Nonionic Surfactant Systems Research Articles

Surfactant-mediated gelation by 12-hydroxyoctadecanoic acid in a nonionic surfactant system

In this study, we present a hydrogel fabrication utilizing a water-insoluble, low-molecular-weight organogelator by the surfactant-mediated gelation (SMG). Specifically, we employed a nonionic surfactant (poly(oxyethylene) sorbitan monooleate, Tween 80) and an organogelator (12-hydroxyoctadecanoic acid, 12-HOA) to produce hydrogels. Gelation experiments conducted at varying concentrations of surfactant and gelator demonstrated successful hydrogel formation in the water/Tween 80/12-HOA system. Moreover, we observed a significant dependence of surfactant concentration on gelation ability. The sol-gel transition temperature was found to be influenced by both the gelator and surfactant concentrations. Optical and electron microscopy analyses revealed that the SMG hydrogels comprised an entangled network of fibers with micrometer-scale widths, formed as bundles of submicron-wide fibers, and further composed of fine fibers measuring several tens of nanometers in width. These fine fibers exhibited a left-handed helical structure. Small- and wide-angle X-ray scattering corroborated the presence of a lamellar structure within the fine fibers, displaying a triclinic subcell morphology. The coexistence of micelles with the fiber network was confirmed through small-angle neutron scattering and UV–vis spectroscopy. Furthermore, dynamic viscoelasticity tests demonstrated that the SMG hydrogels exhibited typical solid-like properties indicative of gel behavior.

Chemical strategies for enhancing CO2-Hydrocarbon miscibility

Carbon dioxide (CO2) flooding holds immense potential for enhancing hydrocarbon recovery and facilitating geological carbon storage. Among CO2 flooding methods, miscible flooding demonstrates significantly higher production compared to immiscible flooding. However, in certain reservoirs, the high miscibility pressure presents a challenge for achieving miscibility under reservoir pressure conditions. Nonionic surfactants offer a solution by reducing the miscibility pressure in hydrocarbon-CO2 systems. In this study, eight nonionic surfactants were assessed, and two of the most effective surfactants were selected. These surfactants were combined to create a novel nonionic surfactant system aimed at lowering the miscibility pressure. The minimum miscibility pressure (MMP) of the hydrocarbon-CO2 system was measured using a slim-tube experiment, and a comparative analysis was conducted between the vanishing interfacial tension method (VIT) and the slim-tube method. Furthermore, the microscopic mechanism by which surfactants reduce the miscibility pressure was studied and analyzed. The findings indicate that the compound nonionic surfactant SF, with a total concentration of 1.0 wt% and a SMF to Span20 ratio of 1:1, reduces the miscibility pressure by 18.30%. The slim-tube data were processed to obtain a narrower range for MMP using criteria such as the crude oil recovery factor (ORF) and the break-over pressure (BOP). The maximum error between MMP measured by the VIT method and the slim-tube experiment is 5.86%, demonstrating the high accuracy of the VIT method in this study. The surfactant effectively reduces the miscibility pressure by decreasing the interfacial tension (IFT) between oil and gas, enhancing the CO2 extraction efficiency on intermediate hydrocarbons within the crude oil, and improving the solubility of CO2 in the crude oil. The findings of this study hold significant guidance for future investigations on the miscibility in the processes of geological CO2 utilization and storage.

A dilute nematic gel produced by intramicellar segregation of two polyoxyethylene alkyl ether carboxylic acids

MotivationSurfactants like C8E8CH2COOH have such bulky headgroups that they cannot show the common sphere-to-cylinder transition, while surfactants like C18:1E2CH2COOH are mimicking lipids and form only bilayers. Mixing these two types of surfactants allows one to investigate the competition between intramicellar segregation leading to disc-like bicelles and the temperature dependent curvature constraints imposed by the mismatch between heads and tails. ExperimentsWe establish phase diagrams as a function of temperature, surfactant mole ratio, and active matter content. We locate the isotropic liquid-isotropic liquid phase separation common to all nonionic surfactant systems, as well as nematic and lamellar phases. The stability and rheology of the nematic phase is investigated. Texture determination by polarizing microscopy allows us to distinguish between the different phases. Finally, SANS and SAXS give intermicellar distances as well as micellar sizes and shapes present for different compositions in the phase diagrams. FindingsIn a defined mole ratio between the two components, intramicellar segregation wins and a viscoelastic discotic nematic phase is present at low temperature. Partial intramicellar mixing upon heating leads to disc growth and eventually to a pseudo-lamellar phase. Further heating leads to complete random mixing and an isotropic phase, showing the common liquid–liquid miscibility gap. This uncommon phase sequence, bicelles, lamellar phase, micelles, and water-poor packed micelles, is due to temperature induced mixing combined with dehydration of the headgroups. This general molecular mechanism explains also why a metastable water-poor lamellar phase quenched by cooling can be easily and reproducibly transformed into a nematic phase by gentle hand shaking at room temperature, as well as the entrapment of air bubbles of any size without encapsulation by bilayers or polymers.

Effect of a nonionic surfactant and anionic polyelectrolyte binary system on the stability of a calcium and magnesium carbonates dispersion

The effect of sodium polyacrylate, polyethylene glycol of various molecular weights, and their mixtures on the dispersion stability of calcium and magnesium carbonates was studied. It was shown that in the presence of a binary system, the light transmission of the dispersion decreases 1.2–1.5 times, the content of fine fraction particles increases by 1.1–1.3 times compared to the individual components. The stability of the dispersion of carbonates depends on the components ratio in the binary system and their molecular weight. The formation of adsorption solvated layers of polyacrylate and polyethylene glycol molecules at the interphase boundary contributes to an increase in the stability of the carbonate dispersion.

Compound Anionic–Nonionic Surfactant System with Excellent Temperature and Salt Resistance for Enhanced Oil Recovery

Compound Anionic–Nonionic Surfactant System with Excellent Temperature and Salt Resistance for Enhanced Oil Recovery

Anionic-nonionic and nonionic mixed surfactant systems for oil displacement: Impact of ethoxylate chain lengths on the synergistic effect

Compound surfactant system has been extensively studied in enhanced oil recovery (EOR) as the synergistic effect of mixed surfactants can increase the density of surfactants distributed at the oil/water interface, enhancing the interfacial activity and decreasing the interfacial tension. The system can further increase the capillary number and enhance oil recovery for oil-wet reservoirs. Studying the interactions between surfactant molecules is of great significance to the enhancement of practical application performances. In this study, N, N-dihydroxyethyl alkyl amide (CDEA), and Alkylphenol polyoxyethylene carboxylate (APEC) with different EO numbers were mixed to prepare a binary compound oil displacement system. The influence of the EO number on the synergistic effect of the CDEA/APEC system and the EOR potential was measured by interfacial tension, nanomechanical tests and oil-displacement experiments. The results indicate a synergistic effect between CDEA and APEC due to the formation of hydrogen bonds between the hydroxyl groups of CDEA and the EO chains of APEC. An optimal synergistic effect in the system was obtained when the EO number was four. The CDEA/APEC-4 system exhibited an oil/water interfacial tension decrease to 10−2 mN/m at 75 °C and the oil recovery was 57.14 %, which was increased by 19.2 % compared to primary water flooding. However, a longer EO chain length weakened the interaction forces between CDEA and APEC, which diminished the synergistic effect of the system, leading to an increase of the interfacial tension. Due to the flexibility of the EO chain, the increase in the EO number leads to the bending of APEC molecules. The longer EO chain length weakened the interaction forces between CDEA and APEC, which diminished the synergistic effect of the system, leading to an increase of the interfacial tension. The oil-displacement experiment revealed that the EO chains changed the oil recovery and injection pressure by affecting the interfacial tension of the mixed system. This study has significant implications for the formulation design and optimization of agents for oilfield development.

A model for water sorption isotherms and hydration forces in sugar surfactants

HypothesisHydration forces between surfactant bilayers can be assessed using water sorption isotherms of surfactants. For a quantitative description, a water sorption model that relates water activity to water content in surfactant-based systems should be proposed. Theory and simulationsA water sorption model for nonionic surfactant systems based on the idea on partial solvent accessibility is proposed. The model contains only two parameters: one describes the strength of interactions, the other describes the fraction of surfactant available for water. For comparison, molecular dynamics simulations of bilayers of n-octyl β-d-glucoside with different water contents are presented. FindingsThe model provides an excellent fit of experimental data on water sorption isotherms of two sugar surfactants. The results of the fitting are compared with molecular dynamics simulations and show a good correlation between simulations and the theory proposed. Analysis of interaction energies shows weakly endothermic hydration both in the simulations and in the sorption model, which agrees with calorimetric data on hydration. The model also shows a non-exponential decay of hydration forces with respect to the distance between bilayers; an expression for the decay length is derived.

Effect of mixed nonionic surfactants on microemulsion phase boundary, fuel property, and engine performance of biofuels

Microemulsion biofuels can become one of alternative biodiesels using suitable nonionic surfactants and cosurfactant to emulsify vegetable oil and ethanol with the appropriate formulae. Without the further chemical improvement, the low volatility and high viscosity because of triglycerides in vegetable oil can cause a serious problem in engine operation. This work proposed a systematic investigation of microemulsion biofuel prepared from rice bran oil and ethanol using mixed nonionic surfactant systems (Dehydol LS7, Tween 80, and Span 80) as surfactant (S) and 1-octanol as a cosurfactant (C) at molar ratio of 1:30. Microemulsion phase behaviors can be examined through the ternary phase diagram of rice bran oil, ethanol, and S:C. It was observed that Dehydol LS 7 was poor in solubilization of rice bran oil and ethanol because of their preference in hydrophilic compounds rather than lipophilic compounds. Introduction of Tween 80 or Span 80 into the biofuels using Dehydol LS 7 enhanced the solubilization of these systems as the extent of single-phase boundary was significantly enlarged because of the hydrophilic–lipophilic balance of the mixture and chemical structure of surfactants. The fuel properties of microemulsion biofuel were investigated through kinematic viscosity, specific gravity, flash point, cloud point, pour point, and higher heating value. It was found that mixed surfactant also improved some fuel properties due to additional surfactants contain many oxygenated functional groups, however, some parameters were slightly substandard. The combustion characteristics and exhaust emission were investigated in CI diesel engine. It was observed that the in-cylinder pressure was lower under the combustion of microemulsion fuel mainly due to the high latent heat of vaporization of alcohols. The start of combustion was more retarded with the addition of Span 80, especially at low load condition. It was observed that the significant reduction in nitrogen oxides was achieved with the combustion of microemulsion fuel while unburnt hydrocarbon emissions were higher compared to diesel fuel. The obtained experimental data showed that microemulsion biofuels can be a promising alternative biodiesel although the individual usage in engine was slightly less efficient than commercial diesel fuel.

Assessing nanoparticle-surfactant-salt synergistic effects on droplet–droplet electrocoalescence by molecular dynamics simulations

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in-oil emulsions. In this paper, the coalescence behaviors of nanoparticle/surfactant/salt-laden water droplet pairs under direct current (DC) electric fields were investigated by molecular dynamics (MD) simulations. Good qualitative agreements of the present simulations and literature results were obtained. The effects of electric field strengths, surfactant concentrations, and surfactant types on the nanoparticle/surfactant/salt-laden water droplet pair electrocoalescence process were systematically examined, analyzed, and discussed. The results show that the nanoparticle-surfactant-salt synergistic effects mainly include two mechanisms, i.e., the electrostatic interactions of salt ions and surfactant head groups, and the hydrogen bonds of the heteroatoms and water molecules. In addition, strong electric fields lead to high electrocoalescence speed, while weak electric fields result in high electrocoalescence efficiency. At high surfactant concentrations, viscoelastic rigidity of the interface can suppress coalescence, and the aggregations accumulated on the interface result in a significant steric hindrance effect, accounting for the shortest approaching and coalescing time at surfactant number around one single droplet SN = 30 in SDS systems. Regarding the influence of surfactant types, the coalescence efficiencies of the investigated surfactant systems ranked as SDS > Span-80 > Triton X-100 > CTAB. Regarding the nanoparticle-surfactant-salt synergistic effects, in ionic surfactant (CTAB and SDS) systems, the sum of SiO2-Surfactant and Surfactant-NaCl synergistic effects generally dominated the electrocoalescence process; in nonionic surfactant (Span-80 and Triton X-100) systems, the synergistic effects can be generally ranked as SiO2-Surfactant > SiO2-NaCl > Surfactant-NaCl. The results of this work will be potentially valuable for optimizing the design of compact and efficient oil–water separators.

Assessing the performance of foams stabilized by anionic/nonionic surfactant mixture under high temperature and pressure conditions

Foam flooding is an effective tertiary recovery method for oil and gas reservoirs. However, foam performance is very sensitive to the reservoir temperature and pressure. In this study, the formation and collapse of a water-based foam stabilized by a mixed ionic and nonionic surfactant system under typical reservoir conditions (up to 150 °C and 50 MPa) were investigated. A multifunctional foam analyzer, an interfacial rheometer, and a coiled tube are used to assess foam microstructure, surface tension and bulk viscosity under 25 – 80 °C and 0.1 – 10 MPa. Results show that the foam comprehensive value is highest under low temperature and high pressure. With increasing temperature, the gas bubbles become larger, fewer in number, and more irregular in shape coupled with a thinner liquid film. Increased pressure, on the other hand, decreases the bubble size, increases the number of bubbles and contributes to a more uniform and dense foam. At constant temperature, the surface tension decreases as the pressure increases, while at constant pressure, a minimum surface tension is observed with increasing temperature, which in turn increased with increasing pressure. Foam viscosity displayed an opposite trend to that of the surface tension. Understanding the variation of foam properties with temperature and pressure is key toward successful application of foam flooding.

Kelarutan Zat Warna Organik dalam Gelasi Mikroemulsi Water In Oil dari Sistem Air, Surfaktan Nonionik (Brij 35) dan Pentanol

Research on solubility from organic pigments of turmeric (Curcuma longa Linn) and telang flower (Clitoria ternatea L.) in water-in-oil microemulsion gelation on system of water, nonionic surfactant (Brij 35) and pentanol has been studied. The purpose of this research was the preparation of water-in-oil microemulsion gelation, determines solubility, density, and bias index of organic pigments in water-in-oil microemulsion gelation on system of water, nonionic surfactant (Brij 35) and pentanol. The method used is the sol-gel method. The solubility in water-in-oil microemulsion gelation of turmeric is 2,41832% (pH 4,5) and 2,61402% (pH 9,5) and telang flower is 1,21274% (pH 4,5) and 1,6136% (pH 9,5). The bias index of turmeric is 1,4024 (pH 4.5) and 1,4034 (pH 9,5) and telang flower is 1,4004 (pH air 4,5) and 1,4014 (pH 9,5).The density of turmeric is 0,88778g/cm3 (pH 4,5) and 0,88912g/cm3 (pH 9,5) and telang flower is 0,8793g/cm3 (pH 4,5) and 0,8872g/cm3 (pH 9,5).

Key factor of sponge phase formation in commercial polyethoxylated nonionic surfactant/cosurfactant/water systems and its unique feature at interface

A sponge phase is particularly interesting in terms of its features, such as its transparency, low viscosity, low interfacial tension and so on. However, most past research on the sponge phase have focused on pure surfactants, whereas little research exists on commercial polyethoxylated nonionic surfactants that are used in cosmetics and household products. The reason is attributed to the polyethyleneoxide, hydrophilic group of nonionic surfactants, having large distributions in polymerization degree, resulting in many irregular behaviors in the phase equilibrium. In this study, the phase sequence of the sponge phase formation in a commercial polyethoxylated nonionic surfactant/cosurfactant/water system was investigated based not only on HLB, but also on the distribution of polymerization degree of the hydrophilic group to reveal the irregularity of the phase sequence. As a result, in commercial nonionic surfactant systems, the important points for sponge phase formation were revealed to be (1) selecting a surfactant having intermediate HLB, and (2) selecting a structure with sufficient lipophobicity. These factors are for preventing cosurfactant phase separation that is attributed to the wide distribution of polymerization degree of polyethyleneoxide groups. Furthermore, we demonstrated the phenomenal wetting behavior on a hydrophobic surface with unevenness and clarified that the low interfacial tension and low viscosity of the sponge phase among various self-assembling structures were the critical for the wetting behavior.

Aqueous, Mixed Micelles as a Means of Delivering the Hydrophobic Ionic Liquid EMIM TFSI to Graphene Oxide Surfaces

Most ionic liquids (ILs) are not surface-active and cannot, alone, be directed to assemble at surfaces─despite their potential as nonvolatile structure-directing agents and use as advanced materials in a multitude of applications. In this work, we investigate aqueous systems of common nonionic surfactants (Triton X-100 and Tween 20), which we use to solubilize 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The resulting solution of mixed micelle leads to spontaneous adsorption of the IL/surfactant complex onto graphene oxide (GO) surfaces, forming a compact film. Adsorption isotherms generated by fluorescence labeling of the IL and surfactant phases are used to quantify the extent of adsorption. While sensitive to the GO dispersion concentration, upwards of 3 g IL/g GO adsorb under dilute conditions. Atomic force microscopy is used to show that the adsorbed layer uniformly distributes as an ∼1 nm thick coating (per GO side) as the system reaches the first plateau of a Langmuir-type isotherm. Adsorption beyond this plateau is possible but leads to thicker (>30 nm), inhomogeneous adsorbed layers. Both micellar size in solution and adsorbed layer thickness reduce upon the addition of IL to the surfactant phase, suggesting significant interactions among the materials and nonideal mixing of the components.

Combining Active Carbonic Anhydrase with Nanogels: Enzyme Protection and Zinc Sensing.

BackgroundDue to its excellent biocompatibility, the polyacrylamide (PAAm) hydrogel has shown great potential for the immobilization of enzymes used in biomedical applications. The major challenge involved is to preserve, during the immobilization process, both the biological activity and the structural integrity of the enzymes. Here we report, for the first time, a proof-of-concept study for embedding active carbonic anhydrase (CA) into polyacrylamide (PAAm) nanogels. By immobilizing CA in these nanogels, we hope to provide important advantages, such as matrix protection of the CA as well as its targeted delivery, and also for potentially using these nanogels as zinc nano-biosensors, both in-vitro and in-vivo.Methods and ResultsTwo methods are reported here for CA immobilization: encapsulation and surface conjugation. In the encapsulation method, the common process was improved, so as to best preserve the CA, by 1) using a novel biofriendly nonionic surfactant system (Span 80/Tween 80/Brij 30) and 2) using an Al2O3 adsorptive filtration purification procedure. In the surface conjugation method, blank PAAm nanogels were activated by N-hydroxysuccinimide and the CA was cross-linked to the nanogels. The amount of active CA immobilized in the nanoparticles was quantified for both methods. Per 1 g nanogels, the CA encapsulated nanogels contain 11.3 mg active CA, while the CA conjugated nanogels contain 22.5 mg active CA. Also, the CA conjugated nanoparticles successfully measured free Zn2+ levels in solution, with the Zn2+ dissociation constant determined to be 9 pM.ConclusionThis work demonstrates universal methods for immobilizing highly fragile bio-macromolecules inside nanoparticle carriers, while preserving their structural integrity and biological activity. The advantages and limitations are discussed, as well as the potential biomedical applications.

En route to single-step, two-phase purification of carbon nanotubes facilitated by high-throughput spectroscopy

Chirality purification of single-walled carbon nanotubes (SWCNTs) is desirable for applications in many fields, but general utility is currently hampered by low throughput. We discovered a method to obtain single-chirality SWCNT enrichment by the aqueous two-phase extraction (ATPE) method in a single step. To achieve appropriate resolution, a biphasic system of non-ionic tri-block copolymer surfactant is varied with an ionic surfactant. A nearly-monochiral fraction of SWCNTs can then be harvested from the top phase. We also found, via high-throughput, near-infrared excitation-emission photoluminescence spectroscopy, that the parameter space of ATPE can be mapped to probe the mechanics of the separation process. Finally, we found that optimized conditions can be used for sorting of SWCNTs wrapped with ssDNA as well. Elimination of the need for surfactant exchange and simplicity of the separation process make the approach promising for high-yield generation of purified single-chirality SWCNT preparations.

Особенности солюбилизирующего действия амфифильных соединений при обессмоливании целлюлозы

The necessity to improve the existing technology of pulp deresination, in particular, to reduce the surfactants consumption and decrease the environmental load, led to a combination of existing methods of resin removal with the use of enzymatic treatment. The basis of the pulp deresination mechanism by amphiphilic compounds is the solubilization of resinous substances. Thus, the establishment of the patterns of this process and its control predetermines the success of implementation of the selected technology. The features of solubilization of triolein and rosin in the lipase-based systems of individual nonionic surfactants, the enzyme, as well as their synergistic mixtures with the determination of solubilization capacities of micelles and the possible mechanism of solubilizate incorporation into them were studied using spectrophotometry, pH measurement and dynamic light scattering. It was found that synthamide-5 has a low deresination capability in spite of the high solubilization capacity of its micelles and the production of aggregates with a hydrodynamic radius up to 98 nm after diffusion of rosin into them. It is likely that compact micellar structures with a developed surface, which are implemented in mixed systems of amphiphilic compounds, including the presence of synthamide-5 in them, are more preferable for successful deresination of pulp semi-finished products. The addition of lipase leads to an increased solubilization capacity of mixed aggregates and an increase in the intensity of solubilizate molecules incorporation. Thus, depending on the nature of the amphiphilic compound, there is a different mechanism for solubilizate incorporation into micelles. Determination of the size of associates in mixed systems showed the absence of enzyme denaturation, which predicts the successful application of such cooperative systems for deresination of fiber semi-finished products. It is found that the solubilizing capability of the studied systems on resin modeling objects correlates with their deresination capability with respect to different fiber semi-finished products.

Effect of Ethylene Oxide Group in the Anionic–Nonionic Mixed Surfactant System on Microemulsion Phase Behavior

AbstractThe phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12‐14 alcohol ethoxylate (C12 − 14Ej) that contains an ethylene oxide (Ej) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C12 − 14Ej systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C12 − 14E1 was more lipophilic, while SDHS − C12 − 14E9 was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C12 − 14E5 system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.

Quantitative analysis of micellar effect on the reaction rate of cationic triphenylmethine dyes with water according to Berezin’s model

Several approaches quantitatively describe the effect of surfactant micellar solution on the reaction rate. The most used among them are Piszkiewicz’s, Berezin’s, and Pseudophase Ion-Exchange (PIE) models. The last-named was developed by Bunton and Romsted. Piszkiewicz’s model is based on representations of the micellization according to the mass action law with the formation of a catalytic micelle, which consists of some surfactant molecules and a substrate. In our previously paper, this model was used to explain the kinetic micellar effect on the reaction of cationic triphenylmethine dyes with water once again showed the main disadvantages of this approach. Berezin’s model is based on another model of micelle formation viz. the pseudophase model, and the binding of reagents by micelles is considered as the distribution of a substance between two phases. In this work, we aim to consider the applicability of Berezin’s approach for the interaction of malachite green and brilliant green cations with water molecule as a nucleophile in aqueous systems of nonionic, anionic, cationic, and zwitterionic surfactants. On the whole, Berezin's model performed well when applied to the description of the micellar effect on the reaction of similar dye with the hydroxide ion. However, it was revealed that this model does not take into account the change in the local concentration of the HO– ions due to a compression of the double electric layer upon addition of reacting ions to the system, as well as the constant of association of the HO– ions with cationic head groups of surfactant. In this case, when water is used as a nucleophile, the question of the degree of nucleophile binding can be solved differently. The PIE model is also based on a pseudophase model of micellization, but a substrate binding by micelles is considered as an association in a stoichiometric ratio of 1:1, and a nucleophile concentration is expressed in a local concentration based on the neutralization degree of micelles. Given the latter, its approach cannot be applied to the kinetic micellar influence on the reaction of cationic triphenylmethine dyes with water.

FLUORESCENCE CHARACTERISTICS OF RHODAMINE 6G AND RHODAMINE C IN WATER-MICELLAR SURFACTANT ENVIRONMENTS

The influence of cationic, anionic, nonionic surfactants and their mixtures on the fluorescence characteristics of rhodamine 6G and Rho-damine C solutions has been investigated. The fluorescence intensity of aqueous solutions of rhodamine 6G and in the presence of cetylpyridinium chloride and sodium dodecyl sulfate has almost unchanged throughout the pH range. The fluorescence intensity of aqueous and water-micellar rhodamine C solutions has been increased in the pH 1-4 range; the signal has been remained unchanged at high pH values. The studies have been carried out at pH 4 for rhodamine 6G and at pH 10 for rhodamine C. The fluorescence characteristics of water-micellar dye - surfactant - non-ionic surfactant systems have been performed at a concentration of Triton X-100 of 3.4·10‑2 mol/l. The interaction with cationic surfactants has shown differences character between the I=f(n) dependences for aqueous solutions of highly hydrophobic rhodamine 6G and more hydrophilic rhodamine C. The study of the effect of the hydrocarbon radical length on the intensity of the fluorescence of rhodamine 6G and rhodamine C has been carried out at two concentrations of cationic surfactants: under the condition of the formation of stoichiometric associates dye with cationic surfactant and in the region of the micellar concentrations of cationic surfactants. The character of the influence of the length of the hydrocarbon radical cationic surfactants on the fluorescence intensity of the dyes can be explained by the increasing role of hydrophobic interactions and the enhancement of solubilization in systems involving long-chain surfactants. The difference in the nature of the associates of rhodamine 6G and rhodamine C with hydrophobic and moderately hydrophobic cationic surfactants has been counterbalanced in the presence of Triton X-100. Reduction of fluorescence intensity of rhodamine 6G in domicile solutions of anionic sodium dodecyl sulfate has been established. The method of fluorescence detection of sodium dodecyl sulfate in reaction with rhodamine 6G has been proposed. The method has been tested in determining of anionic surfactants in the waters after washing clothes.

Co-solubilization of polycyclic aromatic hydrocarbon mixtures in aqueous micellar systems and its correlation with FRET for enhanced remediation processes.

Surfactant enhanced remediation (SER) is an effective approach for decontaminating the PAH polluted soils. Solubilization and Cosolubilization of Phenanthrene (Ph), Pyrene (Py) and Perylene (Pe) as single, binary and ternary mixtures have been studied employing cationic (CTAB), anionic (SDS), non-ionic surfactant (Brij 30) and block copolymer (P123) micelles. In the single solute solubilization studies, solubility of Pe follows the order Brij 30 > CTAB > SDS whereas Ph or Py followed the order of CTAB > Brij 30 > SDS. In the cosolubilization studies, an increase, decrease or no change in the mutual solubility of PAHs was observed. Synergism in solubilization was observed most in P123 in both binary and ternary PAH mixture where more PAHs could get solubilized in the dense micellar shell region, thereby enhancing the micellar core volume leading to enhanced solubilization of PAHs. The solubilizates as pairs (Ph-Pe and Py-Pe) were further tested for any possible energy transfer in presence of surfactant based restricted host environments using spectrofluorometry and spectrophotometry. Based on the solubilization and cosolubilization an efficient non-radiative energy transfer (FRET) was observed between Ph/Py (donor) and Pe (acceptor) in the non-ionic surfactant system as well as in CTAB-Brij 58 mixed system. The results of this work may improve the effective utilization of surfactants in their correct evaluation for the removal of PAHs from contaminated soils or aquifers treated with SER technology.