Mechanical and gas adsorption properties of graphene and graphynes under biaxial strain.

The exceptional properties of two-dimensional (2D) solids have motivated extensive research, which revealed the possibility of controlling many characteristics of these materials through strain. For instance, previous investigations demonstrated that compressive deformation could be used to direct the chemisorption of atomic hydrogen and oxygen. Still, to our knowledge, there is no work detailing how strain affects the adsorption isotherms of 2D materials and the adsorption properties of materials such as the graphynes, which are monolayers composed of sp and sp[Formula: see text] carbon atoms. In the present work, we analyze how biaxial tensile deformation changes the adsorption properties of four 2D materials (graphene, [Formula: see text]-graphyne, [Formula: see text]-graphyne, and [Formula: see text]-graphyne). To achieve this, we perform Monte Carlo Grand Canonical calculations to obtain the adsorption isotherms of H[Formula: see text], CO[Formula: see text], and CH[Formula: see text] on the monolayers with and without strain. And, to apply the deformation, we carry out Molecular Dynamics simulations. We find a substantial reduction in the amount of gas adsorbed on the monolayers for nearly all gas-solid combinations. This is particularly true for graphene, where 14.5% strain reduces the quantity of H[Formula: see text]/CO[Formula: see text]/CH[Formula: see text] by 44.7/64.1/41.7% at P [Formula: see text] 1 atm. To understand the results, we calculate adsorption enthalpies and analyze the gas distribution above the monolayers. We also characterize the mechanical properties of the considered solids under biaxial deformation. Finally, a comparison of pore sizes with the kinetic diameters of various gases suggests applications for the graphynes, with and without strain, in gas separation.

Improving the Room-Temperature Ferromagnetism in ZnO and Low-Doped ZnO:Ag Films Using GLAD Sputtering.

ZnO and doped ZnO films with non-ferromagnetic metal have been widely used as biosensor elements. In these studies, the electrochemical measurements are explored, though the electrical impedance of the system. In this sense, the ferromagnetic properties of the material can be used for multifunctionalization of the sensor element using external magnetic fields during the measurements. Within this context, we investigate the room-temperature ferromagnetism in pure ZnO and Ag-doped ZnO films presenting zigzag-like columnar geometry. Specifically, we focus on the films' structural and quasi-static magnetic properties and disclose that they evolve with the doping of low-Ag concentrations and the columnar geometry employed during the deposition. The magnetic characterization reveals ferromagnetic behavior at room temperature for all studied samples, including the pure ZnO one. By considering computational simulations, we address the origin of ferromagnetism in ZnO and Ag-doped ZnO and interpret our results in terms of the Zn vacancy dynamics, its substitution by an Ag atom in the site, and the influence of the columnar geometry on the magnetic properties of the films. Our findings bring to light an exciting way to induce/explore the room-temperature ferromagnetism of a non-ferromagnetic metal-doped semiconductor as a promising candidate for biosensor applications.

Controlling Movement at Nanoscale: Curvature Driven Mechanotaxis.

Locating and manipulating nano-sized objects to drive motion is a time and effort consuming task. Recent advances show that it is possible to generate motion without direct intervention, by embedding the source of motion in the system configuration. In this work, an alternative manner to controllably displace nano-objects without external manipulation is demonstrated, by employing spiral-shaped carbon nanotube (CNT) and graphene nanoribbon structures (GNR). The spiral shape contains smooth gradients of curvature, which lead to smooth gradients of bending energy. It is shown that these gradients as well as surface energy gradients can drive nano-oscillators. An energy analysis is also carried out by approximating the carbon nanotube to a thin rod and how torsional gradients can be used to drive motion is discussed. For the nanoribbons, the role of layer orientation is also analyzed. The results show that motion is not sustainable for commensurate orientations, in which AB stacking occurs. For incommensurate orientations, friction almost vanishes, and in this instance, the motion can continue even if the driving forces are not very high. This suggests that mild curvature gradients, which can already be found in existing nanostructures, could provide mechanical stimuli to direct motion.

2D Hexagonal Boron Nitride-Coated Cotton Fabric with Self-Extinguishing Property.

Here, we report on the fabrication of flame retardant hydrophobic cotton fabrics based on the coating with two-dimensional hexagonal boron nitride (2D hBN) nanosheets. A simple one-step solution dipping process was used to coat the fabrics by taking advantage of the strong bonding between diethylenetriamine and hBN on the cotton surface. Exposure to direct flame confirmed the improvement of the flame retardant properties of the coated cotton fabrics. In turn, removal of the flame source revealed self-extinguishing properties. Molecular dynamics simulations indicate that hBN hinders combustion by reducing the rate at which oxygen molecules reach the cotton surface. This time-saving and one-step approach for the fabrication of flame-retardant cotton fabrics offers significant advantages over other, less efficient production methods.

Few-Wall Carbon Nanotube Coils.

While various electronic components based on carbon nanotubes (CNTs) have already been demonstrated, the realization of miniature electromagnetic coils based on CNTs remains a challenge. Coils made of single-wall CNTs with accessible ends for contacting have been recently demonstrated but were found unsuitable to act as electromagnetic coils because of electrical shorting between their turns. Coils made of a few-wall CNT could in principle allow an insulated flow of current and thus be potential candidates for realizing CNT-based electromagnetic coils. However, no such CNT structure has been produced so far. Here, we demonstrate the formation of few-wall CNT coils and characterize their structural, optical, vibrational, and electrical properties using experimental and computational tools. The coils are made of CNTs with 2, 3, or 4 walls. They have accessible ends for electrical contacts and low defect densities. The coil diameters are on the order of one micron, like those of single-wall CNT coils, despite the higher rigidity of few-wall CNTs. Coils with as many as 163 turns were found, with their turns organized in a rippled raft configuration. These coils are promising candidates for a variety of miniature devices based on electromagnetic coils, such as electromagnets, inductors, transformers, and motors. Being chirally and enantiomerically pure few-wall CNT bundles, they are also ideal for fundamental studies of interwall coupling and superconductivity in CNTs.

Ribosomal RNA-Aminoglycoside Hygromycin B Interaction Energy Calculation within a Density Functional Theory Framework.

We intend to investigate the drug-binding energy of each nucleotide inside the aminoglycoside hygromycin B (hygB) binding site of 30S ribosomal RNA (rRNA) subunit by using the molecular fractionation with conjugate caps (MFCC) strategy based on the density functional theory (DFT), considering the functional LDA/PWC, OBS, and the dielectric constant parametrization. Aminoglycosides are bactericidal antibiotics that have high affinity to the prokaryotic rRNA, inhibiting the synthesis of proteins by acting on the main stages of the translation mechanism, whereas binding to rRNA 16S, a component of the 30S ribosomal subunit in prokaryotes. The identification of the nucleotides presenting the most negative binding energies allows us to stabilize hygB in a suitable binding pocket of the 30S ribosomal subunit. In addition, it should be highlighted that mutations in these residues may probably lead to resistance to ribosome-targeting antibiotics. Quantum calculations of aminoglycoside hygromycin B-ribosome complex might contribute to further quantum studies with antibiotics like macrolides and other aminoglycosides.

Scale Effects on the Ballistic Penetration of Graphene Sheets.

Carbon nanostructures are promising ballistic protection materials, due to their low density and excellent mechanical properties. Recent experimental and computational investigations on the behavior of graphene under impact conditions revealed exceptional energy absorption properties as well. However, the reported numerical and experimental values differ by an order of magnitude. In this work, we combined numerical and analytical modeling to address this issue. In the numerical part, we employed reactive molecular dynamics to carry out ballistic tests on single, double, and triple-layered graphene sheets. We used velocity values within the range tested in experiments. Our numerical and the experimental results were used to determine parameters for a scaling law. We find that the specific penetration energy decreases as the number of layers (N) increases, from ∼15 MJ/kg for N = 1 to ∼0.9 MJ/kg for N = 350, for an impact velocity of 900 m/s. These values are in good agreement with simulations and experiments, within the entire range of N values for which data is presently available. Scale effects explain the apparent discrepancy between simulations and experiments.

Ballistic Fracturing of Carbon Nanotubes.

Advanced materials with multifunctional capabilities and high resistance to hypervelocity impact are of great interest to the designers of aerospace structures. Carbon nanotubes (CNTs) with their lightweight and high strength properties are alternative to metals and/or metallic alloys conventionally used in aerospace applications. Here we report a detailed study on the ballistic fracturing of CNTs for different velocity ranges. Our results show that the highly energetic impacts cause bond breakage and carbon atom rehybridizations, and sometimes extensive structural reconstructions were also observed. Experimental observations show the formation of nanoribbons, nanodiamonds, and covalently interconnected nanostructures, depending on impact conditions. Fully atomistic reactive molecular dynamics simulations were also carried out in order to gain further insights into the mechanism behind the transformation of CNTs. The simulations show that the velocity and relative orientation of the multiple colliding nanotubes are critical to determine the impact outcome.

Insight into In Situ Amphiphilic Functionalization of Few-Layered Transition Metal Dichalcogenide Nanosheets.

A facile route toward functionalized amphiphilic layered transition-metal dichalcogenide nanosheets through in situ polymerization of polystyrene-polyacrylamide copolymers is established. The attachment of copolymers greatly affects their dispersibility in different kinds of solvents. Surface-tension components, polarity, and coordination effects of the copolymer are found to be the main factors affecting the dispersibility.

Synthesis of ultralow density 3D graphene-CNT foams using a two-step method.

Here, we report a highly scalable two-step method to produce graphene foams with ordered carbon nanotube reinforcements. In our approach, we first used solution assembly methods to obtain graphene oxide foam. Next, we employed chemical vapor deposition to simultaneously grow carbon nanotubes and thermally reduce the 3D graphene oxide scaffold. The resulting structure presented increased stiffness, good mechanical stability and oil absorption properties. Molecular dynamics simulations were carried out to further elucidate failure mechanisms and to understand the enhancement of the mechanical properties. The simulations showed that mechanical failure is directly associated with bending of vertical reinforcements, and that, for similar length and contact area, much more stress is required to bend the corresponding reinforcements of carbon nanotubes, thus explaining the experimentally observed enhanced mechanical properties.

The structural and dynamical aspects of boron nitride nanotubes under high velocity impacts.

This communication report is a study on the structural and dynamical aspects of boron nitride nanotubes (BNNTs) shot at high velocities (∼5 km s(-1)) against solid targets. The experimental results show unzipping of BNNTs and the formation of hBN nanoribbons. Fully atomistic reactive molecular dynamics simulations were also carried out to gain insights into the BNNT fracture patterns and deformation mechanisms. Our results show that longitudinal and axial tube fractures occur, but the formation of BN nanoribbons from fractured tubes was only observed for some impact angles. Although some structural and dynamical features of the impacts are similar to the ones reported for CNTs, because BNNTs are more brittle than CNTs this results in a larger number of fractured tubes but with fewer formed nanoribbons.

Solid-Liquid Self-Adaptive Polymeric Composite.

A solid-liquid self-adaptive composite (SAC) is synthesized using a simple mixing-evaporation protocol, with poly(dimethylsiloxane) (PDMS) and poly(vinylidene fluoride) (PVDF) as active constituents. SAC exists as a porous solid containing a near equivalent distribution of the solid (PVDF)-liquid (PDMS) phases, with the liquid encapsulated and stabilized within a continuous solid network percolating throughout the structure. The pores, liquid, and solid phases form a complex hierarchical structure, which offers both mechanical robustness and a significant structural adaptability under external forces. SAC exhibits attractive self-healing properties during tension, and demonstrates reversible self-stiffening properties under compression with a maximum of 7-fold increase seen in the storage modulus. In a comparison to existing self-healing and self-stiffening materials, SAC offers distinct advantages in the ease of fabrication, high achievable storage modulus, and reversibility. Such materials could provide a new class of adaptive materials system with multifunctionality, tunability, and scale-up potentials.

Strain Rate Dependent Shear Plasticity in Graphite Oxide.

Graphene oxide film is made of stacked graphene layers with chemical functionalities, and we report that plasticity in the film can be engineered by strain rate tuning. The deformation behavior and plasticity of such functionalized layered systems is dominated by shear slip between individual layers and interaction between functional groups. Stress-strain behavior and theoretical models suggest that the deformation is strongly strain rate dependent and undergoes brittle to ductile transition with decreasing strain rate.

Defect-Free Carbon Nanotube Coils.

Carbon nanotubes are promising building blocks for various nanoelectronic components. A highly desirable geometry for such applications is a coil. However, coiled nanotube structures reported so far were inherently defective or had no free ends accessible for contacting. Here we demonstrate the spontaneous self-coiling of single-wall carbon nanotubes into defect-free coils of up to more than 70 turns with identical diameter and chirality, and free ends. We characterize the structure, formation mechanism, and electrical properties of these coils by different microscopies, molecular dynamics simulations, Raman spectroscopy, and electrical and magnetic measurements. The coils are highly conductive, as expected for defect-free carbon nanotubes, but adjacent nanotube segments in the coil are more highly coupled than in regular bundles of single-wall carbon nanotubes, owing to their perfect crystal momentum matching, which enables tunneling between the turns. Although this behavior does not yet enable the performance of these nanotube coils as inductive devices, it does point a clear path for their realization. Hence, this study represents a major step toward the production of many different nanotube coil devices, including inductors, electromagnets, transformers, and dynamos.

Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yarn muscles.

Artificial muscles are of practical interest, but few types have been commercially exploited. Typical problems include slow response, low strain and force generation, short cycle life, use of electrolytes, and low energy efficiency. We have designed guest-filled, twist-spun carbon nanotube yarns as electrolyte-free muscles that provide fast, high-force, large-stroke torsional and tensile actuation. More than a million torsional and tensile actuation cycles are demonstrated, wherein a muscle spins a rotor at an average 11,500 revolutions/minute or delivers 3% tensile contraction at 1200 cycles/minute. Electrical, chemical, or photonic excitation of hybrid yarns changes guest dimensions and generates torsional rotation and contraction of the yarn host. Demonstrations include torsional motors, contractile muscles, and sensors that capture the energy of the sensing process to mechanically actuate.