Reverse Micelle Solutions Research Articles

Solvothermal Synthesis of Calcium Phosphate Nanowires Under Different pH Conditions

Nano‐size calcium phosphate is prepared via solvothermal synthesis methods, using a reverse micelles solution. The influence of pH value on the crystallinity, morphology, and composition of the nanoparticles are investigated. It was found that the crystallinity increased as pH increased. However, notable changes in the morphology of the final products can be observed. At pH 6.0, long nanowires (800 nm long and 30∼100 nm wide) are observed. For pH=7.5, the nanowires are straight with 60 nm diameter and a length>1500 nm. The materials prepared at pH=8.5 exhibit short‐rod morphologies with a dimension of 130∼160 nm in length and 20∼30 nm in width. As for those prepared at pH=9.5, short rods 80∼100 nm in length and 20∼50 nm in width can be observed. The influence of pH value on the interaction between surfactant molecules and reactant ions are responsible for these differences. In addition, the composition of the finial precipitation also depends on pH. Meanwhile, the ability to generate high axial ratio and well‐crystallized nanowires, by coorganization of reverse micelles solutions and hydrothermal synthesis techniques, as described in this work, could offer an approach to the fabrication of one dimension nanomaterials.

Synthesis of nanosized TiO 2 particles in reverse micelle systems and their photocatalytic activity for degradation of toluene in gas phase

Nanosized pure TiO 2 particles with high crystallinity and large surface area were prepared by hydrolysis of tetrabutyl titanate in water/Triton X-100/isooctane reverse micelle solutions as reaction media followed by hydrothermal treatment to improve crystallinity. The prepared TiO 2 nanoparticles were characterized by XRD, BET, TGA, FT-IR and TEM. The size of ultrafine particles was controlled by changing the water content of the reverse micelle solution. The TiO 2 particles showed monodispersity, large surface area and high degrees of crystallinity and thermostability. The photocatalytic activity of the TiO 2 particles was evaluated by decomposition of toluene in the gas phase. The activity of the TiO 2 nanoparticles was higher than that of commercially available anatase fine particles, such as ST-01, which is one of the most active photocatalysts for degradation of organic compounds in the gas phase.

Studies on the self-assembly behavior of the amphiphilic block copolymer of PSt-b-PAA in apolar solvents with polar fluorescent probe

The block copolymer of polystyrene-b-poly(butyl acrylate) (PSt-b-PBA) with a well-defined structure was synthesized by atom transfer radical polymerization (ATRP); its structure was characterized, and the living polymerization was also validated by gel permeation chromatography, Fourier transform infrared, and 1H NMR measurements. Then, the amphiphilic block copolymer of polystyrene-b-poly(acrylic acid) (PSt-b-PAA) has been prepared by hydrolysis of PSt-b-PBA, and copolymers of PSt-b-PAA with longer PSt blocks and shorter PAA blocks were obtained by controlling the conditions of ATRP polymerization. The reversed micelle solution of PSt-b-PAA in toluene was prepared by using the single-solvent dissolving method, and the reverse micellization behavior of PSt-b-PAA in toluene was mainly investigated in this paper. The fluorescent probe technique was used by using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe to study the reverse micellization behavior of PSt-b-PAA. It was found that the reverse micellization behaviors of PSt-b-PAA in toluene can be clearly revealed by using NEAH as a polar fluorescence probe, and the critical micelle concentrations (cmcs) can be well displayed. The experimental results showed that the self-assembling behavior of PSt-b-PAA in toluene depends apparently on the microstructure of the macromolecules and is also influenced by the temperature. For the copolymers of PSt-b-PAA with the same length of hydrophobic PSt blocks, the copolymer with a longer hydrophilic block PAA has lower cmc, and at higher temperature, the copolymer has lower cmc.

Density, Viscosity, and Speed of Sound of Solutions of AOT Reverse Micelles in 2,2,4-Trimethylpentane

The density, viscosity, and speed of sound for 2,2,4-trimethypentane + sodium bis(2-ethylhexyl) sulfosuccinate (AOT) have been measured. The effect of surfactant concentration upon these physical properties has been analyzed. Different equations employed in the literature have been employed to fit the experimental data.

Insight into Shape Control Mechanism of Calcium Phosphate Nanoparticles in Reverse Micelles Solution

The present experiment demonstrates a systematic morphosynthesis of calcium phosphate crystals with controlled morphology in reverse micelles solution of CTAB/n‐pentanol/water/cyclohexane. Well‐defined morphologies of calcium phosphate particles, such as nanowires, tablets, brushlike particles, and fiber bundles, can be prepared. The microstructural characteristics of the CTAB/n‐pentanol/water/cyclohexane reverse micelles solution has been investigated by FTIR spectroscopic, 31P NMR, and UV‐visible absorption spectra techniques, demonstrating that the molar ratio of water to surfactant (W o ) and n‐pentanol to surfactant (P o ) showed significant effects on the morphology of the resulting particles. At lower W o and P o , CTAB played a role in guiding the growth direction. With increasing W o and P o , crystal growth lost the direction‐guiding capability of CTAB. However, as crystal growth modifiers, water and cosurfactants follow different mechanisms. The solubility of water causes a decrease in bound water layer, resulting in a decrease in interactions between CTA+ and PO4 3− which invalidates the shape control of surfactant molecules. The loading of cosurfactant (n‐pentanol) results in decreasing the rigidity of the reverse micelles interface. This in turn favors the shape fluctuations of reverse micelles, inducing crystal development.

Synthesis and characterization of silver nanoparticles by a reverse micelle process

The preparation of silver nanoparticles by the reduction of AgNO3 with hydrazine in lgepal CO-520/cyclohexane reverse micelle solutions has been studied. Transmission electron microscope, electron diffraction, and X-ray diffraction pattern analyses revealed the resultant particles to be silver. The average size of the synthesized nanoparticles first increased and thereafter approached a constant value with increased molar ratio of water to Igepal CO 520 and with increasing concentration of AgNO3.

Synthesis and agglomeration of gold nanoparticles in reverse micelles

Reverse micelles prepared in the system water, sodium bis-(2-ethylhexyl) sulfoccinate(AOT), and isooctane were investigated as a templating system for the production of goldnanoparticles from Au(III) and the reducing agent sulfite. A core–shell Mie model was usedto describe the optical properties of gold nanoparticles in the reverse micelles. Dynamiclight scattering of gold colloids in aqueous media and in reverse micelle solution indicatedagglomeration of micelles containing particles. This was verified theoreticallywith an analysis of the total interaction energy between pairs of particles as afunction of particle size. The analysis indicated that particles larger than about8 nm in diameter should reversibly flocculate. Transmission electron microscopymeasurements of gold nanoparticles produced in our reverse micelles showed diametersof 8–10 nm. Evidence of cluster formation was also observed. Time-correlatedUV–vis absorption measurements showed a red shift for the peak wavelength.This was interpreted as the result of multiple scattering and plasmon interactionbetween particles due to agglomeration of micelles with particles larger than8 nm.

Effect of PEO–PPO–PEO structure on the compressed ethylene-induced reverse micelle formation and water solubilization

Some of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) tri-block copolymers aggregate in p-xylene upon addition of ethylene and form reverse micelles at higher temperature at which the reverse micelles cannot be formed without addition of compressed ethylene. An abrupt increase of water solubilization is observed at a certain ethylene pressure. The effects of surfactant structure, such as the ratio of EO (EO weight percent) and the molecular mass, on the copolymer micellization and the solubilization of water in such systems are studied. For the copolymers with the same length of PO block, higher EO ratios facilitate the reverse micelle formation. However, as the EO ratio reaches 70%, it cannot form reverse micelles because the hydrophilicity is too high. For the copolymers with same composition, higher molecular weight is favorable to forming the reverse micelle due to the hydrophilic and folding effects, respectively. The reverse micelle solution can solubilize water with W0 (molar ratio of water to EO segment) up to 4.1.

Spectral properties of carbocyanine dyes in solutions of reverse AOT micelles

Spectral and luminescence studies of an anionic carbocyanine dye in solutions of reverse AOT micelles have shown that the dye in micelle pools can occur only in the form of the trans-monomer; although aggregated forms of the dye including J aggregates can be present in micellar solution, they all are localized in the organic phase, not micellar pools.

Formation mechanism of carbon nanotubes in the gas-phase synthesis from colloidal solutions of nanoparticles

Abstract Single- and multi-wall carbon nanotubes have been synthesized by the gas-phase catalytic reaction of colloidal solutions of metal nanoparticles using a vertical flow reactor. The reverse micelle solution of the Co–Mo nanoparticles with the mean diameter of 11 nm dissolved in toluene was injected directly into the reactor maintained at 1200 °C. The nanoparticles and the solvent act as the catalyst and carbon source, respectively. When the concentration of the thiophene additive is low (1 wt.%), the formation of SWNT bundles preferentially occurred. The SWNT bundles were present together with the relatively small metal nanoparticles with the diameter of 0.5–5.5 nm. It is likely that the original nanoparticles with the diameter of 11 nm break into smaller ones, 1–2 nm diameters, which is suitable for the SWNT growth. The synactic effect of Co and Mo was also observed.

Effect of structure of PEO-PPO-PEO copolymers on reverse micelle formation induced by compressed CO2.

The micellization of PEO-PPO-PEO block copolymers in p-xylene has been studied in the presence of CO2. With the application of CO2, some copolymers with suitable molecular weights and EO ratios can form reverse micelles with critical micellization pressure up to 5.8 MPa. For the copolymers with the same length of PO block, higher EO ratios facilitate reverse micelle formation. For the copolymers with the same composition, higher molecular weight is favorable to form reverse micelles. With the suitable composition and molecular weight, the critical micelle pressure (CMP) of copolymers decreases with the increase in the lengths of PEO and PPO blocks due to the hydrophilic and folding effects, respectively. Both the EO ratios and the molecular weights are important for the formation of reverse micelle. The reverse micelle solution can solubilize water with W0 (molar ratio of water to EO segment) up to 3.3.

Water-swellable polyelectrolyte microgels polymerized in an inverse microemulsion using a nonionic surfactant

A series of poly(dimethylacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) microgels slightly crosslinked by methylene-bis-acrylamide (MBA) were polymerized in a novel inverse microemulsion polymerization (IMEP) system. To determine a suitable composition of the IMEP system, the phase diagram of a pseudoternary system was made. The pseudoternary polymerization system consisted of n-hexane, a nonionic surfactant (polyoxyethylene oleyl ether, C 18E n ), and an aqueous monomer solution. Polymerization was performed in a single-phase reversed micelle solution. The reversed micelles were about 50 nm in diameter, as determined by FF-TEM. The viscometric characteristics of the polymers extracted from the IMEP system were studied in 3 mM sodium chloride aqueous solution. The intrinsic viscosity values for the noncrosslinked and crosslinked (0.1 mol% MBA was incorporated) samples were 25 and 7.4 dl/g, respectively. The overlap concentration ( c ∗ ) of crosslinked polymer microgel occurred at c[ η]=1 in the solvent. When the volume fraction ( φ) of the microgel was 0.7, the value of the apparent yield stress of the microgel solution was observed. These results show that the microgel has a significant thickening effect above c ∗ due to friction between the microgel particles. It is assumed that the microgels polymerized in a confined space retain the shape or size of the nanosized reactor with a diameter on the order of 50 nm.

Photophysical Properties of CdS Nanoparticles in Thin Films for Opto-Chemical Sensing

AbstractIn recent years, II-VI compound semiconductor nanoparticles synthesized in a liquid solution have been shown to possess unique optoelectronic properties which are highly attractive for the fabrication of various sensors based on the optical signal readout scheme. The challenge has been to immobilize these nanoparticles into films on solid surfaces, i.e. on a chip, so that they do not suffer any property deterioration as a sensing medium. In the presented work, synthesis of CdS nanoparticles in reverse micelle solution using AOT surfactant as a stabilizer has led to particles with relatively bright photoemission identified as originating from both shallow and deep traps inside the bandgap. Moreover, slightly altering the preparation procedure has produced samples with two distinctive crystal structures. Both types of CdS nanoparticles suspended in commonly utilized solvents such as chloroform and hexane were subject to chemical quenching when various organic compounds were introduced into the solution, demonstrating the sensitivity of trap states to their chemical environment. However, the two structures have shown very different optical properties. While post-synthesis treatment had no effect on one type of particle, the other type was able to undergo a photochemical reaction via prolonged UV irradiation, which resulted in an increased luminescence quantum yield ÖL from 2% to 14%. The same particle type was also responsive to thermal treatment, showing even higher values of ÖL (∼40%). The CdS/AOT particles have been cast into thin films by spin-coating on a Si wafer. Coating parameters have been investigated in order to achieve optimal control over the film thickness, uniformity, overall film durability, etc. These nanostructured films capped with various porous polymeric and sol-gel protective coatings were exposed to a series of organic compounds. Photoluminescence data collected for these samples served for identification of the compounds and their concentrations. This paper offers the discussion of photophysical response in CdS nanoparticle-based thin films with respect to development of novel nanostructured opto-chemical sensors.

Solvation Dynamics of Formamide andN,N-Dimethylformamide in Aerosol OT Reverse Micelles

The solvation dynamics of formamide and N,N-dimethylformamide in Aerosol OT reverse micelles has been investigated in this work. The solvation dynamics of formamide and N,N-dimethylformamide in the reverse micelles is more than 100 times slower than that of the pure solvents. The solvation dynamics of formamide in the reverse micelle solution depends strongly on the molar ratio between formamide and Aerosol OT (w = [polar solvent]/[Aerosol OT]), but that of N,N-dimethylformamide in the reverse micelle solution shows a tiny w dependence. We have estimated the interaction energies of the geometry-optimized clusters of a simple model of the Aerosol OT polar headgroup (CH3SO3-) and formamide or N,N-dimethylformamide by ab initio calculations (the second-order Møller-Plesset perturbation theory) to find their interactions. The interaction energies of the mimic clusters estimated by the ab initio calculations and the features of the slow solvation dynamics and w dependence in formamide and N,N-dimethylformamide reverse micelles are discussed.

Separation of amino acids by polymeric reversed micelle extraction

The polymeric reversed micelles were formed with polyoxyalkylene block copolymers as surfactant and 1-octanol as cosolvent in the polyoxyalkylene block copolymers/1-octanol/p-xylene system. The polyoxyalkylene block copolymers consist of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO). Two types of copolymers, PEO–PPO–PEO-type and PPO–PEO–PPO-type triblock copolymers were used. Our present interests are focused on the formation of the reversed polymeric micelles and subsequently separation of amino acids by the polymeric reversed micelle solutions. Extraction equilibrium partition of amino acids between polymeric reversed micelle solutions and water was investigated to study the extraction behaviours. The copolymer type and aqueous phase pH affected the extraction process. A model for solute solubilisation by the polymeric reversed micelles is proposed.

Synthesis and Surface Derivatization of Processible Co Nanoparticles

Co nanoparticles were prepared by the reverse micelle technique (NaBH₄reduction of cobalt chloride in a reversed micelle solution of didodecyldimethylammoniumbromide (DDAB)/toluene). The size and the shape of Co nanoparticles could be easily controlled by changing the water contents and micelle concentrations, and the solubility of Co nanoparticles was systematically tuned by choosing appropriate surface capping organic ligand molecules. Furthermore, a novel nanofabrication process was clearly demonstrated, which generated oxide over-coated Co nanorods from Co nanoparticles in organic solution by slow oxidation with an external magnetic field.

Separation of phenol from aqueous solutions by polymeric reversed micelle extraction

Polyoxyalkylene block copolymers consisting of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO) or poly(butylene oxide) (PBO) have not attracted much attention until recent years. Variations of the molecular characteristics (PPO/PEO ratio, molecular weight) of the copolymer during the synthesis allows the production of molecules with optimum properties that meet the specific requirements in different areas. Our present interest is focused, on the formation of the reversed polymeric micelles, which are formed in ‘oil’ phases with PEO–PPO–PEO-type as well as PPO–PEO–PPO-type triblock copolymers. A novel process of polymeric reversed micelle extraction is subsequently proposed based upon the concepts of reversed micelle extraction and polymeric micelle extraction. Extraction equilibrium partition of phenol between polymeric reversed micelle solutions was investigated to study the extraction behaviors. PPO content, copolymer and co-surfactant types affected the extraction process.

Preparation of Silver Nanoparticles via Rapid Expansion of Water in Carbon Dioxide Microemulsion into Reductant Solution

Perfluoropolyether ammonium carboxylate stabilized water-in-CO2 microemulsion was used to dissolve silver nitrate salt for the RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent) process. The solution of reverse micelles with an aqueous silver nitrate core in CO2 was rapidly expanded into a room-temperature solution of sodium borohydride to form silver nanoparticles. The nanoparticles were characterized using optical, X-ray diffraction, and microscopy techniques. The nanoparticle properties were found to be dependent on the pre-expansion microemulsion conditions in CO2.

Exciplex-type behavior and partition of 3-substituted indole derivatives in reverse micelles made with benzylhexadecyldimethylammonium chloride, water and benzene.

The fluorescence properties of 3-methylindole (MI), 3-indoleacetic acid (IAA), 3-indoleethyltrimethylammonium bromide (IETA), L-tryptophan (Trp) and tryptamine hydrochloride (TA) were studied in reverse micelles solutions made with the cationic surfactant benzylhexadecyldimethylammonium chloride (BHDC) in benzene as a function of the molar ratio water/surfactant R (= [H2O]/[BHDC]). The fluorescence quenching of the model compound MI by benzene in cyclohexane solutions and by BHDC in benzene solutions were also studied in detail. The fluorescence of MI in benzene is characteristic of a charge-transfer exciplex. The exciplex is quenched by the presence of BHDC, due to the interactions of the surfactant ion pairs with the polar exciplex. In reverse micelle solutions at low R values, all the indoles show exciplex-type fluorescence. As R increases, the fluorescence behavior strongly depends on the nature of the indole derivative. The anionic IAA remains anchored to the cationic interface and its fluorescence is quenched upon water addition due to the increases of interface's micropolarity. For IETA, TA and Trp an initial fluorescence quenching is observed at increasing R, but a fluorescence recovery is observed at R > 5, indicating a probe partition between the micellar interface and the water pool. For the neutral MI, the fluorescence changes with R indicate the partition of the probe between the micellar interface and the bulk benzene pseudophase. A simple two-site model is proposed for the calculation of the partition constants K as a function of R. In all cases, the calculation showed that even at the highest R value, about 90% of the indole molecules remain associated at the micellar interface.

Polar Solvation Dynamics in Nonionic Reverse Micelles and Model Polymer Solutions

The effect of confinement on solvation dynamics has been explored in Brij-30/cyclohexane and Triton X-100/cyclohexane nonionic reverse micelles. Inside the reverse micelles, the polar solvation dynamics become slower and show additional slow relaxation modes not observed for bulk water. The solvation dynamics inside the Triton X-100 reverse micelles is slower than the dynamics inside Brij-30 reverse micelles. The results for solvation dynamics in the reverse micelles contrast solvation dynamics in aqueous tri(ethylene glycol) monoethyl ether solutions comparable to the reverse micellar interiors, which show significantly faster response. Measurements in the nonionic reverse micelles are also compared to previous work on ionic reverse micelles. Results reported here show that the interactions of water with the polyoxyethylene ether, as well as the micellar confinement inside these reverse micelles, effectively immobilize the water in the micellar interiors.