Supramolecular Interactions Lead to Remarkably High Thermal Conductivities in Interpenetrated Two-Dimensional Porous Crystals

Abstract

The design of innovative porous crystals with high porosities and large surface areas has garnered a great deal of attention over the past few decades due to their remarkable potential for a variety of applications. However, heat dissipation is key to realizing their potential. We use systematic atomistic simulations to reveal that interpenetrated porous crystals formed from two-dimensional (2D) frameworks possess remarkable thermal conductivities at high porosities in comparison to their three-dimensional (3D) single framework and interpenetrated 3D framework counterparts. In contrast to conventional understanding, higher thermal conductivities are associated with lower atomic densities and higher porosities for porous crystals formed from interpenetrating 2D frameworks. We attribute this to lower phonon–phonon scattering and vibrational hardening from the supramolecular interactions that restrict atomic vibrational amplitudes, facilitating heat conduction. This marks a new regime of materials design combining ultralow mass densities and ultrahigh thermal conductivities in 2D interpenetrated porous crystals.

Thermally Conductive Self-Healing Nanoporous Materials Based on Hydrogen-Bonded Organic Frameworks

“…51 In this regard, new strategies such as interpenetration or guest−host interactions could potentially enhance the heat transfer efficacy in these types of polymeric framework materials, which could potentially lead to unprecedented, dynamic thermal responses. 47,48,54 In summary, our systematic atomistic simulations based on reactive MD simulations show that HOFs are capable of possessing high thermal conductivities for porous materials, which mainly depend on the orientation of their ultraflexible organic building blocks. Specifically, when uniaxial tension is applied along a direction, the building blocks preferentially align along that direction to facilitate heat transfer.…”

“…However, what separates HOFs in comparison to the 2D COFs is the fact that the thermal conductivity can vary in all three principle directions, whereas the thermal conductivity along the bonded plane remains similar for 2D COFs. Moreover, 3D COFs and MOFs (such as COF-300 and MOF-5) demonstrate isotropic thermal conductivities of ∼0.3 W m –1 K –1 in all three principle directions. , Therefore, this unique physical attribute where the thermal conductivity can change by a factor of 3 depending on the crystalline direction separates HOFs from other organic framework-based materials, where achieving anisotropy in all three principle directions has not been realized so far.…”

“…While the thermal conductivities for HOFs are relatively higher as compared to the azopolymers, for thermal management applications, it is desirable for soft polymeric materials to demonstrate metal-like thermal conductivities . In this regard, new strategies such as interpenetration or guest–host interactions could potentially enhance the heat transfer efficacy in these types of polymeric framework materials, which could potentially lead to unprecedented, dynamic thermal responses. ,, …”

“…Moreover, 3D COFs and MOFs (such as COF-300 and MOF-5) demonstrate isotropic thermal conductivities of ∼0.3 W m −1 K −1 in all three principle directions. 46,47 Therefore, this unique physical attribute where the thermal conductivity can change by a factor of 3 depending on the crystalline direction separates HOFs from other organic framework-based materials, where achieving anisotropy in all three principle directions has not been realized so far.…”

Engineering the Electronic and Thermal Properties of Two-Dimensional Covalent Organic Frameworks

“…To predict the in-plane thermal conductivities of our 2D COF structures, we utilize the GK formalism under the equilibrium molecular dynamics (EMD) simulations framework. In this method, the thermal conductivity is calculated as ,− κ x , y = 1 k normalB V T 2 ∫ 0 ∞ ⟨ J x , y false( t false) J x , y false( 0 false) ⟩ .25em normald t where V , T , and t are the volume of the system, temperature, and time, respectively, and ⟨ J x , y ( t ) J x , y (0)⟩ is the component of the heat current autocorrelation function (HCACF) along the x - or y -directions, which is calculated as boldJ = 1 V ( ∑ i boldv i ϵ i + ∑ i boldS i · v i ) where v i , ϵ i , and S i are the velocity, energy and stress of atom i , respectively. Our calculations (as presented below) show that the in-plane thermal conductivities in the x - and y -directions are similar, and therefore we only report an average value for the in-plane thermal conductivities of our 2D COFs.…”