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.     

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.     

脂肪醇和电解质对丙酸十二铵盐在四氯化碳中增溶水的影响

研究了己醇，辛醇、Ｋｕｉ醇和月桂醇对丙酸十二铵（ＤＡＰ）－四氯化碳反胶束溶液增溶水和氯化钠水溶液的影响，在ＤＡＰ浓度固定时，水增溶量对醇浓度的关系出现极大值，在醇浓度相同时，长碳链醇较短碳链醇有更大的增溶水能力，在固定ＤＡＰ浓度和增溶水量最大时，氯化钠的存在将导致水溶液增溶量的显著下降，乙酸十二铵（ＤＡＡ）、ＤＡＰ和丁酸十二铵（ＤＡＢ ）的四氯化碳溶液对氯化钠水溶液的增溶量随氯化钠浓度的升高而有不     

STUDY ON SOLUBILIZATION MECHANISM IN THE SYNTHESIS OF HIGH MOLECULAR WEIGHT POLY(p-PHENYLENE TEREPHTHALAMIDE)

The salts dissolved in the amide solvent play an important role in the synthesis of high molecular weight poly(p-phenylene terephthalamide) (PPTA). The solubilization of salts was investigated in this paper. The effects of association-dissociation equilibrium of salts and the solvation of their ions as well as hydrogenbond on solubilization were discussed in some detail. The effects were attributed to cations and anions of salts respetively. Finally, the equation of solubilization was established according to the experimental results and some thermodynamic laws. The relations between molecular weight of PPTA and the solubilization were discussed.     

Micropartioning and solubilization enhancement of 1,2-bis(bis(4-chlorophenyl) methyl)diselane in mixed micelles of binary and ternary cationic-nonionic surfactant mixtures

The aqueous solubilization of the organoselenium compound viz., 1,2-bis(bis(4-chlorophenyl)methyl)diselane [(ClC(6)H(4))(2)CHSe](2) has been investigated experimentally in micellar solutions of two cationic (hexadecyltrimethylammonium bromide, CTAB, hexadecyltrimethylammonium chloride, CTAC) and one nonionic (polyoxyethylene(20)mono-n-hexadecyl ether, Brij 58) surfactants possessing the same hydrocarbon "tail" length and in their single as well as equimolar binary and ternary mixed states. Solubilization capacity determined with spectrophotometry and tensiometry has been quantified in terms of molar solubilization ratio and micelle-water partition coefficient. FTIR, UV-vis, fluorescence and zeta potential measurements have been utilized to ascertain the interaction of organochalcogen compound with surfactants. Equimolar cationic-nonionic surfactant combinations show better solubilization capacity than pure cationics or nonionics, whereas equimolar cationic-cationic-nonionic ternary surfactant systems exhibit intermediate solubilization efficiency between their single and binary counterparts. Locus of solubilization of [(ClC(6)H(4))(2)CHSe](2) in different micellar solutions was probed by UV-visible spectroscopy. The investigation has presented precious information for the preference of mixed surfactants for solubilizing water-insoluble compounds. Indeed the solubilization aptitude of these surfactants is not merely related to molar capacity. The results furnish adequate support to justify comprehensive exploration of the surfactant properties that influence solubilization.     

Effect of Pentanol Partitioning on Solubilization of Tetrachloroethylene and Gasoline by Sodium Dodecyl Sulfate Micelles

The effect of interfacial pentanol concentrations on solubilization of tetrachloroethylene (PCE) and gasoline by sodium dodecyl sulfate (SDS) micelles was compared to that for dodecane solubilization, which had been measured in a previous study. The solubilization of PCE and gasoline reached their maximum values at a 1 : 3 SDS-to-pentanol molar ratio in the interface. As pentanol concentrations increased beyond that necessary for interfacial saturation, solubilization of PCE and gasoline decreased. This behavior was similar to that observed when dodecane was the oil phase. Electrical conductivity of aqueous SDS/pentanol solutions followed a trend similar to that for oil solubilization, reaching a maximum value at a 1 : 3 molar ratio of SDS to pentanol in the interface. The results of this and previous studies suggest that pentanol partitioning in SDS micelles can be described by a simple two-region model: Region I is the interface between the water-continuous phase and oil and Region II is the micelle inner core. When the mole fraction of pentanol in the interface is less than 0.75, pentanol partitions strongly into Region I, where it acts as a cosurfactant along with SDS and enhances oil solubilization. Above 0.75 mole fraction in the interface, pentanol partitions strongly into Region II, where it acts as a polar oil and competes with other oils for solubilization. Copyright 2001 Academic Press.     

Peptide dissociation in solution or bound to a polymer: comparative solvent effect

Dissociation of peptide when in solution or attached to a polymer was investigated. Magnified solvation of peptide-resins occurred in solvent with similar polarity. Conversely the solubilization of peptides was not usually directly related to the medium polarity. The greater the difference between acidity and basicity of solvent and its potential to form van der Waals interaction, the stronger its solubilization strength. Solvents with similar electrophilicity and nucleophilicity usually did not solvate aggregated peptide-resins nor dissolve peptides. The peptide solubilization in water-containing mixed solvents depended on combination of acidity/basicity of both components. Some criteria for choosing suitable solvents for peptide-resin solvation or peptide solubilization could be advanced.     

Effects of micellar structure on solubilization ofn-octane andn-octanol

The solubilization ofn-octane andn-octanol in nonionic micelles of octaethylene glycoln-alkyl ethers was investigated by means of various techniques including solubilization, fluorescence, and dynamic light-scattering measurement. With respect to the effect of alkyl chain length of the surfactants, different solubilization behavior was observed betweenn-octane andn-octanol. That is to say, it was shown that the solubilization ofn-octane increases with an increase in the alkyl chain length, while that ofn-octanol decreases. An interpretation of these solubilization mechanisms is explained from the standpoint of the volume of hydrophobic and hydrophilic regions in a micelle.     

A two-state model for selective solubilization of benzene-limonene mixtures in sodium dihexyl sulfosuccinate microemulsions

When surfactants are used to solubilize oil, the oil to be solubilized is often a mixture of components with differing properties, for example, solubilization of drug molecules in microemulsion formulations, remediation of organic polluted aquifers using surfactants, and so forth. Previous research has demonstrated that selective solubilization of one organic component over the other may occur if the organic components are dissimilar. In this research, we investigated selective solubilization from benzene-limonene mixtures in Winsor type I and III microemulsion systems containing water, sodium di-n-hexyl sulfosuccinate, and NaCl. The effect of the oil phase composition and the electrolyte concentration on the selectivity was studied. It was found that the selectivity toward benzene was highest at low electrolyte and benzene concentrations, decreasing as the electrolyte or benzene concentration increased. The results are discussed on the basis of the two-state solubilization theory and by correlating the curvature of the surfactant film in the microemulsion with changes of the electrolyte concentration and the oil phase composition. A simple mathematical model is developed for the selectivity, which combines the two-state solubilization theory and the net-average curvature model of microemulsion solubilization to yield close agreement with the experimental data.     

Solubilization kinetics for polycyclic aromatic hydrocarbons transferring from a non-aqueous phase liquid to non-ionic surfactant solutions

A modified rotating disk apparatus was used to investigate the mass transfer of two polycyclic aromatic hydrocarbon (PAH) compounds, naphthalene and phenanthrene from a synthesized non-aqueous phase liquid (NAPL) comprised of hexadecane and the 2 PAHs into different non-ionic surfactant solutions. Major factors influencing the rate of solubilization of PAHs from a NAPL in micelles of different non-ionic surfactants were determined. As the surfactant concentration increased, the mass transfer coefficients for both PAHs from the NAPL decreased. The maximum rates of solubilization of the PAHs however increase with surfactant dose. The rate of solubilization was found to be limited by rates of desorption of mixed micelles from the NAPL and their rate of diffusion into the bulk solution phase. The influence of the surfactant molecular structure on the kinetics of the solubilization process was investigated. The results suggested that the length of the alkyl portion of the non-ionic surfactant and the micelle volume influenced the solubilization kinetics. The results of the investigation improve our ability to provide a rational basis for selecting the optimum surfactant and dose to enhance the solubilization of PAHs from NAPLs.     

Solubilization properties of aqueous solutions of alkyltrimethylammonium halides toward a water-insoluble dye

The solubility of a water-insoluble dye, Sudan Red B, in aqueous sodium halide solutions of tetradecyl-, cetyl-, and stearyltrimethylammonium halides has been measured at different surfactant and salt concentrations, and the dependence of solubilization properties on alkyl chain length has been discussed with reference to the micelle size and shape. At low ionic strengths where only spherical micelles exist, the solubilization power of micellar surfactant slightly increases with increasing the ionic strength, but it sharply increases at high ionic strengths above the threshold value of sphere-rod transition. However, the solubilization power becomes independent of the ionic strength, if their rodlike micelles are sufficiently long. The solubilization capacity increases linearly with increasing the molecular weight, almost independent of counterion species, but the rod-like micelle has a higher solubilization capacity than the spherical micelle. The solubilization capacity is larger for a surfactant with longer alkyl chain, indicating that the dye is solubilized more readily in a larger hydrophobic core. The solubilized dye is situated in a rodlike micelle of alkyltrimethylammonium halides, on average, 4.5–7.5 nm apart from each other.     

Anomalous solubilization behavior of dimyristoylphosphatidylcholine liposomes induced by sodium dodecyl sulfate micelles

The solubilization dynamics of dimyristoylphosphatidylcholine (DMPC) liposomes, as induced by sodium dodecyl sulfate (SDS), were investigated; this investigation was motivated by several types of atypical behavior that were observed in the solubilization in this system. The liposomes and surfactants were mixed in a microchip, and the solubilization reaction of each liposome was observed using a microscope. We found that solubilization occurred not only via a uniform dissolution of the liposome membrane, but also via a dissolution involving the rapid motion of the liposome, or via active emission of protrusions from the liposome surface. We statistically analyzed the distribution of these patterns and considered hypotheses accounting for the solubilization mechanism based on the results. When the SDS concentration was lower than the critical micelle concentration (CMC), the SDS monomers entered the liposome membrane, and mixed micelles were emitted. When the SDS concentration was higher than the CMC, the SDS micelles directly attacked the liposome membrane, and many SDS molecules were taken up; this caused instability, and atypical solubilization patterns were triggered. The size dependence of the solubilization patterns was also investigated. When the particle size was smaller, the SDS molecules were found to be homogeneously dispersed throughout the whole membrane, which dissolved uniformly. In contrast, when the particle size was larger, the density of SDS molecules increased locally, instability was induced, and atypical dissolution patterns were often observed.     

Contribution of molecular pathways in the micellar solubilization of monodisperse emulsion droplets

It is often proposed that oil solubilization in anionic and nonionic micelles proceeds by different mechanisms, with diffusion of the oil molecule thought to control the former, and the latter interfacially controlled. In order to investigate this hypothesis, the effect of aqueous phase viscosity, salt, and surfactant concentration during the solubilization process was studied. The progressive decrease in average droplet size of nearly monodisperse emulsions during solubilization in SDS or Tween 20 micellar solutions was monitored by light scattering, and the change in turbidity was measured by UV-vis spectrophotometer. The solubilization rates were analyzed using a population balance approach to calculate the mass transfer coefficients. Increasing the aqueous viscosity by adding sucrose reduced the mass transfer coefficients of n-tetradecane and n-dodecane but had a smaller effect on n-hexadecane. The strong dependence of the solubilization rate for the shorter chain length alkanes on aqueous viscosity supported a mechanism in which the oil undergoes molecular diffusion before being taken up by micelles. The dependence of the solubilization kinetics on surfactant concentration appeared consistent with this mechanism but yielded a slower micellar uptake rate than previously predicted theoretically. As the solute chain length increased in nonionic surfactant solutions, an interfacial mechanism mediated by micelles appeared to contribute substantially to the overall rate. Addition of salt only slightly increased the solubilization rate of n-hexadecane in SDS solutions and, thus, indicated a weak role of electrostatic interactions for ionic surfactants on the overall mechanism.     

Solubilization kinetics of phospholipid vesicles by sodium taurocholate

The solubilization kinetics of phospholipid vesicles, about 100 nm in diameter and composed of egg phosphatidylcholine (EPC) and EPC/cholesterol in molar ratio 7/3, by sodium taurocholate (TC) used as a model bile salt were investigated by monitoring the turbidity at 500 nm and by quasielastic light scattering (QELS). The solubilization process was found to be dependent on the rate of TC addition. Although the solubilization profiles were identical whatever the rate of TC addition, an increase in the amount of TC needed to solubilize phosphatidylcholine liposomes was observed at higher rates. These results suggest that at low TC concentrations the permeability of the membrane to taurocholate is the rate-limiting step of the solubilization. In the case of cholesterol-containing vesicles, the effect of the rate of addition of TC was observed only at the solubilization characteristic points, called B and C, corresponding to a sharp decrease in the turbidity. This suggests that cholesterol greatly reduces the permeability of the membrane. In addition, the kinetic process was found to be independent of the micellar concentration of the detergent added to the aqueous medium, indicating that the solubilization of liposomes by TC was independent of the initial state of aggregation of the detergent. The calculated values of lipid/TC aggregates and of the partition coefficient show that the kinetic effect observed at high TC concentrations prior to complete solubilization might also be due to the diffusion of the detergent into the membranes. This gives rise to the differences in composition of the aggregates as a consequence of the variation in the rate of TC addition. In addition, QELS scattered intensity variations confirm the presence of a kinetic process for the solubilization of liposomes by TC. In conclusion, our results suggest that solubilization of lipid vesicles by TC is governed by kinetic parameters that might be controlled by liposome membrane permeability at low TC concentrations and by the lateral diffusion of the detergent into aggregates at higher TC concentrations.     

Solubilization of phenols in anionic polyelectrolyte gels with adsorbed cationic surfactant

Solubilization isotherms for various phenols in cetylpyridinium chloride (CPC)-polyelectrolyte gel aggregates have been determined in order to compare solubilization within these aggregates with that in free micelles and to examine the effects of gel chemistry and structure on solubilization. The isotherms describing solubilization are quite similar to those found for free surfactant in solution. Solutes that are more hydrophobic give rise to larger solubilization constants with trends similar to what is seen for hydrophobic effects in adsorption from aqueous solutions onto hydrophobic solids. The solubilization constants decrease as the fraction of solute in the aggregates increases, indicating that the solutes partition into the palisade region of the aggregates. Solubilization is found to be quite insensitive to changes in gel structure (cross-linker varying from 1% to 3%) and chemistry (poly(acrylic acid) versus poly(methacrylic acid) and neutralization from 50% to 100%). However, the switch from poly(acrylic acid) to poly(methacrylic acid) did give rise to a slight decrease in magnitude of the slope of the isotherm. The most significant factors appear to be the initial concentration of surfactant in solution and the ratio of surfactant solution to gel amount. A decrease in surfactant concentration (especially combined with an increase in solution volume) gives rise to a decrease in solubilization constants.     

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.     

Measurement of Solubilization Location in Micelles Using Anchored Aggregation-Induced Emission Donors

Solubilization locations play a critical role in developing advanced surfactants and improving solubilization power in micelle-based applications. However, the current polarity-based techniques for measuring solubilization locations could come to conflicting conclusions. The key challenge is the unpredictable polarities in the micellar microenvironment. Now, an approach that is independent of micellar polarities is used to measure solubilization locations by covalently linking tetraphenylethylene (TPE) to the alkyl chain end of cationic surfactants. The solubilization locations of solubilized acceptors in the TPE-cored spherical micelles were accurately measured by calculating the Förster resonance energy transfer distance between anchored TPE donors and solubilized acceptors. Solubilization locations of solubilized substances in the micellar interior and at the micellar surface depend on their size and hydrophobicity, respectively.     

Modeling solubilization of oil mixtures in anionic microemulsions II. Mixtures of polar and non-polar oils

Polar/amphiphilic oils, called lipophilic linkers, are sometimes added to oil-water-ionic surfactant microemulsions in order to increase the solubilization of hydrophobic oils. The solubilization increase has been well documented for a number of systems. However, mathematical models to calculate the solubilization increase have been proposed only for optimum microemulsions (i.e., middle phase microemulsions solubilizing equal volumes of oil and water). In this paper we propose a model, which predicts solubilization enhancement for non-optimum microemulsion systems as well. The model is an extension of the net-average curvature model of microemulsion. The net-average curvature model is combined with a surface activity model to account for the increased palisade layer solubilization due to the presence of the polar/amphiphilic oil component. New non-linear mixing rules are also incorporated to account for the optimum salinity and the characteristic length variation of the anionic surfactant microemulsion as a function of the lipophilic linker concentration. The model predicts the effect of the lipophilic linker and the electrolyte concentration on the oil solubilization in accordance with the experimental results.     

Measurement of Solubilization Location in Micelles Using Anchored Aggregation‐Induced Emission Donors

Solubilization locations play a critical role in developing advanced surfactants and improving solubilization power in micelle‐based applications. However, the current polarity‐based techniques for measuring solubilization locations could come to conflicting conclusions. The key challenge is the unpredictable polarities in the micellar microenvironment. Now, an approach that is independent of micellar polarities is used to measure solubilization locations by covalently linking tetraphenylethylene (TPE) to the alkyl chain end of cationic surfactants. The solubilization locations of solubilized acceptors in the TPE‐cored spherical micelles were accurately measured by calculating the Förster resonance energy transfer distance between anchored TPE donors and solubilized acceptors. Solubilization locations of solubilized substances in the micellar interior and at the micellar surface depend on their size and hydrophobicity, respectively.