Nuria Navascues

Facile preparation of transparent and conductive polymer films based on silver nanowire/polycarbonate nanocomposites

Silver nanowires (AgNW) synthesized by a solvothermal method were incorporated into a polycarbonate matrix by a solution mixing procedure. Films with a thickness around 18 μm were obtained, showing a good distribution of the wires within the polymer matrix. The thermal stability of the polymer matrix increased significantly, with the main decomposition peak shifting up to 74 ° C for an AgNW loading of 4.35 wt%. The percolation threshold was obtained at very low AgNW content (0.04 wt%), and the composite electrical conductivity at the maximum loading (4.35 wt%) was 41.3 Ω cm. Excellent transparency was obtained at the percolation threshold, with negligible reduction in the transmittance of the polymer matrix (from 88.2 to 87.6% at 0.04 wt% loading of AgNW). In addition, the polymer matrix protected the silver nanowires from oxidation, as demonstrated by the XPS analysis.

Silver nanowires/polycarbonate composites for conductive films

Silver nanowires (AgNW) with an aspect ratio of 85 were synthesized by a solvothermal process. The AgNW were characterized by SEM and XRD techniques. Nanocomposites of these silver nanowires in a polycarbonate matrix were prepared by simple solution mixing procedure in a concentration filler range 0-4.35 wt%. The obtained films were around 18 μm thick, optical microscopy and SEM characterization showed good dispersion of the nanowires in the polymeric matrix. The obtained composites presented low percolation threshold (0.04 wt%) and the maximum conductivity at 4.35 wt% filler loading was 2.3×10−2 S/cm.

Unintended emission of nanoparticle aerosols during common laboratory handling operations

Common laboratory operations such as pouring, mashing in an agate mortar, transferring with a spatula, have been assessed as potential sources for emission of engineered nanoparticles in simulated occupational environments. Also, the accidental spilling from an elevated location has been considered. For workplace operations, masses of 1500 or 500mg of three dry-state engineered nanoparticles (SiO2, TiO2 and Ce-TiO2) with all dimensions under 30nm, and one fibrous nanomaterial (MWCNT) with diameter under 10nm and length about 1.5μm were used. The measured number emission factors (NEF) for every operation and material in this work were in the range of 10(5) #s(-1). The traceability of emitted nanoparticles has been improved using Ce-doping on TiO2 nanoparticles. With this traceable material it was possible to show that generated aerosol nanoparticles are rapidly associated with background particles to form large-sized aerosol agglomerates.

Laser-treated electrospun fibers loaded with nano-hydroxyapatite for bone tissue engineering

Core-shell polycaprolactone/polycaprolactone (PCL/PCL) and polycaprolactone/polyvinyl acetate (PCL/PVAc) electrospun fibers loaded with synthesized nanohydroxyapatite (HAn) were lased treated to create microporosity. The prepared materials were characterized by XRD, FTIR, TEM and SEM. Uniform and randomly oriented beadless fibrous structures were obtained in all cases. Fibers diameters were in the 150-300nm range. Needle-like HAn nanoparticles with mean diameters of 20nm and length of approximately 150nm were mostly encase inside the fibers. Laser treated materials present micropores with diameters in the range 70-120μm for PCL-HAn/PCL fibers and in the 50-90μm range for PCL-HAn/PVAC material. Only samples containing HAn presented bioactivity after incubation during 30days in simulated body fluid. All scaffolds presented high viability, very low mortality, and human osteoblast proliferation. Biocompatibility was increased by laser treatment due to the surface and porosity modification.

Modulation of bactericidal action in polymer nanocomposites: light-tuned Ag+ release from electrospun PMMA fibers

While silver is widely regarded as a potent antibacterial material, controlling the rate of release of the bactericidal agents (silver ions) remains a challenge. When silver nanoparticles are used as precursors, the release process involves oxidation and dissolution in the surrounding environment. Here we show that it is possible to tune the rate of silver release from polymer matrices containing silver precursors by a simple UV irradiation step. To demonstrate this, silver-containing polymer (PMMA) fibers have been produced by electrospinning, then subjected to different levels of exposure to UV radiation and fully characterized in terms of silver state, presence of nanoparticles, Ag+ release rates and bactericidal power. The as-spun fibers contained mainly silver as Ag+, while samples exposed to UV radiation displayed progressively higher proportions of Ag0 (XPS analysis). Nanoparticles consisting of metallic silver were present in UV-exposed samples, and their size increased with irradiation time. The Ag+ release rates (and the bactericidal action of the nanofibers) were found to directly depend on the degree of UV exposure: a fast Ag+ release was observed for non-irradiated samples, which during the release experiment delivered roughly three times as much silver than samples subjected to 24 h UV exposure.