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。     

Coexistence and growth of micellar species in a sugar-based surfactant/phenol mixture studied by analytical ultracentrifugation

Knowledge of the shape and size of surfactant micelles in the presence of small organic molecules is important for understanding the solubilization properties of micellar phases. In this work, structural information on micelles of mixed n-dodecyl-beta-d-maltoside (DM) and phenol, including the aggregation number, diffusion coefficient, and effective radius, was obtained using an analytical ultracentrifugation technique. The micelles were found to increase in size and undergo shape transition from quasispherical to cylindrical with an increase in the surfactant and phenol concentrations in the micellar phase. Importantly, the coexistence of different micellar species was observed in certain cases with the larger species double the size of the smaller one. Based on the results obtained, a two-step micellar growth model is proposed to describe the micelles shape transition in the system. In the first step, the micelles expand continuously, whereas in the second step, it undergoes a sudden shift from the existing micellar species to a larger species causing the coexistence of two micellar species. This micellar growth is attributed to molecular packing and intermicellar interaction energy parameters. The mechanism proposed can be applied to other mixed systems and utilized for devising chemicals for the efficient removal of pollutants.     

Interfacial solubilization of model amphiphilic molecules in block copolymer micelles

We investigate the solubilization of 2-nitrodiphenylamine, a hydrophobic but polar dye molecule, in aqueous solutions of polystyrene(310)-b-poly(acrylic acid)(47) micelles. The solubilization capacity of the micelles, which consist of a polystyrene core and poly(acrylic acid) corona, and the micelle-water partition coefficient are evaluated as a function of the solubilizate concentration. The solubilization isotherm shows a nonlinear behavior, and the partition coefficient, instead of being constant, is strongly dependent on the dye concentration. These results are explained by treating solubilization as a binding process, and by fitting the data to a Langmuir adsorption model. In addition, we examine the locus of solubilization of 2-nitrodiphenylamine using its solvatochromic properties and solubility in model solvents, and we identify the micellar interface as the solubilization site. Confirmatory studies, including the dependence of solubilization on the interfacial area of the aggregates, the role of the poly(acrylic acid) corona chains in stabilizing the solubilized molecules, and the effect of the solubilizate structure on the extent of incorporation, were also conducted. The results, consistent with surface localization, show that solubilization is dependent on the interfacial area of the aggregates, and on the affinity of the solubilizate for the micellar interface.     

芘在Pluronic两亲嵌段共聚物胶团中的增溶

用稳态荧光法研究芘（Py）在Pluronic两亲嵌段共聚物胶团水溶液中的增溶,结果表明共聚物分子中的PPO实际含量越大,越有利于Py的增溶。加入无机盐KCl导致生成了表面较少水化的较大胶团,并且由于KCl解离产生的离子使溶剂极性增加,这些因素促进了Py的增溶。     

Study of the reaction of methyl 4‐nitrobenzenesulfonate and Br− in water–glycerol cationic micellar solutions

The reaction of methyl 4‐nitrobenzenesulfonate (MNB) and Br^? has been studied in water–glycerol (GLY) alkyltrimethylammonium bromide micellar solutions, with the weight percentage of glycerol up to 50%. A pseudophase kinetic model was used for quantitatively discussing the kinetic data. Results showed that the equilibrium‐binding constant for the organic substrate molecules to the cationic micelles decreases upon increasing the amount of glycerol present in the micellar reaction media. The second‐order rate constant of the reaction in the micellar pseudophase is practically independent of wt% of GLY. Similar results were found in other water–organic solvent alkyltrimethylammonium bromide micellar solutions for the same process. However, the dependence of the reaction rate, for a given surfactant concentration, on the wt% of organic solvent is weaker for glycerol than for the other organic solvents. This was explained by considering that the cationic micellar ionization degree is nearly independent of wt% GLY. As a consequence, bromide ions concentration in the interfacial region (the reaction site) does not change by varying wt% of GLY. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 845–582, 2008     

Structure of sodium alkyl sulfate micelles

Apparent and partial molar volumes of aggregated sodium octyl-, decyl-, dodecyl-, and tetradecyl sulfate molecules have been determined rigorously in terms of the pseudophase separation model. Mass density inside the micellar core—a basic thermodynamic parameter in the research of micelles by nuclear techniques—has been derived from the partial molar volumes.Micellar aggregation numbers of the same surfactants, obtained from small-angle neutron scattering [SANS] by systematically varying the surfactant concentration and solution temperature are published. A survey is given of the physical models and evaluation algorithms applied in SANS, together with a critical comparison of available experimental data published by various research teams.By utilizing a new least-squares fitting algorithm based on a microscopic diffusion model, the formation and annihilation parameters of ortho-positronium Co-Ps) in the micellar pseudophase and in the aqueous solvent, as well as the o-Ps diffusion coefficient in the solvent are deduced by evaluating conventionally measured positron lifetime spectra. From the pickoff annihilation rate of o-Ps in micelles the surface tension of the micellar core around the solubilization site of o-Ps is calculated. SANS results are utilized to determine the diffusion coefficient of o-Ps in normal and in 99.85% heavy water as a function of temperature. A definite isotopic effect in the two solvents can be seen from the results obtained for the diffusion coefficient and its activation energy. The Arrhenius plot of o-Ps diffusion coefficients indicates that o-Ps diffuses in both media without tunnelling.     

芘从H_2O/DMF混合溶剂向聚苯乙烯/聚丙烯酸二嵌段共聚物平头胶团增溶(Ⅱ)

混合溶剂水含量强烈影响芘从Ｈ２Ｏ／ＤＭＦ混合溶剂向聚苯乙烯／ 聚丙烯酸二嵌段共聚物平头胶团的增溶,随着水含量增加而明显增大了芘和胶团内核ＰＳ间的结合力,促进了芘的增溶。实验结果表明,增加混合溶剂极性组分是实现有效增溶的一种简便方法。     

Formation and Characterization of Reversed Micelles Composed of Phospholipids and Fatty Acids

The formation of reversed micellar systems composed of phosphatidylcholine (PC) and fatty acid was newly demonstrated by a significant increase in water content in the organic ethyl oleate phase when the micelles were prepared by the contact method. The solubilized water concentration in the reversed micellar organic phase reached 3 wt%. The new systems are expected to be used as highly biocompatible reversed micellar systems. The structure of the reversed micelles composed of PC and oleic acid was characterized by determining the water concentration and by small-angle X-ray scattering analysis. The reversed micelles composed of PC and oleic acid formed in ethyl oleate were spherical. The radius of gyration was between 30 and 50 Å. The size of the reversed micelles decreased with an increase in the oleic acid concentration and was independent of the PC concentration. Experimental results indicated that the structure of the reversed micellar system was determined by the oleic acid concentration. An increase in the PC concentration caused an increase in the number of reversed micelles of the same size. These reversed micellar systems are expected to be used as solubilization media in pharmaceutical and food industries because they are not toxic.     

Performance of short-chain alcohols versus acetonitrile in the surfactant-mediated reversed-phase liquid chromatographic separation of β-blockers

Organic solvents are traditionally added to micellar mobile phases to achieve adequate retention times and peak profiles, in a chromatographic mode which has been called micellar liquid chromatography (MLC). The organic solvent content is limited to preserve the formation of micelles. However, at increasing organic solvent contents, the transition to a situation where micelles do not exist is gradual. Also, there is no reason to neglect the potentiality of mobile phases containing only surfactant monomers instead of micelles (high submicellar chromatography, HSC). This is demonstrated here for the analysis of β-blockers. The performance of four organic solvents (methanol, ethanol, 1-propanol, and acetonitrile) was compared in mobile phases containing the anionic surfactant sodium dodecyl sulphate in the MLC and HSC modes. The association of the organic solvent molecules with micelles gives rise to a significant loss in the elution strength of the organic solvent; whereas upon disruption of micelles, it tends to that observed in the hydro-organic mode. The elution behaviour of the β-blockers was modelled to predict the retention times. This allowed the detailed exploration of the selectivity and resolution of the chromatographic systems in relatively wide ranges of concentration of surfactant and organic solvent. The best performance in terms of resolution and analysis time was achieved using HSC with acetonitrile, being able to base-line resolve a mixture of eight β-blockers. Ethanol also provided a good separation performance, significantly improved with respect to methanol and 1-propanol. In contrast, the hydro-organic mode using acetonitrile or any of the short-chain alcohols could not succeed with the separation of the β-blockers, owing to the poorer selectivity and wider peaks.     

苯在Pluronic F127和P123胶束水溶液中的增溶动力学

发展了不分离胶束的增溶动力学数据分析模型,以此考察苯在F127和P123胶束水溶液中的增溶动力学行为.实验发现,这二种胶束增溶苯的速度较快,温度升高进一步促进了增溶.     

Evidence for micellar structure in the gas phase

We have compared micelles, reverse micelles, and reverse micelles encapsulating myoglobin using electrospray mass spectrometry. To enable a direct comparison, the same surfactant (cetyltrimethylammonium bromide (CTAB)) was used in each case and micelle formation was controlled by manipulating the aqueous and organic phases. Tandem mass spectra of the resulting micelle preparations reveal differences in the ions that dissociate: those that dissociate from regular micelles have undergone >90% exchange of bromide ions from the headgroup with acetate ions from bulk solvent. By contrast, for reverse micelles, ions are detected without exchange of bromide ions from the headgroup, consistent with their protection in the core of the micellar structure. Tandem mass spectra of micelles and reverse micelles reveal polydispersed assemblies containing several hundred CTAB molecules, indicating the coalescence of the micellar systems to form large assemblies. For reverse micelles incorporating myoglobin, spectra are consistent with one holo myogolobin molecule in association with approximately 270 CTAB molecules. Overall, therefore, our results show that the solution-phase orientation of surfactants is preserved during electrospray and are consistent with interactions being maintained between surfactants and an encapsulated protein.     

Kinetics of micellization: its significance to technological processes

The association of many classes of surface active molecules into micellar aggregates is a well-known phenomenon. Micelles are often drawn as static structures of spherical aggregates of oriented molecules. However, micelles are in dynamic equilibrium with surfactant monomers in the bulk solution constantly being exchanged with the surfactant molecules in the micelles. Additionally, the micelles themselves are continuously disintegrating and reforming. The first process is a fast relaxation process typically referred to as τ₁. The latter is a slow relaxation process with relaxation time τ₂. Thus, τ₂ represents the entire process of the formation or disintegration of a micelle. The slow relaxation time is directly correlated with the average lifetime of a micelle, and hence the molecular packing in the micelle, which in turn relates to the stability of a micelle. It was shown earlier by Shah and coworkers that the stability of sodium dodecyl sulfate (SDS) micelles plays an important role in various technological processes involving an increase in interfacial area, such as foaming, wetting, emulsification, solubilization and detergency. The slow relaxation time of SDS micelles, as measured by pressure-jump and temperature-jump techniques was in the range of 10⁻⁴–10¹ s depending on the surfactant concentration. A maximum relaxation time and thus a maximum micellar stability was found at 200 mM SDS, corresponding to the least foaming, largest bubble size, longest wetting time of textile, largest emulsion droplet size and the most rapid solubilization of oil. These results are explained in terms of the flux of surfactant monomers from the bulk to the interface, which determines the dynamic surface tension. The more stable micelles lead to less monomer flux and hence to a higher dynamic surface tension. As the SDS concentration increases, the micelles become more rigid and stable as a result of the decrease in intermicellar distance. The smaller the intermicellar distance, the larger the Coulombic repulsive forces between the micelles leading to enhanced stability of micelles (presumably by increased counterion binding to the micelles). The Center for Surface Science & Engineering at the University of Florida has developed methods using stopped-flow and pressure-jump with optical detection to determine the slow relaxation time of micelles of nonionic surfactants. The results show relaxation times τ₂ in the range of seconds for Triton X-100 to minutes for polyoxyethylene alkyl ethers. The slow relaxation times are much longer for nonionic surfactants than for ionic surfactants, because of the absence of ionic repulsion between the head groups. The observed relaxation time τ₂ was related to dynamic surface tension and foaming experiments. A slow break-up of micelles, (i.e. a long relaxation time τ₂) corresponds to a high dynamic surface tension and low foamability, whereas a fast break-up of micelles, leads to a lower dynamic surface tension and higher foamability. In conclusion, micellar stability and thus the micellar break-up time is a key factor in controlling technological processes involving a rapid increase in interfacial area, such as foaming, wetting, emulsification and oil solubilization. First, the available monomers adsorb onto the freshly created interface. Then, additional monomers must be provided by the break-up of micelles. Especially when the free monomer concentration is low, as indicated by a low CMC, the micellar break-up time is a rate limiting step in the supply of monomers, which is the case for many nonionic surfactant solutions. Therefore, relaxation time data of surfactant solutions enables us to predict the performance of a given surfactant solution. Moreover, the results suggest that one can design appropriate micelles with specific stability or τ₂ by controlling the surfactant structure, concentration and physico-chemical conditions, as well as by mixing anionic/cationic or ionic/nonionic surfactants for a desired technological application.     

Characterization of the fluorescence emission properties of prodan in different reverse micellar environments

We have examined the steady state and time resolved fluorescence emission properties of the hydrophobic fluorescence probe, prodan, in three representative reverse micellar systems formed by the surfactants poly(oxyethylene) (tetramethylbutyl) phenylether (Triton X-100, neutral), cetyl trimethylammonium bromide (CTAB, cationic) and sodium bis-(2-ethylhexyl) sulfosuccinate (AOT, anionic) in organic solvent media containing different concentrations of water. The results obtained from the experiments indicate conspicuous dependence of the emission behaviour of prodan on the type of surfactant used and the water/surfactant molar ratio (w0). The nature of the emission profiles, along with relevant parameters namely emission maximum (lambda(em)max), anisotropy (r) and lifetime (tau) data are used to infer the distribution and microenvironments of the prodan molecules in the reverse micelles at different w0 values. Furthermore, quantitative estimates have been obtained for the polarities (in terms of the empirical polarity parameter E(T)(30)) of the sites of solubilization of the fluorophore in different reverse micellar systems.     

Monitoring the simultaneous ostwald ripening and solubilization of emulsions

The simultaneous Ostwald ripening of an emulsion and the solubilization of its oil droplets by added micellar surfactant solutions are monitored by measurements of time-averaged scattered intensities. A simple computer simulation model for the interpretation of the measurements is presented. Experimental data are analyzed with this model using one single parameter: an effective ratio of oil to surfactant molecules involved in the withdrawal of oil from the Ostwald ripening process by the added micelles. The fitted value of this parameter appears to be more than twice the one that can be predicted from the equilibrium solubilization of oil by the surfactant micelles, indicating that more oil is involved in the nonequilibrium exchange of oil and surfactant between micelles and droplets.     

Temperature effect on solubilization of n-alkylbenzenes into sodium cholate micelles

The solubilization of n-alkylbenzenes (benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, n-hexylbenzene) into an aqueous micellar solution of sodium cholate was carried out. Solubilizate concentrations at equilibrium were determined spectrophotometrically at 293.2, 298.2, 303.2, 308.2, and 313.2 K. The first stepwise association constants (K(1)) between solubilizate monomers and vacant micelles were evaluated from the equilibrium concentrations and found to increase with increasing hydrophobicity of the solubilizate molecules. From the Gibbs energy change for solubilization at different micelle aggregation numbers and from the molecular structure of the solubilizates, the function of sodium cholate micelles as solubilizer was discussed. Enthalpy and entropy changes of solubilization were calculated from the temperature dependence of the K(1) values, and the solubilization was found to be enthalpy-driven for the solubilizates with shorter alkyl chains. The results obtained were also compared with those for conventional aliphatic micelles.     

Pluronic嵌段共聚物F127和P123胶束对萘、蒽、芘的增溶

35℃时F127和P123在ccm后可生成内核PO成分分别为92.7%和94.5%的胶束,后者胶束内核体积为前者的2.8倍.稠环芳烃和空胶束的第一步缔合平衡常数K₁值均随萘、蒽、芘顺序逐渐增大.萘、蒽、芘在每个F127和P123胶束中的增溶量均随胶束内核体积增大而线性增加,每个PO基团对应的增溶量比十二烷基磺酸胶束内核中相同体积对应的增溶量约大近2倍.Pluronic胶束除与稠环芳烃间具有强相互作用力外,所形成的大内核是导致大增溶量的重要因素.     

Properties of water in triton N-42 reverse micelles during the solubilization of HCl solutions according to FT-IR and photon correlation spectroscopy

FT-IR and photon correlation spectroscopy methods are used to study the distribution of free (bulk) and bound (hydration) water in Triton N-42 reverse micelles under the conditions of injection solubilization of hydrochloric acid solutions. The amount of each type of water is calculated depending on the solubilization capacity (V _s/V _o) and HCl concentration in the aqueous pseudophase. According to the IR spectroscopy data, the distribution of water is largely determined by the solubilization capacity of the micellar solution, while the fraction of bulk water exceeds significantly the value calculated by the geometric approach based on the photon correlation spectroscopy data. The difference shows that there is bulk water in the surface layer formed by oxyethyl groups of Triton N-42 molecules in spherocylindrical micelles.     

Study of amphiphilic polyester micelles by hyper-rayleigh scattering: invertibility and phase transfer

For the first time, hyper-Rayleigh scattering (HRS) of invertible polymeric micellar structures has been measured. HRS measurements on amphiphilic invertible polyesters with alternating hydrophilic and hydrophobic fragments were carried out in solvents of differing polarity. The observed strong variation of the HRS signals is attributed to the switching behavior of the polyester micelles in the different solvents. The hyperpolarizabilities and the size of the micelles increased with decreasing polarity of the solvent. Observing the dynamics of the solubilization of an insoluble dye (malachite green) by the invertible polyester in toluene confirmed the possibility to reveal conformational changes in polyester macromolecules by HRS. In contrast to UV measurements which showed a continuous increase in absorbance and indicated overall solubilization of the dye, the HRS signals decreased after approaching a maximum value. The decrease of the HRS signals is attributed to the change of dye molecules' orientation within the micelles due to the change of polymeric conformation in toluene. The results have shown that HRS is sensitive to reorientation and ordering of the macromolecules and might become a powerful tool for studying polymer micellar structures as well as phase transfer processes at the nanoscale.     

Micellar and Solvent Effects on the Rate of Reaction Between L-Tyrosine and Ninhydrin

Kinetics of the reaction of L-tyrosine and ninhydrin has been studied spectrophotometrically at pH = 5.0 and temperature 80°C in aqueous, aqueous-organic and aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The product formed in all the media remains the same. Also, the reaction is catalyzed in both organic solvent and CTAB micellar media. The results obtained in micellar media are treated quantitatively in terms of pseudo-phase model. The rate constants and binding constants with the micelles have been evaluated.     

Aqueous solubilization of highly fluorinated molecules by semifluorinated surfactants

The physical and chemical properties of organic compounds are deeply affected by the introduction of fluorinated substituents. Perfluorinated and highly fluorinated organic molecules are both hydrophobic and lipophobic. This makes the recognition and the binding of fluorinated molecules extremely difficult to achieve through classical elements of molecular recognition. Here we show that semifluorinated water-soluble block copolymers can generate micellar structures having a fluorous phase-based inner core in aqueous solution. Furthermore, we show that these micelles can be used to encapsulate and bind highly fluorinated molecules through association in the internal fluorous phase (fluorophobic effect). We report that semifluorinated block copolymers can be used for the aqueous solubilization of the widely diffused gaseous anesthetic sevoflurane, thereby suggesting the possibility of the intravenous delivery of this commonly used anesthetic.