4 research outputs found
Nanoscale Azide Polymer Functionalization: A Robust Solution for Suppressing the Carbon Nanotube–Polymer Matrix Thermal Interface Resistance
The
large thermal resistance across the carbon nanotube (CNT)–polymer
matrix interface is a limiting factor for achieving polymer composites
with high thermal conductivities. Using equilibrium molecular dynamics
simulations we show that an azide-terminated aromatic polymer HLK5
(C<sub>22</sub>H<sub>25</sub>O<sub>3</sub>N<sub>3</sub>) functionalized
onto the CNT sidewall can efficiently decrease the thermal resistance
between the nanotube and different types of polymer matrices (polystyrene,
epoxy, and polyethylene). The HLK5 functionalization can also significantly
decrease the CNT–CNT junction resistance. Compared with hydroxyl
and octane functionalizations, the HLK5 one alters less the high intrinsic
CNT thermal conductivity at the same surface coverage ratio. By revealing
the important role played by the atomistic van der Waals interactions
in attaining these key results, our study brings a new perspective
in the nanoscale design of advanced CNT–polymer materials
Randomness-Induced Phonon Localization in Graphene Heat Conduction
Through nonequilibrium molecular
dynamics simulations, we report
the direct numerical evidence of the coherent phonons participating
in thermal transport at room temperature in graphene phononic crystal
(GPnC) structure and evaluate their contribution to thermal conductivity
based on the two-phonon model. With decreasing period length in GPnC,
the transition from the incoherent to coherent phonon transport is
clearly observed. When a random perturbation to the positions of holes
is introduced in a graphene sheet, the phonon wave-packet simulation
reveals the presence of notable localization of coherent phonons,
leading to the significant reduction of thermal conductivity and suppressed
length dependence. Finally, the effects of period length and temperature
on the coherent phonon contribution to thermal conductivity are also
discussed. Our work establishes a deep understanding of the coherent
phonons transport behavior in periodic phononic structures, which
provides effective guidance for engineering thermal transport based
on a new path via phonon localization
Anomalous thermal conductivity enhancement in low dimensional resonant nanostructures due to imperfections
Nanophononic metamaterials have broad applications in fields such as heat management, thermoelectric energy conversion, and nanoelectronics. Phonon resonance in pillared low-dimensional structures has been suggested to be a feasible approach to reduce thermal conductivity (TC). In this work, we study the effects of imperfections in pillared nanostructures based on graphene nanoribbons (GNR), using classical molecular dynamics simulations and harmonic lattice dynamics. The TC of perfect pillared GNR is only about 13% of that of pristine GNR due to the strong phonon resonant hybridization in pillared GNR. However, introducing imperfections such as vacancy defects and mass mismatch between the pillars and the base material, and alloy disorder in the pillars, can weaken the resonant hybridization and abnormally increase the TC. We show that both vacancy defects and mass mismatch can reduce the penetration of the resonant modes from the pillars into the base material, while the alloy disorder in the pillars can scatter the phonons inside them, which turns regular resonance into a random one with weaker hybridization. Our work provides useful insight into the phonon resonance mechanisms in experimentally relevant low dimensional nanostructures containing various imperfections.</p
Supplementary information files for: Anomalous thermal conductivity enhancement in low dimensional resonant nanostructures due to imperfections
Supplementary files for article: Anomalous thermal conductivity enhancement in low dimensional resonant nanostructures due to imperfections.Nanophononic metamaterials have broad applications in fields such as heat management, thermoelectric energy conversion, and nanoelectronics. Phonon resonance in pillared low-dimensional structures has been suggested to be a feasible approach to reduce thermal conductivity (TC). In this work, we study the effects of imperfections in pillared nanostructures based on graphene nanoribbons (GNR), using classical molecular dynamics simulations and harmonic lattice dynamics. The TC of perfect pillared GNR is only about 13% of that of pristine GNR due to the strong phonon resonant hybridization in pillared GNR. However, introducing imperfections such as vacancy defects and mass mismatch between the pillars and the base material, and alloy disorder in the pillars, can weaken the resonant hybridization and abnormally increase the TC. We show that both vacancy defects and mass mismatch can reduce the penetration of the resonant modes from the pillars into the base material, while the alloy disorder in the pillars can scatter the phonons inside them, which turns regular resonance into a random one with weaker hybridization. Our work provides useful insight into the phonon resonance mechanisms in experimentally relevant low dimensional nanostructures containing various imperfections.</div