Davide Morselli

Single step in situ formation of porous zinc oxide/PMMA nanocomposites by pulsed laser irradiation: kinetic aspects and mechanisms

The simultaneous in situ formation of zinc oxide nanoparticles and controlled porosity in poly(methyl methacrylate) films is presented herein as an innovative method for the preparation of polymer based porous nanocomposites. The process is based on the conversion of zinc acetate in spherical zinc oxide nanoparticles of 9 nm on average, by pulsed laser activated precursor decomposition. The kinetics of the nanoparticles formation, followed by UV-visible spectroscopy, show a remarkable increase of the reaction rate with respect to the conventional thermally activated process. Most importantly, as revealed by scanning electron microscopy investigations, the laser treatment leads to the simultaneous formation of a porous structure in the polymer matrix, which can be ascribed to the yielded gaseous by-products during the zinc oxide nanoparticle formation. The combination of all these characterizations allowed a deeper insight in the kinetic aspects and mechanisms involved in the single step formation of porous poly(methyl methacrylate)/zinc oxide nanocomposites with tailored characteristics that cannot be achieved by the conventional thermal treatment.

Laser-induced localized formation of silver nanoparticles on chitosan films: study on particles size and density variation

We present the in situ localized formation of silver nanoparticles in chitosan films by pulsed UV laser irradiation, as a result of the photoreduction of the silver nitrate precursor loaded throughout the volume of the polymer. The UV pulsed irradiation is also found to be responsible for the photofragmentation of the previously formed nanoparticles, leading to their average size reduction as the number of pulses increases. In fact, their diameter changes from ~150 to ~30 nm for irradiation with 5 to 200 pulses, respectively. After irradiation the formation of nanoparticles continues for several days, since the already formed nanoparticles act as seeds for the reduction of the unreacted precursor. Indeed, few weeks after irradiation, the chitosan films present a metallic mirror-like appearance on the previously irradiated areas, as they are fully covered by silver. Taking advantage of all these simultaneous mechanisms, and controlling the number of pulses and elapsed time after irradiation, Ag nanoparticles of specific size can be formed in situ on desired areas of the film. Through this process is envisioned the fabrication of nanocomposites with functional properties.

An Efficient Pure Polyimide Ammonia Sensor

Pyromellitic dianhydride–4,4-oxydianiline (PMDA–ODA), broadly known as Kapton, is investigated for detection and quantification of ammonia (NH3) vapors from ammonia solutions of different molarities. The PMDA–ODA films are made by solution casting on microscope glass slides and cured at 200 °C. Ammonia sensing is performed by measuring the changes in the electric current intensity under ambient conditions of temperature and humidity. The sensor exhibits fast response to ammonia vapors, for aqueous ammonia solutions with molarity as low as 3.5 mM. The adsorption processes of ammonia to the polyimide surface after exposure to ammonia vapors are investigated by FTIR and XPS, revealing that ammonia results in the disruption of imide linkages and the simultaneous creation of amides I and II. Control experiments performed on commercial Kapton adhesive tape show negligible sensitivity of the commercial product to ammonia vapors from different ammonia solution molarities. A device is also presented, demonstrating the real-time detection of ammonia vapors.

Organic-inorganic nanocomposites prepared by reactive suspension method: investigation on filler/matrix interactions and their effect on the nanoparticles dispersion

Epoxy resin/TiO2 nanocomposites prepared by both reactivesuspension method, based on in situ synthesis, and conventional mechanical mixing are analysed by solid-state nuclear magnetic resonance and transmission electron microscopy in order to have a deeper insight into the nature of interactions at the polymer/particle interface and their effect on the nanoparticles dispersion. Specifically, solid-state nuclear magnetic resonance experiments showed that the nanoparticles, synthesized by reactive suspension method, can efficiently link the matrix by hydrogen bonds forming a hybrid organic-inorganic 3D network. Such evidences strongly supports our previously reported theory, in which the nanoparticles in situ synthesized by reactive suspension method act not only as rigid filler, but also as actual cross-linking points, dramatically improving the mechanical properties of the polymeric matrix. Moreover, as revealed by transmission electron microscopy investigations, the formation of such hydrogen bonds significantly affect also the nanoparticles distribution, thanks to a stabilizing effect on the nanoparticles’ surface that prevents their aggregation and improves their dispersion.