Molecular dynamics study of phonon transport in graphyne nanotubes

Multiscale Design of Graphyne‐Based Materials for High‐Performance Separation Membranes

“…Numerous studies of the thermal conductivity (TC) along both the zigzag and armchair directions of α-, β-, γ-, δ-, and 6,6,12-graphyne nanosheets, nanoribbons, and nanotubes were determined with combinations of RNEMD or EMD simulations with the AIREBO or REBO interatomic potentials. [52][53][54][55][56][57][58][59] These graphyne variants had significantly reduced TC compared to pristine graphene and carbon nanotubes (CNTs), even when extrapolated to infinite lengths (Table 1, Figure 5A). A number of fundamental reasons were proposed to explain this dramatic reduction in TC.…”

“…In particular, in a detailed comparison of the thermal properties of α-, β-, and γ-GYNTs with CNTs, [56] analysis of the phonon DOS showed that increased percentages of acetylenic bonds correspondingly increased the number of high-energy phonon modes as the higher stretching frequency of these bonds became more dominant. There were increases in scattering events in tandem with the widening of the characteristic peaks in the phonon DOS as temperatures increased.…”

“…[55] Numerous studies had also examined the influence of temperature on the TC of graphyne allotropes, where the general consensus was that the TC was significantly reduced as the temperature rose. [52][53][54][55][56] At extremely low temperatures below 60 K, γ-graph-n-yne's thermal conductance had a quadratic dependence with temperature, thus behaving similarly to graphene ( Figure 5E). Below 30 K, the γgraph-n-yne's thermal conductance was even predicted to be approximately equivalent to graphene.…”

“…[68] Further comparisons ought to be performed with a consistent set of parameters, force fields, and simulation methods to resolve these conflicting results. The TC of both armchair and zigzag α-, β-, and γ-GYNTs slightly decreased below 150 K if quantum-corrections were applied, but the general trend was still an increasing TC as the temperature decreased from 400 to 150 K. [56] A number of other methods to tune the thermal properties of graphyne allotropes had also been proposed, particularly by applying lateral and rotational strain. [52,54,70] Application of both uniaxial and biaxial strain on γ-graphyne nanosheets decreased the TC, although the change is marginal if the strain small.…”

“…As a result of the unique thermal and electronic properties detailed herein, several studies considered the application of graphyne in phonovoltaic and thermoelectric devices for energy conversion. [56,69,[76][77][78][79][80] Similar in function to photovoltaic devices, phonovoltaic devices convert energy from phonons into electrical currents, where electron-hole pairs generated by harnessing nonequilibrium optical phonons that are more energetic than the material's bandgap. In particular, zigzag α-GYNTs that had diameters of 2.22 nm and 2.89 nm fulfilled the requirements for such phonovoltaic devices as the direct bandgap could be excited by the optical phonons while the energy was an order of magnitude higher than the thermal energy at 300 K. [56] However, there is greater interest in implementing graph-n-ynes in thermoelectric devices due to their electronic semiconductivity (see Section 3 herein) and considerably lower thermal conductivity compared to graphene.…”