Ultralow and Twist-Tolerant Thermal Conductivity in Two-Dimensional Pentagonal Covalent Organic Frameworks
Xinyuan Ma1, Peng-Hu Du1, Chenxin Zhang1
1School of Materials Science and Engineering, Peking University, Beijing 100871, China.
None:
Motivated by recent advances in the synthesis of pentagonal covalent organic frameworks (penta-COFs) and the experimental realization of twisted COF bilayers, we present a theoretical investigation into the thermal transport properties of these synthesized materials and their twisted bilayer counterparts. Based on molecular dynamics simulations, we show that monolayer penta-COFs exhibit ultralow in-plane thermal conductivities as low as 0.44 W·m-1·K-1 at 300 K with an exceptionally weak temperature dependence due to the strongly localized phonon vibrational modes in the strained linkers and vertices, which contribute minimally to the thermal transport. More interestingly, introducing interlayer twisting slightly enhances the in-plane thermal conductivities, increasing from 0.41 ± 0.01 to 0.48 ± 0.02 W·m-1·K-1 at 300 K as the twist angle decreases from 36.87° to 16.26°, yielding twist-tolerant behavior. This contrasts with the commonly observed suppression trends in twisted atom-based bilayers. Further detailed analysis of the spatial and time-resolved vibrational characterizations reveals that this behavior results from a competition between the twist-induced moiré disorder that typically suppresses thermal transport and the structural recoupling facilitated by the intrinsic porosity and flexibility of the organic skeletons that enhances phonon transport. These findings deepen the fundamental understanding of the thermal transport properties of penta-COFs, which are distinct from those of atom-based materials.
Related Concept Videos
02:18Network Covalent Solids
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:37Metallic Solids
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability....
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:11Conformations of Cyclohexane
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
02:56Intermolecular Forces and Physical Properties