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Jomehzadeh E.,Kerman Graduate University of Technology | Saidi A.R.,Shahid Bahonar University of Kerman | Jomehzadeh Z.,Kerman Medical University | Bonaccorso F.,Italian Institute of Technology | And 7 more authors.
Computational Materials Science | Year: 2015

We investigate the nonlinear responses of graphene-matrix composite to harmonic and subharmonic resonances. Assuming anisotropic mechanical properties of graphene, we derive size-dependent governing equations of motion for graphene resting on a matrix based on the von Karman hypotheses and nonlocal elasticity theory. Response of graphene oscillation under a uniform pressure is obtained using the averaging method. We study the effects of length scale as well as the presence of the elastic matrix on harmonic and subharmonic oscillations of graphene. Our results reveal that subharmonic oscillation of order 1/3 can occur when the ratio of excitation to natural frequencies exceeds three. Also, the subharmonic oscillation of the system is triggered in an appropriate initial condition. ©2014 Elsevier B.V. All rights reserved.


Panzavolta S.,University of Bologna | Bracci B.,University of Bologna | Gualandi C.,University of Bologna | Focarete M.L.,University of Bologna | And 13 more authors.
Carbon | Year: 2014

In this work we study the mechanical properties and failure mechanism of nano-composites of graphene oxide sheets embedded in polymeric systems, namely films and electro-spun nanofibers. In this last system, contrary to conventional bulk composites, the size of the nano-reinforcement (GO sheets) is comparable to the size of the nanofibers to be reinforced (≈ 200 nm). As polymeric matrix we use gelatin. We demonstrate that the high chemical affinity of the two materials hinders the renaturation of gelatin into collagen and causes a nearly ideal mixing in the GO-gelatin composite. Adding just 1% of GO (wt of GO with respect to gelatin) we obtain an increase of Young's modulus >50% and an increase of fracture stress >60%. We use numerical simulations to study the failure mechanism of the fibers. Calculations well agree with experimental data and show that, even if cracks start at GO sheet edges due to stress concentrations, crack propagation is hindered by the nonlinear behaviour of the matrix. Moreover, the presence of the GO sheets in continuous gelatin films improves the material stability to phosphate buffer solutions from 2 days to 2 weeks, making it a better material than gelatin for applications in biological environments. © 2014 Elsevier Ltd. All rights reserved.


Melucci M.,CNR Institute for Organic Syntheses and Photoreactivity | Melucci M.,National Research Council Italy | Durso M.,CNR Institute for Organic Syntheses and Photoreactivity | Zambianchi M.,CNR Institute for Organic Syntheses and Photoreactivity | And 9 more authors.
Journal of Materials Chemistry | Year: 2012

We describe a new approach to attach organic dyes to graphene oxide (GO) sheets with high loading and minimal perturbation of the electronic and optical properties of the dye. The dye unit used (a pH-sensitive terthiophene) is grafted to GO using a new modular synthetic approach, passing through a C6-aminic linker which makes GO more soluble in different organic solvents and allows straightforward attachment at high yield not only of terthiophene but of many commercially available amino-reactive dyes. The covalent engraftment to GO does not perturb the absorption and emission properties of the dye, and in particular the pH sensing capability through amidic group reversible protonation. This approach can allow (i) high solubility of the GO intermediate in organic solvents, (ii) convenient coupling with commercial, stable amino-reactive dyes under mild conditions, (iii) easy control of the spacer length between the GO and oligothiophene dye and finally (iv) high (up to 5 wt%) dye functionalization loadings. © 2012 The Royal Society of Chemistry.


Xia Z.Y.,CNR Institute for Organic Syntheses and Photoreactivity | Pezzini S.,University of Pavia | Treossi E.,CNR Institute for Organic Syntheses and Photoreactivity | Treossi E.,Laboratorio Miste R Bologna | And 6 more authors.
Advanced Functional Materials | Year: 2013

The different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation and electrochemical oxidation are compared. The exfoliation process and roughening of a flat graphite substrate is directly visualized at the nanoscale by scanning probe and electron microscopy. The etching damage in graphite and the properties of the exfoliated sheets are compared by Raman spectroscopy and X-ray diffraction analysis. The results show the trade-off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non-covalent exfoliation and preservation of graphene properties on a molecular scale. The different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation, and electrochemical oxidation are compared. The results obtained show the trade-off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non-covalent exfoliation and preservation of graphene properties on a molecular scale. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Pathipati S.R.,University of Nova Gorica | Pavlica E.,University of Nova Gorica | Treossi E.,CNR Institute for Organic Syntheses and Photoreactivity | Treossi E.,Laboratorio Miste R Bologna | And 10 more authors.
Organic Electronics: physics, materials, applications | Year: 2013

We have examined the effect of submonolayer coverage of 1-pyrene butyric acid on charge carrier transport in reduced graphene oxide. We have modeled the interaction of 1-pyrene butyric acid molecules with graphene and determined the amount of charge transfer at the interface between the two materials. The effect of 1-pyrene butyric acid as electron acceptor was determined by transfer characteristics measurements on thin film transistors for thick layers. By using time-resolved photocurrent measurements we were able to detect a reduction of electron mobility in reduced graphene oxide for coverage as low as 0.08%. © 2013 Elsevier B.V. All rights reserved.


Kouroupis-Agalou K.,CNR Institute for Organic Syntheses and Photoreactivity | Kouroupis-Agalou K.,University of Bologna | Liscio A.,CNR Institute for Organic Syntheses and Photoreactivity | Treossi E.,CNR Institute for Organic Syntheses and Photoreactivity | And 8 more authors.
Nanoscale | Year: 2014

The main advantage for applications of graphene and related 2D materials is that they can be produced on large scales by liquid phase exfoliation. The exfoliation process shall be considered as a particular fragmentation process, where the 2D character of the exfoliated objects will influence significantly fragmentation dynamics as compared to standard materials. Here, we used automatized image processing of Atomic Force Microscopy (AFM) data to measure, one by one, the exact shape and size of thousands of nanosheets obtained by exfoliation of an important 2D-material, boron nitride, and used different statistical functions to model the asymmetric distribution of nanosheet sizes typically obtained. Being the resolution of AFM much larger than the average sheet size, analysis could be performed directly at the nanoscale and at the single sheet level. We find that the size distribution of the sheets at a given time follows a log-normal distribution, indicating that the exfoliation process has a "typical" scale length that changes with time and that exfoliation proceeds through the formation of a distribution of random cracks that follow Poisson statistics. The validity of this model implies that the size distribution does not depend on the different preparation methods used, but is a common feature in the exfoliation of this material and thus probably for other 2D materials. © 2014 the Partner Organisations.


Xia Z.Y.,CNR Institute for Organic Syntheses and Photoreactivity | Giambastiani G.,National Research Council Italy | Christodoulou C.,Humboldt University of Berlin | Nardi M.V.,Humboldt University of Berlin | And 10 more authors.
ChemPlusChem | Year: 2014

A facile and efficient method based on electrochemistry for the production of graphene-based materials for electronics is demonstrated. Uncharged acetonitrile molecules are intercalated in graphite by electrochemical treatment, owing to the synergic action of perchlorate ions dissolved in acetonitrile. Then, acetonitrile molecules are decomposed with microwave irradiation, which causes gas production and rapid graphite exfoliation, with an increase in the graphite volume of up to 600 %. Upon further processing and purification, highly dispersible nanosheets are obtained that can be processed into thin layers by roll-to-roll transfer or into thicker electrodes with excellent capacitance stability upon extensive charging/discharging cycles. The good exfoliation yield (>50 % of monolayers), minimal oxidation damage and good electrochemical stability of the nanosheets obtained were confirmed by scanning force and electron microscopy, as well as Raman spectroscopy and galvanostatic analyses. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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