Effect of 1-butanol on the surface structure of ionic micelles and location of its solubilization site: Electron spin echo modulation study with x-doxylstearic acid spin probes

Electron spin echo modulation studies with a series of x-doxylstearic acids (x = 5, 7, 10, 12, and 16) have been carried out for sodium- and tetramethylammonium dodecylsulfate and dodecyltrimethylammonium chloride frozen micellar solutions containing protiated and perdeuterated 1-butanol. Modulation effects due to nitroxide interactions with deuterium in water and butanol have been measured versus doxyl group position. The effect of 1-butanol on the micellar surface and internal micellar structure has been evaluated and the average location of 1-butanol in these micelles has been deduced to be in the outer annulus of the micelle core.     

Studies on bio-antioxidants--micellar effects on the reduction of nitroxides by vitamin C

The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPO and 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic, non-ionic and anionic micelles, i.e. CTAB, Triton X-100 and SDS, respectively, have been studied by FSR spectroscopy by a stopped-flow technique. A mechanism for the reaction conducted in micelles is proposed and the rate constants for the elementary reactions are evaluated. It is found that the rates of single electron transfer reactions involving the nitroxides are dependent on the nature of the micelle and the lipophilicity of the nitroxide. The rates are increased in CTAB, decreased in SDS, whereas unaffected in Triton X-100. And the greater the lipophilicity of the nitroxide, the more pronounced the rate variation. As high as a 3600-fold increase in the rate was observed for 4-hexanoyloxy-TEMPO in CTAB over that in SDS. The micellar effects are rationalized on the basis of analysis of parameters and line shape of the ESR spectra for the nitroxides in the micelles.     

Effect of nitroxide radicals on chemically induced dynamic electron polarization of spin-correlated radical pairs in aqueous micellar solutions of sodium dodecyl sulfate

The multispin systems consisting of spin-correlated radical pairs (SCRPs) and stable nitroxide radicals, localized in micelles of sodium dodecyl sulfate (SDS), were studied by ESR and pulse laser photolysis techniques. In all the systems studied, the stable nitroxide radicals exert no effect on the shape of the ESR spectra of the SCRPs (in particular, on the shape of their antiphase structure) and on the decay kinetics of the ESR signal of the SCRPs. In the SDS micelles, the electron spin polarization transfer from the nonequilibrium electron spin states of the molecular triplets (SCRP precursors) is the most efficient mechanism of generation of the electron spin polarization in nitroxide radicals. The experimental data also show that the nitroxide radicals and SCRP radicals are most probably distributed uniformly in the micellar phase. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1390–1401, July, 2008.     

STUDIES ON BIO-ANTIOXIDANTS——MICELLAR EFFECTS ON THE REDUCTION OF NITROXIDES BY VITAMIN C

The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPOand 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic,non-ionic and anionic micelles, i. e. CTAB, Triton X-100 and SDS, respectively, have beenstudied by ESR spectroscopy by a stopped-flow technique. A mechanism for the reactionconducted in micelles is proposed and the rate constants for the elementary reactions areevaluated. It is found that the rates of single electron transfer reactions involving the ni-troxides are dependent on the nature of the micelle and the lipophilicity of the nitroxide.The rates are increased in CTAB, decreased in SDS, whereas unaffected in Triton X-100.And the greater the lipophilicity of the nitroxide, the more pronounced the rate variation.As high as a 3600-fold increase in the rate was observed for 4-hexanoyloxy-TEMPO in CTABover that in SDS. The micellar effects are rationalized on the basis of analysis of parame-ters and line shape of the ESR spectra for     

Small angle neutron scattering studies on micellar systems part 1. Ammonium octanoate,ammonium decanoate and ammonium perfluoroocatanoate

Small angle neutron scattering has been used to examine the size and shape of micelles of ammonium octanoate, ammonium decanoate and ammonium perfluoro-octanoate. Ammonium octanoate was found to form micelles with a micellar weight of 1640 and ammonium decanoate with a micellar weight of 12,576; both materials appeared to form spherical micelles. Ammonium perfluoro-octanoate formed micelles with a micellar weight of 17,610. Evidence from the scattering experiments suggested that the micelles were cylindrical and a model for the micelle is proposed.     

Light scattering study of solubilization of organic molecules by block copolymer micelles in aqueous media

Block copolymers, when dissolved in a selective solvent, form spherical micelles. These micelles can selectively solubilize organic molecules otherwise insoluble in the pure solvent. In this study, we report solubilization of organic molecules by styrene-methacrylic acid block copolymer micelles in aqueous buffers. A light scattering technique was developed to determine the extent of micellar solubilization. Our results indicate that the extent of micellar solubilization depends on the chemical nature of organic molecules, specifically, on the interactions between the organic compound and polystyrene. A thermodynamic model has been developed to describe micellar solubilization. The theoretical calculation agrees reasonably well with the experimental results for two micellar samples examined. ©1995 John Wiley & Sons, Inc.     

表面活性剂溶胀胶束：性能及应用

溶胀胶束是表面活性剂胶束增溶其它物质后使胶束膨胀的一种胶束状态,因其能显著提高难溶性物质的溶解度而备受关注。针对近年来对溶胀胶束的研究进展,综述了溶胀胶束的最大增溶量、增溶过程以及增溶后形貌尺寸的变化等问题,总结了影响胶束增溶作用的因素,厘清了溶胀胶束与微乳液的异同,介绍了溶胀胶束的应用,展望了其应用前景与发展方向。     

Physicochemical studies on hydrophobic PEO‐PPO‐PEO triblock copolymer micelles in SDS micellar environment

The shape, size, aggregation, hydration, and correlation times of water insoluble PEO‐PPO‐PEO triblock copolymer micelles with sodium dodecylsulfate (SDS) micelles were investigated using transport studies and dynamic light scattering technique. From the conductance of micellar solutions of the polymer in 25 mM SDS and 5 mM NaCl, the hydration of polymer micelles were determined using the principle of obstruction of electrolyte migration by the polymer. The asymmetry of the micellar particles of polymer and polymer‐SDS mixed micellar systems in 5 mM NaCl and their average axial ratios were calculated using intrinsic viscosity and hydration data obeying Simha–Einstein equation. Hydration number and micellar sizes were variable with temperature. The shape of the polymer micelles has been ellipsoidal rather than spherical. The micellar volume, hydrodynamic radius, radius of gyration, diffusional coefficients as well as translational, rotational and effective correlation times have been calculated from the absolute values of the axes. The partial molal volume of polymer micelles has also been determined and its comparison with the molar volume of pure polymer suggested a volume contraction due to immobilization of the water phase by the hydrophilic head groups of the polymer. The thermodynamic activation parameters for viscous flow favor a more ordered water structure around polymer micelles at higher temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2410–2420, 2007     

Clouding phenomenon and SANS studies on tetra-n-butylammonium dodecylsulfate micellar solutions in the absence and presence of salts

Clouding phenomenon in aqueous micellar solutions of an anionic surfactant tetra-n-butylammonium dodecylsulfate (TBADS) has been observed as a function of surfactant concentration. Small-angle neutron scattering (SANS) experiments in these systems show clustering of micelles as the temperature approaches the cloud point (CP). The individual micelles and the clusters of micelles coexist at CP. The clustering of micelles depends on the surfactant concentration and temperature. It is proposed that clustering is due to depletion of H-bonded water present around the butyl chains at the micellar surface. This is associated with entropy gain which is considered to be the major thermodynamic factor related to micellar aggregation. The structures (clusters) that emerge depend on the relative lengths of the alkyl chains of the counterion and can be tuned by the temperature.     

Study of the Reaction 2-(p-Nitrophenyl)Ethyl Bromide + OH(-) in Sulfobetaine Aqueous Micellar Solutions in the Presence and Absence of Added Salts

The reaction of dehydrobromination of 2-(p-nitrophenyl)ethyl bromide with hydroxide ions has been studied in aqueous micellar solutions of N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, SB3-14. The kinetic effects of added salts (NaF, NaCl, NaBr, and NaNO(3)) on the reaction rate in SB3-14 aqueous micellar solutions have also been studied. They were rationalized by considering the binding of the anions, which come from the salt, to the sulfobetaine micelles and their competition with the reactive hydroxide ions for the micellar surface. The equilibrium binding constant of the 2-(p-nitrophenyl)ethyl bromide to the sulfobetaine micelles was estimated by recording the changes in the spectra of the organic substrate when the SB3-14 concentration in the micellar medium changed. This value was in agreement with that obtained from fitting of kinetic data. The second-order rate constant in the micellar pseudophase revealed that the reaction is faster in SB3-14 micelles than in water. This acceleration seems independent of the presence of added salts and can be explained by considering that SB3-14 micelles favor reactions in which charge is delocalized in the transition state. Copyright 2001 Academic Press.     

Characterization of the micellar ring opening metathesis polymerization in water of a norbornene derivative initiated by Hoveyda‐Grubbs' catalyst

Solubilization of the hydrophobic Hoveyda‐Grubbs' catalyst in micellar aqueous phase has been achieved using dodecyl and cetyl ammonium chloride as surfactants. The domain of solubilization has been estimated before carrying out ring‐opening metathesis polymerization in these micellar solutions with a hydrophilic monomer. Kinetics orders have been determined relative to monomer, initiator, and surfactant. A good control of the molecular weight has been obtained for ratios [micelles]/[initiator] over 1. The better control of the polymerization obtained in micellar solution has been explained by a difference of reactivity leading to a more efficient initiation step in the presence of the micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2833–2844, 2008     

苯甲醇对CTAB/KBr胶束体系流变性及CTAB分子1HNMR谱影响的研究

报道了苯甲醇对CTAB/KBr胶束体系粘度的影响,利用1HNMR法研究了苯甲醇在CTAB胶束中的增溶位置.结果表明,在KBr盐溶液中,随着苯甲醇的加入,0.01mol/LCTAB胶束体系的粘度增大至最大值.对CTAB分子的1HNMR分析表明,少量的苯甲醇增溶在棒状胶束的界面,促使胶束体积增大和相互缠结,体系的粘度随之增大;当苯甲醇浓度较高时,将增溶在胶束的栅栏层靠近极性头一侧,胶束发生棒-球转变和解缠,体系的粘度降低.     

THE EFFECT OF SURFACTANT MICELLES ON THE ALKALINE HYDROLYSIS OF DIMETHYLFORMAMIDE

The alkaline hydrolysis of dimethylformamide has been studied at 40'C in micellar solutions of single surfactant (CTAB. SDS. Brij 35) with the analog thermoanalytical curve method of thermokinetics. A kinetic equation of micellar catalysis under the condition of highter reactant concentration than micellar concentration ([S]>[M]) has been derived from the pseudophase model of micellar catalysis and some relative assumptions, The kinetic parameters. k_m, k_2mand the association constant of reactant with micelle K₁, have been calculated in this way. the results indicate that these surfactant micelles exhibit catalytic effect on the reaction. This is attributed to the micropolarity and local concentration effect of micelles.     

Intrinsic parameters for the structure control of nonionic reverse micelles in styrene: SAXS and rheometry studies

Shape, size, and internal structure of nonionic reverse micelle in styrene depending on surfactant chain length, concentration, temperature, and water addition have been investigated using a small-angle X-ray scattering (SAXS) technique. The generalized indirect Fourier transformation (GIFT) method has been employed to deduce real-space structural information. The consistency of the GIFT method has been tested by the geometrical model fittings, and the micellar aggregation number (N(agg)) has been determined. It was found that diglycerol monocaprate (C(10)G(2)), diglycerol monolaurate (C(12)G(2)), and diglycerol monomyristate (C(14)G(2)), spontaneously self-assemble into reverse micelles in organic solvent styrene under ambient conditions. The micellar size and the N(agg) decrease with an increase in surfactant chain length, a scenario that could be understood from the modification of the critical packing parameter (cpp). A clear picture of one-dimensional (1-D) micellar growth was observed with an increase in surfactant weight fraction (W(s)) in the C(10)G(2) system, which eventually formed rodlike micelles at W(s) ≥ 15%. On the other hand, micelles shrunk favoring a rod-to-sphere type transition upon heating. Reverse micelles swelled with water, forming a water pool at the micellar core; the size of water-incorporated reverse micelles was much bigger than that of the empty micelles. Model fittings showed that water addition not only increase the micellar size but also increase the N(agg). Zero-shear viscosity was found to decrease with surfactant chain but increase with W(s), supporting the results derived from SAXS.     

Variation of characteristics of pentaoxyethylene decyl C10E5 and hexaoxyethylene tetradecyl C14E6 ether micelles with uptake of n-octanol

Wormlike micelles of the surfactant pentaoxyethylene decyl C10E5 and hexaoxyethylene tetradecyl C14E6 ethers were characterized by static (SLS) and dynamic light scattering (DLS) experiments to examine effects of uptake of n-octanol on the micellar characteristics. The SLS results have been successfully analyzed by the light scattering theory for micelle solutions to yield the molar mass Mw(c) as a function of concentration c along with the cross-sectional diameter d of the micelle. The apparent hydrodynamic radius RH,app(c) determined by DLS as a function of c has also been successfully analyzed by a fuzzy cylinder theory which takes into account the hydrodynamic and direct collision interactions among micelles, providing us with the values of the stiffness parameter lambda(-1). It has been found that the micellar length Lw increases with increasing surfactant weight fraction ws and increasing n-octanol content wo in the micelles or with raising temperature T. The values of d and lambda(-1) are found to increase with increasing wo, whereas the spacing s between hydrophilic tails of adjacent surfactant molecules on the micellar surface decreases with increasing wo. Comparison with our previous results for the C10E5 and C14E6 micelles containing n-dodecanol has revealed the salient features in change of the micellar characteristics with uptake of n-alcohols as follows: (i) The Lw values increase more significantly for the C14E6 micelles containing n-dodecanol than those containing n-octanol, whereas Lw of the C10E5 micelles increases by including n-dodecanol and n-octanol without a significant difference for the two alcohols. (ii) The values of d and lambda(-1) of the C10E5 and C14E6 micelles increase with uptake of n-octanol and n-dodecanol into the micelles. They are larger for the C10E5 micelles than for the C14E6 micelles, and their increase with alcohol content is less significant for the C14E6 micelles in comparison with the C10E5 micelles. (iii) The s values of the C10E5 and C14E6 micelles decrease with uptake of n-octanol and n-dodecanol into the micelles. They are somewhat larger in the latter micelles than in the former. (iv) The variation in d, s, and lambda(-1) with uptake of n-alcohol occurs with no difference in the effects for the two alcohols n-octanol and n-dodecanol.     

Spectroscopic studies of interaction of Safranine T with nonionic micelles and mixed micelles

The visible spectra of Safranine T (ST) in micellar solution of Brij 58, Tween 20 and Tween 40 and mixed micellar solution of Brij 58/Tween 20 and Brij 58/Tween 40 indicate formation of 1:1 charge transfer (CT) complex between acceptor ST and donor nonionic micelles and mixed micelles. The experimental CT transition energies are well correlated (through Mulliken's equation) with the vertical ionization potential of the donors. The solvent parameters, i.e. the intramolecular charge transfer energy ET(30) have been determined from the Stokes spectral shift. Variations of ionization potential and micropolarity in the mixed micellar region have been investigated as a function of surfactant composition and the obtained results in mixed micellar medium has been compared to the normal micelles. The critical micelle concentration (CMC) values determined at various surfactant compositions are lower than the ideal values indicating a synergistic interaction. The interaction parameter (beta) and micellar stability has been calculated using regular solution theory.     

Distribution of fluorocarbon quencher among micelles via pyrene fluorescence probe method

 Fluorescence-quenching of pyrene in micellar system has been investigated using 1,1,2,2-tetrahydroheptadecafluorodecylpyridinium chloride (HFDePC). The new fluorocarbon quencher has a similar quenching ability as hexadecyl-pyridinium chloride (CPC) towards pyrene in hydrocarbon micelles if only a quencher molecule is solubilized in a micelle. The fluorocarbon quencher randomly distributed among micelles if the average occupancy number of probes per a micelle was small enough. The fluorescence behavior of pyrene was examined for hexadecyl-trimethylammonium chloride (CTAC) and HFDePC mixtures. The variation of fluorescence intensity gave second cmc, reflecting the micellar immiscibility of fluorocarbon and hydrocarbon surfactants. The second cmc can be simulated by material balances of both surfactants supposing the coexistence of two kinds of mixed micelles. The fluorescence-quenching behavior suggested the enhanced micellar immiscibility probably due to nonrandom distribution of fluorocarbon quenchers among micelles. Received: 13 March 1997 Accepted: 24 May 1997     

Micellar solubilization thermodynamics of acetophenone in surfactant mixtures: Case of benzyldimethyltetradecylammonium chloride and trimethyltetradecylammonium chloride

The thermodynamics of micellar solubilization of acetophenone in mixtures of two cationic surfactants [benzyldimethyltetradecylammonium chloride +trimethyltetradecylammonium chloride] has been derived from calorimetric measurements at controlled solute activity. The partition coefficient between micelles and water as well as the standard enthalpy and entropy of transfer between micelles and water were calculated. The results were compared to the case of benzylalcohol in the same cationic mixtures. For acetophenone, the variation of all thermodynamic transfer functions with micellar composition may be described by the regular solution formalism. The same conclusion has been achieved for most polar solutes in various surfactant mixtures: favorable interaction between unlike surfactants induces an unfavorable micellar solubilization. Exceptions should be found with the cases where solute solubilization induces profound micellar changes. It seems to be the case with some alcohols in the cationic surfactant mixtures studied.     

Effects of nonionic,cationic, and anionic micelles on the kinetics of the complexation reaction of nickel (II) with pyridine-2-azo-p-dimethylaniline

The stopped-flow technique has been used to study the effect of cationic (CTAN), nonionic (Triton X-100), andanionic (SDS) micelles on the rate of the reaction between nickel(II) ion and the ligand pyridine-2-azo-p-dimethylaniline (PADA) at 20.0°C and ionic strength 0.03 mol dm^?3. The complex formation reaction is markedly inhibited by both CTAN and Triton X-100 micelles. The kinetic dataare found to conform to a reaction mechanism which implies only partitioning of the ligand between water and the micellar phase, the estimated bindingconstant of PADA being significantly larger in the presence of CTAN aggregates. Anionic micelles strongly speed the complexation reaction, Which occurs in the micellar phase with the same rate and the same mechanism as in water. The extent of binding of PADA to anionic micelles is similar to that found for the cationic micellar aggregates.     

Partitioning of macrocyclic compounds in a cationic and an anionic micellar solution: a small-angle neutron scattering study

Following a previous investigation on partitioning of some macrocycle compounds in sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) aqueous solutions and their effect on the micellar structure, a small-angle neutron scattering (SANS) study has been performed at fixed surfactant content (0.20 mol/L) and varying macrocycle concentrations from 0.20 up to 1.0 mol/L. Conductivity measurements have been also performed in order to evaluate the effect of the presence of macrocycles on the critical micellar concentration (cmc) of the two surfactants. SANS experimental data were fitted successfully by means of a core-plus-shell monodisperse prolate ellipsoid model. It has been found that 1,4,7,10,13,16-esaoxacyclooctadecane (18C6) and 4,7,13,16-tetraoxa-1,10-diazacyclooctadecane (22) do not interact with DTAB micelles whereas their sodium complexes interact with SDS aggregates and partially localize, as a consequence of electrostatic interaction, on the micellar surface or in the Stern layer. 2,5,8,11,14,17-Hexaoxabicyclo[16.4.0] dicosane (B18C6), as a consequence of the increased hydrophobic character with respect to 18C6, interacts with DTAB hydrocarbon chains and partially localizes in the inner part of micelles. This finding has been successfully used to justify the higher amount of B18C6 compared to the 18C6 one found in the SDS micellar phase. The substituted crown ether has been found localized both on the micelle surface via complex formation and in the inner part of micelles as a consequence of the increased hydrophobic character. For all systems, the aggregate size primarily decreases with the amount of macrocycle in the micellar phase. The interpretation of cmc trends as a function ofmacrocycle concentration gives information on its distribution between micellar and aqueous phases that is in line with SANS results.