Sergio Scognamillo

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.

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.