Engineering the interface in mechanically responsive graphene-based films

Direct insight into the structure-property relation of interfaces from constrained crystal structure prediction

A major issue that prevents a full understanding of heterogeneous materials is the lack of systematic first-principles methods to consistently predict energetics and electronic properties of reconstructed interfaces. In this work we address this problem with an efficient and accurate computational scheme. We extend the minima-hopping method implementing constraints crafted for two-dimensional atomic relaxation and enabling variations of the atomic density close to the interface. A combination of density-functional and accurate density-functional tight-binding calculations supply energy and forces to structure prediction. We demonstrate the power of this method by applying it to extract structure-property relations for a large and varied family of symmetric and asymmetric tilt boundaries in polycrystalline silicon. We find a rich polymorphism in the interface reconstructions, with recurring bonding patterns that we classify in increasing energetic order. Finally, a clear relation between bonding patterns and electrically active grain boundary states is unveiled and discussed.

Thermal Property Studies of In Situ Blended Graphene/Nature Rubber Nanocomposites

In this work, graphene/nature rubber (GE/NR) composites with filler content from 0 wt% to 1 wt% were prepared by an in situ reduction process. Thermal properties of the nanocomposites were studied by thermogravimetric (TG) analysis and thermogravimetric difference (ΔTG). Composites with higher GE content evidenced stronger thermal stability-enhancing effect. Kinetic analysis showed that the activation energies (Ea) during degradation of composites were always higher than pure NR. However, Ea reached its maximum at 0.1 wt% GE content and started to decrease with further increase in GE loading. The changes in the thermal properties were attributed to the chemical structure and heat transfer properties of graphene sheets.

Superstrong Noncovalent Interface between Melamine and Graphene Oxide

There have been growing academic interests in the study of strong organic molecule-graphene [or graphene oxide (GO)] systems, owing to their essential noncovalent nature and the consequent chemomechanical behavior within the interface. A more recent experimental measurement [ Chem 2018, 4, 896-910] reported that the melamine-GO interface exhibits a remarkable noncovalent binding strength up to ∼1 nN, even comparable with typical covalent bonds. But the poor understanding on the complex noncovalent nature in particular makes it challenging to unveil the mystery of this high-performance interface. Herein, we carry out first-principles calculations to investigate the atomistic origin of ultrastrong noncovalent interaction between the melamine molecule and the GO sheet, as well as the chemomechanical synergy in interfacial behavior. The anomalous O-H···N hydrogen bonding, formed between the triazine moiety of melamine and the -OH in GO, is found cooperatively enhanced by the pin-like NH₂-π interaction, which is responsible for the strong interface. Following static pulling simulations validates the 1 nN level rupture strength and the contribution of each noncovalent interaction within the interface. Moreover, our results show that the -OH hydrogen bonding will mainly augment the interfacial adhesion strength, whereas the -NH₂ group cooperating with the -OH hydrogen bonding and conjugating with the GO surface will greatly improve the interfacial shear performance. Our work deepens the understanding on the chemomechanical behaviors within the noncovalent interface, which is expected to provide new potential strategies in designing high-performance graphene-based artificial nacreous materials.