxyethylene glycol ethers, n = 4, 7, 10), was investigated using both the tensiometry and the 1H NMR technique. Also, the effect of the addition of nonionic surfactant with a longer or shorter hydrophilic chain, e.g., OP-10 or OP-4, on the micellization of the binary mixture of C12AS/OP-7 with a maximum synergism was probed. Based on the regular solution theory, thermodynamic models were adopted to obtain the composition, activity coefficient of mixed micelle and some thermodynamic parameters. The addition of OP-10 or OP-4 into the binary mixture of C12AS/OP-7 induces the change in the mixed critical micelle concentration, which can be explained by the change in the composition of mixed micelle and the effect of hydrophilic chain. Thermodynamic data show that the addition of OP-10 or OP-4 results in the change from the enthalpy overwhelming process of micellization to the entropy-driven process. The chemical shift of proton in the terminal hydroxy group of OP-n in binary or ternary surfactant mixture is also adopted to describe the obtained results. The findings will help with understanding the interaction behavior between molecules in the multicomponent mixture, especially, the effect of the addition of homologues or other components on the properties of surfactant formulation.

Adsorption at the Air-Water Interface in Biosurfactant-Surfactant Mixtures: Quantitative Analysis of Adsorption in a Five-Component Mixture.

The composition of the air-water adsorbed layer of a quinary mixture consisting of three conventional surfactants, octaethylene glycol monododecyl ether (C12E8), dodecane-6-p-sodium benzene sulfonate (LAS6), and diethylene glycol monododecyl ether sodium sulfate (SLE2S), mixed with two biosurfactants, the rhamnolipids l-rhamnosyl-l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoyl, R2, and l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoyl, R1, has been measured over a range of compositions above the mixed critical micelle concentration. Additional measurements on some of the subsets of ternary and binary mixtures have also been measured by NR. The results have been analyzed using the pseudophase approximation (PPA) in conjunction with an excess free energy, GE, that depends on the quadratic and cubic terms in the composition. The compositions of the binary, ternary, and quinary mixtures could all be fitted to two sets of interaction parameters between the pairs of surfactants, one for micelles and one for adsorption. No ternary interactions or ternary corrections were required. Because the system contains two strongly anionic surfactants, the PPA can be extended, in practice, to ionic surfactants, contrary to the prevailing view. The values of the interaction parameters show that the quinary mixture, SLE2S-LAS6-C12E8-R1-R2, which is known to be a highly effective surfactant system, is characterized by a sequence of strong surface but weak micellar interactions. About half of the minima in GE for the strong surface interactions occur well away from the regular solution value of 0.5.

A molecular‐thermodynamic approach to predict the micellization of binary surfactant mixtures containing amino sulfonate amphoteric surfactant and nonionic surfactant

A molecular‐thermodynamic approach was adopted to predict the value of mixed critical micelle concentration (cmc) for the binary surfactant mixtures constituted by an amino sulfonate amphoteric surfactant, sodium 3‐(N‐dodecyl ethylenediamino)‐2‐hydropropyl sulfonate (abbr. C12AS), and a nonionic surfactant, octylphenol polyethylene ether (OP‐n, where n denotes the average number of oxyethylene glycol ether). In this investigation, considering two positive charges on the hydrophilic group of C12AS, which is unlike to conventional zwitterionic surfactants having one positive charge (such as, alkylbetaine, etc.), three schemes were designed to obtain the geometric parameter describing the dipole structure of C12AS. According to the selected optimum scheme, four cases corresponding to the different conformations of both the headgroup and the hydrocarbon chain of surfactant were discussed. The results show that the predicted value of mixed cmc for the C12AS/OP‐n mixtures agrees well with the experiment value. The deviation of the predicted value from the experimental value can be explained by the effect of the hydrophilicity of OP‐n on the process of micellization. © 2017 American Institute of Chemical Engineers AIChE J, 2017

Interaction and Micellar Behavior of Binary Mixture of Amino Sulfonate Amphoteric Surfactant with Octadecyltrimethylammonium Bromide in Aqueous Solutions of NaCl

The interaction behavior and the process of mixed micellization for binary mixtures of an amino sulfonate amphoteric surfactant sodium 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) and a cationic surfactant octadecyltrimethylammonium bromide (OTAB) in aqueous solution of NaCl (0.250 M) at 313.15 K were investigated using both the tensiometry and the UV–vis spectrometry using pyrene as a probe. The mixed critical micelle concentration (cmc) of the C12AS/OTAB mixtures were determined by two techniques. Based on regular solution theory, pseudophase separation model, Clint’s model, Rosen’s model, and Rubingh’s model, some parameters (including the ideal mixed cmc, the compositions in mixed micelle, the interaction parameters between two surfactants, the activity coefficients in mixed micelle, some thermodynamic parameters, etc.) were evaluated and calculated. The deviation of mixed cmc from its ideal value indicates a nonideal mixing between two surfactants. In comparison with those in aqueous...

Impact of Electrolyte on Adsorption at the Air-Water Interface for Ternary Surfactant Mixtures above the Critical Micelle Concentration.

The composition of the air-water adsorbed layer of the ternary surfactant mixture, octaethylene monododecyl ether, C12E8, sodium dodecyl 6-benzenesulfonate, LAS, and sodium dioxyethylene glycol monododecyl sulfate, SLES, and of each of the binary mixtures, with varying amounts of electrolyte, has been studied by neutron reflectivity. The measurements were made above the mixed critical micelle concentration. In the absence of electrolyte adsorption is dominated by the nonionic component C12E8 but addition of electrolyte gradually changes this so that SLES and LAS dominate at higher electrolyte concentrations. The composition of the adsorbed layer in both binary and ternary mixtures can be quantitatively described using the pseudo-phase approximation with quadratic and cubic interactions in the excess free energy of mixing (GE) at both the surface and in the micelles. A single set of parameters fits all the experimental data. A similar analysis is effective for a mixture in which SDS replaces SLES. Addition of electrolyte weakens the synergistic SLES-C12E8 and LAS-C12E8 interactions, consistent with them being dominated by electrostatic interactions. The SLES-LAS (and SDS-LAS) interaction is moderately strong at the surface and is little affected by addition of electrolyte, suggesting that it is controlled by structural or packing factors. Most of the significant interactions in the mixtures are unsymmetrical with respect to composition, with the minimum in GE at the 1:2 or 2:1 composition. There is a small structural contribution to the LAS-C12E8 interaction that leads to a minimum intermediate in composition between 1:2 and 1:1 (LAS:C12E8) and to a significant residual GE in strong electrolyte.

Surface Adsorption in Ternary Surfactant Mixtures above the Critical Micelle Concentration: Effects of Asymmetry on the Composition Dependence of the Excess Free Energy.

The composition of the adsorbed layer of a ternary surfactant mixture at the air-water interface has been studied by neutron reflectivity. The adsorption of the ternary mixture of octaethylene monododecyl ether (C12E8) sodium dodecyl 6-benzene sulfonate (LAS), and sodium dioxyethylene glycol monododecyl sulfate (SLES), as well as each of the binary mixtures, at solution concentrations greater than the mixed critical micelle concentration is highly nonideal. In the ternary mixture, the surface adsorption is dominated by C12E8 and LAS, and there is little SLES at the interface. The departure from ideality in the binary mixtures can be quantitatively described by applying the pseudophase approximation with quadratic and cubic terms in the excess free energy of mixing (GE) both at the surface and in the micelles. The same parameters that describe the binary interactions give a quantitative fit to the adsorbed fractions in the ternary mixture over a wide range of composition. A similar analysis is effective for the mixture containing sodium dodecyl sulfate instead of SLES. Of the set of six GE required to fit the ternary data, one is ideal (SLES-LAS) and three, LAS-C12E8 (micelle) and C12E8-SLES (micelle and surface), have minima occurring at a composition (mole fraction) of the anionic species of 1/3.

Micellization of Binary Mixture of Amino Sulfonate Amphoteric Surfactant and Octylphenol Polyoxyethylene Ether (10) in Aqueous Solution: Different Electrolyte Effect

The micellization behaviors of binary mixtures constituted by an amphoteric surfactant, sodium 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate, and a nonionic surfactant octylphenol polyoxyethylene ether (10), OP-10, in aqueous solutions containing seven inorganic salts were investigated. The values of mixed critical micelle concentration (cmcM) were determined by both the tensiometry and the UV–vis spectroscopy method using pyrene as a probe. The dependence of cmcM on inorganic salt was established. According to different theoretical models, the components in mixed micelle, interaction parameters between two surfactants, etc. were obtained. Upon adding inorganic salt, the component in real mixed micelle is inferior to the ideal case, indicating nonideal mixing. Different inorganic salts result in the variation of component in mixed micelle. For all mixed surfactant systems, a negative interaction parameter between surfactants shows synergistic effect. Thermodynamic parameters show that the process ...

Monte Carlo simulation and theoretical approach to mixed surfactant system consisting gemini and conventional surfactants in aqueous solutions

In the present study, mixtures of gemini surfactant (T3H1S2H1T3) and a conventional surfactant (A4B4) in aqueous solutions have been investigated through coarse-grained Monte Carlo simulation. The Critical Micelle Concentration (CMC) and aggregation numbers have been calculated at different ratios of the T3H1S2H1T3/A4B4 surfactant mixture. The mixed CMC of the binary combinations falls between those of constituent surfactants. To explain the simulation results, theoretical models like Clint, Rubingh, and Maeda have been used to evaluate the interaction parameter, micellar composition, activity coefficients and the free energies of micellization. By increasing the overall composition until it reaches 0.5, all these parameters indicate non-ideal behavior and synergistic interactions between the surfactants, which is explained in terms of reduction of repulsion between head groups of T3H1S2H1T3 due to the presence of conventional surfactants. At higher ratios, the formation of the aggregations would be harder due to the higher concentration of A4B4.

Synergistic effect between amino sulfonate amphoteric surfactant and octylphenol polyoxyethylene ether (10) in aqueous solutions with different acidicities: consideration of different thermodynamic models

The micellization behavior of binary mixtures of sodium n-dodecyl diamine sulfonate (C12AS) and octylphenol polyoxyethylene ether (10), OP-10, in aqueous solutions at pH 3.5, 6.0, and 8.5 was investigated, and the values of mixed critical micelle concentration (CM) were determined by both UV–vis spectroscopy using pyrene as a probe and by tensiometry. Within the framework of the pseudophase separation model, four thermodynamic models were adopted to describe the micellization parameters including the interaction parameters (β12) between two surfactants, the components in real and ideal mixed micelles, the activity coefficients in mixed micelles, the thermodynamic parameters, and the thermodynamic stability. The experimental values of CM, inferior to the ideal values, show nonideal mixing; the negative values of β12 obtained from Rubingh's, Rodenas's, and Motomura's models mean the synergistic effect. Although there exist some divergences in the micellization parameters predicted by the three treatments, similar results were obtained, indicating the validity of these models in this investigation. Based on the calculation errors, Rubingh's model is best to describe the interacting behavior between the two surfactants in this investigation. Thermodynamic parameters predicted by the three treatments show a spontaneous process of micellization and an entropic contribution in the formation of mixed micelles. Different acidities of solutions result in different stabilities of micellization. The stability in feeble acidic solution is higher than in acidic or basic solution, and the stability in basic solution is slightly superior to that in acidic solution. All the above described phenomena can be explained rationally by the electrostatic effect of head groups of C12AS, the steric effect of head group for two surfactants, the molecular structures of surfactants, the influence of added counterion, and so on. © 2015 Society of Chemical Industry

Micellization of Amphiphilic Drug with Pharmaceutical Excipients in Aqueous Electrolytic Solution: Composition, Interaction, and Stability of the Aggregates

In the present study, we report on the interaction between an antidepressant drug, amitriptyline hydrochloride, and nonionic surfactants (t-octylphenoxypolyethoxyethanol (TX-100), polyethoxyglycol t-octylphenyl ether (TX-114)), in aqueous electrolyte solutions, with special attention paid to the possible contribution from the ion–dipole type of interaction, by using a spectroscopic approach. The structural difference in the drug and nonionic surfactants also plays a role in tuning the aggregational behavior of the drug–surfactant mixtures. From the I 1/I 3 versus total surfactant concentration plots, the mixed critical micelle concentration (cmc) of various mixtures was computed. Critical assessments by applying Clint, Rubingh, and Motomura models confirm strong interactions in mixed micelle in the bulk of aqueous electrolytic solution. The various micellar parameters, such as micelle mole fraction (), interaction parameter (βm), micropolarity, and micelle aggregation number (N agg), have been determined for all different ratio mixtures. Micelle aggregation numbers (N agg) indicate that the contribution of nonionic surfactants was always more than that of the drug. Stern–Volmer binding constants (K sv) and dielectric constant of mixed systems have also been evaluated from the ratios of respective peak intensities (I 1/I 3 or I 0/I 1).