Piezoelectric effect and electroactive phase nucleation in self-standing films of unpoled PVDF nanocomposite films

Novel 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 CF2group 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 d33reaches 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

SCALE-UP PRODUCTION OF MULTIFUNCTIONAL NANOSTRUCTURED MATERIALS FOR ENERGY AND ENVIRONMENT APPLICATIONS

Energy and Environment are the sectors of critical significance and concern to the world. New inventions and improvements in technologies addressing the key challenges in these sectors are rapidly emerging over the past decade. Varieties of engineered functional nanomaterials are playing a vital role in the related fields such as energy harvesting, energy storage, catalysis, water purification/desalination and environmental toxicology etc. In all of these sectors, novel forms of carbon and metal oxide nanostructures have been identified to play a prominent role. Graphene nanoplatelets (GNPs) which are one among the potential carbon based materials and zinc oxide (ZnO) is notably technological material owing to its inherent piezoelectric, semi-conductive, non-toxic and biocompatible properties. Novel hybrid GNP/ZnO nanostructured materials possess intriguing functional properties as they combines the unique physical and chemical properties of both ZnO and Graphene nanomaterials, in addition to their high surface to volume ratio. Therefore, there is a rise in demand for their use in diverse applications related to energy and environment. The unique features of such novel materials can be further tailored by their size, shape, composition, structure, and surface. Hence, it is of utmost importance to develop an environmentally friendly and cost effective production method feasible for large scale production of such engineered multifunctional nanomaterials. The current thesis includes the preparation of the engineered multifunctional nanomaterials with good control over morphology, composition and uniformity through the control of process parameters. Having developed interesting forms of nanomaterials based on semiconductor metal oxides and conductive carbon forms, we explored applications of such multifunctional materials to obtain electroactive piezoelectric/energy harvesting polymer nanocomposites, cultural heritage/environmental, and antimicrobial adhesive dental materials. The strong materials chemistry effort embodied in the stated activities is also strongly supported by advanced physics based characterizations. We are also trying to commercialize this expertise in the particular domain of energy and environment for industrial innovation. Overall, the simplicity, cost-effectiveness and ease of synthesized nanostructured materials with multifunctional properties are ideal candidates for use in energy and environmental applications

PRODUZIONE DI NANOSTRUTTURE COMPOSITE A BASE GRAFENE OTTENUTE MEDIANTE CRESCITA IN SOSPENSIONE DI NANOROD E MICROROD DI ZnO SU FIOCCHI DI GNP NON SUPPORTATI

Per produrre nano placchette di grafene funzionalizzate con nanorod o microrod di ossido di zinco (eventualmente dopato con metallo) con migliorate proprietà elettriche, elettroniche, meccaniche, un processo innovativo consente di controllare la morfologia delle nano strutture di ZnO e la densità di ricopertura dei fiocchi di grafene. Il processo avviene in sospensione acquosa o idroalcolica e porta alla produzione di nano materiali utilizzabili come filler in matrici polimeriche per realizzare nano compositi aventi specifiche proprietà elettriche, elettromagnetiche, elettromeccaniche. L'opportuna definizione delle condizioni di processo, e nello specifico la deposizione di uno strato seed-layer sulla superfice dei GNP e l'utilizzo di tecniche di crescita con miscelamento continuo della sospensione, consentono il controllo della morfologia delle nanostrutture e l'ottenimento di una elevata ed uniforme densità di ricopertura della superficie dei GNP

Nanofiller Induced Electroactive Phase formation in Solution Derived Poly(Vinylidene Fluoride) Polymer Composites

Electroactive self-standing flexible composite poly(vinylidene fluoride) ( PVDF) films were prepared by simple solution casting method. In this study we investigated the effect of two different nanofillers, namely GNPs and ZnO NRs and the use of five different hexahydrate salts (HS) on the nucleation of the electroactive phase in the solution derived PVDF films. FT-IR analysis revealed that both HS dissolution and nanofillers dispersion in the PVDF matrix induced the electroactive phase formation without any electrical poling ascribed to their strong surface interaction with the polymeric chains. Moreover, we observed that the electroactive phase is still present when HS dissolution is combined with nanofiller dispersion, thus opening the route to the possibility of tailoring the operating frequency of the resulting electroactive material. This versatile electroactive phase induction by the nanofillers is a prominent way for production of large-area flexible piezoelectric films

PVDF composite films including graphene/ZnO nanostructures and their antimicrobial activity

Poly(vinylidene fluoride) (PVDF) is a biocompatible polymer commonly used for biomedical applications, food packaging and hygiene products. Within these contexts, the polymer surface is typically exposed to microorganisms and bacteria, with consequent biofilm formation. In this paper, self-standing flexible composite poly(vinylidene fluoride) (PVDF) films with antimicrobial properties were prepared by simple solution casting method. We investigated the effect of three different types of nanofillers, namely graphene nanoplatelets (GNPs), zinc oxide nanorods (ZnO-NRs) and ZnO-NR-decorated GNPs (ZNGs), on the antimicrobial activity of PVDF composite films against Pseudomonas aeruginosa. ZnO-NRs were also grown directly over the surface of PVDF composite films filled with ZnO nanoparticles, acting as nucleation seeds. In all cases, vitality tests performed in static conditions demonstrated a strong antimicrobial property of the produced specimens. This effect can be mainly ascribed to the bacteria/nanomaterials strong surface interaction, which results in the biofilm integrity disruption

PFM characterization of PVDF nanocomposite films with enhanced piezoelectric response

The piezoelectric properties of PVDF mainly depend on its β-phase. In this work, we investigated through Piezoresponse Force Microscopy (PFM) the piezoelectric properties of PVDF composite films when we induce the formation of β-phase crystals adding a nanofiller, like graphene nanoplatelets (GNPs) or zinc-oxide nanorods (ZnO-NRs), but without applying any electrical poling. At first, we fabricated piezoelectric PVDF nanocomposite films by the solution casting method. Then, we investigated the piezoelectric response of the different samples produced and we investigated the correlation between piezoresponse, morphology and structural characteristics of the nanocomposite. The morphology of the produced samples was investigated through field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The β-phase formation was assessed through Fourier Transform Infrared Spectroscopy (FT-IR) measurements

Synthesis and DC Electrical Conductivity Studies of Multilayer Graphene/Zinc Oxide Nanowires Composite Foils

Flexible composite foils made up of multilayer graphene (MLG) and ZnO nanowires (ZnO-NW) are produced via vacuum filtration of acetone-based suspension. The sheet resistance and effective dc electrical conductivity of the foils, with increasing content of ZnO-NW over a fixed amount of MLG, is measured in order to investigate the effect of ZnO inclusion in MLG papers. An enhancement in the dc conductivity of the composite foils with respect to a plain MLG-foil is noticed only for very low amounts of ZnO loading. The peak conductivity of 16.8 kS/m, representing an increase of 31% with respect to the conductivity of a plain MLG-foil, is observed at the optimum concentration of 10%wt ZnO over the MLG content. This confirms the physical and electronic interaction at the interface between MLG and ZnO-NW. At higher concentration of ZnO-NW, a linear decay in the effective conductivity of the foils is observed

Synthesis and characterization of ZnO nanorods with a narrow size distribution

The 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

Challenges of low-temperature synthesized ZnO nanowires and their integration into nanogenerators

International audienceFrom the multitude of nanostructures under active research, Zinc Oxide (ZnO) nanowires (NWs) have attracted enormous attention due to the materials’ unique electrical, optical, mechanical and piezoelectric properties. Since 10 years, piezoelectric nanocomposites based nanogenerators (NGs) have gained extensive attention for their applications in mechanical energy harvesters and self-powered tactile sensors. Hydrothermal approach is used for the synthesis of ZnO NWs and is a low cost manufacturing process, compatible with large area substrates. We present here a flexible and stretchable nanogenerator (SNG) which is manufactured thanks to a facile, cost-effective and industrially scalable process, on a polydimethylsiloxane (PDMS) substrate. The SNG exhibits excellent performance with a 35 μW peak output power achieved from a 8 cm2 device under a pressure of 100 kPa. The key issues of efficient NGs will be presented, in order to maximize the performance of these devices dedicated to low frequency mechanical energy harvesting