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

Electrical, mechanical and electromechanical properties of graphene-thermoset polymer composites produced using acetone-DMF solvents

Recently, graphene-polymer composites gained a central role in advanced stress and strain sensing. A fundamental step in the production of epoxy-composites filled with graphene nanoplatelets (GNPs) consists in the exfoliation and dispersion of expanded graphite in a proper solvent, in the mixing of the resulting GNP suspension with the polymer matrix, and in the final removal of the solvent from the composite before curing through evaporation. The effects of traces of residual solvent on polymer curing process are usually overlooked, even if it has been found that even a small amount of residual solvent can affect the mechanical properties of the final composite. In this paper, we show that residual traces of N,N′-Dimethylformamide (DMF) in vinylester epoxy composites can induce relevant variations of the electrical, mechanical and electromechanical properties of the cured GNP-composite. To this purpose, a complete analysis of the morphological and structural characteristics of the composite samples produced using different solvent mixtures (combining acetone and DMF) is performed. Moreover, electrical, mechanical and electromechanical properties of the produced composites are assessed. In particular, the effect on the piezoresistive response of the use of DMF in the solvent mixture is analyzed using an experimental strain dependent percolation law to fit the measured electromechanical data. It is shown that the composites realized using a higher amount of DMF are characterized by a higher electrical conductivity and by a strong reduction of Young’s Modulus

Electro-mechanical properties of multilayer graphene-based polymeric composite obtained through a capillary rise method

A new sensor made of a vinyl-ester polymer composite filled with multilayer graphene nanoplatelets (MLG) is produced through an innovative capillary rise method for application in strain sensing and structural health monitoring. The new sensor is characterized by high stability of the piezoresistive response under quasi-static consecutive loading/unloading cycles and monotonic tests. This is due to the peculiarity of the fabrication process that ensures a smooth and clean surface of the sensor, without the presence of filler agglomerates acting as micro- or macro-sized defects in the composite

Graphene-based dental adhesive with anti-biofilm activity

BACKGROUND: Secondary caries are considered the main cause of dental restoration failure. In this context, anti-biofilm and bactericidal properties are desired in dental materials against pathogens such as Streptococcus mutans. To this purpose, graphene based materials can be used as fillers of polymer dental adhesives. In this work, we investigated the possibility to use as filler of dental adhesives, graphene nanoplatelets (GNP), a non toxic hydrophobic nanomaterial with antimicrobial and anti-biofilm properties. RESULTS: Graphene nanoplatelets have been produced starting from graphite intercalated compounds through a process consisting of thermal expansion and liquid exfoliation. Then, a dental adhesive filled with GNPs at different volume fractions has been produced through a solvent evaporation method. The rheological properties of the new experimental adhesives have been assessed experimentally. The adhesive properties have been tested using microtensile bond strength measurements (µ-TBS). Biocidal activity has been studied using the colony forming units count (CFU) method. The anti-biofilm properties have been demonstrated through FE-SEM imaging of the biofilm development after 3 and 24 h of growth. CONCLUSIONS: A significantly lower vitality of S. mutans cells has been demonstrated when in contact with the GNP filled dental adhesives. Biofilm growth on adhesive-covered dentine tissues demonstrated anti-adhesion properties of the produced materials. µ-TBS results demonstrated no significant difference in µ-TBS between the experimental and the control adhesive. The rheology tests highlighted the necessity to avoid low shear rate regimes during adhesive processing and application in clinical protocol, and confirmed that the adhesive containing the 0.2%wt of GNPs possess mechanical properties comparable with the ones of the control adhesive

Electromagnetic and electromechanical applications of graphene-based materials

This volume contains the extended abstracts of the contributions presented at the workshop Nanoscale Excitations in Emergent Materials (NEEM 2015) held in Rome from 12 to 14 October 2015, an event organized and supported in the framework of the Bilateral Cooperation Agreement between Italy and India within the project of major relevance "Investigating local structure and magnetism of cobalt nano-structures", funded by the Italian Ministry of Foreign Affairs and the Department of Science and Technology in India

Comparative genomics and transcriptional profiles of Saccharopolyspora erythraea NRRL 2338 and a classically improved erythromycin over-producing strain

<p>Abstract</p> <p>Background</p> <p>The molecular mechanisms altered by the traditional mutation and screening approach during the improvement of antibiotic-producing microorganisms are still poorly understood although this information is essential to design rational strategies for industrial strain improvement. In this study, we applied comparative genomics to identify all genetic changes occurring during the development of an erythromycin overproducer obtained using the traditional mutate-and- screen method.</p> <p>Results</p> <p>Compared with the parental <it>Saccharopolyspora erythraea </it>NRRL 2338, the genome of the overproducing strain presents 117 deletion, 78 insertion and 12 transposition sites, with 71 insertion/deletion sites mapping within coding sequences (CDSs) and generating frame-shift mutations. Single nucleotide variations are present in 144 CDSs. Overall, the genomic variations affect 227 proteins of the overproducing strain and a considerable number of mutations alter genes of key enzymes in the central carbon and nitrogen metabolism and in the biosynthesis of secondary metabolites, resulting in the redirection of common precursors toward erythromycin biosynthesis. Interestingly, several mutations inactivate genes coding for proteins that play fundamental roles in basic transcription and translation machineries including the transcription anti-termination factor NusB and the transcription elongation factor Efp. These mutations, along with those affecting genes coding for pleiotropic or pathway-specific regulators, affect global expression profile as demonstrated by a comparative analysis of the parental and overproducer expression profiles. Genomic data, finally, suggest that the mutate-and-screen process might have been accelerated by mutations in DNA repair genes.</p> <p>Conclusions</p> <p>This study helps to clarify the mechanisms underlying antibiotic overproduction providing valuable information about new possible molecular targets for rationale strain improvement.</p

Antibacterial effect of zinc oxide-based nanomaterials on environmental biodeteriogens affecting historical buildings

The colonization of microorganisms and their subsequent interaction with stone substrates under different environmental conditions encourage deterioration of materials by multiple mechanisms resulting in changes in the original color, appearance and durability. One of the emerging alternatives to remedy biodeterioration is nanotechnology, thanks to nanoparticle properties such as small size, no-toxicity, high photo-reactivity, and low impact on the environment. This study highlighted the effects of ZnO-based nanomaterials of two bacteria genera isolated from the Temple of Concordia (Agrigento’s Valley of the Temples in Sicily, Italy) that are involved in biodeterioration processes. The antimicrobial activities of ZnO-nanorods (Zn-NRs) and graphene nanoplatelets decorated with Zn-NRs (ZNGs) were evaluated against the Gram positive Arthrobacter aurescens and two isolates of the Gram negative Achromobacter spanius. ZNGs demonstrated high antibacterial and antibiofilm activities on several substrates such as stones with different porosity. In the case of ZNGs, a marked time- and dose-dependent bactericidal effect was highlighted against all bacterial species. Therefore, these nanomaterials represent a promising tool for developing biocompatible materials that can be exploited for the conservation of cultural heritage. These nanostructures can be successfully applied without releasing toxic compounds, thus spreading their usability

Transcriptional profiling in response to terminal drought stress reveals differential responses along the wheat genome

Background: Water stress during grain filling has a marked effect on grain yield, leading to a reduced endosperm cell number and thus sink capacity to accumulate dry matter. The bread wheat cultivar Chinese Spring (CS), a Chinese Spring terminal deletion line (CS_5AL-10) and the durum wheat cultivar Creso were subjected to transcriptional profiling after exposure to mild and severe drought stress at the grain filling stage to find evidences of differential stress responses associated to different wheat genome regions. Results: The transcriptome analysis of Creso, CS and its deletion line revealed 8,552 non redundant probe sets with different expression levels, mainly due to the comparisons between the two species. The drought treatments modified the expression of 3,056 probe sets. Besides a set of genes showing a similar drought response in Creso and CS, cluster analysis revealed several drought response features that can be associated to the different genomic structure of Creso, CS and CS_5AL-10. Some drought-related genes were expressed at lower level (or not expressed) in Creso (which lacks the D genome) or in the CS_5AL- 10 deletion line compared to CS. The chromosome location of a set of these genes was confirmed by PCR-based mapping on the D genome (or the 5AL-10 region). Many clusters were characterized by different level of expression in Creso, CS and CS_AL-10, suggesting that the different genome organization of the three genotypes may affect plant adaptation to stress. Clusters with similar expression trend were grouped and functional classified to mine the biological mean of their activation or repression. Genes involved in ABA, proline, glycine-betaine and sorbitol pathways were found up-regulated by drought stress. Furthermore, the enhanced expression of a set of transposons and retrotransposons was detected in CS_5AL-10. Conclusion: Bread and durum wheat genotypes were characterized by a different physiological reaction to water stress and by a substantially different molecular response. The genome organization accounted for differences in the expression level of hundreds of genes located on the D genome or controlled by regulators located on the D genome. When a genomic stress (deletion of a chromosomal region) was combined with low water availability, a molecular response based on the activation of transposons and retrotransposons was observed

Material jetting of carbon nano onions for printed Eeectronics

: As an additive manufacturing process, material jetting techniques allow to selectively deposit droplets of materials in liquid or powder form through a small-diameter aperture, such as a nozzle of a print head. For the fabrication of printed electronics, a variety of inks and dispersions of functional materials can be deposited by drop-on-demand printing on rigid and flexible substrates. In this work, zero-dimensional multi-layer shell-structured fullerene material, also known as carbon nano-onion (CNO) or onion-like carbon (OLC), is printed on polyethylene terephthalate (PET) substrates using drop-on-demand inkjet printing. CNOs are produced using a low-cost flame synthesis technique and characterized by electron microscopy, Raman, X-ray photoelectron spectroscopy, and specific surface area and pore size measurements. The produced CNO material has an average diameter of ~33 nm, pore diameter in the range ~2-40 nm and a specific surface area of 232 m2.g-1. The CNO dispersions in ethanol have a reduced viscosity (~1.2 mPa.s) and are compatible with commercial piezoelectric inkjet heads. The jetting parameters are optimized to avoid satellite drops and to obtain a reduced drop volume (52 pL), resulting in optimal resolution (220 µm) and line continuity. A multi-step process is implemented without inter-layer curing and a fine control over the CNO layer thickness is achieved (~180 nm-thick layer after 10 printing passes). The printed CNO structures show an electrical resistivity of ~600 Ω.m, a high negative temperature coefficient of resistance (-4.35x10-2 ºC-1) and a marked dependency on relative humidity (-1.29x10-2 RH%-1). The high sensitivity to temperature and humidity, combined to the large specific area of the CNOs, make this material and the corresponding ink a viable prospect for inkjet-printed technologies, such as environmental and gas sensors

Combined Modifications of Mexiletine Pharmacophores for New Lead Blockers of Nav1.4 Channels

AbstractPreviously identified potent and/or use-dependent mexiletine (Mex) analogs were used as template for the rational design of new Nav-channel blockers. The effects of the novel analogs were tested on sodium currents of native myofibers. Data and molecular modeling show that increasing basicity and optimal alkyl chain length enhance use-dependent block. This was demonstrated by replacing the amino group with a more basic guanidine one while maintaining a proper distance between positive charge and aromatic ring (Me13) or with homologs having the chirality center nearby the amino group or the aromatic ring. Accordingly, a phenyl group on the asymmetric center in the homologated alkyl chain (Me12), leads to a further increase of use-dependent behavior versus the phenyl Mex derivative Me4. A fluorine atom in paraposition and one ortho-methyl group on the xylyloxy ring (Me15) increase potency and stereoselectivity versus Me4. Charge delocalization and greater flexibility of Me15 may increase its affinity for Tyr residues influencing steric drug interaction with the primary Phe residue of the binding site. Me12 and Me15 show limited selectivity against Nav-isoforms, possibly due to the highly conserved binding site on Nav. To our knowledge, the new compounds are the most potent Mex-like Nav blockers obtained to date and deserve further investigation