Massimo Piccinini

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.

Graphene-containing thermoresponsive nanocomposite hydrogels of poly(N-isopropylacrylamide) prepared by frontal polymerization

Frontal polymerization has been successfully used to synthesize poly(N-isopropylacrylamide) nanocomposite hydrogels containing graphene. The latter was directly achieved by ultrasound treatment of a dispersion of graphite in N-methylpyrrolidone. The dispersion, having the concentration of 2.21 g L−1, was characterized by TEM analysis and mixed with suitable amounts of N-isopropylacrylamide for the synthesis of graphene-containing nanocomposite polymer hydrogels. The nanocomposite hydrogels were analyzed by SEM and Raman spectroscopy, and their swelling and rheological properties were investigated. It was found that graphene strongly influences the swelling ratio, dramatically increasing it, even if present in small amounts. Finally, the rheological properties of the hydrogels were correlated with the graphene content: G′ modulus and complex viscosity were found to increase with increasing nanofiller concentration, thus indicating the occurrence of good interactions between the two phases. Nevertheless, at a high concentration (i.e., 0.13 wt.%), graphene showed a lubrication effect, lowering the rheological parameters and approaching the same pseudoplastic behaviour of the unfilled material.

Development of novel cationic chitosan-and anionic alginate–coated poly(d,l-lactide-co-glycolide) nanoparticles for controlled release and light protection of resveratrol

Background Resveratrol, like other natural polyphenols, is an extremely photosensitive compound with low chemical stability, which limits the therapeutic application of its beneficial effects. The development of innovative formulation strategies, able to overcome physicochemical and pharmacokinetic limitations of this compound, may be achieved via suitable carriers able to associate controlled release and protection. In this context, nanotechnology is proving to be a powerful strategy. In this study, we developed novel cationic chitosan (CS)- and anionic alginate (Alg)-coated poly(d,l-lactide-co-glycolide) nanoparticles (NPs) loaded with the bioactive polyphenolic trans-(E)-resveratrol (RSV) for biomedical applications. Methods NPs were prepared by the nanoprecipitation method and characterized in terms of morphology, size and zeta potential, encapsulation efficiency, Raman spectroscopy, swelling properties, differential scanning calorimetry, and in vitro release studies. The protective effect of the nanosystems under the light-stressed RSV and long-term stability were investigated. Results NPs turned out to be spherical in shape, with size ranging from 135 to about 580 nm, depending on the composition and the amount of polyelectrolytes, while the encapsulation efficiencies increased from 8% of uncoated poly(d,l-lactide-co-glycolide) (PLGA) to 23% and 32% of Alg- and CS-coated PLGA NPs, respectively. All nanocarriers are characterized by a biphasic release pattern, and more effective controlled release rates are obtained for NPs formulated with higher polyelectrolyte concentrations. Stability studies revealed that encapsulation provides significant protection against light-exposure degradation, by reducing the trans–cis photoisomerization reaction. Moreover, the nanosystems are able to prevent the degradation of trans isoform and the leakage of RSV from the carrier for a period of 6 months. Conclusion Our findings indicated that the newly developed CS- and Alg-coated PLGA NPs are suitable to be used for the delivery of bioactive RSV. The encapsulation of RSV into optimized polymeric NPs provides improved drug loading, effective controlled release, and protection against light-exposure degradation, thus opening new perspectives for the delivery of bioactive related phytochemicals to be used for (nano)chemoprevention/chemotherapy.

In situ production of high filler content graphene-based polymer nanocomposites by reactive processing

This work deals with the preparation of graphene dispersed in a monomer (tetraethylene glycol diacrylate) and the subsequent polymerization of the latter to the corresponding polymer nanocomposite, which is the first obtained so far by direct polymerization of the graphene-dispersing medium. The method used for its obtainment allows reaching the highest concentration of graphene reported until now in any medium (9.45 mg mL−1); besides, a certain amount of graphene nanoribbons is also well visible. Furthermore, this goal is achieved by directly sonicating graphite without any chemical manipulation, which generally results in a final material still containing a significant number of defects. Because of its obtainment in the monomer itself, no filtration of graphene is needed, thus avoiding the reaggregation process to graphite, which partially compromises any previous exfoliation process. The obtained graphene-based polymer nanocomposites, fully characterized by Raman and transmission electron microscopy, differential scanning calorimetry, thermogravimetry, and dynamic–mechanical thermal analysis, exhibit a very homogeneous distribution of the graphene sheets within the polymer matrix. In addition, the interactions between the polymer and nanofiller are very strong, as evidenced by a significant increase in the Tg values even in the presence of a very low graphene content, together with a strong increase in the mechanical features (flexural and storage moduli). Finally, the thermo-oxidative stability of the polymer matrix is not affected by the presence of graphene nanosheets.

The production of concentrated dispersions of few-layer graphene by the direct exfoliation of graphite in organosilanes

We report the formation and characterization of graphene dispersions in two organosilanes, 3-glycidoxypropyl trimethoxysilane (GPTMS) and phenyl triethoxysilane (PhTES) as new reactive solvents. The preparation method was mild and easy and does not produce any chemical modification. The dispersions, which exhibit the Tyndall effect, were characterized by TEM and Raman spectroscopy to confirm the presence of few-layer graphene. Concentrations as high as 0.66 and 8.00 mg/ml were found for PhTES and GPTMS, respectively. The latter is one of the highest values reported for a dispersion of graphene obtained by any method. This finding paves the way for the direct synthesis of polymer nanofiller-containing composites consisting of graphene and reactive silanes to be used in sol–gel synthesis, without any need for solvent removal, thus preventing graphene reaggregation to form graphite flakes.

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.

Novel route to high-yield synthesis of sp2-hybridized boron nitride nanoplates on stainless steel

The synthesis of randomly distributed sp2-BN nanoplates embedded in a steel matrix was achieved by using boron doped AISI 316 stainless steel as substrates and a dissociated anhydrous NH3 atmosphere at 1070 °C as the nitrogen source. The chemical and morphological nature of the BN nanoplates has been studied by means of the combined use of XPS, FESEM-EDS, FTIR, XRD and SIMS techniques. The BN nanoplates are generally 100–400 nm wide and in many cases are characterised by a triangular or quasitriangular shape with some truncated and broken nanoplates that form a film whose thickness varies from 45 to 60 nm as a function of the boron content. This synthesis has the potential for coating stainless steel vacuum components and vessel walls with a stable film inert to gas adsorption to be used for the production of the next-generation of high performance stainless steel components for vacuum technology such as particle accelerators, thin film deposition and surface analysis equipment and further, as precursors for the fabrication of c-BN nanoplates.