Silvia Bittolo Bon

High concentration few-layer graphene sheets obtained by liquid phase exfoliation of graphite in ionic liquid

In the present work, the use of a commercial ionic liquid as a convenient solvent medium for graphite exfoliation in mild and easy conditions without any chemical modification is presented. To confirm the presence of few layer graphene, its dispersion, which exhibits Tyndall effect, was characterized by Raman and UV spectroscopies, and atomic force and field emission electron microscopies. It is noteworthy that, by gravimetric analysis, a graphene concentration as high as 5.33 mg ml−1 was determined, which is the highest value reported so far in any solvent.

Use of butylamine modified graphene sheets in polymer solar cells

We describe a facile method to use soluble chemically derived few-layer graphene sheets (GSs) as part of a transparent electrode for the preparation of polymer solar cells. Chemically functionalized GSs were obtained by first covalently attaching fluorine and then exposing the obtained fluorinated graphene sheets to an aliphatic amine at room temperature. Scanning electron microscopy, atomic force microscopy and UV-Vis analyses confirmed that transparent graphene sheets with an average thickness of 0.7–0.9 nm had been obtained. Their application in a polymer solar cell is demonstrated. Such functionalized graphene, which is cheap and easily prepared, is expected to be used as hole acceptor material in polymer photovoltaic applications.

Deposition of amino-functionalized polyhedral oligomeric silsesquioxanes on graphene oxide sheets immobilized onto an amino-silane modified silicon surface

The reaction between amino-functionalized polyhedral oligomeric silsesquioxanes (POSS-NH2) and graphene oxide (GO) sheets was used to graft POSS-NH2 onto a GO layer immobilized onto a layer of (3-aminopropyl)triethoxysilane, self-assembled onto Si substrate. The chemical composition and surface morphology as well as the surface properties of the prepared films were investigated by means of Fourier transform infrared spectroscopy, water contact angle measurements and field emission electron microscopy. Tribological measurements performed with a nanoindenter showed that such hydrophobic trilayer film exhibited a reduced friction coefficient suitable for applications in lubricant coatings.

Transparent and conductive graphene oxide/poly(ethylene glycol) diacrylate coatings obtained by photopolymerization

Water-dispersed graphene oxide sheets were used to prepare graphene/poly(ethylene glycol) diacrylate resin composites by photopolymerization. It was found that graphene sheets undergo excellent morphological distribution within the resin system, giving rise to transparent composites with unaltered thermal properties with respect to the neat resin, that are electrically conductive at loading ratios as low as 0.02 wt.-% of graphene oxide. The proposed strategy based on photopolymerization provides an easy, energy-saving and environmental friendly technique that can find a wide application in coating technology, mainly for electromagnetic shielding and antistatic coatings.

Fermentation based carbon nanotube multifunctional bionic composites.

The exploitation of the processes used by microorganisms to digest nutrients for their growth can be a viable method for the formation of a wide range of so called biogenic materials that have unique properties that are not produced by abiotic processes. Here we produced living hybrid materials by giving to unicellular organisms the nutrient to grow. Based on bread fermentation, a bionic composite made of carbon nanotubes (CNTs) and a single-cell fungi, the Saccharomyces cerevisiae yeast extract, was prepared by fermentation of such microorganisms at room temperature. Scanning electron microscopy analysis suggests that the CNTs were internalized by the cell after fermentation bridging the cells. Tensile tests on dried composite films have been rationalized in terms of a CNT cell bridging mechanism where the strongly enhanced strength of the composite is governed by the adhesion energy between the bridging carbon nanotubes and the matrix. The addition of CNTs also significantly improved the electrical conductivity along with a higher photoconductive activity. The proposed process could lead to the development of more complex and interactive structures programmed to self-assemble into specific patterns, such as those on strain or light sensors that could sense damage or convert light stimulus in an electrical signal.

Multistimuli-responsive hydrogels of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) containing graphene

Nanocomposite hydrogels of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) containing graphene were prepared by radical polymerization. Their swelling properties in response to ionic strength and electrical stimuli were assessed. Graphene was obtained through an easy and convenient method lately developed by our research group, which consists in the exfoliation of graphite by sonicating it in a proper solvent medium. It was found that the graphene content influences the swelling properties of hydrogels; in particular, those containing graphene swell more than the filler-free ones; graphene content influences also the swelling ratio variation between the swollen and deswollen states.

Emerging methods for producing graphene oxide composites in coatings with multifunctional properties

The most common preparation method of graphene starts from the oxidation and exfoliation of graphite to graphene oxide (GO). Such graphitic planes, decorated with oxygen-containing groups, are hydrophilic and soluble in water. From an industrial point of view, wet-chemistry approaches are the most desirable methods for the large scale integration of GO based polymer nanocomposites. The critical issue remains in the aggregation of the GO sheets after the dispersant evaporation which is detrimental for the coating uniformity. We present several methods for the development of such functional coatings preserving the physical properties such as optical transparency and electrical conductivity.

Poly(methyl methacrylate)/graphene oxide layered films as generators for mechanical energy harvesting.

In this work we introduce a simple practical way to transfer large flakes of partially reduced graphene oxide (rGO) as well as poly(methyl methacrylate)/rGO films onto arbitrary substrates where the electrode geometry is defined before the film deposition to fabricate devices. It was reported how such films when stimulated by an ultrasound transducer convert mechanical energy to electricity. The possibility to utilize polymer nanocomposites as nanogenerators is of current interest to enhance mechanical energy harvesting and to add new functionalities to polymer nanocomposites.

Ice-regenerated flame retardant and robust film of Bombyx mori silk fibroin and POSS nano-cages

In this study, we present a simple method to prepare and control the structure of regenerated hybrid silkworm silk films through icing. A regenerated hybrid silk (RHS) film consisting of a micro-fibrillar structure was obtained by partially dissolving amino-functionalized polyhedral oligomeric silsesquioxanes (POSS) and silk fibers in a CaCl2–formic acid solution. After immersion in water and icing, the obtained films of RHS showed polymorphic and strain-stiffening behaviors with mechanical properties that were better than those observed in dry or wet-regenerated silk. It was also found that POSS endowed the burning regenerated silk film with anti-dripping properties. The higher β-sheet content observed in the ice-regenerated hybrid micro-fibrils indicates a useful route to fabricate regenerated silk with physical and functional properties, i.e. strain-stiffening, similar to those observed to date in natural spider silk counterpart and synthetic rubbers, and anti-dripping of the flaming melt. Related carbon nanotube composites are considered for comparison.

Combining Living Microorganisms with Regenerated Silk Provides Nanofibril-Based Thin Films with Heat-Responsive Wrinkled States for Smart Food Packaging

Regenerated silk (RS) is a protein-based “biopolymer” that enables the design of new materials; here, we called “bionic” the process of regenerated silk production by a fermentation-assisted method. Based on yeast’s fermentation, here we produced a living hybrid composite made of regenerated silk nanofibrils and a single-cell fungi, the Saccharomyces cerevisiae yeast extract, by fermentation of such microorganisms at room temperature in a dissolution bath of silkworm silk fibers. The fermentation-based processing enhances the beta-sheet content of the RS, corresponding to a reduction in water permeability and CO2 diffusion through RS/yeast thin films enabling the fabrication of a mechanically robust film that enhances food storage durability. Finally, a transfer print method, which consists of transferring RS and RS/yeast film layers onto a self-adherent paraffin substrate, was used for the realization of heat-responsive wrinkles by exploiting the high thermal expansion of the paraffin substrate that regulates the applied strain, resulting in a switchable coating morphology from the wrinkle-free state to a wrinkled state if the food temperature overcomes a designed threshold. We envision that such efficient and smart coatings can be applied for the realization of smart packaging that, through such a temperature-sensing mechanism, can be used to control food storage conditions.