Mariano Palomba

Mechanical properties of low-density polyethylene filled by graphite nanoplatelets

The mechanical properties of GNP/LDPE nanocomposites (graphite nanoplatelets/low density polyethylene) have been investigated, in order to establish the effect of nanoscale reinforcement within the polymer matrix. Results show that the presence of the filler does not involve a change in the microscopic structure of the polymer. However, on a macroscopic scale, GNPs limit the mobility of the polymer chains, resulting in an increase in stiffness for the final composite. Orientation of GNPs within the LDPE matrix is also an important issue that affects mechanical properties and it has been evaluated by testing nanocomposites made by different manufacturing techniques (compression moulding and blown extrusion). The comparison between the experimental data and the Halpin-Tsai model shows that the orientation of GNPs due to the extrusion process leads to values of tensile modulus higher than that obtained with the randomly oriented disposition resulting from the compression moulding technique.

Ultrafine Magnetite Nanopowder: Synthesis, Characterization, and Preliminary Use as Filler of Polymethylmethacrylate Nanocomposites

Magnetite (Fe3O4) nanoparticles prepared by microwave-assisted hydrothermal synthesis have been characterized in terms of morphological and structural features. Electron micrographs collected in both scanning (SEM) and transmission (TEM) modes and evaluations of X-ray powder diffraction (XRD) patterns have indicated the achievement of a monodispersed crystallite structure with particles having an average size around 15–20 nm. Structural investigations by Micro-Raman spectroscopy highlighted the obtainment of magnetite nanocrystals with a partial surface oxidation to maghemite (γ-Fe3O4). Preliminary attention has been also paid to the use of these magnetite nanoparticles as filler for a commercial polymethylmethacrylate resin. Hybrid formulations containing up to 3 wt% of nanoparticles were prepared by melt blending and characterized by calorimetric and thermogravimetric tests. For sake of comparison, same formulations containing commercial Fe3O4 nanoparticles are also reported. Calorimetric characterization indicates an increase of both glass transition temperature and thermal stability of the nanocomposite systems when loaded with the synthesized magnetite nanoparticles rather then loaded with the same amount of commercial Fe3O4. This first observation represents just one aspect of the promising potentiality offered by the novel magnetic nanoparticles when mixed with PMMA.

Activity of antimicrobial silver polystyrene nanocomposites

A simple technique based on doping polymers with in situ generated silver nanoparticles (Ag/PS films) has been developed. In particular, an antiseptic material has been prepared by dissolving silver 1,5-cyclooctadiene-hexafluoroacetylacetonate in amorphous polystyrene, and the obtained solid solution has been heated for ca. 10 s at a convenient temperature (180°C). Under such conditions the metal precursor decomposes producing silver atoms that diffuse into the polymer and clusterize. The antimicrobial characteristics of the resulting polystyrene-based material have been accurately evaluated toward Escherichia coli (E. coli) comparing the cytotoxicity effect of 10wt.% and 30wt.% (drastic and mild annealing) silver-doped polystyrene to the corresponding puremicrometric silver powder. Two different bacterial viability assays were performed in order to demonstrate the cytotoxic effect of Ag/PS films on cultured E. coli: (1) turbidimetric determination of optical density; (2) BacLight fluorescencebased test. Both methods have shown that silver-doped polystyrene (30wt.%) provides higher antibacterial activity than pure Ag powder, under similar concentration and incubation conditions.

Optical limiters based on silver nanoparticles embedded in amorphous polystyrene

Abstract A simple technique to prepare plastic color-filters based on the surface plasmon resonance (SPR) of silver nanoparticles has been developed. In particular, silver/polystyrene nanocomposites have been prepared by dissolving silver acetylacetonate in amorphous polystyrene and heating the obtained solid solution at a convenient temperature (ca. 200°C). When the metal precursor decomposes, the produced silver atoms diffuse into the polymeric matrix and clusterize, leading to the formation of a contact-free dispersion of hyperfine silver phase. The obtained films have been characterized by UV-VIS spectroscopy and the optical extinction spectra have been fitted by the Mie’s theory, introducing the limitation of the mean free path due to the collisions of conduction electrons with the boundary of the nanoparticles.

Nanocomposite synthesis by thermolysis of (Ag(hfac)(COD)) in amorphous polystyrene

Abstract Lightfast color filters (intensively and brightly colored) can be easily produced by dying optical plastics with the surface plasmon resonance (SPR) of metal nanoparticles such as silver and gold. Here, color filters based on silver nanoparticles embedded in amorphous polystyrene have been prepared by dissolving and thermally decomposing (1,5-cyclooctadiene)(hexafluoro-acetylacetonate)silver(I) in amorphous polystyrene. The metal precursor quickly decomposes (10 s, at 180°C), leading to silver atoms that clusterize and produce a non-aggregated dispersion of silver particles in the polymer matrix. The intensity of the yellow coloration due to the SPR of nanoscopic silver can be widely tuned simply by varying the cluster numerical density in the polymer matrix that depends on the silver precursor concentration. The obtained nanocomposite films have been characterized by X-ray power diffraction, transmission electron microscopy, and UV-Vis spectroscopy.

Graphene–polymer coating for the realization of strain sensors

In this work we present a novel route to produce a graphene-based film on a polymer substrate. A transparent graphite colloidal suspension was applied to a slat of poly(methyl methacrylate) (PMMA). The good adhesion to the PMMA surface, combined with the shear stress, allows a uniform and continuous spreading of the graphite nanocrystals, resulting in a very uniform graphene multilayer coating on the substrate surface. The fabrication process is simple and yields thin coatings characterized by high optical transparency and large electrical piezoresitivity. Such properties envisage potential applications of this polymer-supported coating for use in strain sensing. The electrical and mechanical properties of these PMMA/graphene coatings were characterized by bending tests. The electrical transport was investigated as a function of the applied stress. The structural and strain properties of the polymer composite material were studied under stress by infrared thermography and micro-Raman spectroscopy.

A new high-soluble precursor for in situ silver nanoparticle generation in polymers

Abstract Perfectly transparent silver-polystyrene nanocomposites, characterized by a very strong SPR absorption band centered at 421nm, have been prepared by dissolving silver 1,5-cyclooctadiene hexafluoroacetylacetonate into amorphous polystyrene and thermally annealing this solid solution for 10s at 180 °C. The silver atoms generated during the [Ag(hfac)(COD)] thermal decomposition process slowly diffuse into the molten polymeric phase and clusterize, leading to the formation of a contact-free dispersion of silver nanoparticles characterized by a very intensive SPR absorption. Finally, silver 1,5-cyclooctadienehexafluoroacetylacetonate can be conveniently used to dye optical plastics by the strong SPR absorption of nanoscopic silver without transparency loss. In addition, the intensity of coloration can be varied by changing the amount of organic salt dissolved into the polymer.

Optical and electrical characterizations of graphene nanoplatelet coatings on low density polyethylene

Coatings of graphene nanoplatelets (GNPs) were deposited on a low density polyethylene (LDPE) substrate by a micromechanical method based on rubbing graphite platelets against the surface of the polymer. Transmission electron microscopy measurements reveal that the coatings were composed of nanoplatelets containing 13–30 graphene layers. Thermal gravimetric analysis shows that the investigated GNP coatings on LDPE (GNP/LDPE) samples are thermally stable up to 250 °C. Optical spectra of these samples, compared to those of pristine LDPE in the ultraviolet-visible-near-infrared range, indicate an increase in both reflectance and absorptance. On the other hand, the coating is able to markedly improve the surface conductivity of the polymeric substrate, indeed in the case of electrical contacts in the coplanar configuration (1 cm long and spaced 1 mm), the resistance of LDPE is 1015 Ω, while that of GNP/LDPE is 670 Ω. Electrical measurements under white light illumination point out a decrease in the conductance and a linear behavior of the photoconductance as a function of the optical power density. GNP/LDPE materials can be used for their optical, electrical, thermal, and flexibility properties in large area plastic electronics and optoelectronics.Coatings of graphene nanoplatelets (GNPs) were deposited on a low density polyethylene (LDPE) substrate by a micromechanical method based on rubbing graphite platelets against the surface of the polymer. Transmission electron microscopy measurements reveal that the coatings were composed of nanoplatelets containing 13–30 graphene layers. Thermal gravimetric analysis shows that the investigated GNP coatings on LDPE (GNP/LDPE) samples are thermally stable up to 250 °C. Optical spectra of these samples, compared to those of pristine LDPE in the ultraviolet-visible-near-infrared range, indicate an increase in both reflectance and absorptance. On the other hand, the coating is able to markedly improve the surface conductivity of the polymeric substrate, indeed in the case of electrical contacts in the coplanar configuration (1 cm long and spaced 1 mm), the resistance of LDPE is 1015 Ω, while that of GNP/LDPE is 670 Ω. Electrical measurements under white light illumination point out a decrease in the conductanc...

Tellurium-based nanocomposites for plastic electronic applications

Owing to the very brittle nature of the tellurium powder, nanoscopic grains with average size of 4.8nm were produced by dry vibration milling technique using a Mixer mill apparatus. A novel material was obtained by binding the nanosized tellurium grains with poly(methyl methacrylate) (PMMA). The morphology, elemental composition, and structural properties of Te/PMMA films were investigated. The prepared material was composed of hexagonal tellurium and α-phase of tellurium oxide. The electrical properties of the films were studied in dark condition and under white light illumination varying the optical power density from 10 to 170 mW/cm2 and turning on and off the light cyclically.

Polymer-supported graphene obtained by a micromechanical tecnique based on shear-stress

A novel, simple and effective micromechanical technique for the synthesis of graphene supported by low density polyethylene (LDPE) is reported. This technique is based on the application of a combination of shear stress and friction force to nanographite to induce its complete exfoliation to graphene. LDPE-supported graphene multilayers of large area were prepared and their morphological, structural and electrical properties were investigated. The samples showed negative photoconductivity under white-light illumination, varying the power density from 27 to 170 mW/cm2.