Anionic Aerosol OT Research Articles

Ultrafast Excited-State Proton Transfer of a Cationic Superphotoacid in a Nanoscopic Water Pool.

The excited-state proton transfer (ESPT) of a cationic superphotoacid, N-methyl-7-hydroxyquinolium, was studied within the water pool of an anionic aerosol-OT (AOT), bis(2-ethylhexyl) sulfosuccinate, reverse micelle (RM). Previously, we had found that the cationic photoacid residing at the anionic AOT interface was conducive to ESPT to the bound water having concentric heterogeneity on the time scale of hundreds of picoseconds to nanoseconds. In our present study, on the time scale of hundreds of femtoseconds to a few tens of picoseconds, the photoacid underwent an ultrafast ESPT influenced by mobile water constituting the core of the RM. The two subpopulations of the core water molecules that determine the ultrafast biphasic deprotonation of the photoacid on time scales differing by an order of magnitude were identified. The core water molecules solvating the counteranion of the photoacid showed a higher basicity than typical water clusters in bulk resulting in ESPT on a subpicosecond time scale. Bare water clusters sensed by the photoacid showed a slower ESPT, over several picoseconds, as typically limited by the rotational motion of water molecules for similar types of the photoacid.

Investigation of NLO Properties of Eriochrome Black T Colloidal Solution: Role of Surfactant and Reverse Micelles

The photophysical and nonlinear optical properties of Eriochrome Black T (EBT) in micelles, with two charge types of surfactant and reverse micelles (RMs) in a wide range of sizes, were investigated via ultraviolet–visible absorption, fluorescence spectroscopy, and a Z-scan technique. Accordingly, a significant redshift in absorbance and fluorescence quenching of the EBT was observed with an increase in cetyltrimethylammonium bromide (CTAB) concentration. Comparably, the nonlinear absorption coefficient (β) of the EBT decreased following an increase in cationic CTAB concentration, due to an increasing trend in the CTAB:EBT complex in the solution, and it decreased following an increase in anionic aerosol OT concentration. The same behavior was further detected for the nonlinear index of refraction (n2). The β value of the EBT also decreased with an increase in the size and concentration of the RMs, while the n2 was enhanced.

Residence and diffusion of a dynamically prototropic hydration probe in AOT reverse micelles

We investigated the hydration dynamics in the nanosized water pool of an Aerosol-OT (AOT) reverse micelle (RM) using a prototropic (proton-donating) fluorescent dye, N-methyl-7-hydroxyquinolinium (NM7HQ+), as the probe. NM7HQ+ is a photoacid, and the deprotonation of its excited-state cationic form (C*) gives rise to a neutral keto species (K*). In the present study, the residence sites of C* and K* in water pools of various sizes were determined by monitoring their time-resolved fluorescence anisotropy. Additionally, the evolutions of the C* and K* bands in the time-resolved fluorescence spectra were analyzed by fitting the spectra to the sum of two lognormal peak functions. The time-dependent spectral shifts of the species with different formal charges revealed the characteristic hydration behavior at the interface of the anionic AOT headgroups and the bound water region, as well as the rotational and translational diffusion of the probe within the RM.

Interactions and Solubilization of Poorly Soluble Drugs in Aerosol‐OT Micelles

AbstractAbsorption spectroscopy, conductivity, and surface tension measurements were carried out at 298 K to study the solubilization of poorly soluble drugs sulfamethoxazole (SMX) and trimethoprim (TMP) in Aerosol‐OT (AOT) micellar media. The binding constants of SMX and TMP to AOT micelles were determined by applying the Benesi–Hildebrand equation. A comparison of the binding constants indicates that the binding tendency of TMP with AOT micelles is higher than that of SMX. To better analyze the incorporation of drugs into anionic AOT micellar media, surface tension measurements were performed in the presence of SMX and TMP in aqueous media. The influence of TMP and SMX on the surface properties of AOT was determined using the Gibbs Adsorption Isotherm. Changes in the surface properties of AOT determined by surface tension measurements in the presence of drugs are in good agreement with the binding constants determined spectrophotometrically. Calculated surface parameters indicate higher incorporation of TMP with AOT than that of SMX. Comparison of the aqueous solubility of TMP and SMX with micellar media indicated solubility enhancements for both poorly soluble drugs. A special attempt was made to highlight simultaneous interactions of TMP and SMX with AOT using both surface tension and conductometric measurements that can be used to determine counterion‐binding parameters.

Different locations of adenine in AOT and CTAB reverse micelles

We explore the locations of adenine encapsulated in the anionic Aerosol-OT (AOT) and cationic cetyltrimethylammonium bromide (CTAB) reverse micelles (RMs) utilizing steady-state spectroscopy and molecular dynamics simulations. In AOT RMs with various water contents, adenine forms stacked conformers at the AOT/water interface, determined by the appearance of emission from adenine excimers and molecular dynamics simulations. In contrast, adenine resides in the water core of CTAB RMs without the formation of stacked conformers. The interbase distance of stacked adenines at the AOT/water interface has a significant fluctuation, especially in RMs of low water content. Hydrogen bonding interactions between adenine and AOT molecules play a role in the formation of stacked adenines.

Selective cationic surfactant detection in aqueous solution by polyurethane copolymer linked with metal ion indicator

Polyurethane (PU) copolymer is laterally linked with three kinds of metal ion indicator (calcein, calmagite, or eriochrome black T), with which free metal ion in aqueous solution is intended to be detected by PU color change. Metal ion detection by the indicator-PU fails due to the poor permeation of hydrophilic metal ion into hydrophobic PU layer. Instead, three surfactants with different ionic head groups, aerosol OT (AOT), cetyltrimethylammonium bromide (CTAB), and sodium dodecylsulfate (SDS), are tested for metal ion. Cationic CTAB exhibits an instant PU color change, but anionic AOT and SDS do not respond at all. Reason for the selective detection of cationic surfactant is the complex formation between cationic surfactant and indicator. Molecular interactions between PUs are affected by the laterally linked indicators based on the results by infrared spectra and differential thermal analysis. UV-vis spectra reveal that extra peak arising from the linked indicator appears compared to plain PU. The lateral linking of indicator to PU demonstrates, as well as the selective surfactant detection, a 454 % increase in tensile strength and reproducible shape recovery as high as 99 % compared to plain PU.

Clouding behavior of nonionic–cationic and nonionic–anionic mixed surfactant systems in presence of carboxylic acids and their sodium salts

The study is focused on evaluation of clouding phenomena of the aqueous single nonionic surfactant system Triton X-100 (TX-100) and its mixed systems with anionic aerosol-OT (AOT) and cationic dodecylpyridinium chloride (DPC) in presence of hydrophobic ions furnished by sodium salts of carboxylic acids, viz., sodium ethanoate, sodium propanoate, sodium butanoate, and sodium hexanoate and the respective carboxylic acids [ethanoic acid, propanoic acid, butanoic acid, and hexanoic acid]. The influence of salts on the cloud point (CP) has been explained on the basis of salt effect as well as the solubilization of higher alkyl chain hydrophobic ions furnished by these salts. Moreover, the co- and counterion effect has been taken into account to explain the variation of the CP in the mixed systems. However, the effect of acids on CP has been explained in the light of their aqueous solubility and their partitioning ability between octanol and water as reflected by their K OW values.

Synthesis of CdS and Alloyed CdMnS Nanocrystals Using Aqueous Foams

Certain surfactant-stabilized aqueous foams provide a potentially efficient and simple chemical route for the synthesis of various nanomaterials with controllable structure, size, and shape. In the present work, a one-step process for the synthesis of CdS and Cd1-xMn(x)S (0 < x < 10) nanocrystals has been described. Aqueous CdCl2 and the aerosol-OT solutions are homogeneously mixed together and thereafter, nitrogen is bubbled through this solution to produce stable aqueous foam. After drainage of the foam, the freestanding dry foam consisting of cadmium cations electrostatically complexed with the anionic aerosol-OT molecules at the liquid-gas interface is treated with H2S vapor. The foam turns yellowish-orange and collapses, in the process yielding CdS nanoclusters of variable morphology. This morphology variation is appropriately attributed to growth of the CdS as well as alloyed Cd1-xMn(x)S nanoparticles in different regions of the foam contributing to the varying topological structure. Optical absorption spectra of both CdS and Cd1-xMn(x)S nanoparticles clearly show a well-defined exciton absorption feature around 450 nm due to quantum confinement effects. The interesting band edge emission characteristics of these AOT-capped CdS and Cd1-xMn(x)S nanoparticles produced in the foam are discussed with respect to their size and shape. Particular interest in the present novel aqueous foam approach arises due to the fact that the cubic zincblende CdS and alloyed Cd1-xMn(x)S nanocrystals could easily be obtained even under ambient experimental conditions itself.

Sorption of Anionic Surfactants SDS, AOT and Cationic Surfactant Hyamine 1622 on Natural Soils

Sorption of anionic surfactants Aerosol-OT (AOT) and Sodium Dodecyl Sulfate (SDS), as well as cationic surfactant Hyamine1622 on two soil surfaces were investigated. Batch equilibriumtechniques were used under laboratory conditions to observe the amount of surfactant adsorbed and desorbed to and from thesoil surfaces. Data obtained were fitted to two sorption isotherms in order to characterise the sorption process. The nature of the sorbate (i.e. the surfactant) was found to be important in the sorption process. Anionics adsorbed via hydrophobic bonding, whereas `cation-exchange' mechanism was dominant in the sorption of cationic Hyamine 1622. Anionic AOT,with a double chain, and hence a higher critical packing parameter, adsorbed more strongly onto the surface compared tothe singly-chained SDS.

Effect of Temperature on the Mobility of Nitroxide Probes in Cyclohexane and at the Alumina–Cyclohexane Interface

Nitroxide spin probes have been widely used to study the behavior of surfactants in solution as well at solid–liquid interfaces. In this study the effect of temperature on the mobility of nitroxide spin probes in cyclohexane and at the alumina/cyclohexane interface is investigated in the presence of anionic aerosol-OT (AOT). The probe mobility in AOT micelles in solution is markedly dependent on the amount of solubilized water. The variation with temperature of the mobilities of adsorbed doxyl stearic acid with the nitroxide probe at the 5th, 10th, and 16th positions from the –COOH group has shed some light on the mechanisms of interaction of the probe with the solid surface as well as the molecular structure of the adsorbed layer. The results indicate that the adsorption of the probe occurs mainly through interactions of the –COOH group with the surface while the –NO group interacts only weakly with the surface. The adsorption of AOT causes changes in probe mobility with the changes being most significant when the nitroxide group on the stearic acid chain is farthest from the anchoring group. It is suggested that the adsorption of the surfactant causes an orientational rearrangement of the probe molecules. The relatively low-temperature effect on the probe mobility observed in the presence of surfactant is attributed to the compactness of the adsorbed layer which is found to be stable even at elevated temperatures.

EFFECT OF SURFACTANT ADDITION ON THE MICROSTRUCTURE OF COAL FILTER CAKES

ABSTRACT Currently, water removal from fine coal fractions is affected by vacuum filtration of a coal slurry followed by thermal drying. Due to high operating costs and the potentially hazardous nature of the drying operation, alternate methods are sought. This work investigated the change of filter cake microstructure resulting from one such method, namely, surfactant addition to the coal slurry. By impregnating a coal filter cake with an epoxy resin, micrographic analysis of the cake structure could be made by using an image analyzer with the aid of quantitative stereology. This analysis provided a particle and pore size distribution of the filter cake which is fundamental to the understanding of the dewatering mechanism. Three surfactants were investigated in this work: non-ionic Triton X-114, anionic Aerosol-OT, and cationic dodecyl pyrindinium chloride. The behavior of Triton X-114 and DPC was similar; they both enhanced dewatering by reducing the amount of particle segregation while increasing the p...