Surfactant Micelles In Solution Research Articles

Interactions of fluorescent surfactant micelles in solution with colloidal silica nanoparticles and their penetrant diffusion in hydrated fumed silica films

The preparation and properties of surfactant micelles labeled with the dye, Nile Red (NR), are described. Fluorescence emission and excitation spectroscopy establish the localization of NR in the hydrophobic core of nonionic Brij® S10, Brij® S20, and Triton X-100 micelles, and in ionic mixed micelles prepared from sodium dodecyl sulfate (SDS) and Triton X-100 mixtures of varying composition. Stokes diameter analysis of NR-micelles by fluorescence correlation spectroscopy (FCS) yields mean diameters ranging from 3.0 to 10.6 nm depending on the surfactant composition and its concentration used for micelle preparation. Adsorption of NR-micelles on a 20 nm, charged-stabilized, sol-gel silica nanoparticle is characterized by FCS. NR-micelle-nanoparticle solutions are analyzed as two-species mixtures of free and nanoparticle-bound NR-micelles allowing determinations of mean Stokes diameters and fractions of nanoparticle-bound NR-micelles. Incorporation of SDS into nonionic Triton X-100-NR-micelles progressively diminishes the adsorption of the mixed ionic NR-micelles on the nanoparticles with increasing SDS in the micelles. FCS analysis NR-micelle adsorption interactions with silica nanoparticles is shown to occur at the single NR-micelle level, providing a means for advancing the fundamental understanding of these interactions. The kinetics of a NR-micelle’s penetration into a hydrated fumed silica determined by FCS are shown to be a one-dimensional Fickian process and indicative of pores with low tortuosity. The use of NR-micelles as fluorescent diffusion probes in porous fumed silica films is concluded to be a viable general approach for the characterization of pore tortuosity in films composed of irregularly shaped (fractal) nanoparticles.

Determining threadlike micelle lengths from rheometry

We show that the average length ⟨L⟩ of threadlike micelles in surfactant solutions predicted by fitting results of a mesoscopic simulation, the “pointer algorithm,” to experimental G′(ω), G″(ω) data, is longer than, and more accurate than, that from a scaling law that equates ⟨L⟩/le to the modulus ratio G0/Gmin′′. Here, G0 is the plateau modulus, Gmin′′ is obtained at the local minimum in G″, and le is the entanglement length. The accuracy of the pointer algorithm is supported by the agreement of its predictions with results from a recent application of the slip-spring simulation method to threadlike micelles. Improved fits of the pointer algorithm to the slip-spring results are obtained for weakly entangled micelles (with an average number of entanglements of Z < 15) if the full spectrum of Rouse modes is included in the description rather than just the high-frequency modes included in an earlier version. For sodium laureth-1 sulfate and cocamidopropyl betaine in NaCl solutions, we find scaling relations for micelle length, the plateau modulus, and the persistence length that are in rough agreement with the predictions of mean field theory and with the modified scaling relation in which ⟨L⟩/le is raised to the 0.82 power, rather than unity, that we recommend as an improvement to the original scaling law.

Selective removal of phenanthrene from SDBS or TX100 solution by sorption of resin SP850

Surfactant enhanced remediation (SER) is a promising technology for the removal of hydrophobic organic compounds (HOCs) from contaminated soils. Recycling of soil washing effluent by selective removing of HOCs from surfactant solutions, using techniques such as sorption, is a keyway to reduce the operation costs of SER. In this study, a potential and economical method to recycle washing effluent and lower operation costs of SER, i.e., selective sorption of phenanthrene from an anionic surfactant (sodium dodecylbenzene sulfonate, SDBS) or a nonionic surfactant (Triton X-100, TX100) solution by a resin, SP850, was developed. A modified selectivity parameter (S*), having a parabolic equation with a maximum S* value, was developed to evaluate the efficiency of the selective sorption process, the optimal surfactant concentration and SP850 dose for SER. For example, at the given SP850 dose of 1.0 g/L, the optimal concentrations of SDBS and TX100 for SER are about 15000 mg/L and 8000 mg/L, respectively. Moreover, the optimal added SP850 dose for recycling washing effluents is 1.5 g/L, which is independent of surfactant concentration. At the relatively high concentrations of surfactant used in SER, the selective sorption is depended on the sorption of phenanthrene by SP850 and the solubility enhancement of phenanthrene into surfactant micelles in solutions. The observed recycling soil washing effluent method by selective sorption using resins (e.g., SP850) as the adsorbents would be helpful for the application of SER in remediating contaminated soils.

Stability of Ionic Magnetic Surfactants in Aqueous Solutions: Measurement Techniques and Impact on Magnetic Processes.

Predicting the behavior of magnetic surfactants in magnetic fields is critical for designing magnetically driven processes such as chemical separations or the tuning of surface tensions. The ability of magnetic fields to alter the interfacial properties of magnetic surfactant solutions may be dependent upon the strength of association between the magnetic and surfactant moieties of the surfactant molecules. This research shows that the stability of a magnetic surfactant in an aqueous environment is dependent upon the type of complex that contains the paramagnetic ion, and these findings provide valuable insight for the design of magnetic surfactants for applications in aqueous media. The surfactants investigated were ionic surfactants, which contained paramagnetic counterions. This investigation looked at both anionic and cationic surfactants; it utilized solution conductivity, cyclic voltammetry (CV), sampled current voltammetry (SCV), and solution pH measurements to qualitatively evaluate the stability of the magnetic counterions in aqueous solution. In addition, solution conductivity was used to quantify the degree of binding between the paramagnetic ions and surfactant micelles in solution. These results indicate metal halide-based cationic surfactants are unstable in aqueous solutions. We hypothesize that this instability results in the difference in the magnetic response of the anionic vs cationic surfactants examined in this study.

Analytical description of molecular mechanism of fast relaxation of spherical micelles with the extended Becker–Döring differential equation

To improve and expand kinetic analysis of fast relaxation (via attachments and detachments of surfactant molecules) in an ensemble of spherical micelles in surfactant solutions, a general scheme for reducing the linearized difference Becker–Döring equations to the differential equation of an arbitrary order with respect to the aggregation number is proposed. A perturbation theory is formulated for any model of spherical micelles, where the main approximation corresponds to the kinetic Aniansson equation for the case of a symmetrical potential well of the aggregation work and the perturbation operator is written in the Hermitian form. The latter allows one to use standard perturbation techniques to find the fast relaxation times with the help of extended differential kinetic equation. The calculations were carried out in the second order of the perturbation theory, and the longest fast relaxation times were found as a function of the surfactant concentration for the droplet and the quasi-droplet models of direct spherical micelles and the star model of diblock polymeric spherical micelles. In the case of the droplet model, inclusion of corrections gives the concentration dependence of the longest fast relaxation time that virtually coincides with results of numerical solution of the system of linearized Becker–Döring difference equations. For the quasi-droplet model, the fast relaxation time found in the main approximation considerably deviate from the numerical result (up to 50%). Addition of corrections allows us to reduce these deviations to a considerably smaller value (to 10%). For the star micelle model, a fine agreement between the analytical and numerical solutions is obtained.

0416 界面活性剤による円管内流抵抗低減の流れ方向変化

Drag reduction effect of surfactant solution is caused by SIS(Shear-induced structure). SIS is aggregation of the micelles in surfactant solution. In this study, we experimentally investigated drag-reducing flow using cationic surfactant. The SISs were visualized in turbulent flow to elucidate the induced mechanism and role of a micelle structure in drag reduction. The streamwise changes in the SISs and drag reduction were measured and their relationship was discussed. In our experiment we measured velocity properties and visualized inner flow in upstream and downstream, and there related the results.

Nonlinear kinetics of fast relaxation in solutions with short and lengthy micelles

An analytical treatment of the nonlinear kinetic equations for fast relaxation of coexisting short and lengthy micelles in surfactant solutions is presented. The kinetic equations can be written as a hierarchical set of differential equations for the moments of the aggregation number distribution function of micelles. It is shown that the moment equations can be successively integrated. As examples of the general approach, particular cases of short spherical micelles, lengthy cylindrical micelles, and coexisting short and lengthy micelles have been considered and compared to the results of linear kinetic theory of micellar fast relaxation. The results show that there is a strong interplay between coexisting short and lengthy micelles, even in the case when the total number of surfactant molecules aggregated in short micelles is small in comparison with that in lengthy micelles.

The thermodynamics of micelles in surfactant solution: Lattice mean field theory

The lattice self-consistent mean field theory is applied to study the thermodynamics of micelles in surfactant solution. The model surfactants used are H 4 T 4 and H 2 T 4. The formation of spherical micelles is considered. The effect of the head length on the thermodynamic stability of the micellar solution is examined. The critical micelle concentration is studied at different lengths of head, fractional charge, solvent quality, and univalent salt concentration. A lower critical micelle concentration is associated with a larger aggregation number, while the smallest micelles are found at the lowest univalent salt concentration.

Enhanced soil flushing of phenanthrene by anionic–nonionic mixed surfactant

Laboratory column experiments were conducted to investigate the performance of anionic–nonionic mixed surfactant, sodium dodecyl sulfate (SDS) with Triton X-100 (TX100), in enhancing phenanthrene flushing for contaminated soil in an aim to improve the efficiency of surfactant remediation technology. The experimental results showed that the sorption of TX100 onto soil was severely restricted in the presence of SDS in batch and column experiments and decreased with the increasing mass fraction of SDS in mixed surfactant solutions; meanwhile the enhanced solubilization of phenanthrene by SDS–TX100 mixed surfactant was greater than that by individual surfactant. These results can be attributed to the formation of mixed surfactant micelles in solution. The column flushing experiments showed that the flushing efficiencies for phenanthrene-contaminated soil by SDS–TX100 mixed surfactants were greater than that by individual surfactant and increased with the increasing mass fraction of SDS in mixed surfactant solutions.

Partitioning of polycyclic aromatic hydrocarbons to solid-sorbed nonionic surfactants

The partition of hydrophobic organic compounds (HOCs) into solid-sorbed surfactant has a crucial role in describing and predicting the distribution of HOCs in solid–water–surfactant systems. The experimental results of this study indicated that the partition coefficients of polycyclic aromatic hydrocarbons (PAHs) into the solid-sorbed surfactant ( K sm) increased with an increase in the sorption amount of surfactants onto solid and reached a stable maximum value ( K sm m) at the sorption of surfactants in saturation state, at which the solid surface was completely covered with the surface micelle (or admicelle). The fitted K sm m values for PAHs with different surfactants were found to have a good linear relationship with the corresponding partition coefficient of PAHs to surfactant micelles in solution ( K mc), and then a model was developed to describe and predict the distribution of PAHs in solid–water–surfactant systems. These results are of practical interest for developing effective and safe surfactant-enhanced remediation technologies.

Hydrophilic Inorganic Macro-Ions in Solution: Unprecedented Self-Assembly Emerging from Historical "Blue Waters"

For more than 200 years, the beautiful â��molybdenum blue solutionsâ� have been a puzzle for chemists because they could not determine the molecular structures of the solutes while experiments showing the Tyndall effect proved the presence of â��giant speciesâ�. This problem was finally solved in Bielefeld. As a result of this discovery, novel inorganic clusters belonging to the family of polyoxomolybdates (POMs)�or, generally speaking polyoxometalates�could be synthesized and characterized. These species, usually existing as giant ions in solutions, are fully hydrophilic but still tend to self-associate into supramolecular structures, based on complicated driving forces other than the usual hydrophobic interactions, bringing new progress in the physical chemistry of solutions. Such fascinating solution behaviors are different from those of other well-categorized solutes and suspensions, such as simple ions, polymers, surfactant micelles in solution, and colloidal suspensions. The new results may change some of our common knowledge on inorganic ionic solutions. For example, our fundamental principles on concepts like soluble inorganic ions distribute homogeneously in dilute solutions and soluble ions reach an equilibrium very quickly in dilute solutions might not be valid for large ions. In the future, with additional evidence being accumulated and summarized, macro-ionic solutions might become a separate topic of the chemistry curriculum.

Enhanced desorption of phenanthrene from contaminated soil using anionic/nonionic mixed surfactant

A new approach using an anionic/nonionic mixed surfactant, sodium dodecyl sulphate (SDS) with Triton X-100 (TX100), was utilized for the desorption of phenanthrene from an artificial contaminated natural soil in an aim to improve the efficiency of surfactant remediation technology. The experimental results showed that the presence of SDS not only reduced the sorption of TX100 onto the natural soil, but also enhanced the solubilization of TX100 for phenanthrene, both of which resulted in the distribution of phenanthrene in soil–water systems decreasing with increasing mole fraction of SDS in surfactant solutions. These results can be attributed to the formation of mixed micelles in surfactant solution and the corresponding decrease in the critical micelle concentration of TX100 in mixed solution. The batch desorption experiments showed that the desorption percentage of phenanthrene from the contaminated soil with mixed solution was greater than that with single TX100 solution and appeared to be positively related to the mole fraction of SDS in surfactant solution. Thus, the anionic/nonionic mixed surfactants are more effective for the desorption of phenanthrene from the contaminated soil than a single nonionic surfactant.

The effect of surfactants on the distribution of organic compounds in the soil solid/water system

The efficiency of soil remediation by surfactant washing was evaluated via the measured distribution coefficients of a number of nonpolar compounds in several soil–water mixtures. The studied compounds (contaminants) are BTEX (benzene, toluene, ethylbenzene, and p-xylene) and three chlorinated pesticides (lindane, α-BHC, and heptachlor epoxide), which span several orders of magnitude in water solubility ( S w). A peat, and two natural soils were used that comprise a wide range in soil organic matter (SOM) content. The surfactants tested included cationic, anionic and nonionic types, with concentrations up to five to six times the critical micelle concentration (CMC). The K d * / K d , values were used to evaluate the remediation efficiency under various operation conditions. For relatively water soluble BTEX compounds, the surfactant adsorption on the soil surface is the deciding factor on contaminant desorption from soil. For the less-soluble pesticides, surfactant micelles in solution influence the contaminant desorption more. The contaminants partitioning to SOM or adsorbed surfactants lowers the desorption efficiency. Anionic surfactants are found to be a better choice on soil remediation because they do not form admicelle on soil surface that enhances the SOM content. Cationic surfactant, which adsorb onto soil surfaces, leads to poor remediation efficiency. An improper selection of surfactant would result in inefficiency in soil remediation by surfactant washing.

Heat Transfer Enhancement to the Drag-Reducing Flow of Surfactant Solution in Two-Dimensional Channel With Mesh-Screen Inserts at the Inlet

The heat transfer enhancement of drag-reducing flow of high Reynolds number in a two-dimensional channel by utilizing the characteristic of fluid was studied. As the networks of rod-like micelles in surfactant solution are responsible for suppressing the turbulence in drag-reducing flow, destruction of the structure of networks was considered to eliminate the drag reduction and prevent heat transfer deterioration. By inserting wire mesh in the channel against the flow, the drag-reducing function of the micellar structure in surfactant aqueous solution was successfully switched off. With the Reynolds number close to the first critical Reynolds number, the heat transfer coefficient in the region downstream of the mesh can be improved significantly, reaching the same level as that of water. The region with turbulent heat transfer downstream of the mesh becomes smaller as the concentration of surfactant in the solution increases. Three types of mesh of different wire diameter and opening space were evaluated for their effect in promoting heat transfer and the corresponding pressure loss due to blockage of the mesh. The turbulent intensities were measured downstream from the mesh by using a Laser Doppler Velocimetry (LDV) system. The results indicated that the success of heat transfer enhancement is due to the strong turbulence promoted by the mesh which destroys the network of rod-like micelles by applying high shear stress and thus relaxing the shear induced state (SIS).

The Shape and Properties of Mixed Micelles in Surfactant Solutions of Tetradecyldimethylaminoxide and Tetradecyltrimethylammoniumbromide in the L1 Phase: The Influence of Ionic Charge Density and Cosurfactant Concentration

Aqueous surfactant solutions of tetradecyldimethylaminoxide (TDMAO) and tetradecyltrimethylammoniumbromide (TTMAB) in the presence of increasing amounts of hexanol were studied in the L 1-phase region. TDMAO forms rod-like and TTMAB globular micelles in the concentration range between 50 and 100 m M. In all mixtures with a mol fraction X c > 0.1 of cationic surfactant globular micelles are found. Hexanol was added to the surfactant mixtures until the phase boundary of the L 1 phase was reached. The micellar structures and the properties of the surfactant solutions were studied with surface and interfacial tension, electric birefringence, viscosity, and conductivity measurements. A sphere-rod transition was observed in all surfactant mixtures with increasing hexanol concentration. In the pure cationic system globular micelles were observed with increasing mol fraction of alcohol X a, up to the phase boundary. Electric birefringence measurements turned out to be most sensitive to the sphere-rod transition. The hexanol concentration which was necessary to reach the sphere-rod transition increased continuously with X c . The concentration of hexanol to reach the phase boundary increased also. The viscosities, the rotational time constants, and the Kerr constants of the mixed surfactant solutions increased exponentially with the hexanol concentration from the sphere-rod transition to the phase boundary. The viscosity which was reached close to the phase boundary decreased with increasing mol fraction of the cationic surfactant. The lengths of the rods at the phase boundary which were determined from the electric birefringence measurements decreased with increasing X c. The persistence length for all charged and unshielded rods seems to be longer than their total length and the rods under these conditions can be visualized as being stiff. The surface and the interfacial tension for all micellar solutions decreased in a similar fashion with increasing X a. Independently of X c the interfacial tension of the micellar solution measured against decane, reached a value of about 0.2 mN/m at the phase boundary. The surface tension was around 25 mN/m and also more or less independent on the surfactant ratio.

Measurement of concentrations of micelles in solutions of surfactants and their micellar masses by a light-scattering method

Measurement of concentrations of micelles in solutions of surfactants and their micellar masses by a light-scattering method

Nonequilibrium electrodialysis of aqueous solution of sodium dodecyl sulfate

Special dialysis apparatus was constructed which enabled to trace a short time nonequilibrium dialysis by the continuous measurement of electric resistance of dialyzing solution. The apparatus is particularly suited for the study of the formation of micelles in surfactant solution. The dialysis curves were constructed by plotting the change of electric resistance against dialysis time. The diagrams consisted of a nearly straight line at low concentration and two nearly straight lines above a certain concentration, from which CMC was sharply determined and the constancy of a single ion concentration above CMC was also demonstrated.