Optimized solvent-exchange synthesis method for C60 colloidal dispersions

An existing solvent exchange method used to produce aqueous suspensions of fullerene C(60) aggregates (nC(60)) using the solvents toluene, tetrahydrofuran, acetone, and water, has been optimized for producing 75 nm diameter particles. Numerous synthesis parameters were evaluated for their effects on colloid yield and particle size distribution. Varying the relative volumes used of the intermediate solvents relative to the initial toluene volume allowed the controlled tuning of the resulting particle size up to a diameter of 210 nm. The resulting suspensions produced 10-20 ppm concentrations and reduced the residual organic solvents to less than the detection limit of 1 ppm.     

Chemiluminescence during ozonation of adamantane on silica gel

Ozonation of adamantane adsorbed on silica gel produces visible chemiluminescence in the wavelength range of 400–650 nm. When the supply of O₃ stops, chemiluminescence decays in a first order reaction with the effective rate constant k. Its dependence on the initial amount of adamantane and temperature has been studied.     

Hierarchical aqueous self-assembly of C60 nano-whiskers and C60-silver nano-hybrids under continuous flow

The ubiquitous starch-iodine complex can be used to organize hydrophobic fullerene C(60) in water into nano-whiskers shrouded by the biopolymer, and are approximately 5-8 nm in cross section, and 250-350 nm in length, as a hierarchical self assembly process. The preformed starch-iodine complex reacts with solid pristine C(60) affording nano-whiskers with iodine surrounding the fullerene array, the iodine then being removed on treatment with ascorbic acid. The hydrophobic surface of the nano-whiskers of C(60) can be coated with silver metal in a controlled way using 'soft energy' spinning disc processing.     

Raman characterization of C60 salts electroformed in aqueous media

Electrochemical intercalation of C₆₀ films from aqueous LiOH, KOH, NaOH, RbOH and CsOH solutions was studied by electrochemical methods and Raman spectroscopy. The intercalation of these alkali metals cations gives rise to reduction peaks at different applied potentials depending on the chemical nature of the cation used. Reduction of the C₆₀ films was observed to rather different extents depending on the composition of the working solution. Electrochemical and Raman experiments show that K⁺ and Cs⁺ ions form the most stables and active salts, while Li⁺, Na⁺ and Rb⁺ are not significantly intercalated. Furthermore, Raman characterization of the K⁺ and Cs⁺ doped films leads to the identification of the its main components, namely the K₂C₆₀ and CsC₆₀ species.     

Rheology of aqueous carbon black dispersions

The interaction of carbon black with an acrylic resin has been investigated by rheology. Two carbon blacks, with similar particle size and surface characteristics but quite different particle morphologies, have been examined. These are somewhat arbitrarily denoted as "spherical" and "fractal" as shown by small-angle neutron scattering (SANS) and ultrasonic spectroscopy studies. In the absence of polymer, stable aqueous dispersions could not be obtained. Stable dispersions could be obtained, however, upon addition of polymer to a level corresponding to a ratio of 50 mg of polymer per 13 m2 (+/- m2) of surface area (i.e., 15 wt% particles). These stable dispersions exhibit flow typical of concentrated dispersions-Newtonian behavior up to some apparent "yield" or critical value, above which pronounced shear thinning is observed. The critical stress increases with increasing polymer concentration. When a significant amount of nonadsorbed polymer is also present, a second Newtonian plateau is superimposed on the shear-thinning behavior. This feature is observed for both particle types but is more pronounced for the fractal particle. When there is little or no nonadsorbed polymer, the viscosity of the fractal particle dispersions is greater than the viscosity of the spherical particle dispersions. At low polymer concentrations, the dispersions are predominantly viscous at low shear stresses. The phase angle decreases significantly over a narrow shear stress range and the rheology tends to more elastic behavior. At higher shear stresses, the dependence on particle morphology is weak.     

Spectral characteristics of aqueous dispersions enriched in oxygen

The IR absorption and reflection spectra of aqueous dispersions consisting of (H₂O)_n, O₂(H₂O)_n, and (O₂)₂(H₂O)_n clusters (10 ≤ n ≤ 50) were calculated by the method of molecular dynamics using a flexible model of molecules. The frequency distribution of the power scattered by the cluster systems was obtained in the range 0 ≤ ω ≤ 3000 cm^?1. The capture of one oxygen molecule by the clusters is accompanied by a decrease in the absorption of the low-frequency IR radiation and by a peak of the absorption intensity in the vicinity of ω 2704 cm^?1. This is also accompanied by a decrease in the reflection coefficient throughout the frequency range and a decrease in the emission power at ω < 1030 and ω > 1700 cm^?1. Addition of two oxygen molecules to the clusters decreases the capability of the dispersions for the absorption, reflection, and scattering of IR radiation.     

Laser flash photolysis of fullerols of C60 and of C70 in aqueous solutions

Fullerols of C₆₀ and of C₇₀ [C₆₀(OH)_n, C₇₀(OH)_m], water-soluble fullerene derivatives, unlike some other fullerene derivatives (such as C₆₀ (C₄H₆O), C₆₀ (C₃H₇N) and C₆₀ [C(COOEt)₂]_x), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron (Φ_e ⁻) are determined to be 0.08 and 0.11 for fullerols of C₆₀ and of C₇₀ respectively at room temperature (ca. 15°C) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO₄ ⁻, the fullerol radical cation or neutral radical of C₆₀ is confirmed to be existent and the transient absorption spectra of fullerol radical cation of C₇₀ are observed for the first time. Project supported by the National Natural Science Foundation of China     

Colloidal stability of aqueous nanofibrillated cellulose dispersions

Cellulose nanofibrils constitute an attractive raw material for carbon-neutral, biodegradable, nanostructured materials. Aqueous suspensions of these nanofibrils are stabilized by electrostatic repulsion arising from deprotonated carboxyl groups at the fibril surface. In the present work, a new model is developed for predicting colloidal stability by considering deprotonation and electrostatic screening. This model predicts the fibril-fibril interaction potential at a given pH in a given ionic strength environment. Experiments support the model predictions that aggregation is induced by decreasing the pH, thus reducing the surface charge, or by increasing the salt concentration. It is shown that the primary mechanism for aggregation upon the addition of salt is the surface charge reduction through specific interactions of counterions with the deprotonated carboxyl groups, and the screening effect of the salt is of secondary importance.     

Polymer dispersions from catalytic polymerization in aqueous systems

By contrast to traditional free radical emulsion polymerization, catalytic polymerization allows for polymer microstructure control. In terms of polymerizable monomers, both techniques are largely complementary. Since the beginning of this decade, an increasing number of reports on polyolefin, polybutadiene, polyalkenamer, polynorbornene, polyketone, and polyacetylene dispersions prepared by catalytic polymerization in disperse aqueous systems has appeared. This contribution reviews the preparation of these dispersions, their colloidal properties, particle formation mechanisms, particle morphologies, and polymer microstructures.     

A salt-free zero-charged aqueous onion-phase enhances the solubility of fullerene C60 in water

An onion-phase (multilamellar vesicular phase or Lalpha-phase) was prepared from salt-free zero-charged cationic and anionic (catanionic) surfactant mixtures of tetradecyltrimethylammonium hydroxide (TTAOH)/lauric acid (LA)/H2O. The H+ and OH- counterions form water (TTAOH + LA --> TTAL + H2O), leaving the solution salt free. The onion-phase solution has novel properties including low conductivity, low osmotic pressure and unscreened electrostatic repulsions between cationic and anionic surfactants because of the absence of salt. The spherical multilamellar vesicles have an average 250 nm radius as measured by freeze-fracture transmission electron microscopy (FF-TEM) and the maximum interlayer distance, i.e., the thickness of the hydrophobic bilayer and the water layer, was calculated to be around 52 nm by small-angle X-ray scattering (SAXS). Extremely hydrophobic C60 fullerene can be solubilized in this salt-free zero-charged aqueous onion-phase. As a typical result, 0.588 mg.mL(-1) (approximately 0.82 mmol.L(-1)) C60 has been successfully solubilized into a 50 mmol.L(-1) catanionic surfactant onion-phase aqueous solution. The weight ratio of fullerene to TTAL is calculated to be around 1:40. Solubilization of C60 in the salt-free catanionic onion-phase solution was investigated by using different sample preparation routes, and a variety of techniques were used to characterize these vesicular systems with or without encapsulated C60. The onion-phase solution changed color from slightly bluish to yellow or brown after C60 was solubilized. 1H and 13C NMR measurements indicated that the C60 molecules are located in the hydrophobic layers, i.e., in the central positions [omega-CH3 and delta-(CH2)x] of the hydrophobic layers of the TTAL onion-phase. Salt-free zero-charged catanionic vesicular aqueous solutions are good candidates for enhancing the solubility of C60 in aqueous solutions and may broaden the functionality of fullerenes to new potential applications in biology, medicine, and materials. Hopefully, our method can also be extended to solubilize functionalized carbon nanotubes in aqueous solutions.     

Light-controlled single-walled carbon nanotube dispersions in aqueous solution

We have succeeded in dispersing single-walled carbon nanotubes (SWNTs) into an aqueous solution of poly(ethylene glycol)-terminated malachite green derivative (PEG-MG) through simple sonication. It was found that UV exposure caused reaggregation of these predispersed SWNTs in the same aqueous medium, as adsorbed PEG-MG photochromic chains could be effectively photocleavaged from the nanotube surface. The observed light-controlled dispersion and reaggragation of SWNTs in the aqueous solution should facilitate the development of SWNT dispersions with a controllable dispersity for potential applications.     

Lignin transformations and reactivity upon ozonation in aqueous media

The reaction of ozone with lignin in aqueous acidic solutions is investigated. The Danckwerst model is used to describe the kinetics of gas/liquid processes occurring in a bubble reactor. The efficient ozonation rate of a soluble lignin analog, sodium lignosulfate, is determined. The main lines of the reaction between ozone and lignin are revealed on the basis of kinetic analysis results and IR and UV spectroscopy data.     

Photochemical synthesis of copper nanoparticles in aqueous polystyrene dispersions

Photochemical deposition of copper nanoparticles onto polystyrene surface under monochromatic (λ 254 nm) and unfiltered irradiation was studied. The kinetic parameters of this process depending on the concentration of copper(II) coordination compound and the size of polystyrene microspheres were determined. A procedure was tested for the preparation of monodisperse copper nanoparticles from colloidal copper chemically synthesized in ethylene glycol matrix in the presence of polystyrene with a microsphere size of 100 nm.     

Preparation of aqueous dispersions of paraffin and ceresin

The process of preparing aqueous dispersions of solid petroleum hydrocarbons was studied. Stable aqueous dispersions of petroleum paraffin can be prepared using polyvinyl alcohol in combination with a hydrotropic additive as a stabilizer. While for stabilization of dispersion of ceresin, which is a microcrystalline wax, it is necessary to use an anionic surfactant.     

Production of aqueous colloidal dispersions of carbon nanotubes

Stable homogeneous dispersions of carbon nanotubes (CNTs) have been prepared by using sodium dodecyl sulfate (SDS) as dispersing agent. To our knowledge, it is the first report to quantitatively characterize colloidal stability of the dispersions by UV-vis spectrophometric measurements. When the sediment time reaches 500 h, the supernatant CNT concentration drops as much as 50% for the bare CNT suspension, compared to 15% with the addition of SDS. Furthermore, after 150 h, no precipitation is found for CNT/SDS dispersions, exhibiting an extreme stability. Zeta potential, auger electron microscopy, and FTIR analysis are employed to investigate the adsorption mechanism in detail. It has been concluded that the surfactant containing a single straight-chain hydrophobic segment and a terminal hydrophilic segment can modify the CNTs-suspending medium interface and prevent aggregation over long periods. The morphology of the CNT dispersions is observed with optical microscopy. An intermediate domain of homogeneously dispersed nanotubes exhibits an optimum at 0.5 wt% CNTs and 2.0 wt% SDS.     

Chemiluminescence in the reaction of ozone with 1,3-dioxans in aqueous solutions

Chemiluminescence in the visible part of spectrum is found to assist the oxidation of substituted 1,3-dioxans by ozone in aqueous media. The kinetics of the chemiluminescence decay was studied in the temperature interval 323-353 K, and the activation parameters of this process were determined. A kinetic scheme is proposed to explain the results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Curing of aqueous epoxy dispersions in the presence of a cycloaliphatic amine

The possibility of using a cycloaliphatic amine NC-558 as a curing agent for water-based epoxy compounds was examined. The effect of the component concentrations and temperature on the properties of the films obtained was studied.

     

The mechanism and pathway of the ozonation of 4-chlorophenol in aqueous solution

Chlorophenols (CPs) have been widely used in dif- ferent formulations as preservatives, herbicides, insec- ticides, bactericides and solvents. Parts of chlorophe- nols were released to the natural environment during the usage. As a result, many water sources were con- taminated with CPs[1,2]. Furthermore, they also can be formed during the disinfection of phenol containing water by chlorination. Several CPs are recognized as the priority pollutants by the United States EPA (En- vironmenta…     

The mechanism of polymerisation of butyl cyanoacrylate in aqueous dispersions

Butyl cyanoacrylate has been polymerised by dispersion in acidified water to yield nanoparticles. Reactions have been carried out at various temperatures and the molecular weight of the growing polymer measured. In all cases polymerisation proceeds by generation of discrete populations of oligomers, which are then re‐initiated and undergo further growth. The peak molecular weight is around 1300 g/mol and it is considered that a stepwise initiation, termination and re‐initiation process continues until diffusionally limited by the internal viscosity within the nanoparticle.