1,721,098 research outputs found
Piezoelectric effect and electroactive phase nucleation in self-standing films of unpoled PVDF nanocomposite films
No full textNovel polymer-based piezoelectric nanocomposites with enhanced electromechanical properties open new opportunities for the development of wearable energy harvesters and sensors. This paper investigates how the dissolution of different types of hexahydrate metal salts affects β-phase content and piezoelectric response (d33) at nano-and macroscales of polyvinylidene fluoride (PVDF) nanocomposite films. The strongest enhancement of the piezoresponse is observed in PVDF nanocomposites processed with Mg(NO3)2·6H2O. The increased piezoresponse is attributed to the synergistic effect of the dipole moment associated with the nucleation of the electroactive phase and with the electrostatic interaction between the CF2 group of PVDF and the dissolved salt through hydrogen bonding. The combination of nanofillers like graphene nanoplatelets or zinc oxide nanorods with the hexahydrate salt dissolution in PVDF results in a dramatic reduction of d33, because the nanofiller assumes a competitive role with respect to H-bond formation between PVDF and the dissolved metal salt. The measured peak value of d33 reaches the local value of 13.49 pm/V, with an average of 8.88 pm/V over an area of 1 cm2. The proposed selection of metal salt enables low-cost production of piezoelectric PVDF nanocomposite films, without electrical poling or mechanical stretching, offering new opportunities for the development of devices for energy harvesting and wearable sensors. © 2018 by the authors. Licensee MDPI, Basel, Switzerland
Piezoelectric response of graphene-filled PVDF nanocomposites through Piezoresponse Force Microscopy (PFM)
No full textThe piezoelectric properties of Poly(vinylidene fluoride) (PVDF) mainly depend on its most polar y9-phase. In this work, we investigated through Piezoresponse Force Microscopy (PFM) the piezoelectric properties of PVDF composite films when we induce the formation of y9-phase crystals adding graphene nanoplatelets (GNPs) without any chemical modification or poling. At first, we fabricated GNP-filled PVDF composite films by the solution casting method. Then, we investigated the piezoelectric response of different samples: neat PVDF, PVDF-based nanocomposites filled with 0.3 wt%, 0.5 wt% and 0.7 wt% GNPs. The morphology of the produced PVDF/GNP composites was investigated through field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The y9-phase formation was assessed through Fourier transform infrared spectroscopy (FT-IR) measurements. © 2017 IEEE
Synthesis and characterization of ZnO nanorods with a narrow size distribution
No full textThe development of novel materials for energy harvesting applications or strain sensing has generated great interest towards zinc oxide (ZnO) nanostructures, and in particular towards the synthesis of ZnO nanowires or nanorods with well controlled morphology and properties. The high-yield mass production of such nanostructures by catalyst-free methods is a crucial aspect to enable a cost-effective large-scale development of new ZnO-based piezoelectric devices and materials. In the present work, we propose a method for the mass-production of high-purity ZnO-nanorods with a uniform size distribution, based on the combination of thermal decomposition of zinc acetate dihydrate and probe sonication in acetone. The quality of the produced ZnO nanorods is assessed through multi-technique characterization using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photo-luminescence spectroscopy (PL). The adopted synthesis method is simple, cost effective and feasible for large-scale production. Various process parameters such as precursor amount and growth time have been found to play an important role in controlling the formation of the as grown nanostructures with high uniformity in size and morphology. Size distribution curves were employed to depict the effect of various process parameters for tailoring the morphology, homogeneity and aspect ratio of the nanorods. Our results reveal that the high crystallographic quality of ZnO nanorods grown by a long-time thermal decomposition method is not affected by probe sonication, which is proposed as a post-synthesis step necessary to produce ZnO nanorod powder with a uniform distribution of diameters and lengths. © 2015 The Royal Society of Chemistry
Transparent films for electromagnetic shielding of plastics
No full textThe interest in the development of lightweight transparent electromagnetic (EM) shields for the radio frequency range has been growing up in the last years together with the expansion of the electronic market and the increasing use of plastics. Example of industrial applications are video displays of electrical and electronic apparatus, of electromedical devices, of portable electronic equipment. Applications in the aerospace sector are also very attractive, such as in protecting the electronic systems of aircrafts from the high-intensity electromagnetic fields emitted by radio emitters, TV, radars and telecommunication systems. Moreover, the recent limits of radio frequency electromagnetic fields suggest the use of transparent shields for building windows. Thin films can provide an effective solution in EM shielding of plastic substrates or enclosures. In particular, the use of 1-D photonic band gap structures named as 'transparent metals' has been recently investigated and tested for EM shielding applications in the radiofrequency range, by using physical vapor deposition technique. In this work, the design method and the technological issues concerhing the realization and electromagnetic testing of the shields will be described. Some recent results will be presented, and both perspectives and limits of the proposed technique will be discussed and compared with other solutions
The conceptual structure and evolutionary pattern of CEM studies: a literature review and research agenda?
No full textExploring board human capital in the Italian context: The role of financial expertise and education for company performance
No full textResistenze osmotiche, fosfatasi alcalina e perossidasi leucocitarie in soggetti esposti professionalmente ad ozono
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Schermo attivo di campi magnetici a bassa frequenza trasparente nel visibile e procedimento per la sua realizzazione
No full textL'invenzione riguarda la progettazione e la realizzazione di uno schermo elettromagnetico a bassa frequenza attivo, trasparente nel visibile, nel quale la griglia conduttrice per la circolazione della corrente è costituita non da fili metallici ma da un rivestimento sottile multistrato metallo/dielettrico, conduttivo e trasparente, innovativo, avente il primo strato adiacente il substrato costituito da metallo. Per garantire l’uniformità cromatica della superficie schermante, sulle aree non rivestite dal film conduttivo è depositato un film multistrato dielettrico avente una distribuzione spettrale della trasmittanza ottica nell’intervallo del visibile uguale a quella del film multistrato conduttivo. Lo schermo elettromagnetico trasparente è costituito da: un substrato trasparente (vetro, polycarbonato, pellicola di plastica trasparente); uno strato metallico; un rivestimento multistrato conduttivo; un rivestimento multistrato dielettrico. La corrente esterna è iniettata nello schermo in misura tale da produrre un campo elettromagnetico opposto a quello da schermare, che lo annulli. Il procedimento per la realizzazione dello schermo si basa sulla tecnica dello sputtering selettivo
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