Surfactant-polymer interactions: Mixed micelles of hexadecylpyridinium bromide and trimethyltetradecylammonium bromide in aqueous poly(vinylpyrrolidone) solution

The conductance of hexadecylpyridinium bromide (HPyBr) and trimethyltetradecylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyBr (α_HPyBr) was measured in aqueous poly(vinylpyrrolidone) (PVP) solution containing 1, 5, and 10 wt% PVP at 30°C. Each conductivity curve showed two breaks corresponding to two aggregations throughout the whole mole fraction range of HPyBr and TTAB mixtures except for pure TTAB for which a single break corresponding to the conventional critical micelle concentration was observed. The two aggregation processes in the presence of low amounts of PVP were mostly similar to those in pure water, however, 10 wt% PVP shifted the break, corresponding to the second aggregation, toward the higher value. This was attributed to HPyBr/PVP interactions, which were also evident from the appearance of a second break in the conductivity (κ) plot of pure HPyBr in aqueous 10 wt% PVP. From conductivity data, various micellar parameters in the presence of PVP were determined and discussed from the standpoint of micelle-polymer interactions. The mixing behavior of HPyBr and TTAB corresponding to the first break in the presence of PVP was ideal for the most part and identical to that in pure water.     

Mixed micelles of hexadecylpyridinium bromide + tetradecyltrimethylammonium bromide in aqueous glycol oligomers

Conductances of hexadecylpyridinium bromide (HPyBr) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyBr (α_HPyBr) were measured in pure water as well as in the presence of various aqueous ethylene glycol oligomers containing 10 and 30 wt% of each additive in their respective binary mixtures at 30°C. Each conductivity curve shows two breaks corresponding to two critical micelle concentrations (cmc; C₁ and C₂ over the whole mole fraction range of HPyBr + TTAB mixtures except in the presence of pure HPyBr and TTAB, where a single break was observed. From the conductivity data, various micellar paramelers in the absence and presence of glycol additives were computed. A variation in the micellar parameters in the presence of additive showed that additive introduction mainly influence the medium properties and therefore the micellar properties. However, no significant micelle-glycol interactions were observed even with an increase in the number of repeating units from ethylene glycol to polyethylene glycol 600. The mixing behavior of HPyBr + TTAB is close to nonideal and is identical in pure water and in the presence of various glycols. This has been attributed to the presence of synergistic interactions between unlike monomers at C₁ that are not influenced even by the presence of additives. The appearance of the second cmc is mainly attributed to structural transitions of the mixed micelles at C₁ with a further increase in surfactant concentration.     

Hydrophobic hydration of cationic mixed micelles by alkoxyethanols in aqueous media

The conductances of hexadecylpyridinium chloride (HPyCl) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyCl (α_HPyCl) were measured in aqueous binary mixtures of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether containing 10 to 30 wt% additive in their respective binary mixtures at 30°C. Each conductivity curve showed a single break over the whole mole fraction range of HPyCl + TTAB mixtures. From the break in the conductivity curve, various micellar parameters were calculated and the results were discussed on the basis of alkoxyethanol's hydrophobic hydration of the mixed micelle. The micellar parameters of HPyCl, TTAB, and of their mixtures showed a strong dependence both on the amount and on the number of repeating units of ethylene and diethylene glycol derivatives. The hydrophobic hydration was considerably higher in the case of diethylene glycol derivatives owing to the presence of an extra ether oxygen. An evaluation of the non-ideality in the HPyCl + TTAB mixtures in the presence of additives revealed that alkoxyethanols reduce the unlike surfactant monomer interactions in order to form the mixed micelles in comparison to those in pure water. It has also been observed that such interactions systematically decrease with an increase in the number of repeating units from monomethyl ether to monobutyl ether, both in the case of ethylene and diethylene glycol derivatives.     

Physico-Chemical Investigations of Mixed Micelles of Cationic Gemini and Conventional Surfactants: a Conductometric Study

The interaction of cationic gemini and cationic conventional surfactants by conductivity was systematically overviewed, paying attention to synergism observed in micellization. These mixed systems were found to show remarkable synergism in micelle formation. The experimental critical micelle concentration values being lower than the value predicted by ideal solution theory indicate that the mixed micellization is due to attractive interaction between the two components. Gemini/conventional systems form mixed micelle due to attractive interactions (negative β values). The values of micellar mole fraction of constituent 1 (X ₁) in surfactant mixtures are more than in the ideal state (X ₁ ^ideal ), which means that, the mixed micelles are rich in conventional surfactants in comparison to that in the ideal state.     

Interaction of tetradecyltrimethylammonium bromide with bovine serum albumin in different compositions: Effect of temperatures and electrolytes/urea

Herein, the interaction of a protein, bovine serum albumin (BSA), with tetradecyltrimethylammonium bromide (TTAB, a cationic surfactant), has been investigated using the conductivity measurement technique in pure water and some sodium salts (NaCl, Na₂SO₄, Na₂CO₃, and Na₃PO₄) solutions at temperature range of 295.15-320.15 K. Results reveal that, in the plot of specific conductivity versus the concentration of TTAB, only a single critical micelle concentration (cmc) was found for the TTAB + BSA mixed system in all solvents media studied. The addition of BSA in aqueous TTAB solution, the value of cmc undergoes a change from its pure form, which indicates the presence of strong interaction operating between the BSA and TTAB molecules. In aqueous system, the cmc values of the TTAB + BSA mixtures are obtained higher compared to the values found for single TTAB surfactant. However, the addition of salt decreases the cmc value of mixed TTAB + BSA system. The values of cmc of the BSA + TTAB mixed system at 310.15 K and 1.00 mmol·kg^-1 ionic strength of salt followed the order: cmc_Na2CO3 > cmc_Na3PO4 > cmc_NaCl > cmc_Na2SO4. The cmc values of TTAB + BSA mixture were found to be lowered in urea solution within the concentrations studied. The values of degree of dissociation (α) and fraction of counter ion binding (β) were found to be dependent on additives and temperature. The free energy of micellization (△G_m^o) is negative for all the systems, which manifests that the micellization phenomenon is energetically spontaneous. The enhancement of the negative value of △G_m^o in aqueous salt solutions reveals an increase of spontaneity of the TTAB + BSA micellization process. The values of △G_m^o also reveal that the spontaneity of micelle formation is enhanced at higher temperatures in all media studied. The values of free energy of transfer (△G_{m, t}^o) were also determined for numerous solvent media used in the present study and described with appropriate reasoning.     

Micellar and Surface Properties of Some Monomeric Surfactants and a Gemini Cationic Surfactant

The physicochemical and interfacial properties of the monomeric surfactants cetyltrimethyl ammonium bromide (CTAB), cetyltriphenyl phosphonium bromide (CTPB), tetradecyl triphenyl phosphonium bromide (TTPB), cetyldiethylethanol ammonium bromide (CDEEAB), cetyltrimethyl ammonium chloride (CTACl), tetradecyltrimethyl ammonium bromide (TTAB), and a gemini surfactant (C₁₆-3-C_16, 2Br⁻) at different pH (3.1, 7.0, and 7.75) have been investigated by conductivity and surface tension measurements at 300 K. The critical micellar concentration (CMC), degree of micellar ionization (α), surface excess concentration (Г_max), minimum surface area per molecule of surfactant (A _min), Gibbs free energy of micellization (∆G _m⁰), surface pressure at the CMC (π _CMC), and the Gibbs energy of adsorption (∆G _ads⁰) of the monomeric surfactants have also been determined. The CMC, α and Г_max, increase with increasing pH whereas A _min decreases.     

Conductometric Probe Analysis of the Effect of Benzyldimethylhexadecylammonium Chloride on the Micellization Behavior of Dodecyltrimethylammonium Bromide in Aqueous/Urea Solution: Investigation of Concentration and Temperature Effect

Surfactant mixtures are used in many different industrial formulations. In this study, the mixed micelle formation behavior of 2 different cationic surfactants, namely dodecyltrimethylammonium bromide (DTAB) and benzyldimethylhexadecylammonium chloride (BDHAC), in the absence and presence of urea at various temperatures (298.15–318.15 K) was studied using the conductometric method. The attractive interaction between DTAB and BDHAC was estimated from the values of critical micelle concentration (CMC) and the CMC for ideal mixing (CMC^id). Urea increases the CMC value as a result of the enrichment in the surface charge of the micelles/mixed micelles. The values of micellar mole fraction (X₁^Rub [Rubingh], X₁^M [Motomura], X₁^Rod [Rodenas]) and ideal micellar (X₁^id) of surfactant BDHAC were obtained by different models and are shown to exhibit the high contribution or effective involvement of BDHAC in mixed micelles and increase with increasing BDHAC mole fraction (α₁). Activity coefficients (f₁ and f₂) were also evaluated from the relevant formula given in the literature. The negative values of the interaction parameters (β) show the attractive interaction among the studied components. Excess Gibbs free energy (?G_ex) of micellization revealed that the stability of mixed micelles is higher in aqueous solution than in urea solution. The thermodynamic parameters, namely the Gibbs free energy change, enthalpy change, and entropy change (?G^o_m, ΔH^o_m, and ?S^o_m, respectively), were also calculated from the conventional standard equations.     

Aggregation and Phase Separation Phenomenon of Amitriptyline Hydrochloride Under the Influence of Pharmaceutical Excipients

The interaction between the amphiphilic drug amitriptyline hydrochloride (AMT) and the nonionic surfactants used in drug delivery has been investigated. Herein, we report the micellization behavior of AMT in presence of ethoxylated alkyl phenols in aqueous medium and the clouding phenomenon in the absence and presence of different nonionic surfactants in buffer solution. The values of critical micelle concentration (CMC) of AMT obtained using the conductivity method, decrease as nonionic surfactant concentration increases. With an increase in temperature, the CMC first increases and then decreases. At 303.15 K, the maximum CMC values were obtained with or without nonionic surfactant. The results obtained indicate attractive interactions (synergism) between the two mixing amphiphiles in solution. The experimentally obtained critical micelle concentration (CMC) values are always lower than ideal CMC values. Micellar mole fraction (X₁) values, calculated by different proposed models, show the contribution of nonionic surfactant concentration. At a fixed drug concentration (50 mmol kg^?1) and pH (=6.7) nonionic surfactants show continuous increase in cloud point (CP). Increase in drug concentration and pH, in the presence of fixed amounts of nonionic surfactant, increases and decreases the CP, respectively.     

The Effect of Ethanol on Nanostructures of Mixed Cationic and Anionic Surfactants

Micellization of tetradecyl trimethyl ammonium bromide (TTAB) and sodium dodecyl sulfate (SDS) in water–ethanol (ET) micellar solutions, with the weight percent of ET changing within the range 0–30, was studied by means of surface tension and conductivity measurements. Surface tension measurements also provided information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. Information about the degree of counterion dissociation and phase transition was obtained through conductivity measurements. Cyclic voltammetry (CV) and dynamic light scattering (DLS) was also employed to investigate the mixed micellar behavior of the binary mixtures. It was shown that an excess of cationic surfactant and ET resulted in a phase transition of vesicles and large micelles to mixed micelles. The regular solution theory approximation was used to determine various micellar parameters of ideal systems. The regular solution interaction parameter (β) suggests that the formation of mixed micelles is due to the synergistic interactions in the case of TTAB/SDS systems and becomes affected by the water/ET ratio.     

Experimental and theoretical investigation of micellization behavior of sodium dodecyl sulfate with cetyltrimethylammonium bromide in aqueous/urea solution at various temperatures

Mixed micelle formation behavior of cationic surfactant-cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS) in aqueous as well as in urea medium from 303.15 K to 323.15 K at 5 K interval was carried out by conductometric method. The differences between the experimental values of critical micelle concentrations (cmc) and ideal critical micelle concentrations (cmc^id) illustrate the interaction between the amphiphiles studied. The values of micellar mole fraction (\(\text{X}_1^{Rub}\) (Rubingh), \(\text{X}_1^{M}\) (Motomura), \(\text{X}_1^{Rod}\)(Rodenas) and \(\text{X}_1^{id}\)(ideal) of surfactant CTAB determined by different proposed models and outcome indicate high involvement of CTAB in SDS-CTAB mixed micellization, which enhance by means of the augment of mole fraction of CTAB. The negative value of interaction parameter (β) showed an attractive interaction involving CTAB and SDS. Activity coefficients were less than unity in all case, which also reveals the presence of interaction between CTAB & SDS. The negative \(\Delta{\text{G}}_m^0\)values imply the spontaneous mixed micellization phenomenon. The attained values of \(\Delta{\text{H}}_m^0\)were positive at inferior temperature, while negative at superior temperature. The negative \(\Delta{\text{H}}_m^0\)values in urea (NH₂CONH₂) medium illustrate exothermic micellization process. The magnitudes of \(\Delta{\text{S}}_m^0\)were positive in almost all cases. The excess free energy of mixed micelle formation (ΔG_ex) was found to be negative, which indicates the stability of mixed micelle as compared to the individual’s components micelles.     

Effects of sodium glycocholate and sodium taurocholate on the mixed micelles of bile salts and nonionic surfactant

Effects of sodium glycocholate (NaGC) and sodium taurocholate (NaTC) on the mixed micelles for two systems consisting of NaGC-octaoxyethylene glycol monon-decyl ether (C₁₀E₈) and NaTC-C₁₀E₈ have been studied as a function of the mixed micelles’ compositions, polarities of the micelles’ interior and mean aggregation numbers. The compositions of the mixed micelles are calculated from critical micelle concentration (CMC) data by using excess thermodynamic quantities. The polarities and mean aggregation numbers are determined from pyrene fluorescence in the mixed micelles. Both mixed systems were nonideal, and the mole fraction of NaGC or NaTC in a mixed micelle near the CMC was less than that in the aqueous mixed solution. However, the mixed micelle of the NaTC-C₁₀E₈ system contained more bile salt molecules than that of the NaGC-C₁₀E₈ system because of a good miscibility of NaTC and C₁₀E₈ molecules. The pyrene fluorescence results suggested that the mixed micelles changed from C₁₀E₈-rich micelles to NaGC- or NaTC-rich micelles, and mean aggregation numbers of the mixed micelles decreased abruptly with increasing mole fraction of bile salts. In the low mole fraction range of bile salts, however, both the polarities and the mean aggregation numbers for the NaTC-C₁₀E₈ system are lower than those for the NaGC-C₁₀E₈ system because of the high mole fraction of NaTC in a mixed micelle, and also because of the different effect of the conjugated group between NaTC and NaGC molecules in the mixed micelles.     

Mixed Micellar and Interfacial Interactions of a Triblock Polymer (EO37PO56EO37) with a Series of Monomeric and Dimeric Surfactants

The mixed micellar and interfacial properties of mixtures of triblock polymer (TBP) with a series of monomeric (dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and cetyltrimethylammonium bromide, and dimeric (dimethylene bis[alkyldimethylammonium bromide], m-2-m, where m = 10, 12, and 14) cationic surfactants were investigated using surface tension and viscosity measurements in aqueous solutions at different temperatures. Various physicochemical properties such as critical micelle concentration, mixed micellar mole fraction, interaction parameter, interfacial, and thermodynamic parameters were evaluated. All the binary mixtures exhibit synergistic interactions which increase with temperature and pass through a minimum with the increase in hydrophobic chain length of the cationic surfactants. The contribution of TBP in mixed micelle formation also increases with the hydrophobic chain length of the surfactants. The interfacial and thermodynamic parameters reveal that the adsorption of the surfactant mixtures at the air–solution interface is more favorable than that of micelle formation and the unfavorable enthalpy changes are overwhelmed by favorable entropy changes. Further, the mixtures of TBP with smaller chain length surfactants show a sharp rise in relative viscosity at higher mole fractions of these surfactants.     

Theoretical Approaches on the Synergistic Interaction between Double-Headed Anionic Amino Acid-Based Surfactants and Hexadecyltrimethylammonium Bromide

Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, −aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X^σ), interaction parameters at the bulk/interface (β^R/β^σ), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (α_AAS), the magnitude of the (β^R/β^σ) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing α_AAS, the micellar mole fraction of HTAB (X₂) decreased insignificantly and X₂ values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS () differed from micellar mole fraction of AAS (X₁), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( ∆G_m ) values are more negative than the free energy of micellization for ideal mixing (), indicating the micellization process is spontaneous. With increasing α_AAS, the enthalpy of micellization (ΔH_m) and entropy of micellization (ΔS_m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.     

Mixed Micellization of Sodium Dodecylbenzene Sulfonate with Polyoxyethylene Lauryl Ether Surfactants (POLE4 and POLE23) in n-Butanol Aqueous Solution

The values of critical micelle concentration and counterion binding constant for the mixed micellizations of sodium dodecylbenzenesulfonate (DBS) with polyoxyethylene(4) lauryl ether (POLE4) and polyoxyethylene(23) lauryl ether (POLE23) in aqueous solution of n-butanol at 25 °C were determined as a function of the overall mole fraction of DBS by using the electric conductivity and the surface tension methods. Various thermodynamic parameters were calculated and analyzed for the mixed micellization of DBS/POLE4 and DBS/POLE23 systems by means of the equations derived from the nonideal mixed micellar model. The results show that DBS/POLE23 mixed system has a greater deviation from the ideal model than DBS/POLE4 mixed system. These deviations of thermodynamic parameters for both mixed systems become greater with the addition and concentration increase of n-butanol.     

Mixed-surfactant system of dodecylbenzene sulfonate and alpha-olefin sulfonate: Micellar and volumetric studies

Critical micelle concentrations of sodium salts of dodecylbenzene sulfonate, alpha-olefin (C₁₆) sulfonate, and their mixtures have been evaluated by measuring the surface tensions of solutions at 298.15 K. Interaction parameters for mixed monolayer formation (β^σ) and mixed-micelle formation (β^M) have been calculated from the critical micelle concentration data. Densities of solutions of surfactants and their mixtures were measured with a vibrating-tube densimeter at 298.15 K. Apparent and partial molar volumes have been evaluated from solution density data. Results of the micellar properties have been eplained on the basis of a nonideal multicomponent mixed-micelle model. The mixed-surfactant system exhibits synergism in all aspects when the mole fraction of alpha-olefin sulfonate in the mixture is 0.2. Volumetric properties correlate well, as the partial molar volumes also show a minimum at the same composition of the mixture. Formation of a compact mixed micelle at this composition has been envisaged.     

Properties of aqueous solutions for two binary mixed systems between two kinds of bile salts and nonionic surfactants

The micellar properties of aqueous binary mixed solutions for two systems consisting of sodium cholate (NaC)-octaoxyethylene glycol mono n-decyl ether (C₁₀E₈) and sodium glycocholate (NaGC)-C₁₀E₈ have been studied on the basis of surface tensions, polarity of the micelle interior and the mean aggregation number. Application of two theoretical treatments, based on regular solution and excess thermodynamic quantities for critical micellar concentration (CMC) data from surface tension curves of two mixed systems showed that the mole fraction of each bile salt in the mixed micelles near the CMC is lower than that of the corresponding prepared mole fraction in the mixed solution. The polarity of the interior suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of bile salt in the mixed solution and that the mixed micelles become dramatically more hydrophobic at a mole fraction of 0.68 for NaGC−C₁₀E₈ system and 0.75 for NaC−C₁₀E₈ system, respectively. This implies that the micelles become richer in the bile salt molecules and the tendency appears strongly for NaGC−C₁₀E₈ system due to the strong cohesion between the conjugated glycines in the NaGC molecules. The decrease of aggregation number with the increase of the mole fraction of bile salts shows that the micelles approach those of the single system of each bile salt. This supports the previously mentioned facts.     

Peroxide dependent and independent lipid peroxidation: Site-specific mechanisms of initiation by chelated iron and inhibition by α-tocopherol

Peroxidation of linoleic acid (LA) was catalyzed by Fenton reagent (H₂O₂, and Fe²⁺) in positively charged tetradecyltrimethylammonium bromide (TTAB) micelles, but not in negatively charged sodium dodecylsulfate (SDS) micelles. However, more hydroxyl radicals formedvia the Fenton reaction were trapped byN-t-butyl-α-phenylnitrone (PBN) in SDS micelles than in TTAB micelles. Generation of linoleic acid alkoxy (LO) radicals by Fe²⁺ via reductive cleavage of linoleic acid hydroperoxide (LOOH) resulted in peroxidation of LA and formation of PBN-LO· adducts in SDS micelles, but not in TTAB micelles. This LOOH dependent lipid peroxidation could be catalyzed in TTAB micelles in the presence of a negatively charged iron chelator, nitrilotriacetic acid (NTA). LO radicals formed by the LOOH dependent Fenton reaction were also trapped by PBN at the surface of TTAB micelles in the presence of NTA, but not in its absence. The consumption of a spin probe, 16-(N-oxyl-4,4′-dimethyloxazolidin-2-yl)stearic acid (16-NS) during the LOOH dependent Fenton reaction in the presence of NTA was higher in TTAB micelles of LA than in those of lauric acid (LauA), although the rates and amounts of LO radicals formed in the two types of fatty acid micelles were similar. The rates of 5-NS consumption in LA and LauA micelles were almost the same, and were lower than the rate of 16-NS in LA micelles. NTA-Fe²⁺ initiated peroxidation of LA in TTAB micelles without a lag time in the presence of LOOH, but after a lag period, peroxidation occurred without LOOH. α-Tocopherol inhibited peroxidation of LA catalyzed by Fenton reagent by scavenging OH radicals in TTAB micelles. In contrast, α-tocopherol enhanced free Fe²⁺ induced LOOH dependent lipid peroxidation through the regeneration of Fe²⁺ in SDS micelles. However, it inhibited NTA-Fe²⁺ induced LOOH dependent lipid peroxidation in TTAB micelles. The rate and amount of α-tocopherol oxidized by the Fe²⁺ induced, H₂O₂ dependent Fenton reaction were almost the same in TTAB micelles of LA and LauA. The oxidation of α-tocopherol by the NTA-Fe²⁺ induced, LOOH dependent Fenton reaction was greater and faster in LA micelles than in LauA micelles, although the rates of LO radical production in the two types of micelles were the same. During NTA-Fe²⁺ induced, LOOH dependent lipid peroxidation, α-tocopherol inhibited more effectively the consumption of 16-NS than 5-NS. The results are discussed in relation to the location of iron, the unsaturated bonding region of LA, the OOH group of LOOH, the radical trapping site of PBN, the spin sites of 5-NS and 16-NS, and the phenolic hydroxyl group of α-tocopherol in micelles with different charges. Based on a paper presented at the Symposium on Metals and Lipid Oxidation, held at the AOCS Annual Meeting in Baltimore, MD, April 1990.     

Interaction Between Nonionic and Gemini (Cationic) Surfactants: Effect of Spacer Chain Length

The interaction between mixtures of nonionic surfactant polyethylene glycol p-(1,1,3,3-tetramethyl butyl)-phenyl ether and cationic gemini surfactants alkanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-s-12, where s = 2, 4 and 6) was studied using surface tension and small-angle neutron scattering measurements. Marked interaction was observed for the investigated surfactants mixtures which depend upon the hydrophobic spacer length of the gemini surfactant and also on the fraction of nonionic surfactant in the mixed systems. The results are discussed in terms of interaction parameters calculated according to the theory of regular solutions which uses the critical micelle concentration determined tensiometrically to calculate the molecular interaction parameter and the mole fractions of the two components in the mixed micelles. A relatively high negative molecular interaction parameter value (up to −3.40) obtained for mixtures of nonionic and cationic gemini surfactant indicates a presence of strong attractive interaction in the mixed system that increases with the spacer length of the gemini surfactant. Micellar parameters deduced from small-angle neutron scattering measurements also compliment the surface tension results.     

Salt Effect on Mixed Micelle and Interfacial Properties of Conventional Cationic Surfactants and the Ionic Liquid Surfactant 1-Tetradecyl-3-methylimidazolium Bromide ([C14mim]Br)

The surface properties and mixed micellization behavior of binary combinations of an ionic liquid surfactant, namely, 1-tetradecyl-3-methylimidazolium bromide ([C₁₄mim]Br) with common cationic surfactants viz. tetradecyltrimethylammonium bromide and tetradecylpyridinium bromide in the presence of sodium bromide (NaBr) were investigated by surface tension and conductivity measurements. The critical micelle concentration (CMC) and interfacial parameters, such as the maximum surface excess (Γ_max), minimum area per molecule (A_min) and surface pressure at the CMC (π_CMC) were determined from the surface tension data. The CMC and Γ_max values were found to decrease with increasing salt concentrations. The $ \Updelta G_{\text{ad}}^{ \circ } $ and $ \Updelta G_{\text{m}}^{ \circ } $ values are negative indicating the spontaneity of micelle formation.     

Interaction of Azo Dye with Cationic Surfactant Under Different pH Conditions

The aggregation induced by Alizarin Yellow R (AYR) in the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was investigated by measuring their UV–visible absorption spectra. Conductance measurements as a function of surfactant concentration below and above the critical micelle concentration (CMC) were studied. CTAB aggregation takes place at the concentration far below its normal CMC in the presence of AYR. Both hydrophobic and electrostatic interactions affect the aggregation process in aqueous solution. The dye effect on the CMC of CTAB was noted by a specific conductivity method as well. AYR–CTAB binding constant (K_s) and water–micelle partition co-efficient (K_x) were quantified with the help of mathematical models employed to determine the partitioning of organic additives in the micellar phase. The number of dye molecules per micelle was estimated at particular CTAB concentrations above CMC, during this study.