Francesca Pignatelli

P(VDF-TrFE)/BaTiO3 Nanoparticle Composite Films Mediate Piezoelectric Stimulation and Promote Differentiation of SH-SY5Y Neuroblastoma Cells.

Poly(vinylidene fluoride-trifluoroethylene, P(VDF-TrFE)) and P(VDF-TrFE)/barium titanate nanoparticle (BTNP) films are prepared and tested as substrates for neuronal stimulation through direct piezoelectric effect. Films are characterized in terms of surface, mechanical, and piezoelectric features before in vitro testing on SH-SY5Y cells. In particular, BTNPs significantly improve piezoelectric properties of the films (4.5-fold increased d31 ). Both kinds of films support good SH-SY5Y viability and differentiation. Ultrasound (US) stimulation is proven to elicit Ca(2+) transients and to enhance differentiation in cells grown on the piezoelectric substrates. For the first time in the literature, this study demonstrates the suitability of polymer/ceramic composite films and US for neuronal stimulation through direct piezoelectric effect.

Nylon 6,6/graphene nanoplatelet composite films obtained from a new solvent

Solution processing of aliphatic polyamides (nylon) is quite challenging due to the fact that only a few solvents, such as formic acid and cresol, dissolve nylon. In general, polyamide 6,6 (nylon 6,6) is dissolved in formic acid to produce porous membranes or electrospun fibers. Herein, we propose for the first time a mixture of trifluoroacetic acid (TFA) and acetone that dissolves nylon 6,6, resulting in crystalline and non-porous films. Furthermore the same mixture of solvents was proved to be an excellent co-solvent for graphene nanoplatelets that were homogeneously dispersed in the solutions to produce reinforced nylon 6,6 polymer composites. The dispersion of the nanoplates in the polymer solution was found to be very stable over time. The mechanical and electrical properties of the developed composites were studied as a function of filler content. The Youngs modulus of the nylon 6,6 films increases more than two times upon the addition of the nanoplates. Furthermore, the flexible composites exhibit semiconducting behavior, with their electrical conductivity reaching 10−2 S cm−1 for 20 wt% graphene nanoplatelet concentration.

Spontaneous creation of discrete breathers in Josephson arrays

We report on the experimental generation of discrete breather states (intrinsic localized modes) in frustrated Josephson arrays. Our experiments indicate the formation of discrete breathers during the transition from the static to the dynamic (whirling) system state, induced by a uniform external current. Moreover, spatially extended resonant states, driven by a uniform current, are observed to evolve into localized breather states. Experiments were performed on single Josephson plaquettes as well as open-ended Josephson ladders with 10 and 20 cells. We interpret the breather formation as the result of the penetration of vortices into the system.

Traversal Time in Josephson Junctions

Direct measurements of the lifetime of the zero-voltage state in a Josephson junction, operating at a temperature where the quantum contribution is comparable with the thermal escape, have been performed as a function of the bias current [1]. From these measurements the traversal time of the barrier can be deduced according to a semiclassical analysis, analogously to what was previously done by measuring the dependence of the lifetime on the load of the junction [2]. The semiclassical traversal time, which turns out to be on the order of 100 ps, is presumably only the imaginary part of a complex quantity whose real part remains unknown (and is also not accessible to direct measurement). An estimate of this quantity can be done along the lines of a theoretical model which considers tunneling to be a stochastic process, and the real part of the traversal time turns out to be on the order of a few picoseconds. The connection with the Zeno time is also considered.

Observation of breatherlike states in a single Josephson cell.

We present experimental observation of broken-symmetry states in a superconducting loop with three Josephson junctions. These states are generic for discrete breathers in Josephson ladders. The existence region of the breatherlike states is found to be in good accordance with the theoretical expectations. We observed three different resonant states in the current-voltage characteristics of the broken-symmetry state, as predicted by theory. The experimental dependence of the resonances on the external magnetic field is studied in detail.

Laser-induced disaggregation of TiO2 nanofillers for uniform nanocomposites

Exploiting the intrinsic photosensitivity of TiO₂ nanoparticles, we demonstrated how ultraviolet (UV) pulsed laser irradiation of acrylate polymer nanocomposite solutions can separate the initial clusters of these colloidal semiconductor nanorods into clearly distinct units. From the irradiated solutions, optically clear nanocomposite films are obtained which exhibit enhanced optical properties with respect to the nanocomposites obtained without previous UV treatment.

Ultraconformable Freestanding Capacitors Based on Ultrathin Polyvinyl Formal Films

Conformable Electronics refers to a class of electronic devices that have the ability to conformally adhere onto non-planar surfaces and materials, resulting particularly appealing for skin applications, such as the case of skin-worn unobtrusive (bio)sensors for healthcare monitoring. Conformability can be addressed by integrating basic electronic components on ultrathin polymeric film substrates. Among other basic electronic components, capacitors are fundamental ones for energy storage, sensing, frequency tuning, impedance adaptation and signal processing. In this work we present a novel approach for conformable capacitors based on a free-standing, ultrathin and ultra-conformable nanosheets of poly (vinyl formal) (PVF), which serve both as structural and dielectric component of the capacitor. A novel fabrication approach is proposed and applied to fully free-standing ultrathin capacitors fabrication, having an overall thickness as low as 200 nm; that represents, to the best of our knowledge, the thinnest free-standing capacitors ever reported. Thanks to the ultra-low thickness, the proposed capacitors are able to sustain flexure to extremely small curvature radii (as low as 1.5 {\mu}m) and to conform to complex surfaces, such as a nylon mesh with micrometric texture without compromising their operation.