Dissolution of polycyclic aromatic hydrocarbons from a non-aqueous phase liquid into a surfactant solution using a rotating disk apparatus

The mass transfer of two polycyclic aromatic hydrocarbons (PAHs), naphthalene and phenanthrene from a multicomponent non-aqueous phase liquid (NAPL) into a nonionic surfactant solution, Brij 35 was investigated using a rotating apparatus. Few experimental methods have been applied to the study of solubilization kinetics in organic liquids because in those systems, the interfacial area during mixing is more difficult to maintain and measure. This challenge was overcome by permeating the NAPL through a membrane. Mass transfer experiments were conducted in the absence and presence of surfactant, and the concentrations of naphthalene and phenanthrene in the bulk aqueous phase were determined in samples collected at different time intervals from the time of initial contact of the NAPL phase with the aqueous solution phase. Experiments in pure water demonstrated that the rotating apparatus behaves as in much the same way as the Levich's rotating disk. The mass transfer coefficients and the dissolution of PAHs into the surfactant solution were measured at different doses of Brij 35. As the surfactant concentration increased, the mass transfer coefficients for both PAHs from the NAPL decreased.     

Investigation on the locus of solubilization of polycyclic aromatic hydrocarbons in non-ionic surfactant micelles with H NMR spectroscopy

This research investigates the locus of solubilization of two significant compounds, the polycyclic aromatic hydrocarbons (PAHs) naphthalene and phenanthrene from a synthesized organic liquid phase comprised of the two PAHs and hexadecane in micelles of five polyoxyethylene non-ionic surfactants. The locus was inferred by the examination of the nuclear magnetic resonance (NMR) spectra. In this method, the ring current shifts on the ¹H resonance of the surfactant chain protons are monitored. ¹H NMR spectra were recorded for the five surfactant solutions in absence and presence of PAHs. The presence of the PAH induced the ¹H to shift along the surfactant chain. The proton shift changes were obtained by comparing the NMR spectra for the pure surfactant solutions with those for surfactant solution contacted with various non-aqueous phase liquids. It was demonstrated that the distribution of PAHs between the shell and the core of the micelles changed with the concentration of PAHs in the micelles and in the NAPL phase. The ¹H NMR analysis identified the presence of both PAHs in the shell region of the non-ionic micelles. This is an important observation because it is commonly assumed that in multi-component systems the solutes with relatively greater hydrophobicity are partitioned only in core of the non-ionic micelles. The results demonstrated the potential of the ¹H NMR analysis for the identification of the locus of solubilization of PAHs in micelles of non-ionic surfactant.     

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 of triphenylamine, triphenylphosphine, triphenylphosphineoxide and triphenylmethanol in single and binary surfactant systems

Solubilization and co-solubilization of triphenyls (TPs) viz., triphenylphosphine (TPP), triphenylphosphineoxide (TPPO), triphenylamine (TPA) and triphenylmethanol (TPM) were studied in various single and binary surfactant systems at 25 °C using UV-visible spectroscopy and HPLC. The solubilization capacities of different micelles towards TPs were found to be a function of the nature and structure of solubilizates, locus of solubilization, size of micelles and the nature of interactions between the solubilizate and micelles. The effect of surfactant mixing on the solubilization of TPs was evaluated using the Regular Solution Approach (RSA). The solubility enhancement of TPs within mixed micelles relative to that observed in single surfactant systems was explained in light of the structural micellar changes associated with the mixing of ionic and non-ionic surfactants. Moreover, kinetics of oxidation of TPP by hydrogen peroxide investigated in these surfactant systems was found to be sensitive to the nature of micelle and the locus of solubilization of TPP within the micelles.     

Effects of surfactant micelles on solubilization and DPPH radical scavenging activity of Rutin

The interaction of the antioxidant Rutin with the radical DPPH (2,2-diphenyl-1-picrylhydrazyl) in presence of cationic (CTAB, TTAB, DTAB), non-ionic (Brij78, Brij58, Brij35), anionic (SDS) and mixed surfactant systems (CTAB-Brij58, DTAB-Brij35, SDS-Brij35) has been followed by spectrophotometric and tensiometric methods to evaluate the DPPH radical scavenging activity (RSA) of Rutin in these model self-assembled structures. The results show that the solubilization capacity of various single surfactant systems for both DPPH as well as Rutin followed the order cationics > non-ionics > anionic. The radical scavenging activity of Rutin in the solubilized form was higher within ionic micelles than in non-ionic micelles. However, the antioxidant exhibited enhanced activity for the radical in mixed cationic-non-ionic micelles compared with any of the single component micelles. In contrast, anionic-non-ionic mixed micelles modulated the activity of Rutin in-between that seen for pure anionic and non-ionic micelles only.     

Solubilization in monodisperse emulsions

The kinetics of oil solubilization into micelles from nearly monodisperse alkane-in-water emulsion droplets was investigated. Emulsions containing either hexadecane or tetradecane oils were fractionated to be narrowly distributed, using a method developed by Bibette [J. Bibette, J. Colloid Interface Sci. 147 (1991) 474]. These monodisperse emulsions were mixed with SDS or Tween 20 aqueous micellar solutions of various concentrations. Time-dependent solubilization was monitored using light scattering and a decrease in average droplet size over time was observed, in contrast to what has been observed previously with polydisperse emulsions. The rate at which the droplet size decreased was found to be independent of the initial droplet size. Turbidity measurements were also used to track the solubilization kinetics, and a population balance analysis used on both types of measurements to extract effective mass transfer coefficients. The dependence of these transfer coefficients on droplet size, alkane type, surfactant type and concentration provide insights into plausible mechanisms of emulsion droplet solubilization within micellar solutions.     

A model for interfacial resistance observed during solubilization with micellar solution

The quantitative behavior of interfacial resistance to mass transfer at an oil-water interface in presence of a surfactant, which occurs in addition to the diffusional resistance, is modeled. Successive approximations are used to simplify the detailed behavior to show that the experimentally determined quantitative behavior of solubilization kinetics, is also theoretically justified. The solubility of oil, the frequency of collision of micelles with the oil-water interface, and the resistance to the entry of the solubilizate into the micelle (activation energy) are identified as the key quantities governing this resistance.     

Degradation of kinetically-stable o/w emulsions

This article summarizes the studies on the degradation of the thermodynamically unstable o/w (nano)emulsion--a dispersion of one liquid in another, where each liquid is immiscible, or poorly miscible in the other. Emulsions are unstable exhibiting flocculation, coalescence, creaming and degradation. The physical degradation of emulsions is due to the spontaneous trend toward a minimal interfacial area between the dispersed phase and the dispersion medium. Minimizing the interfacial area is mainly achieved by two mechanisms: first coagulation possibly followed by coalescence and second by Ostwald ripening. Coalescence is often considered as the most important destabilization mechanism leading to coursing of dispersions and can be prevented by a careful choice of stabilizers. The molecular diffusion of solubilizate (Ostwald ripening), however, will continuously occur as soon as curved interfaces are present. Mass transfers in emulsion may be driven not only by differences in droplet curvatures, but also by differences in their compositions. This is observed when two or more chemically different oils are emulsified separately and the resulting emulsions are mixed. Compositional ripening involves the exchange of oil molecules between emulsion droplets with different compositions. The stability of the electrostatically- and sterically-stabilized dispersions can be controlled by the charge of the electrical double layer and the thickness of the droplet surface layer formed by non-ionic emulsifier. In spite of the similarities between electrostatically- and sterically-stabilized emulsions, there are large differences in the partitioning of molecules of ionic and non-ionic emulsifiers between the oil and water phases and the thickness of the interfacial layers at the droplet surface. The thin interfacial layer (the electrical double layer) at the surface of electrostatically stabilized droplets does not create any steric barrier for mass transfer. This may not be true for the thick interfacial layer formed by non-ionic emulsifier. The interactive sterically-stabilized oil droplets, however, can favor the transfer of materials within the intermediate agglomerates. The stability of electrosterically-stabilized emulsion is controlled by the ratio of the thickness of the non-ionic emulsifier adsorption layer (delta) to the thickness of the electrical double layer (kappa(-1)) around the oil droplets (delta/(kappa(-1))) = (deltakappa). The monomer droplet degradation can be somewhat depressed by transformation of coarse emulsions to nano-emulsion (miniemulsion) by intensive homogenization and by the addition of a surface active agent (coemulsifier) or/and a water-insoluble compound (hydrophobe). The addition of hydrophobe (hexadecane) to the dispersed phase significantly retards the rate of ripening. A long chain alcohol (coemulsifier) resulted in a marked improvement in stability, as well, which was attributed to a specific interaction between alcohol and emulsifier and to the alcohols tendency to concentrate at the o/w interface to form stronger interfacial film. The rate of ripening, according to the Lifshitz-Slyozov-Wagner (LSW) model, is directly proportional to the solubility of the dispersed phase in the dispersion medium. The increased polarity of the dispersed phase (oil) decreases the stability of the emulsion. The molar volume of solubilizate is a further parameter, which influences the stability of emulsion or the transfer of materials through the aqueous phase. The interparticle interaction is expected to favor the transfer of solubilizate located at the interfacial layer. The kinetics of solubilization of non-polar oils by ionic micelles is strongly related to the aqueous solubility of the oil phase (the diffusion approach), whilst their solubilization into non-ionic micelles can be contributed by interparticle collisions.     

Joint solubilization of lipophilic drug amlodipine and glyceryl monolaurate in aqueous micellar solutions of Tween 80

The solubilization of lipophilic amlodipine (Am is a antihypertensive drug) and nonionic surfactant glyceryl monolaurate (GML is a skin permeation enhancer), as well as their joint solubilization (co-solubilization) have been measured by UV spectroscopy and refractometry in aqueous micellar solutions of Tween 80 (Tw). The properties of mixed micelles (Tw + GML, Tw + Am, Tw + GML + Am) have been studied, including the aggregation number of components, the localization of solubilizates, diffusion coefficients, the size and the degree of hydration. As a result of co-solubilization, (Tw + GML + Am) three-component micelles contain 4.2 times more molecules of the drug than (Tw + Am) two-component micelles. The experimental data on the kinetics of mass transfer of Am by micelles based on Tw are in good agreement with the calculations under diffusion theory; furthermore, three-component micelles carry Am more effectively than two-component micelles.     

Calculation of Partition Coefficients of Organic Reagents in Micellar Thin-Layer Chromatography

Equilibrium partition processes were quantitatively estimated for acidic reagents of the xanthene and triphenylmethane series in the system water–surfactant micelle–stationary phase. An anionic surfactant (sodium dodecyl sulfate) was used as the micelle-forming compound. Partition coefficients were calculated, and the preferential solubilization of reagents in surfactant micelles was demonstrated. Energies of reagent transfer to sodium dodecyl sulfate micelles and their adsorption energies at the stationary phase were calculated.     

Parameters Involved in the Sol-Gel Transition of Titania in Reverse Micelles

Titania nanoparticles and gels are synthesized in reverse micelles with either an ionic (AOT) or a non-ionic (Triton X-100) surfactant in alkanes with low water contents. Acids were in some cases dissolved in the aqueous phase. Whereas the size of the sol nanoparticles is independent of the micellar composition, the kinetics of the sol-gel transition are not. The gelation time is shorter for the non-ionic surfactant and becomes longer as the acid content in the water increases, and for smaller anions of equal charge.     

Solubilization of Polycyclic Aromatic Compounds into n-Decyltrimethylammonium Perfluorocarboxylate Micelles

Solubilization of polycyclic aromatic compounds in aqueous dilute solutions of three cationic amphiphiles was studied. The maximum additive concentrations (MACs) of the aromatic compounds were constant below their critical micelle concentrations (cmcs) and monotonically increased above the cmcs. The first stepwise association constants (K(1)) between a solubilizate monomer and a vacant micelle were evaluated from the MACs for the solubilizates using the mass action model for solubilization into micelles in the dilute solution. The standard Gibbs energy changes of solubilization (DeltaG degrees ) were calculated from K(1), and the enthalpy and entropy changes of solubilization were estimated from the temperature dependence. MACs of each surfactant at the same surfactant concentration above the cmc were different depending on the cmc, but there was little difference in the DeltaG degrees values. Some differences appeared in the enthalpy and entropy values in accordance with their micellar size or degrees of counterion binding to micelles. DeltaG degrees for solubilization decreased linearly with carbon number of aromatic solubilizate for each micellar solution. Copyright 2000 Academic Press.     

Removal of Solid Organic Films from Rotating Disks Using Emulsion Cleaners

Measurements have been made of the rate of removal of a solid organic film (phenanthrene) from the surface of a rotating disk using emulsions containing water, the nonionic surfactant Tween 20, and d-limonene as the organic phase. The results show that phenanthrene removal initially occurs by the uptake of phenanthrene into the emulsion drops as small aggregates. Simultaneously, the organic phase penetrates into the phenanthrene film, diminishing the adhesive force between the film and the substrate. After sufficient time, the phenanthrene film detaches from the rotating disk surface as a solid. This detachment mechanism accounts for the vast majority of the phenanthrene removal ( approximately 90%). Initial solubilization rates were analyzed using two solubilization models. Both models assume that phenanthrene removal occurs via a mass transfer limited removal of phenanthrene-laden emulsion drops from the phenanthrene film surface into the bulk solution. One model treats the emulsion as homogeneous while the other accounts for the finite size of the emulsion droplets. The latter model was also used to relate the flux of organic phase impacting the phenanthrene film to the detachment times. Copyright 2000 Academic Press.     

Micellar Aggregation Behavior and Electrochemically Reversible Solubilization of a Redox-Active Nonionic Surfactant

For the purpose of studying the potential of a novel nonionic switchable surfactant, 11-ferrocenylundecyl polyoxyethylene ether (FPEG), applied to surfactant-enhanced remediation (SER), the surface properties and micelle solubilization behavior of FPEG were investigated with different inorganic salts. With the addition of inorganic salts (NaCl and CaCl₂), the critical micelle concentration (CMC) of FPEG dropped from 15 to 12 and 8 mg·L^?1, respectively, due to the salting-out effect on the alkyl chain. Thermodynamic parameters based on the CMCs indicated that micelle formation was an entropy-driven process. Dynamic light scattering measurements verified that these inorganic salts can decrease the hydrodynamic diameters (D _h) of the micelles. Solubilization experiments with three typical polycyclic aromatic hydrocarbons (PAHs) demonstrated that the system of FPEG with NaCl shows the highest solubilization ability, and the molar solubilization ratio and micelle–water partition coefficient (K _m ) values follow the order pyrene > phenanthrene > acenaphthene. After oxidation, PAHs can be released from the micelles through breaking up of the micelles, and the cumulative release efficiency of pyrene, phenanthrene and acenaphthene are 31.2, 42.8 and 44.6 %; the order of release efficiency is opposite to that of the reduced form for solubilization abilities. All the results suggest that the ferrocene-containing, redox-active surfactant FPEG has the potential to be recycled in SER technology through electrochemistry approaches.     

Effects of protonation on the thermodynamic properties of alkyl dimethylamine oxides

The effects of protonation on alkyldimethyl amine oxide micelles are reviewed, mainly with regard to dodecyl and tetradecyl homologs. The topics discussed are hydrogen ion titration properties, critical micelle concentration (CMC), area per surfactant and micelle aggregation number. A hydrogen bond hypothesis is proposed to interpret the several characteristic results associated with protonation: between two cationic species as well as between the non-ionic-cationic pair. The dipole-dipole interaction of the non-ionic micelle is discussed in relation to both: (a) the unusually high CMC values of the non-ionic micelles compared with other non-ionic surfactants with the same hydrocarbon chain; and (b) the reversal of the stability of the non-ionic and the cationic micelles at high ionic strengths. Two different approaches of the salting out effect on the ionic micelles are compared, the Chan-Mukerjee approach and ours, in relation to the non-linear Corrin-Harkins relation. The obtained salting out constants of the surfactants carrying a dodecyl chain decreased as the head group becomes more polar. Infrared and 13C-NMR spectra data are examined from the point of the specific interaction claimed by the hydrogen bond model. Mixed surfactant systems including amine oxides and the solid state phase behavior of amine oxides are both briefly reviewed.     

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.     

Effect of the electrostatic charge on the mechanism inducing liposome solubilization: a kinetic study by synchrotron radiation SAXS

The anionic surfactant sodium dodecyl sulfate (SDS) was used to induce the initial steps of the solubilization of liposomes. The structural transformations as well as the kinetics associated with this initial period were studied by means of time-resolved small-angle X-ray scattering (SAXS) using a synchrotron radiation source. Neutral and electrically charged (anionic and cationic) liposomes were used to investigate the effect of the electrostatic charges on the kinetics of these initial steps. The mechanism that induces the solubilization process consisted of adsorption of surfactant on the bilayers and desorption of mixed micelles from the liposomes surface to the aqueous medium. In all cases the time needed for desorption of the first mixed micelles was shorter than that for complete adsorption of the surfactant on the liposomes surface. The present work demonstrates that adsorption of the SDS molecules on negatively charged liposomes was slower and release of mixed micelles from the surface of these liposomes was faster than for neutral liposomes. In contrast, in the case of positively charged liposomes, the adsorption and release processes were, respectively, faster and slower than those for neutral vesicles.     

Solubilization of triglycerides in liquid crystals of nonionic surfactant

The solubilization of triglycerides [1,2,3-tributanoylglycerol (TBG) and 1,2,3-trihexanoylglycerol (THG)] in water/octa(oxyethylene) dodecyl ether (C(12)EO(8)) systems has been investigated. Oil-induced changes in the structure of liquid crystals in water/C(12)EO(8) system have been studied by optical observation and small-angle X-ray scattering (SAXS) measurements. In the water/C(12)EO(8)/oil systems, solubilization of THG and TBG induces a transition between H(1) (hexagonal) and L(alpha) (lamellar) liquid crystals at high C(12)EO(8) concentrations, whereas at low surfactant concentrations a H(1)-I(1) (discontinuous micellar cubic phase) transition occurs. This anomalous behavior is attributed to the partitioning of solubilized oil in the micelles. At low surfactant concentrations THG is mainly solubilized into the hydrophobic cores of the surfactant micelles, indicating high swelling or low penetration tendency, resulting in a steep increase in the radius of the aggregates (r(H)), thereby inducing a rod-sphere transition. At high surfactant concentrations, THG is not mainly solubilized into the core but distributed between the palisade layer and the core of the aggregates. The TBG is considerably solubilized into the surfactant palisade layer, indicating a high penetration tendency, resulting in an increase in the effective cross-sectional area per surfactant molecule, a(s). The thermal stability of the I(1) phase increases with the solubilization of THG into the aggregate cores. The percentage deviation of the experimental interlayer spacings (P(d)) from complete swelling was also evaluated for different triglycerides in the H(1) and L(alpha) phases or different surfactant concentrations. It is found that the penetration tendency of triglycerides could be used as a tuning parameter for I(1) phase formation depending on the surfactant concentration and the molecular weight of the oil.     

有机电解质在胶束催化聚苯乙烯氯甲基化反应中的作用

在实施聚苯乙烯氯甲基化反应的胶束催化体系中加入四丁基溴化铵 ((Bu)₄NBr, TBAB), 研究了有机电解质TBAB对胶束催化反应的影响规律. 实验结果表明, 在非离子表面活性剂NP-10及阴离子表面活性剂SDS的胶束催化体系中, TBAB的加入使聚苯乙烯氯甲基化反应的速率明显增大, 前者尤为突出；而在阳离子表面活性剂CTAB的胶束催化体系中, TBAB的加入几乎对反应速率无促进作用. 这种结果一方面归因于加入电解质TBAB会降低SDS的临界胶束浓度, 从而增强对聚苯乙烯四氯化碳溶液的增溶能力；更主要的原因是TBAB的丁基与表面活性剂碳氢链间的疏水相互作用会使季铵离子(Bu)₄N⁺嵌入SDS的胶束之中, 结合到NP-10的胶束表面, 使SDS胶束的阴离子头基对亲核取代反应(控制步骤)的禁阻作用得以减缓, 使NP-10的胶束表面携带了正电荷, 显著促进亲核取代反应的进行, 而对于CTAB的胶束, 由于静电排斥作用, 季铵离子(Bu)₄N⁺不能接近CTAB的胶束, 故TBAB的加入对聚苯乙烯氯甲基化反应不产生作用.     

Effects of non-ionic micelles on transient chaos in an unstirred Belousov-Zhabotinsky reaction

The behaviour of the Ce(IV)-catalyzed Belousov-Zhabotinsky (BZ) system has been monitored at 20.0 degrees C in unstirred batch conditions in the absence and presence of different amounts of the non-ionic micelle-forming surfactants hexaethylene glycol monodecyl ether (C10E6) and hexaethylene glycol monotetradecyl ether (C14E6). The influence of the non-ionic surfactants on both the kinetics of the oxidation of malonic acid (MA) by Ce(IV) species and the behaviour of the BZ reaction in stirred batch conditions has also been studied over a wide surfactant concentration range. The experimental results have shown that, in unstirred batch conditions, at surfactant concentrations below the critical micelle concentration (c.m.c.) no significant change in the dynamics of the Belousov-Zhabotinsky system occurs. Beyond this critical concentration the presence of micelles forces the BZ system to undergo a chaos-->quasi-periodicity-->period-1 transition. Thus, the surfactant concentration has been considered as a bifurcation parameter for a Ruelle-Takens-Newhouse (RTN) scenario. Addition of increasing amounts of non-ionic surfactants has no significant effect on the kinetics of the reaction between MA and Ce(IV), but it influences the oscillatory parameters of the stirred BZ system. At surfactant concentrations below the c.m.c. all the oscillatory parameters are practically unaffected by the presence of surfactant, while beyond this critical value the induction period is the same as in aqueous solution but both the oscillation period and the duration of the rising portion of the oscillatory cycle decrease. In all cases, the experimental trends have been ascribed to the enhancement in the medium viscosity due to the presence of micelles.