Nanoparticles In Microemulsions Research Articles

Preparation and Antiwear Property of Monodisperse Silver Nanoparticles in Microemulsion

Monodisperse Ag nanoparticles were prepared in quaternary W/O microemulsions containing Span 80-Tween 80,liquid paraffin and 1-butanol.It was found that mass ration of Span 80 and Tween 80 had an obvious effect on the morphology and size distribution of the Ag nanoparticles.Morphologies,structure and thermal properties of the silver nanoparticles were characterized by means of X-ray diffraction(XRD),transmission electron microscopy(TEM),Fourier transform infrared(FT-IR),thermogravimetry(TG)and differential thermal analysis(DTA).The results show that the Ag nanoparticles have cube crystal structure;exhibit uniform size distribution and have an average size of 6 nm at the mass ratio of Span 80∶Tween 80=7∶3;and are coated with long chain fatty acid through carboxyl.H2O and 1-butanol in microemulsions were removed through vacuum distillation,and Ag nanoparticles were dispersed stably in liquid paraffin.The tribological properties of liquid paraffin containing Ag nanoparticles were evaluated on a four-ball test machine.Results showed that the Ag nanoparticles in liquid paraffin exhibited good antiwear property and could improve load carrying capacity of base oil remarkably.

Preparation of AgBr Nanoparticles in Microemulsions Via Reaction of AgNO3 with CTAB Counterion

Nanoparticles of AgBr were prepared by precipitating AgBr in the water pools of microemulsions consisting of CTAB, n-butanol, isooctane and water. An aqueous solution of AgNO3 added to the microemulsion was the source of Ag+ ions. The formation of AgBr nanoparticles in microemulsions through direct reaction with the surfactant counterion is a novel approach aimed at decreasing the role of intermicellar nucleation on nanoparticle formation for rapid reactions. The availability of the surfactant counterion in every reverse micelle and the rapidity of the reaction with the counterion trigger nucleation within individual reverse micelles. The effect of the following variables on the particle size and size distribution was investigated: the surfactant and cosurfactant concentrations, moles of AgNO3 added, and water to surfactant mole ratio, R. High concentration of the surfactant or cosurfactant, or high water content of the microemulsion favored intermicellar nucleation and resulted in the formation of large particles with broad size distribution, while high amounts of AgNO3 favored nucleation within individual micelles and resulted in small nanoparticles with narrow size distribution. A blue shift in the UV absorption threshold corresponding to a decrease in the particle size was generally observed. Notably, the variation of the absorption peak size with the nanoparticle size was opposite to those reported by us in previous studies using different surfactants.

In situ formation of dispersed palladium nanoparticles in microemulsion: Efficient reaction system for ligand-free Heck reaction

The ligand-free Heck reaction catalyzed by Pd(OAc) 2 performed well in a TX10 oil-in-water microemulsion. TEM proved in situ formation distributed palladium nanoparticles in the microemulsion. The role of TX10 in the reaction system is the palladium nanoparticles reducing agent and stabilizer. The effect of reaction parameters on the Heck reaction conversion were discussed. The results indicated that the aqueous phase concentration, the base concentration, and the temperature played key roles in the conversion of the reaction. Iodobenzene was converted to the corresponding trans-stilbene quantitatively within 90–150 min. Therefore, the heptane/TX 10/butanol/water/propylene glycol microemulsion containing in situ formed palladium nanoparticles was a very efficient catalyst system for the ligand-free Heck reaction.

A computer simulation study on the influence of the critical nucleus on the mechanism of formation of nanoparticles in microemulsions

We carried out computer simulations to study the influence of the critical nucleus size on the mechanism of formation of nanoparticles synthetized in microemulsions. One can conclude that nucleation process is strongly affected by the critical nucleus size, but this influence is less pronounced when a flexible surfactant film is used. Final nanoparticle size also depends on critical nucleus, obtaining larger particles as the critical nucleus increases.

Enzyme-Catalyzed Regioselective Modification of Starch Nanoparticles

The selective esterification of starch nanoparticles was performed using as catalyst Candida antartica Lipase B (CAL-B) in its immobilized (Novozym 435) and free (SP-525) forms. The starch nanoparticles were made accessible for acylation reactions by formation of Aerosol-OT (AOT, bis(2-ethylhexyl)sodium sulfosuccinate) stabilized microemulsions. Starch nanoparticles in microemulsions were reacted with vinyl stearate, e-caprolactone, and maleic anhydride at 40 °C for 48 h to give starch esters with degrees of substitution (DS) of 0.8, 0.6, and 0.4, respectively. Substitution occurred regioselectively at the C-6 position of the glucose repeat units. Infrared microspectroscopy (IRMS) revealed that AOT-coated starch nanoparticles diffuse into the outer 50 μm shell of catalyst beads. Thus, even though CAL-B is immobilized within a macroporous resin, CAL-B is sufficiently accessible to the starch nanoparticles. When free CAL-B was incorporated along with starch within AOT-coated reversed micelles, CAL-B was als...

Formation of Silver Chloride Nanoparticles in Microemulsions by Direct Precipitation with the Surfactant Counterion

Nanoparticles of silver chloride were prepared by direct precipitation of silver ions with the surfactant counterion in the water pools of microemulsions formed by dioctyldimethylammonium chloride in an organic n-decanol/isooctane phase. This work represents a new concept to form nanoprecipitates using a single reverse micellar system. The net result is a fast reaction with less dependency on the intermicellar exchange of solubilizate. The effects of the surfactant and cosurfactant concentrations, of the mole ratio of water to surfactant, R, and of the loading of silver nitrate were evaluated. Increasing the surfactant concentration at fixed values of R and moles of silver nitrate resulted in a higher dependency on the reverse micellar exchange dynamics and increased the particle size. At high n-decanol concentration, the particle size increased due to decreasing the interaction between the nanoparticles and the stabilizing surfactant layer. Similar results were found at high values of R. Increasing the amount of silver nitrate resulted in the formation of more nuclei, and hence in the production of smaller particles. The trends in the particle size and the size distribution were followed using UV spectrophotometry and transmission electron microscope photographs.

Synthesis of platinum nanoparticles in microemulsions and their catalytic activity for the oxidation of carbon monoxide

Abstract Platinum nanoparticles have been prepared by the reduction of metal ions with hydrazine in oil–water microemulsions consisting of sodium bis(2-ethylhexyl)sulphosuccinate (AOT)+cyclohexane+water of varying composition. The catalytic efficiency of the synthesized metal nanoclusters has been tested for oxidation of carbon monoxide. Effects of the nature of the platinum salt, [H 2 O]/[surfactant] ratio in the microemulsions and the addition of polymers on the catalytic efficiency of the synthesized metal nanoparticles have been investigated. Catalytic oxidation of CO gas was carried out in a vertical quartz tube connected to a quadrupole mass spectrometer. Whereas, using pure alumina as a catalyst, complete conversion of CO to CO 2 was observed at 325 °C, platinum nanoparticles adsorbed on alumina was found to carry out such conversion at 145 °C.

Formation of BaSO4 Nanoparticles in Microemulsions with Polymerized Surfactant Shells

Formation of BaSO₄ Nanoparticles in Microemulsions with Polymerized Surfactant Shells

Synthesis and Characterization of Silica-Coated Iron Oxide Nanoparticles in Microemulsion: The Effect of Nonionic Surfactants

A water-in-oil microemulsion method has been applied for the preparation of silica-coated iron oxide nanoparticles. Three different nonionic surfactants (Triton X-100, Igepal CO-520, and Brij-97) have been used for the preparation of microemulsions, and their effects on the particle size, crystallinity, and the magnetic properties have been studied. The iron oxide nanoparticles are formed by the coprecipitation reaction of ferrous and ferric salts with inorganic bases. A strong base, NaOH, and a comparatively mild base, NH4OH, have been used in each surfactant to observe whether the basicity has some influence on the crystallization process during particle formation. Transmission electron microscopy, X-ray electron diffraction, and superconducting quantum interference device magnetometry have been employed to study both uncoated and silica-coated iron oxide nanoparticles. All these particles show magnetic behavior close to that of superparamagnetic materials. By use of this method, magnetic nanoparticles as small as 1−2 nm and of very uniform size (percentage standard deviation is less than 10%) have been synthesized. A uniform silica coating as thin as 1 nm encapsulating the bare nanoparticles is formed by the base-catalyzed hydrolysis and the polymerization reaction of tetraethyl orthosilicate in microemulsion. All experimental results are also compared with those for particles synthesized in pure water.

Femtosecond Z-scan investigation of nonlinear refraction in surface modified PbS nanoparticles

The third-order optical nonlinearities of surface modified PbS nanoparticles have been measured using the Z-scan technique with femtosecond laser pulses at 780 nm wavelength. The samples studied are the nanoparticles in microemulsion with the PbS concentration ranging from 0.3×10 −3 to 1.9×10 −3 M (mol/l). A Z-scan analysis method based on the Huygens–Fresnel (H–F) propagation integral is employed to extract the nonlinear refractive index from the experimental Z-scan data with a large nonlinear phase shift. The nonlinear refractive index of the PbS nanoparticles in microemulsion is found to increase linearly with the PbS concentration. The highest concentration microemulsion gives a nonlinear refractive index of −4.7×10 −12 cm 2/W, which is approximately 3 orders of magnitude higher than those of commercially available bulk semiconductors, such as ZnS and CdS. In addition, nonlinear absorption in these samples remained unmeasurable up to 0.9 GW/cm 2. The mechanisms responsible for the observed large refractive nonlinearity are discussed.

Catalysis by Palladium Nanoparticles in Microemulsions

The oxidation by Co(NH3)5Cl2+ of N,N,N‘,N‘-tetramethyl-p-phenylenediamine (TMPPD) catalyzed by nanoparticles of palladium in an aqueous buffer/AOT/n-heptane microemulsion has been studied. The init...

Preparation of Ni Nanoparticles and Evaluation of Their Tribological Performance as Potential Additives in Oils

The application of nanoparticles in tribology has received considerable attention in recent years. In this paper, we described the preparation of Ni nanoparticles in microemulsions of sodium dodecyl sulphate (SDS)/isopentanol/cyclohexane/water and their tribological performance as additives in oils. The size of these nanoparticles is about 10 nm, and their shape is spherical. The four-ball test results indicate that Ni nanoparticles are potential additives for lubricating oils, and the tribological performance of lubricating oils can be improved significantly by dispersing Ni nanoparticles in oils. The maximum non-seizure load (PB) has been increased by 67 percent as compared with background oil. The wear scar diameter has been reduced from 0.71 mm to 0.49 mm. The relative percentage in friction coefficient has decreased 26 percent. The tribological mechanism is that a deposit film in the contacting regions was formed, which prevented the direct contact of rubbing surfaces and greatly reduced the frictional force between the contacting surfaces.

Preparation of Nanoparticles in Microemulsions: A Monte Carlo Study of the Influence of the Synthesis Variables

Monte Carlo simulations were performed to study the formation of nanoparticles in microemulsions. The influence of the following parameters on particle size distribution (PSD) was investigated: number of reagent molecules per droplet, surfactant film flexibility, droplet size, presence or absence of autocatalysis by the product, and the fraction of bulk volume made up by droplets. It was found that autocatalyzed reactions with high reagent concentrations and low surfactant film flexibility afforded bimodal PSDs. Particle size increased with reagent concentration when this was low, but at higher reagent concentrations it depended chiefly on droplet size. The dependence of PSD on reaction time confirmed the successive occurrence of well-defined nucleation and growth processes. We have compared the simulation results with experimental data taken from different authors and carried out in our laboratory. Good agreement between both kind of results supports the conclusions of this paper.

Kinetics of the Formation of Particles in Microemulsions

In this paper the kinetics of the formation of nanoparticles in microemulsions is studied by Monte Carlo computer simulation. It is observed that compartmentalization of the reactants induces a separation of the nucleation and growth processes, which is more clearly observed when the concentration of reactants is relatively high. It is also observed that growth by autocatalysis and by ripening overlaps at low concentrations but occurs on different time scales at high concentration. A comparison between the results of these simulations and those from Smoluchowski's rapid-coagulation mechanism is made, showing that this theory is adequate to model the kinetics of these reactions.