Thermal rectification in novel two-dimensional hybrid graphene/BCN sheets: A molecular dynamics simulation.

The graphene-like monolayer of carbon, boron and nitrogen that maintains the native hexagonal atomic lattice (BCN), is a novel semiconductor with special thermal properties. Herein, with the aid of a non-equilibrium molecular dynamics approach (NEMD), we study phonon thermal rectification in a hybrid system of pure graphene and BCN (G-BCN) in various configurations under a series of positive and negative temperature gradients. We begin by investigating the relation of thermal rectification to sample's mean temperature, T, and the imposed temperature difference, ΔT, between the two heat baths at its ends. We then move to explore the effect of varying strain levels of our sample on thermal rectification, followed by Kapitza resistance calculations at the G-BCN interface, which shed light on the interface effects on thermal rectification. Our simulation results reveal a BCN-configuration-dependent behavior of thermal rectification. Finally, the underlying mechanism leading to a preferred direction for phonons is studied using phonon density of states (DOS) on both sides of the G-BCN interface.

Thermal properties and mechanical behavior of hot pressed PEEK/graphite thin film laminate composites.

This work studies high-performance laminate composite materials made of graphite and poly(ether-ether-ketone) (PEEK). The main objective was to enhance graphite's inherent properties by the addition of PEEK to produce materials with improved thermal and mechanical stability for high-performance applications. The composites were fabricated using a hot press method at a temperature below 310 °C. The newly formed materials were then subjected to various tests, including Scanning Electron Microscopy, Thermogravimetric Analysis, mechanical properties tests, nanoindentation tests, and X-Ray Diffraction to assess their structural, thermal, and mechanical properties. Our findings showed a substantial interfacial interaction between PEEK and graphite, indicating successful composite formation. Both three-layered PEEK/graphite/PEEK (PGP) and five-layered PEEK/graphite/PEEK/graphite/PEEK (PG)2P composites exhibited superior thermal stability at high temperatures compared to neat PEEK. Moreover, our mechanical tests demonstrated a 172% increase in ultimate tensile strength of PGP compared to neat graphite. Additionally, nanoindentation tests confirmed an increase in both Young's modulus and hardness of composites. Furthermore, XRD analysis revealed a 35.5% increase in crystallinity in the fabricated composites compared to pristine PEEK. These findings significantly contribute to the field of high-performance composite materials, confirming that the hot pressing of PEEK and graphite sheets results in enhanced thermal and mechanical properties.

Mechanical properties of multi-walled beryllium-oxide nanotubes: a molecular dynamics simulation study.

Molecular dynamic (MD) simulation was employed to take the molecular fingerprint of mechanical properties of beryllium-oxide nanotubes (BeONTs). In this regard, the effect of the radius, the number of walls (single-, double-, and triple-walled), and the interlayer distance, as well as the temperature on the Young's modulus, failure stress, and failure strain, are visualized and discussed. It was unveiled that larger single-walled BeONTs have lower Young's modulus in zigzag and armchair direction, and the highest Young's modulus was obtained for the (8,0) zigzag and (4,4) armchair SWBeONTs as of 645.71 GPa and 624.81 GPa, respectively. Unlike Young's modulus, however, the failure properties of the armchair structures were higher than those of zigzag ones. Furthermore, similar to SWBEONTs, an increase in the interlayer distance of double-walled BeONTs (DWBeONTs) led to a slight reduction in Young's modulus value, while no meaningful trend was found among failure behavior. For double-walled BeONTs (TWBeONTs), the elastic modulus was obviously higher in both armchair and zigzag directions compared to DWBeONTs.

Thermal rectification in polytelescopic Ge nanowires.

Herein we served non-equilibrium molecular dynamics (NEMD) approach to simulate thermal rectification in the mono- and polytelescopic Ge nanowires (GeNWs). We considered mono-telescopic structures with different Fat-Thin configurations (15-10 nm-nm or Type (I); 15-5 nm-nm or Type (II); and 10-5 or Type (III) nm-nm) as generic models. We simulated the variation of thermal conductivity against interfacial cross-sectional temperature as well as the direction of heat transfer, where a higher thermal conductivity correlating to thicker nanowires, and a more significant drop (or discontinuity) in the average interface temperature in the positive (or negative) direction were detected. Noticeably, interfacial thermal resistance followed the order of Type (II) (48 K/µW, maximal) ˃ Type (III) ˃ Type (I) (5 K/µW, minimal). In the second stage, a series of polytelescopic nanostructures of GeNWs were born with consecutive cross-sectional interfaces. Surprisingly, larger interfacial cross-sectional areas equivalent to smaller diameter changes along the GeNWs were responsible for higher temperature rectification. This led to a very limited thermal conductivity loss or a very high unidirectional heat transfer along the polytelescopic structures - the key for manufacturing next generation high-performance thermal diodes.

A theoretical insight into phonon heat transport in graphene/biphenylene superlattice nanoribbons: a molecular dynamic study.

Manipulating the thermal conductivity of nanomaterials is an efficacious approach to fabricate tailor-made nanodevices for thermoelectric applications. To this end, superlattice nanostructures can be used to achieve minimal thermal conductivity for the employed nanomaterials. Two-dimensional biphenylene is a recently-synthesized sp2-hybridized allotrope of carbon atoms that can be employed in superlattice nanostructures and therefore further investigation in this context is due. In this study, we first determined the thermal conductivity of biphenylene at 142.8 W mK-1which is significantly lower than that of graphene. As a second step, we studied the effect of the superlattice period (lp) on thermal conductivities of the employed graphene/biphenylene superlattice nanoribbons, using molecular dynamics simulations. We calculated a minimum thermal conductivity of 105.5 W mK-1atlp= 5.066 nm which indicates an achieved thermal conductivity reduction of approximately 97% and 26% when compared to pristine graphene and biphenylene, respectively. This superlattice period denotes the phonon coherent length at which the wave-like behavior of phonons starts prevailing over the particle-like behavior. Finally, the effects of temperature and temperature gradient on the thermal conductivity of superlattice were also investigated.

Heat transfer through hydrogenated graphene superlattice nanoribbons: a computational study.

Optimization of thermal conductivity of nanomaterials enables the fabrication of tailor-made nanodevices for thermoelectric applications. Superlattice nanostructures are correspondingly introduced to minimize the thermal conductivity of nanomaterials. Herein we computationally estimate the effect of total length and superlattice period ([Formula: see text]) on the thermal conductivity of graphene/graphane superlattice nanoribbons using molecular dynamics simulation. The intrinsic thermal conductivity ([Formula: see text]) is demonstrated to be dependent on [Formula: see text]. The [Formula: see text] of the superlattice, nanoribbons decreased by approximately 96% and 88% compared to that of pristine graphene and graphane, respectively. By modifying the overall length of the developed structure, we identified the ballistic-diffusive transition regime at 120 nm. Further study of the superlattice periods yielded a minimal thermal conductivity value of 144 W m-1 k-1 at [Formula: see text] = 3.4 nm. This superlattice characteristic is connected to the phonon coherent length, specifically, the length of the turning point at which the wave-like behavior of phonons starts to dominate the particle-like behavior. Our results highlight a roadmap for thermal conductivity value control via appropriate adjustments of the superlattice period.

Dynamics of Antimicrobial Peptide Encapsulation in Carbon Nanotubes: The Role of Hydroxylation.

INTRODUCTION: Carbon nanotubes (CNTs) have been widely employed as biomolecule carriers, but there is a need for further functionalization to broaden their therapeutic application in aqueous environments. A few reports have unraveled biomolecule-CNT interactions as a measure of response of the nanocarrier to drug-encapsulation dynamics. METHODS: Herein, the dynamics of encapsulation of the antimicrobial peptide HA-FD-13 (accession code 2L24) into CNTs and hydroxylated CNTs (HCNTs) is discussed. RESULTS: The van der Waals (vdW) interaction energy of CNT-peptide and HCNT-peptide complexes decreased, reaching -110.6 and -176.8 kcal.Mol-1, respectively, once encapsulation of the peptide inside the CNTs had been completed within 15 ns. The free energy of the two systems decreased to -43.91 and -69.2 kcal.Mol-1 in the same order. DISCUSSION: The peptide was encased in the HCNTs comparatively more rapidly, due to the presence of both electrostatic and vdW interactions between the peptide and HCNTs. However, the peptide remained encapsulated throughout the vdW interaction in both systems. The negative values of the free energy of the two systems showed that the encapsulation process had occurred spontaneously. Of note, the lower free energy in the HCNT system suggested more stable peptide encapsulation.

An insight into thermal properties of BC3-graphene hetero-nanosheets: a molecular dynamics study.

Simulation of thermal properties of graphene hetero-nanosheets is a key step in understanding their performance in nano-electronics where thermal loads and shocks are highly likely. Herein we combine graphene and boron-carbide nanosheets (BC3N) heterogeneous structures to obtain BC3N-graphene hetero-nanosheet (BC3GrHs) as a model semiconductor with tunable properties. Poor thermal properties of such heterostructures would curb their long-term practice. BC3GrHs may be imperfect with grain boundaries comprising non-hexagonal rings, heptagons, and pentagons as topological defects. Therefore, a realistic picture of the thermal properties of BC3GrHs necessitates consideration of grain boundaries of heptagon-pentagon defect pairs. Herein thermal properties of BC3GrHs with various defects were evaluated applying molecular dynamic (MD) simulation. First, temperature profiles along BC3GrHs interface with symmetric and asymmetric pentagon-heptagon pairs at 300 K, ΔT = 40 K, and zero strain were compared. Next, the effect of temperature, strain, and temperature gradient (ΔT) on Kaptiza resistance (interfacial thermal resistance at the grain boundary) was visualized. It was found that Kapitza resistance increases upon an increase of defect density in the grain boundary. Besides, among symmetric grain boundaries, 5-7-6-6 and 5-7-5-7 defect pairs showed the lowest (2 × 10-10 m2 K W-1) and highest (4.9 × 10-10 m2 K W-1) values of Kapitza resistance, respectively. Regarding parameters affecting Kapitza resistance, increased temperature and strain caused the rise and drop in Kaptiza thermal resistance, respectively. However, lengthier nanosheets had lower Kapitza thermal resistance. Moreover, changes in temperature gradient had a negligible effect on the Kapitza resistance.

Graphene-carbon nitride interface-geometry effectson thermal rectification: A molecular dynamicssimulation.

We apply the non-equilibrium molecular dynamics approach (NEMD) to study thermal rectification in a hybrid graphene-carbon nitride system (G - C3N) under a series of positive and negative temperature gradients with varying interface geometries. In this study, we investigate the effects of a) temperature differences, (∆T), between the two employed baths, b) mediainterface geometry, and c) sample size, on thermal rectification. Our simulation results portray a sigmoid relation between thermal rectification and temperature difference, with a sample-size depending upper asymptote occurring at generally large temperature differences. The achieved thermal rectification values are significant and go up to around 120% for ∆T = 150 K. Furthermore, the consideration of varying media-interface geometries yields a non-negligible effect on thermal rectification and highlights areas for further investigation. Finally, calculations of Kapitza resistance at the G - C3N interface are performed for assisting us in the understanding of interface-geometry effects on thermal rectification.

Crosslinking Multilayer Graphene by Gas Cluster Ion Bombardment.

In this paper, we demonstrate a new, highly efficient method of crosslinking multilayer graphene, and create nanopores in it by its irradiation with low-energy argon cluster ions. Irradiation was performed by argon cluster ions with an acceleration energy E ≈ 30 keV, and total fluence of argon cluster ions ranging from 1 × 109 to 1 × 1014 ions/cm2. The results of the bombardment were observed by the direct examination of traces of argon-cluster penetration in multilayer graphene, using high-resolution transmission electron microscopy. Further image processing revealed an average pore diameter of approximately 3 nm, with the predominant size corresponding to 2 nm. We anticipate that a controlled cross-linking process in multilayer graphene can be achieved by appropriately varying irradiation energy, dose, and type of clusters. We believe that this method is very promising for modulating the properties of multilayer graphene, and opens new possibilities for creating three-dimensional nanomaterials.