One-pot exfoliation of graphite and synthesis of nanographene/dimesitylporphyrin hybrids.

A simple one-pot process to exfoliate graphite and synthesize nanographene-dimesitylporphyrin hybrids has been developed. Despite the bulky mesityl groups, which are expected to hinder the efficient π-π stacking between the porphyrin core and graphene, the liquid-phase exfoliation of graphite is significantly favored by the presence of the porphyrins. Metallation of the porphyrin further enhances this effect. The resulting graphene/porphyrin hybrids were characterized by spectroscopy (UV-visible, fluorescence, and Raman) and microscopy (STEM, scanning transmission electron microscopy).

From Nanoscale to Macroscale Characterization of Sulfur-Modified Oxidized Carbon Nanotubes in Styrene Butadiene Rubber Compounds.

The homogeneous dispersion of carbon nanotubes (CNTs) in a rubber matrix is a key factor limiting their amazing potential. CNTs tend to agglomerate into bundles due to van der Waals interactions. To overcome this limitation, CNTs have been surface-modified with oxygen-bearing groups and sulfur. Using atomic force microscopy (AFM) techniques, a deep nanoscale characterization of the morphology, the degree of dispersion of the CNTs in the styrene butadiene rubber (SBR) matrix, and the thickness of the interfacial layer was carried out in this study. In this context, the results from nanoscale characterization showed that the thermal oxidation-sulfur treatment leads to a composite with better dispersion in the matrix, as well as a thicker interfacial layer, indicating a stronger filler-rubber interaction. The second part of this work focused on the macroscale results, such as the Payne effect, vulcanization curves, and mechanical properties. The Payne effect, vulcanization curves, and mechanical properties confirmed the lower reinforcing effect observed in the case of the chemical oxidation treatment because, on the one hand, this composite showed the highest agglomeration of CNTs after the acid treatment. On the other hand, the presence of acid residues provoked the absorption of basic accelerators on the surface of the CNTs.

Sulfur-Modified Carbon Nanotubes for the Development of Advanced Elastomeric Materials.

The outstanding properties of carbon nanotubes (CNTs) present some limitations when introduced into rubber matrices, especially when these nano-particles are applied in high-performance tire tread compounds. Their tendency to agglomerate into bundles due to van der Waals interactions, the strong influence of CNT on the vulcanization process, and the adsorptive nature of filler-rubber interactions contribute to increase the energy dissipation phenomena on rubber-CNT compounds. Consequently, their expected performance in terms of rolling resistance is limited. To overcome these three important issues, the CNT have been surface-modified with oxygen-bearing groups and sulfur, resulting in an improvement in the key properties of these rubber compounds for their use in tire tread applications. A deep characterization of these new materials using functionalized CNT as filler was carried out by using a combination of mechanical, equilibrium swelling and low-field NMR experiments. The outcome of this research revealed that the formation of covalent bonds between the rubber matrix and the nano-particles by the introduction of sulfur at the CNT surface has positive effects on the viscoelastic behavior and the network structure of the rubber compounds, by a decrease of both the loss factor at 60 °C (rolling resistance) and the non-elastic defects, while increasing the crosslink density of the new compounds.

Bispyrene Functionalization Drives Self-Assembly of Graphite Nanoplates into Highly Efficient Heat Spreader Foils.

Thermally conductive nanopapers fabricated from graphene and related materials are currently showing great potential in thermal management applications. However, thermal contacts between conductive plates represent the bottleneck for thermal conductivity of nanopapers prepared in the absence of a high temperature step for graphitization. In this work, the problem of ineffective thermal contacts is addressed by the use of bifunctional polyaromatic molecules designed to drive self-assembly of graphite nanoplates (GnP) and establish thermal bridges between them. To preserve the high conductivity associated to a defect-free sp2 structure, non-covalent functionalization with bispyrene compounds, synthesized on purpose with variable tethering chain length, was exploited. Pyrene terminal groups granted for a strong π-π interaction with graphene surface, as demonstrated by UV-Vis, fluorescence, and Raman spectroscopies. Bispyrene molecular junctions between GnP were found to control GnP organization and orientation within the nanopaper, delivering significant enhancement in both in-plane and cross-plane thermal diffusivities. Finally, nanopapers were validated as heat spreader devices for electronic components, evidencing comparable or better thermal dissipation performance than conventional Cu foil, while delivering over 90% weight reduction.

Fluid dynamics of evolving foams.

The physical properties of many multiphase systems are determined by coarsening phenomena. From raindrops to polycrystal grains and foams, the formation and stability of these systems continuously evolve towards lower-energy configurations through events such as coalescence, Ostwald ripening and drainage. Here we propose a procedure to identify and characterise key topological transformations of coarsening phenomena using a physically-based fluid dynamic framework. In situ, real-time foaming processes of a polymeric matrix reinforced with two morphologically different nanofillers, carbon nanotubes and graphene sheets were observed by synchrotron X-ray radioscopy. We obtained detailed information on the evolution of the growth patterns and coarsening events. Filled samples showed differences in both trend and speed compared with the unfilled sample. Furthermore, we found different dominating coarsening phenomena due to the wetting nature of carbon nanoparticles. Our procedure can be extended to sequences of any type of 2D projection or 3D images and to other multiphase systems.

Thermally and Electrically Conductive Nanopapers from Reduced Graphene Oxide: Effect of Nanoflakes Thermal Annealing on the Film Structure and Properties.

In this study, we report a novel strategy to prepare graphene nanopapers from direct vacuum filtration. Instead of the conventional method, i.e., thermal annealing nanopapers at extremely high temperatures prepared from graphene oxide (GO) or partially reduced GO, we fabricate our graphene nanopapers directly from suspensions of fully reduced graphene oxide (RGO), obtained after RGO and thermal annealing at 1700 °C in vacuum. By using this approach, we studied the effect of thermal annealing on the physical properties of the macroscopic graphene-based papers. Indeed, we demonstrated that the enhancement of the thermal and electrical properties of graphene nanopapers prepared from annealed RGO is strongly influenced by the absence of oxygen functionalities and the morphology of the nanoflakes. Hence, our methodology can be considered as a valid alternative to the classical approach.

Inherent predominance of high chiral angle metallic carbon nanotubes in continuous fibers grown from a molten catalyst.

We present evidence that high temperature CVD growth of SWNTs under conditions of continuous spinning of macroscopic fibers leads to an inherent predominance of high chiral angle CNTs, peaking at the armchair end. Raman, UV-vis-NIR absorption, and photoluminescence spectroscopy measurements show the prevalence of metallic SWNTs. The complete chiral angle distribution is obtained by electron diffraction of over 390 CNTs. It is biased towards high chiral angles and peaks at the armchair end (30°), in good agreement with the established atomistic models for SWNT growth from a liquid catalyst. Based on the Fe-C-S constituent binary and ternary phase diagrams, thermodynamic calculations of phase compositions from fast cooling and experimental evidence of a post-synthesis catalyst, the proposed thermodynamic path of the catalyst is to form a solid FCC Fe core and a liquid Fe-S shell. S in the outer liquid shell first stabilizes the edge of the nascent CNT, but once a graphitic wall forms it is rejected due to the high interfacial energy of the Fe-C-S alloy.

Threading through Macrocycles Enhances the Performance of Carbon Nanotubes as Polymer Fillers.

In this work, we study the reinforcement of polymers by mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs). We compare the mechanical properties of fibers made of polymers and of composites with pristine SWNTs, mechanically interlocked derivatives of SWNTs (MINTs), and the corresponding supramolecular models. Improvements of both Young's modulus and tensile strength of up to 200% were observed for the polystyrene-MINT samples with an optimized loading of just 0.01 wt %, while the supramolecular models with identical chemical composition and loading showed negligible or even detrimental influence. This behavior is found for three different types of SWNTs and two types of macrocycles. Molecular dynamics simulations show that the polymer adopts an elongated conformation parallel to the SWNT when interacting with MINT fillers, irrespective of the macrocycle chemical nature, whereas a more globular structure is taken upon facing with either pristine SWNTs or supramolecular models. The MINT composite architecture thus leads to a more efficient exploitation of the axial properties of the SWNTs and of the polymer chain at the interface, in agreement with experimental results. Our findings demonstrate that the mechanical bond imparts distinctive advantageous properties to SWNT derivatives as polymer fillers.