No abstract

a b s t r a c tIn this paper we report for the first time on the emissive behavior of two polyaniline (PANI) nanoparticle systems produced via oxidative chemical polymerization in the presence of either poly(vinyl alcohol) (PVA) or chitosan as polymeric stabilizers in water. The emission from PANI nanoparticles is irreversibly quenched by an increase of pH of the suspending medium from acid to neutral (chitosan-PANI) or alkaline (PVA-PANI). Conversely, PANI nanorods synthesized in the same conditions of the above, but in presence of poly(N-vinyl pyrrolidone), is not emissive at any pH. The role of the polymeric surfactant as a soft template is key in controlling the morphology and the properties of the obtained PANI dispersions. FTIR, UV-Vis absorption and photoluminescence excitation (PLE) spectra studies suggest that the emissive properties are related to the establishment of strong, non-covalent interactions between nanoscalar PANI particles and the polymeric surfactant at the pH of synthesis. Morphology examination of the three systems, by both dynamic light scattering (DLS) and Transmission Electron Microscopy (TEM), reveal that photoluminescence is associated to the presence of a genuinely 3D nanoscalar morphology, together with an ordered disposition of PANI chains into aligned crystal planes. Concomitant to the irreversible quenching of the emission signal with increasing pH, there is an evolution of the morphology leading to particle coalescence, coarsening and ultimately phase-separation, with consequent modification of PANI-polymeric surfactant interactions, PANI chains supra-molecular organization and optical properties of the PANI nanoparticles dispersion.

a b s t r a c t PANI aqueous nanocolloids in their acid-doped, inherently conductive form were synthesised by means of suitable water soluble polymers used as stabilisers. In particular, poly(vinyl alcohol) (PVA) or chitosan (CT) was used to stabilise PANI nanoparticles, thus preventing PANI precipitation during synthesis and upon storage. Subsequently, e-beam irradiation of the PANI dispersions has been performed with a 12 MeV Linac accelerator. PVA-PANI nanocolloid has been transformed into a PVA-PANI hydrogel nanocomposite by radiation induced crosslinking of PVA. CT-PANI nanoparticles dispersion, in turn, was added to PVA to obtain wall-to-wall gels, as chitosan mainly undergoes chain scission under the chosen irradiation conditions. While the obtainment of uniform PANI particle size distribution was preliminarily ascertained with laser light scattering and TEM microscopy, the typical porous structure of PVA-based freeze dried hydrogels was observed with SEM microscopy for the hydrogel nanocomposites. UV À visible absorption spectroscopy demonstrates that the characteristic, pH-dependent and reversible optical absorption properties of PANI are conferred to the otherwise optically transparent PVA hydrogels. Selected formulations have been also subjected to MTT assays to prove the absence of cytotoxicity.

No abstract

Nanotechnology is one of the fastest developing new areas in science and technology. Ionizing radiation is widely applied for nanostructure synthesis and nanomaterials modification. The ability to fabricate structures with nanometric precision is of fundamental importance to any exploitation of nanotechnology. Nanofabrication involves various lithographies to write extremely small structures. An interesting field of radiation nanotechnological application concerns the development of nano-ordered hydrogels for biosensors. New trends and more precise treatment technology were applied: surface curing and modification, polymer functionalization are good examples of such developments. Patents on application of ionizing radiation in nanotechnology focused on many different approaches to this topic, not only nanoparticles synthesis but also nanostructure modification or functionalization.