Aerosol OT Concentration Research Articles

Flow synthesis of silver nanoparticles using water in supercritical CO2 emulsion

Rapid and continuous synthesis of metal nanoparticles using green solvent system is still a serious challenge for both fundamental and practical research. In this work, we report a new flow process using water in supercritical CO2 (w/scCO2) emulsion and applied it to the synthesis of silver nanoparticles (AgNPs). To investigate the performance of our system, AgNPs were synthesized by batch, flow and w/scCO2 emulsion flow system at 40 ºC while using AgNO3, NaBH(OAc)3, trisodium citrate and Aerosol-OT as precursor, reducer, stabilizer and emulsifier. As a result, we demonstrated that water droplets in w/scCO2 emulsion significantly contribute to a rise in the size controllability and productivity (product yield). Additionally, w/scCO2 emulsion flow process allowed the control of mean size from 4.0 to 36.6 nm and yield from 25% to 65% by changing the CO2 pressure and Aerosol-OT concentration. Furthermore, synthesized AgNPs successfully gave citrate-modified surface with high zeta potential of –54 mV and the transparent water dispersion with unimodal size distribution, showing promising potential to allow various practical applications.

A study on the dynamic surface tension of surfactant solutions at dilute concentrations

The dynamic surface tension (ST) for Aerosol-OT (AOT) molecules adsorbing onto a freshly created bubble surface in a 10 mM NaCl(aq) solution was measured at extremely dilute concentrations using a pendant bubble tensiometer. An air bubble was formed one after another inside the same uniform solution at two different states of the free surface on the top of the solution in quartz cell: (i, bubble #1) a nearly clean air-water interface and (ii, bubble #2) a thermodynamic equilibrated air-water interface. Whilst the dynamic ST of bubble #1 decreased noticeably faster than that of bubble #2, both these bubbles reached the same equilibrium ST. AOT molecules kept adsorbing onto the free surface during the ST measurement of bubble #1, which caused the concentration of AOT in bulk to decrease significantly at dilute concentrations. During the measurement of bubble #2, the bulk concentration remained constant. Subsequently, the dynamic ST data of bubble #2 precisely described the adsorption of AOT molecules onto a freshly created air-water interface. Consequently, the adsorption onto the free surface played an important role in the dynamic ST measurement for surfactant solutions at extremely dilute concentrations. This new experimental procedure was capable of precisely measuring the dynamic ST of surfactant solution at extremely low concentrations.

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.

Adsorption kinetics of the partially dissociated anionic surfactant Aerosol-OT in 10 mM NaCl solution

The adsorption kinetics of anionic surfactant Aerosol-OT (AOT) in 10 mM NaCl solution was investigated by measuring and simulating the dynamic and equilibrium surface tension (ST) data. The relaxation of ST for AOT molecules adsorbing onto a freshly created bubble surface was measured using a video-enhanced pendant bubble tensiometer at eighteen AOT concentrations. The partially ionized Langmuir model was applied to best-fit the dynamic/equilibrium ST data. The subsequent findings revealed that the model with a dissociation degree α of 0.1 − 0.2 described the dynamic and equilibrium ST data very well. This implied that AOT behaved as a partially ionized surfactant in 10 mM NaCl solution. The adsorption for AOT onto a clean air–water interface was found to be either (i) diffusion-controlled with a diffusivity value that varied [between 2.5 and 4.6 (10−6 cm2/s)] depending on the bulk concentration or (ii) mixed-controlled with an adsorption rate constant of 2.4 ± 0.8 (107 cm3/mol.s).

The effect of surfactant micellization on the cytotoxicity of silver nanoparticles stabilized with aerosol-OT

The toxic action of surfactant used as a stabilizer of metal nanoparticles have been studied with the aim to determine separate contributions of surfactant monomers and micelles to cell viability decrease. Basing on (1) the well-known ability of surfactant molecules to form micelles in solution at a critical micelle concentration (CMC) and (2) the results reported in literature, showing that toxicity of various surfactants increases when their concentration exceeds CMC, we supposed that surfactant molecules and micelles may differ in their toxic effect on cells. This supposition was verified on the anionic surfactant aerosol-OT (AOT) used as a stabilizer of silver nanoparticles (AgNPs) in studies of their cytotoxicity on Jurkat cells by means of the MTT test. Two samples of AgNPs stabilized with AOT in concentrations higher (3 mM) and lower (1 mM) than its CMC in water were introduced to the cell medium as water solutions diluted to obtain nanoparticle concentrations in the range 1–7 μg/mL. Cell viability changes were registered after 24 h incubation. It was found that AgNPs of similar average size (about 16 nm), synthesized by the same procedure, introduced to the same concentrations in cell medium, produced a different effect on cell viability. Namely, decrease in cell viability was observed for AgNPs with 3 mM AOT, while no noticeable changes were registered for AgNPs with 1 mM AOT. A similar difference was detected for the corresponding dilutions of 3 mM and 1 mM AOT water solutions. We assumed that the toxicity dependence on AOT concentration originated from the difference in toxic action of the two different AOT forms – molecules (monomers) and micelles – present in the AgNPs and AOT solution. The approach was suggested for estimation of the separate contributions of monomers and micelles to the total AOT toxicity; changes of these contributions with AgNPs or AOT concentration were also determined. The results obtained may prove to be useful in studies of the biological activity of surfactants applied both as nanoparticle stabilizers and as agents working in medicine as suppressors of various infections.

Kinetics study of a palladium–nickel colloidal nanocatalyst synthesized by a wet-chemical method for reduction of nitrophenol, nitroaniline, and 4-nitrobenzo-15-crown compounds

ABSTRACTA bimetallic, palladium–nickel (Pd–Ni) stable colloidal nanocatalyst was synthesized by a wet-chemical reduction technique using Aerosol OT (AOT) as the surfactant and hydrazine hydrate as a reducing agent. The particle size of a colloidal nanocatalyst was controlled by varying precursor concentration, reducing agent, and surfactant concentration. The particle size and morphology of the colloidal catalyst were investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. TEM images show the actual particle size of Pd‒Ni nanocatalysts to be in the range of 10‒28 nm at 10 mM concentration of AOT and hydrazine hydrate. The activity of the colloidal catalyst (bimetallic) was evaluated for reduction of nitro aromatic compounds which includes 4-NP, 3-NP, 2-NP, 4-nitrobenzo-15-crown, and 4-NA. The rate constant of the Pd–Ni colloidal nanocatalyst indicates that the activity of bimetallic catalysts was higher than the monometallic catalyst for various nitro compounds. The rate constant of 4-nitrophenol was found to be ∼61 × 10−2 min−1 at room temperature.

A study of sodium bis(2-ethylhexyl) sulfosuccinate adsorption on silica from silver and gold organosols

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT) and silver and gold nanoparticles on SiO2 from heptane solutions has been investigated by spectophotometery and CHN analysis. The adsorption isotherm of Aerosol OT is described by the Langmuir equation. Sorption capacity (2.4 × 10–4 mol/g), sorption constant (9.0 m3/mol), and area per Aerosol OT molecule in an adsorption layer (0.83 nm2) have been determined. It has been shown that, at Aerosol OT concentrations lower than 6 × 10–4 M, gold and silver ((0.3–6) × 10–4 M) are simultaneously extracted by 98%; however, they have no effect on the adsorption and determination of the surfactant.

Studies on Extraction Behaviour of Reserpineduring Reverse Micellar Extraction fromRauwolfia Vomitoria

Reserpine a well known phytochemical molecule found in the dried roots of plants such as Rauwolfia Serpentina and Rauwolfia Vomitoria. It is a hypertension drug molecule used in drug formulation. Reserpine ranks as one of the most complex natural product of its size and contains 21 skeletal atoms compactly arranged in five rings. The stereo chemical complexity and biological significance of Reserpine have made it a fascinating target for evaluation of new strategies that are conceived upon emergence of new methods for processing, since the conventional methods of extraction like HPLC, two phase extraction are not economical and efficient. Reverse micellar extraction, a novel method for separation of natural drug molecule has been explored for the purpose based on its success in isolating and separating other bio molecules like matrine and enzymes. Reverse micellar extraction adopts micro emulsions as a media of separation. The present work focuses on use of micro emulsions to enhance the rate of separation and extract Reserpine. The extraction behavior of Reserpine was investigated using reverse micellar extraction. It is found that during the forward extraction fractions of the Reserpine did not vary considerably with an increase in Aerosol OT concentration in the organic phase. However the backward extraction of Reserpine increased by 13% with increasing in concentration of cyclohexane in the stripping aqueous phase. The concentration of Reserpine obtained was analyzed in a UV-Vis spectrophotometer.

Sequential adsorption of an irreversibly adsorbed nonionic surfactant and an anionic surfactant at an oil/aqueous interface.

Aerosol-OT (AOT) and Tween 80 are two of the main surfactants in commercial dispersants used in response to oil spills. Understanding how multicomponent surfactant systems interact at oil/aqueous interfaces is crucial for improving both dispersant design and application efficacy. This is true of many multicomponent formulations; a lack of understanding of competition for the oil/water interface hinders formulation optimization. In this study, we have characterized the sequential adsorption behavior of AOT on squalane/aqueous interfaces that have been precoated with Tween 80. A microtensiometer is used to measure the dynamic interfacial tension of the system. Tween 80 either partially or completely irreversibly adsorbs to squalane/aqueous interfaces when rinsed with deionized water. These Tween 80 coated interfaces are then exposed to AOT. AOT adsorption increases with AOT concentration for all Tween 80 coverages, and the resulting steady-state interfacial tension values are interpreted using a Langmuir isotherm model. In the presence of 0.5 M NaCl, AOT adsorption significantly increases due to counterion charge screening of the negatively charged head groups. The presence of Tween 80 on the interface inhibits AOT adsorption, reducing the maximum surface coverage as compared to a clean interface. Tween 80 persists on the interface even after exposure to high concentrations of AOT.

Crystallization and reentrant melting of charged colloids in nonpolar solvents.

We explore the crystallization of charged colloidal particles in a nonpolar solvent mixture. We simultaneously charge the particles and add counterions to the solution with aerosol-OT (AOT) reverse micelles. At low AOT concentrations, the charged particles crystallize into body-centered-cubic (bcc) or face-centered-cubic (fcc) Wigner crystals; at high AOT concentrations, the increased screening drives a thus far unobserved reentrant melting transition. We observe an unexpected scaling of the data with particle size, and account for all behavior with a model that quantitatively predicts both the reentrant melting and the data collapse.

In Situ X-ray Polymerization: From Swollen Lamellae to Polymer–Surfactant Complexes

The influence of the monomer diallyldimethylammonium chloride (D) on the lamellar liquid crystal formed by the anionic surfactant aerosol OT (AOT) and water is investigated, determining the lamellar spacings by SAXS and the quadrupolar splittings by deuterium NMR, as a function of the D or AOT concentrations. The cationic monomer D induces a destabilization of the AOT lamellar structure such that, at a critical concentration higher than 5 wt %, macroscopic phase separation takes place. When the monomer, which is dissolved in the AOT lamellae, is polymerized in situ by X-ray initiation, a new collapsed lamellar phase appears, corresponding to the complexation of the surfactant with the resulting polymer. A theoretical model is employed to analyze the variation of the interactions between the AOT bilayers and the stability of the lamellar structure.

Microstructure, drug binding and cytotoxicity of Pluronic P123–aerosol OT mixed micelles

The interaction between triblock copolymer Pluronic P123 and anionic surfactant Aerosol OT (AOT) has been studied using dynamic light scattering (DLS) and small angle neutron scattering (SANS). The copolymer/surfactant system has been investigated at a constant copolymer concentration of 0.5 wt% and with varying surfactant concentration up to ∼5 mM. DLS results reveal that addition of AOT suppresses the micellization of P123. With the addition of AOT, P123–AOT mixed micelles are formed via hydrophobic association of the surfactant with the block copolymer micelles leading to the development of negative surface charge on copolymer micelles. The solubilization of the hydrocarbon chains of the surfactant, AOT, into the polypropylene oxide core of the block-copolymer micelle leads to increased electrostatic repulsion between the P123–AOT mixed micelles. SANS studies show a steady decrease in the core size and aggregation number of the micelles with the increasing concentration of AOT, consistent with the DLS results. The binding ability of AOT to the anticancer drug doxorubicin hydrochloride (DOX) was confirmed by dynamic surface tension measurements. The in vitro cytotoxicity studies in various cancer cell lines revealed that anticancer activity of the drug is not affected by complexation with AOT and DOX-loaded micelles are more potent to MCF-7 human breast cancer cells compared to other cell lines. The present findings can form a basis to design block copolymer based micellar carriers for drug delivery.

Nonstoichiometric polymer-surfactant complexes obtained in a lamellar lyotropic medium

The addition of a polyelectrolyte to lamellar media formed by an oppositely charged surfactant often leads to the coexistence of several phases without macroscopic phase separation, which makes their characterization difficult. Here, the effect of the polydiallyldimethylammonium chloride (PD) on the lamellar liquid crystal formed by the anionic surfactant Aerosol OT (AOT) and water is investigated. Small-angle X-ray scattering results are discussed regarding the changes in the lamellar spacing as a function on the PD or AOT concentrations. In most of the samples, two lamellar phases, without macroscopic phase separation, are detected. One of them is a typical swollen phase, while the other is a collapsed phase, which corresponds to the polymer-surfactant complex. At concentrations of polymer up to 3 wt%, the two lamellar phases coexist; however, at a critical concentration higher than 3 wt%, the swollen phase becomes isotropic, and a macroscopic phase separation takes place. A simple model is proposed to calculate the composition of the phases when macroscopic phase separation does not occur. The results thus calculated show that generally the polymer-surfactant complexes are nonstoichiometric containing a lesser amount of polymer than ideally expected.

Circular Dichroism and Derivative Spectra Study of the Excitonic Aggregation of Pinacyanol by Aerosol-OT

Different structures are proposed for the complexes formed from the interaction between the cationic cyanine dye 1, 1’-diethyl-2, 2’-carbocyanine chloride (Pinacyanol chloride) and the anionic surfactant sodium bis (2-ethylhexyl) sul- fosuccinate (Aerosol-OT) in ethanol-water solutions. UV/vis and electronic circular dichroism (CD) spectra provide tools to study the concentration and solvent dependence of this interaction. The aggregation spectra of the dye are dominated by a strongly blue-shifted, sharp and single visible band, which appears at concentrations much below the critical micelle concentration (cmc) of Aerosol-OT. Above the cmc, the spectra in pure aqueous solution indicate disso- ciation into monomer and dimer species, and the system becomes completely empty of chirality. Two different CD spectra with a distinct isosbestic point are observed for complexes with different surfactant to dye ratios. Both the addi- tion of ethanol (more than 7.5%) and increasing the temperature retards the metachromatic process between the dye and Aerosol-OT. By using the peakFit program, the two overlapping excitonic absorption bands together with the optically inactive absorption band for one spectrum (the most optimal one) at a specific Aerosol-OT concentration were sepa- rated.

Photocatalytic and Conductive MWCNT/TiO2 Nanocomposite Thin Films

A conductive and photocatalytic nanocomposite thin film comprising multiwalled carbon nanotubes (MWCNTs) and TiO2 nanoparticles is fabricated based on layer-by-layer (LbL) assembly in a nonpolar solvent, toluene. An amphiphilic surfactant, aerosol OT (AOT), is used to impart opposite surface charge onto MWCNTs and TiO2 in toluene. Our fabrication technique enables the incorporation of unoxidized MWCNTs into the nanocomposite thin films, and at the same time, provides a versatile method of fabricating conformal thin films over a large area. The physicochemical properties of MWCNT/TiO2 nanocomposite thin films, including composition and photocatalytic activity, can be varied by changing the concentration of AOT during assembly. The electrical properties of the nanocomposite film, specifically its sheet resistance and conductivity, can also be tuned through changing the assembly conditions. In addition, we demonstrate that the incorporation of MWCNTs within our films leads to a significant enhancement of the photocatalytic activity of TiO2. The conductivity and enhanced photocatalytic activity of MWCNT/TiO2 thin films make them promising for the generation of highly efficient dye-sensitized solar cells (DSSCs).

Layer-by-Layer Assembly of Charged Particles in Nonpolar Media

Layer-by-layer (LbL) assembly of charged species such as nanoparticles and polymers has been widely used to generate functional thin films with unique wetting, optical, catalytic, and biological properties. Although LbL assembly is a versatile tool for creating functional thin films on a variety of substrates, it is generally restricted to aqueous media, in which electrolytes ionize readily due to the large dielectric constant of water. LbL assembly of non-water-soluble materials would expand the range of film properties and functionalities that are attainable. In this study, we have successfully performed LbL deposition of charged particles in a nonpolar solvent, toluene. In toluene, carbon black (CB) and alumina acquired negative and positive surface charge, respectively, in the presence of a charge-inducing agent, Aerosol OT (AOT). The dependence of particle surface charge on the concentration of AOT in toluene was probed by electrophoretic mobility analysis. The two oppositely charged particles were sequentially deposited onto glass slides to form CB/Al(2)O(3) nanocomposite thin films. UV-vis spectroscopy, optical profilometry, and thermogravimetric analysis (TGA) were used to investigate the effect of assembly conditions (i.e., the concentration of AOT in each suspension) on the composition and growth behavior of CB/Al(2)O(3) nanocomposite films. Our results demonstrate that LbL assembly can indeed be performed using charged particles in nonpolar media. Such possibility will widen the library of materials that can be incorporated into thin films based on the LbL technique, which can ultimately lead to the generation of multifunctional nanocomposite thin films.

Effects of Fe–AOT complex on the properties of iron oxide particles formed by an AOT isooctane/water emulsion system

AbstractFormation of iron oxide particles with aerosol‐OT (AOT)/isooctane/water emulsion was carried out employing a coprecipitation reaction for Fe3O4 particles. Emulsions containing Fe2+/Fe3+ were mixed with those containing OH−. Iron oxide particles were formed by changing the concentration ratio of AOT to iron ions and maintaining the volume fraction of water in the emulsion at 0.25. Particle formation was also carried out using nonemulsified aqueous solutions as a reference. The morphology, crystal structure, magnetic property and hydration degree of the particles formed under various conditions were compared. The α‐FeOOH or amorphous particles are formed instead of Fe3O4 when the AOT concentration is comparable to, or higher than, the iron ion concentration. These particles contain an OH group and water, and are oxidized to become α‐Fe2O3 by heating in N2. The Fe–AOT complex as the origin of OH‐rich particle formation was the focus of this investigation. The IR measurement was carried out for the Fe–AOT complex, separately prepared with the aqueous solution. It was found that the Fe–AOT complex was hydrated, indicating that hydration of the complex affects the properties of particles formed by the emulsion. A possible mechanism for formation of α‐FeOOH or amorphous particles with emulsion is proposed. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Effect of Ciprofloxacin Hydrochloride on the Micellization in Double Tailed Surfactants Aqueous Solution

The effects of ciprofloxacin hydrochloride (CF) on the micellization of double tailed surfactants in aqueous solutions, aerosol‐OT (AOT) and didodecyldimethylammonium bromide (DDAB), were studied by surface tension and UV spectra measurements. The results from surface tension measurements demonstrated that CF could decrease the equilibrium values of the surface tension and critical micelle concentration (cmc) of AOT, but increase that of DDAB. Their standard thermodynamic functions of micellization, ΔG m°, ΔH m°, and ΔS m°, have been obtained in aqueous solutions at 298K. The further conclusions were got from UV spectrophotometry. It is demonstrated that CF is solubilized close to the interface of micelle/water for DDAB cationic surfactant. However, CF could be localized in the palisade layer of the AOT micelle.

Dissipative Particle Dynamics Simulation of Phase Behavior of Aerosol OT/Water System

The phase behaviors of the binary mixture of an anionic surfactant aerosol OT (AOT) and water are investigated on a mesoscopic level using dissipative particle dynamics (DPD) computer simulations. With a simple surfactant model, various aggregation structures of AOT in water including the lamellar, viscous isotropic, and reverse hexagonal phases are obtained, which agree well with the experimental phase diagram. Special attention is given on the unusual lamellar regions. Water diffusivity shows much useful information to understand how the phase behaviors varied with concentration and temperature. It is proposed that the anomalous lamellar phenomena at intermediate AOT concentration (about 40%) are due to the formation of a defective structure, pseudoreversed hexagonal phase, which evidently decreases the water diffusivity. After increasing temperature above 328 K, the pseudoreversed hexagonal structure will be partly transformed to a normal lamellar phase structure and the system lamellar ordering is therefore enhanced.

Charging Behavior in the Silica/Aerosol OT/Decane System

We report an investigation of the effect of Aerosol OT on the surface charge of silica particles suspended in decane. The electrophoretic mobilities were measured using phase analysis light scattering, and supporting evidence was provided by conductivity and adsorption isotherm measurements. The results showed that, as the Aerosol OT concentration was increased, a sign reversal of the electrophoretic mobility occurred. This observation is explained qualitatively by a site-binding model of the charging mechanism.