Cationic Mixed Micelles in the Presence of beta-Cyclodextrin: A Host-Guest Study

The conductances of trimethyltetradecylammonium bromide (TTAB)+triphenyltetradecylphosphonium bromide (TTPB) and TTAB+trimethylhexadecylammonium bromide (HTAB) over the entire mole fraction range of TTAB (alpha(TTAB)) were measured in water and in beta-cyclodextrin+water (CD+W) mixtures at fixed 4 and 8 mM of CD at 30 degrees C. The conductivity plots for both binary mixtures show a single break from which the mixed critical micelle concentration (cmc) and degree of micelle ionization (chi) were computed. From the slopes of the conductivity curves, the equivalent ionic conductivities of the monomeric (Lambda(m)), associated (Lambda(ass)), and the micelle (Lambda(mic)) states were calculated and discussed with respect to the surfactant-CD complexation in the whole mole fraction range of both surfactant binary mixtures. The association constant (K) between the respective monomeric surfactant and CD cavity of fixed 4 mM CD was computed by considering 1:1 association from the surface tension measurements. A comparison among the K values for HTAB-CD, TTAB-CD, and TTPB-CD shows that the former complexation is significantly stronger in comparison to the other ones due to the longer hydrophobic tail. The nonideality in mixed micelle formation in pure water was evaluated by using the regular solution theory, and it was observed that both binary mixtures exhibit close to ideal behavior. Copyright 2000 Academic Press.     

Determination of the Critical Micelle Concentration of Cationic Surfactants by Capillary Electrophoresis

The determination of the critical micelle concentration (CMC) of cationic surfactants by capillary electrophoresis was demonstrated. In this study, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DoTAB) were selected as cationic surfactants and propazine was chosen as test solute. In the evolution of the effective electrophoretic mobility of propazine as a function of surfactant concentration, a dramatic change in slope at a particular concentration is a good indication of the CMC of this surfactant. The CMC values determined experimentally were further confirmed by a curve-fitting approach. Simulation of the electrophoretic mobility curves as a function of surfactant concentration in both micellar electrokinetic chromatography and capillary zone electrophoresis using cationic surfactants as an electrolyte modifier was performed for propazine, and the intersection of these two mobility curves allowed us to precisely predict the CMC of the surfactant. The CMC values determined for TTAB and DoTAB are 1.6 ± 0.1 and 11.0 ± 0.1 mM, respectively, in the case of an electrolytic solution consisting of 70 mM phosphate buffer at pH 6.0. Moreover, the applicability of the electroosmotic mobility as a parameter for the determination of the CMC was examined.     

Alkaline hydrolysis of brilliant green in mixed cationic surfactant systems

Kinetic measurements were performed for the alkaline hydrolysis of brilliant green — a triphenylmethane dye used as a model compound for probing micellar rate effects. This reaction was studied both in the presence of tetradecyltrimethylammonium bromide (TTAB) and tetradecyltriphenylphosphonium bromide (TTPPBr) and also in binary mixtures of these surfactants at different mole fractions of each. All rate surfactant profiles were analyzed using the pseudo-phase model in order to obtain the regression parameters, including binding constants and rate constants in the micellar pseudo-phase. The reaction was catalyzed by both surfactants. The catalytic factor increases from about 10 for pure TTPPBr to about 38 for pure TTAB. Binding of BG to micellar surface is greater in pure TTAB than in pure TTPPBr but significantly reduced in the surfactant mixtures than in pure components. Reduction of the binding constant becomes more significant as the mole fraction of TTAB is increased in the mixture. The kinetic data have been analyzed in terms of models of Piszkiewicz and Raghavan-Srinivasan which are in good agreement.      

Reverse micellar aggregates: effect on ketone reduction. 2. Surfactant role

Kinetics of the reduction of 3-chloroacetophenone (CAF) with sodium borohydride (NaBH(4)) were followed by UV-vis spectroscopy at 27.0 degrees C in different reverse micellar media, toluene/BHDC/water and toluene/AOT/water, and compared with results in an isooctane/AOT/water reverse micellar system. AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate, and BHDC is benzyl-n-hexadecyl dimethylammonium chloride. The kinetic profiles were investigated as a function of variables such as surfactant and NaBH(4) concentration and the amount of water dispersed in the reverse micelles, W(0) = [H(2)O]/[surfactant]. In all cases, the first-order rate constant, k(obs), increases with the concentration of surfactant as a consequence of incorporating the substrate into the interface of the reverse micelles where the reaction takes place. The reaction is faster at the cationic interface than at the anionic one probably because the negative ion BH(4)(-) is part of the cationic interface. The effect of the external solvent on the reaction shows that reduction is favored in the isooctane/AOT/water reverse micellar system than that with an aromatic solvent. This is probably due to BH(4)(-) being more in the water pool of the toluene/AOT/water reverse micellar system. The kinetic profile upon water addition depends largely on the type of interface. In the BHDC system, k(obs) increases with W(0) in the whole range studied while in AOT the kinetic profile has a maximum at W(0) approximately 5, probably reflecting the fact that BH(4)(-) is part of the cationic interface while, in the anionic one, there is a strong interaction between water and the polar headgroup of AOT below W(0) = 5 and, above that, BH(4)(-) is repelled from the interface once the water pool has formed. Application of a kinetic model based on the pseudophase formalism, which considers the distribution of the ketone between the continuous medium and the interface and assumes that reaction takes place only at the interface, has enabled us to estimate rate constants at the interface of the reverse micellar systems. At W(0) < 10, it was considered that NaBH(4) is wholly at the interface and, at W(0) >/= 10, where there are free water molecules, also the partitioning between the interface and the water pool was taken into account. The results were used to evaluate CAF and NaBH(4) distribution constants between the different pseudophases as well as the second-order reaction rate constant of the reduction reaction in the micellar interface.     

Thermodynamic properties of ibuprofen sodium salt in aqueous/urea micellar solutions at 298.15 K

Thermodynamic, surface and micellar properties of anti-inflammatory drug sodium 2-(4-isobutylphenyl) propionate (sodium salt of ibuprofen (NaIBF)) in aqueous/urea solution were studied by surface tension measurements at 298.15 K in the presence of anionic surfactant sodium dodecylsulfate (SDS). Critical micelle concentration (cmc), surface tension at cmc (γcmc), maximum Gibbs surface excess (Γ_max), minimum surface area per surfactant molecule at the air/water interface (A _min) etc. were determined in pure water as well as in aqueous urea solution. The theories of Clint, Rosen and Rubingh have been applied to describe the interactions between these amphiphiles at the interface and in the micellar solution. Various thermodynamic parameters have been calculated and discussed in detail.     

Micellar Electrokinetic Chromatography Using a Cationic Surfactant for Rapid Separation and Determination of Bisbenzylisoquinoline Alkaloids from Embryo of the Seed of Nelumbo nucifera Gaertn

Liensinine (LIE), isoliensinine (ISO) and neferine (NEF) from embryo of the seed of Nelumbo nucifera Gaertn were first separated and quantitatively analyzed by micellar electrokinetic chromatography with internal standard (IS) using a cationic surfactant, tetradecyltrimethyl ammonium bromide (TTAB). Complete separation of the analytes was optimally achieved within 15 min using 40 mM sodium dihydrogenphosphate (pH 6.40) containing 10 mM TTAB and 15% (v/v) methanol as buffer. Tetrahydropalmatine was used as IS to improve the repeatability and linearity relativity. The IS method resulted in excellent linearity, with correlation coefficients of regression equations of 0.9997, 0.9997 and 0.9992 for LIE, ISO and NEF, respectively. Finally, two sample extraction methods were used to investigate the contents of different parts of the embryos.     

Experimental and theoretical investigation of the micellar-assisted solubilization of ibuprofen in aqueous media

Surfactants can be used to increase the solubility of poorly soluble drugs in water and to increase drug bioavailability. In this article, the aqueous solubilization of the nonsteroidal, antiinflammatory drug ibuprofen is studied experimentally and theoretically in micellar solutions of anionic (sodium dodecyl sulfate, SDS), cationic (dodecyltrimethylammonium bromide, DTAB), and nonionic (dodecyl octa(ethylene oxide), C12E8) surfactants possessing the same hydrocarbon "tail" length but differing in their hydrophilic headgroups. We find that, for these three surfactants, the aqueous solubility of ibuprofen increases linearly with increasing surfactant concentration. In particular, we observed a 16-fold increase in the solubility of ibuprofen relative to that in the aqueous buffer upon the addition of 80 mM DTAB and 80 mM C12E8 but only a 5.5-fold solubility increase upon the addition of 80 mM SDS. The highest value of the molar solubilization capacity (chi) was obtained for DTAB (chi = 0.97), followed by C12E8 (chi = 0.72) and finally by SDS (chi = 0.23). A recently developed computer simulation/molecular-thermodynamic modeling approach was extended to predict theoretically the solubilization behavior of the three ibuprofen/surfactant mixtures considered. In this modeling approach, molecular-dynamics (MD) simulations were used to identify which portions of ibuprofen are exposed to water (hydrated) in a micellar environment by simulating a single ibuprofen molecule at an oil/water interface (modeling the micelle core/water interface). On the basis of this input, molecular-thermodynamic modeling was then implemented to predict (i) the micellar composition as a function of surfactant concentration, (ii) the aqueous solubility of ibuprofen as a function of surfactant concentration, and (iii) the molar solubilization capacity (chi). Our theoretical results on the solubility of ibuprofen in aqueous SDS and C12E8 surfactant solutions are in good agreement with the experimental data. The ibuprofen solubility in aqueous DTAB solutions was somewhat overpredicted because of challenges associated with accurately modeling the strong electrostatic interactions between the anionic ibuprofen and the cationic DTAB. Our results indicate that computer simulations of ibuprofen at a flat oil/water interface can be used to obtain accurate information about the hydrated and the unhydrated portions of ibuprofen in a micellar environment. This information can then be used as input to a molecular-thermodynamic model of self-assembly to successfully predict the aqueous solubilization behavior of ibuprofen in the three surfactant systems studied.     

Kinetic micellar effects in tetradecyltrimethylammonium bromide-pentanol micellar solutions

The reactions 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane + OH(-) and 2-(p-nitrophenyl)ethyl bromide + OH(-) were studied in tetradecyltrimethylamonium bromide, TTAB, and TTAB-pentanol micellar solutions. The influence of changes in the surfactant concentration as well as changes in the hydroxide ion concentration on the observed rate constant was investigated. If changes in the cmc and ionization degree provoked by the presence of the different amounts of n-pentanol in the micellar solutions are taken into account, the experimental kinetic data can be rationalized quantitatively by using the PIE model. Assuming that the ion-exchange equilibrium constant, K(OH(-)/Br(-)), for the competition between the bromide and the hydroxide ions in all TTAB and in TTAB-pentanol micellar solutions studied is the same, a good agreement between the theoretical and the experimental kinetic data was found in all the micellar media for the two processes studied. This assumption was checked by experimentally determining the ion-exchange equilibrium constant K(OH(-)/Br(-)) in TTAB and TTAB-pentanol micellar solutions through a spectroscopic method, results showing that the presence of n-pentanol does not affect substantially the value of K(OH(-)/Br(-)). The second-order rate constants obtained from the fittings decrease slightly when the amount of pentanol increases, being greater than that in aqueous solution. This acceleration can be explained considering that micelles accelerate the reactions in which the charge is delocalized in the transition state.     

Influence of sodium sulfate or sodium sulfite on the solubilization of benzylalcohol in cationic micellar solutions

The enthalpy of benzylalcohol (BzOH) solution has been determined as a function of alcohol concentration in aqueous trimethyltetradecylammonium bromide (TTAB) solutions in the presence of sodium sulfite or sodium sulfate up to high salt concentration. The electrolytes studied do not seem to induce TTAB sphere-torod transition at least up to 0.6 mol/kg of salt. Comparison with the enthalpic behavior of BzOH in sodium dodecylsulfate solutions and with that of 1-pentanol in both cationic and anionic micellar solutions suggests that the solubilization of BzOH in TTAB solutions is specifically favored by intramolecular interactions between alcohol molecules within the cationic micelles. The replacement of the bromide counterions by the sulfite or sulfate ions has been studied using potentiometry with an ionselective electrode in the case of trimethylhexadecylammonium bromide (CTAB). No difference could be detected between the effects of either divalent anions on the rate of change of the bromide ion-condensation with the salt/surfactant concentration ratioR. The degree of counter-ion condensation on micellar surface depends not only on theR values, but also on the total surfactant concentration.     

Enantioseparation of phenothiazines in cyclodextrin-modified micellar electrokinetic chromatography

In this study, enantioseparations of five phenothiazines in cyclodextrin (CD)-modified micellar electrokinetic chromatography (MEKC) were investigated using a citrate buffer containing tetradecyltrimethylammonium bromide (TTAB) as a cationic surfactant at low pH. Beta-cyclodextrin (beta-CD) and hydroxylpropyl-beta-CD (HP-beta-CD) were selected as chiral selectors. The results indicate that the separation window is greatly enlarged by beta-CD concentration and that the separability and selectivity of phenothiazines are remarkably influenced by the concentrations of both beta-CD and TTAB, as well as buffer pH. The interaction of thioridazine with beta-CDs is considerably reduced in the presence of TTAB micelles due to competitive complexation of thioridazine with TTAB micelles, which is pH-dependent. As a result, effective enantioseparation of thioridazine is simultaneously achievable with that of trimeprazine and promethazine or ethopropazine in MEKC with addition of either beta-CD or HP-beta-CD, respectively, to a micellar citrate buffer containing TTAB at pH 3.5. Better enantioresolution of thioridazine in MEKC than in capillary zone electrophoresis can be obtained.     

MICELLE FORMATION BY ANIONIC AND CATIONIC SURFACTANTS IN AQUEOUS 18-CROWN-6 ETHER,P-CYCLODEXTRIN,AND 1,10-PHENANTHROLINE SOLUTIONS AT DIFFERENT TEMPERATURES

The conductances of sodium perfluorooctanoate (SPFO), sodium dodecylsulphate (SDS), dodecyltrimethylammonium bromide (DTAB), and tetradecyltrimethylammonium bromide (TTAB) in 18-crown-6 ether + water (CR+W), p-cyclodextrin + water (CY+W), and 1,10-phenanthroIine + water (Phen+W) mixtures with fixed 4 mM of each additive were determined over the temperature range of 5-55 °C. The conductivity plots for all the surfactants showed single break from which the critical micellization concentration (cmc) and degree of micelle ionization (x) were computed. From the pre and the post micellar slopes of the conductivity curves, the equivalent conductivities of the monomeric (Aass) and the micellar states (Amjc), respectively, were calculated and discussed with respect to the surfactant-additive complexation. It was observed that the micelle formation of all the ionic surfactants irrespective of the nature of their head groups were delayed in CYC+W in comparison to that in CR+W and Phen+W systems over the temperature range studied. The micelle formation of SPFO and SDS in CR+W and Phen+W systems showed stabilization of the respective micelles due to the adsorption of Na⁺-CR and Na+-Phen complexes at the micelle solution interface in comparison to that of DTAB and TTAB.     

A comparative study of interfaces for microchip micellar electrokinetic chromatography-electrospray ionization mass spectrometry using the surfactant ammonium dodecyl sulfate

Using ammonium dodecyl sulfate (ADS) as the surfactant, the response of three common interfaces in the direct coupling of microchip micellar electrokinetic chromatography with electrospray ionization mass spectrometry was studied. In the range of 10-40 mM surfactant, a conventional sheath liquid interface provided poorer sensitivity than both sheathless interface and low-sheath-flow interface. At a surfactant concentration <20 mM, a low-sheath-flow interface exhibited less sensitivity than a sheathless interface; however, it outperformed the sheathless interface above a concentration of 20 mM. At a surfactant concentration above 20 mM, signal reduction due to dilution of the analyte compensated by signal enhancement gained from a reduction in ion suppression effect. The difference in responses of the interfaces was mainly due to the dilution effect, whereas the effect of flow rate became an important factor when the difference in responses between the interfaces was not significant. The utility of the PMMA microchip MEKC/MS using a low-sheath-flow interface was demonstrated by the analysis of sulfonamides at a concentration of 40 mM. The interday precision was in the range of 4.9-14.5%, and the LOD was in the range of 0.34-1.03 ng/mL (MEKC/MS/MS).     

Geometric constraints at the surfactant headgroup: effect on lipase activity in cationic reverse micelles

The primary objective of the present article is to understand how the geometric constraints at the surfactant head affect the lipase activity in the reverse micellar interface. To resolve this issue, surfactants were designed and synthesized, and activity was measured in /water/isooctane/n-hexanol reverse micellar systems at z ([alcohol]/[surfactant])=5.6, pH 6.0 (20 mM phosphate), 25 degrees C across a varying range of W0 ([water]/[surfactant]) using p-nitrophenylalkanoates as the substrate. It was observed that lipase activity increases from surfactants to with the increment in surface area per molecule (Amin) because of the substitution by the bulky tert-butyl group at the polar head. However, the activity was found to be similar for despite an enhancement in the hydrophilic moieties at the interface. This unchanged lipase activity is presumably due to the comparable surface area of to originating from the rigidity at the surfactant head. Noticeably, the enzyme activity improved from with the simultaneous increment of both the hydroxyl group and the flexibility of the headgroup whereas that for increased exclusively with the flexibility of the headgroup. The common parameter in both groups of surfactants and is the flexibility of the headgroup, which possibly enhance Amin and consequently the lipase activity. Thus, the geometric constraints at the surfactant headgroup play a crucial role in modulating the lipase activity profile probably because of the variation in interfacial area.     

Effects of nonionic micelles on the rate of alkaline hydrolysis of N-(2'-methoxyphenyl)phthalimide (1): kinetic and rheometric evidence for a transition from spherical to rodlike micelles under the typical reaction conditions

Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-(2'-methoxyphenyl)phthalimide (1) decrease nonlinearly with increasing total concentration of nonionic surfactant C(m)E(n) (i.e. [C(m)E(n)](T) where m and n represent the respective number of methyl/methylene units in the tail and polyoxyethylene units in the headgroup of a surfactant molecule and m/n=16/20, 12/23 and 18/20) at constant 2% v/v CH(3)CN and 1.0 mM NaOH. The k(obs)vs. [C(m)E(n)](T) data follow the pseudophase micellar (PM) model at ≤ 50 mM C(16)E(20), ≤ 1.4 mM C(12)E(23) and ≤ 2.0 mM C(18)E(20) where rate of hydrolysis of 1 in micellar pseudophase could not be detected. The values of k(obs) fail to follow the PM model at > ～50 mM C(16)E(20), > ～1.4 mM C(12)E(23) and > ～2.0 mM C(18)E(20) which has been attributed to a micellar structural transition from spherical to rodlike which in turn increases C(m)E(n) micellar binding constant (K(S)) of 1 with increasing values of [C(m)E(n)](T). Rheological measurements show the presence of spherical micelles at ≤ 50 mM C(16)E(20), ≤ 1.4 mM C(12)E(23) and ≤ 3.0 mM C(18)E(20). The presence of rodlike micelles is evident from rheological measurements at > ～50 mM C(16)E(20), > ～1.4 mM C(12)E(23) and > ～3.0 mM C(18)E(20).     

The Self-Association and Mixed Micellization of an Anionic Surfactant,Sodium Dodecyl Sulfate,and a Cationic Surfactant,Cetyltrimethylammonium Bromide: Conductometric,Dye Solubilization,and Surface Tension Studies

In the present study, we investigate the self-association and mixed micellization of an anionic surfactant, sodium dodecyl sulfate (SDS), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of SDS, CTAB, and mixed (SDS + CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), and A_min (the minimum area per surfactant molecule at the air/water interface)) of SDS, CTAB, and (SDS + CTAB) micellar/mixed micellar systems were evaluated. The thermodynamic parameters of the micellar (SDS and CTAB), and mixed micellar (SDS + CTAB) systems were evaluated.

A schematic representation of micelles and mixed micelles.     

Micellization and mixed micellization of cationic gemini (dimeric) surfactants and cationic conventional (monomeric) surfactants: Conductometric,dye solubilization,and surface tension studies

In the present study, we have investigated the self-association, mixed micellization, and thermodynamic studies of a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide (16-6-16)) and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of pure (16-6-16 and CTAB) and mixed (16-6-16+CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), A_min (the minimum area per surfactant molecule at the air/water interface), etc.) of micellar (16-6-16 or CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were evaluated. The thermodynamic parameters of the micellar (16-6-16 and CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were also evaluated.     

MIXED MICELLES OF CATIONIC SURFACTANTS IN AQUEOUS POLYETHYLENE GLYCOL 1000

The conductances of tetradecyltrimethylammonium bromide (TTAB) + dodecyltrimethylammonium bromide (DTAB) mixtures over the entire mole fraction range of TTAB (^αOITTAB) were measured in aqueous polyethylene glycol 1000 (PEG) containing 1, 2, 5 and 10 wt% of PEG at 30 °C. From the conductivity data, various micellar parameters were computed. The results have been explained on the basis of the medium effects as well as the adsorption of additive molecules at micelle-solution interface. The non-ideality in TTAB+DTAB mixtures was evaluated by using the regular solution theory and Motomura's formulation based on the excess thermodynamic quantities. It has been found that the regular solution interaction parameter (β) and micellar mole fraction (¯x ^m ₂) remain almost unaffected even in the presence of upto 10 wt% of PEG. These results suggest that the additive remains only in the aqueous phase and perhaps only changing the environment surrounding the micelles by adsorbing at the micelle-solution interface.     

Three distinct water structures at a zwitterionic lipid/water interface revealed by heterodyne-detected vibrational sum frequency generation

Lipid/water interfaces and associated interfacial water are vital for various biochemical reactions, but the molecular-level understanding of their property is very limited. We investigated the water structure at a zwitterionic lipid, phosphatidylcholine, monolayer/water interface using heterodyne-detected vibrational sum frequency generation spectroscopy. Isotopically diluted water was utilized in the experiments to minimize the effect of intra/intermolecular couplings. It was found that the OH stretch band in the Imχ((2)) spectrum of the phosphatidylcholine/water interface exhibits a characteristic double-peaked feature. To interpret this peculiar spectrum of the zwitterionic lipid/water interface, Imχ((2)) spectra of a zwitterionic surfactant/water interface and mixed lipid/water interfaces were measured. The Imχ((2)) spectrum of the zwitterionic surfactant/water interface clearly shows both positive and negative bands in the OH stretch region, revealing that multiple water structures exist at the interface. At the mixed lipid/water interfaces, while gradually varying the fraction of the anionic and cationic lipids, we observed a drastic change in the Imχ((2)) spectra in which spectral features similar to those of the anionic, zwitterionic, and cationic lipid/water interfaces appeared successively. These observations demonstrate that, when the positive and negative charges coexist at the interface, the H-down-oriented water structure and H-up-oriented water structure appear in the vicinity of the respective charged sites. In addition, it was found that a positive Imχ((2)) appears around 3600 cm(-1) for all the monolayer interfaces examined, indicating weakly interacting water species existing in the hydrophobic region of the monolayer at the interface. On the basis of these results, we concluded that the characteristic Imχ((2)) spectrum of the zwitterionic lipid/water interface arises from three different types of water existing at the interface: (1) the water associated with the negatively charged phosphate, which is strongly H-bonded and has a net H-up orientation, (2) the water around the positively charged choline, which forms weaker H-bonds and has a net H-down orientation, and (3) the water weakly interacting with the hydrophobic region of the lipid, which has a net H-up orientation.     

Mixed micelle formation among anionic gemini surfactant (212) and its monomer (SDMA) with conventional surfactants (C12E5 and C12E8) in brine solution at pH 11

The micellization of anionic gemini surfactant, N,N'-ethylene(bis(sodium N-dodecanoyl-beta-alaninate)) (212), and its monomer, N-dodecanoyl-N-methyl alaninate (SDMA), and polyethoxylated nonionic surfactants, C(12)E(5) and C(12)E(8), has been studied tensiometrically in pure and mixed states in an aqueous solution of 0.1 M NaCl at pH 11 to determine physicochemical properties such as critical micellar concentration (cmc), surface tension at the cmc (gamma(cmc)), maximum surface excess (Gamma(max)) and minimum area per surfactant molecule at the air/water interface (A(min)). The theories of Rosen, Rubingh, Motomura, Maeda, and Nagarajan have been applied to investigate the interaction between those surfactants at the interface and in the micellar solution, the composition of the aggregates formed, the theoretical cmc in pure and mixed states, and the structural parameters as proposed by Tanford and Israelachvili. Various thermodynamic parameters (free energy of micellization and interfacial adsorption) have been calculated with the help of regular solution theory and the pseudophase model for micellization.     

Comparative Study on the Effect of NaBr on the Interaction Between Alkyltrimethylammonium Bromide and β-Cyclodextrin

The effect of NaBr on the interaction between alkyltrimethylammonium bromide (CnTAB (n = 14 for TTAB and 16 for CTAB)) and ß-CD was studied by surface tension method. The first decrease in the γ_cmc of TTAB/ß-CD in the presence of NaBr mainly due to the elongated effective chain length of the hydrophobic part of the TTAB/ß-CD complexes; while the increase in the γ_cmc of both of the TTAB/ß-CD and CTAB/ß-CD in the presence of NaBr could be attributed to the close pack of CnTAB at the air/water interface.