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Particle Size Decreased (particle + size_decreased)
Selected AbstractsFactors influencing the partitioning and toxicity of nanotubes in the aquatic environment,,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2008Alan J. Kennedy Abstract Carbon nanotubes (NTs) may be among the most useful engineered nanomaterials for structural applications but could be difficult to study in ecotoxicological evaluations using existing tools relative to nanomaterials with a lower aspect ratio. Whereas the hydrophobicity and van der Waals interactions of NTs may suggest aggregation and sedimentation in aquatic systems, consideration regarding how engineered surface modifications influence their environmental fate and toxicology is needed. Surface modifications (e.g., functional groups and coatings) are intended to create conditions to make NTs dispersible in aqueous suspension, as required for some applications. In the present study, column stability and settling experiments indicated that raw, multiwalled NTs (MWNTs) settled more rapidly than carbon black and activated carbon particles, suggesting sediment as the ultimate repository. The presence of functional groups, however, slowed the settling of MWNTs (increasing order of stability: hydroxyl > carboxyl > raw), especially in combination with natural organic matter (NOM). Stabilized MWNTs in high concentrations of NOM provided relevance for water transport and toxicity studies. Aqueous exposures to raw MWNTs decreased Ceriodaphnia dubia viability, but such effects were not observed during exposure to functionalized MWNTs (>80 mg/L). Sediment exposures of the amphipods Leptocheirus plumulosus and Hyalella azteca to different sizes of sediment-borne carbon particles at high concentration indicated mortality increased as particle size decreased, although raw MWNTs induced lower mortality (median lethal concentration [LC50], 50 to >264 g/kg) than carbon black (LC50, 18,40 g/kg) and activated carbon (LC50, 12,29 g/kg). Our findings stress that it may be inappropriate to classify all NTs into one category in terms of their environmental regulation. [source] Preparation of Polystyrene/Clay Nanocomposites by Free-Radical Polymerization in DispersionMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2009Nagi Greesh Abstract Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na-MMT clay was pre-modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading. [source] Atmospheric Cold Plasmas for Synthesizing Nanocrystalline Anatase TiO2 using Dielectric Barrier DischargesPLASMA PROCESSES AND POLYMERS, Issue 5 2007Long-Hui Nie Abstract Nanocrystalline anatase TiO2 has been successfully synthesized using TiCl4 and O2 as precursors by atmospheric cold plasmas generated by dielectric barrier discharges (DBD) without extra heating or thermal treatment. For the TiO2 powders synthesized by DBD plasma at an energy density of 5.9 kJ,·,L,1, XRD and TEM analyses revealed that the nanocrystallite size is about 10,15 nm. Only a single crystalline structure of anatase was observed performing XRD, HRTEM and SAED measurements. It was found that the particle size decreased with increasing the discharge power, and that the chlorine contamination dramatically decreased when using high discharge power levels. [source] Morphologies and applied properties of PSI/PA composite particles synthesized at low temperaturePOLYMER COMPOSITES, Issue 11 2008Yumin Wu Latex with a poly(dimethyl-siloxane) core and a poly(methylmethacrylate- butylacrylate- 2-hydroxypropyl acrylate) shell have been prepared at low temperature with potassium-persulphate (KPS), sodium formaldehyde sulfoxylate (SFS) and 2,2,-azobis [2-(2-imidazolin- 2-yl)propane] dihydrochloride (VA-044) as composite initiators by staged emulsion polymerization. Reactive surfactants were used to significantly improve the applied properties such as water adsorption ratio and thermo-properties. Transmission electron microscopy (TEM) results indicated that increasing the amount of 2-hydroxypropyl acrylate (HPA) and butylacrylate (BA) was favorable to form the core/shell particles. Particle size distribution results showed with increasing the dosages of surfactants, initiators, and seed-latex, particle size decreased. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) results indicated the high temperature-reserved of copolymer was improved in the presence of polysiloxane. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] |