Session: 11-05-01: Thermophysical Properties: Characterization and Modeling Across Scales

Paper Number: 150795

150795 - High Anisotropic Thermal Conductivity of Imine Linked 2 Dimensional Polymers 

2-dimensional polymers (2DPs), a subclass of covalent organic frameworks (COFs), have gained attention due to their distinct structure and tunable properties. The building blocks of these materials are light elements (H, B, C, N, O) that form stacked 2-dimensional networks of nodes and linkers connected via strong covalent bonds.  Their strong, in-plane covalent bonding and long-range crystallinity demonstrate features of high thermal conductivity, making 2DPs attractive for the development of next generation flexible electronics and microelectronics, which require fast heat dissipation. Furthermore, the large difference between the weak, cross-plane van-der Waals interactions and the strong, in-plane covalent bonding promote anisotropic thermal transport, which can be exploited for directional heat spreading.

Several computational studies have investigated the nature of thermal transport in COFs and found the in-plane thermal conductivity of COF-5 to be 1.7 W/m-K, three times higher than its cross-plane thermal conductivity, showcasing the exceptional anisotropy. In contrast, experimental studies on 2DPs are limited due to challenges related to their synthesis and characterization. As yet, there have been no direct measurements of in-plane thermal conductivity in 2DPs.

The boronate ester linkers used in the initial thermal conductivity study are easily hydrolyzed or oxidized, which limit their practical usage. On the other hand, imine-linked 2DPs exhibit enhanced chemical stability in organic solvents and are applicable over a wider range of applications, including energy storage devices and electron-conductive membranes. Despite the promise of imine-linked 2DPs, studies on their thermal transport properties and mechanisms are lacking.

In this work, we studied the thermal properties of a specific imine linked 2DP, TAPPy-PDA. Crystalline 2DP thin films were synthesized by interfacial method. Crystalline, oriented, transferrable thin films enable both the cross plane and in plane thermal characterization for the first time, both the in-plane and cross-plane thermal conductivity of a 2DP are measured using the suspended platform and FDTR techniques respectively. Frequency-domain thermoreflectance (FDTR), a non-contact, laser-based technique, was employed to measure the cross-plane thermal conductivity of 2DPs. In this method, a modulated pump laser periodically heats the sample, and the phase lag of the surface temperature in response to the heat flux is detected by a probe laser relative to the pump laser. This phase lag measured for a range of modulated frequencies is then fitted to an analytical solution of the heat diffusion equation to determine the thermal conductivity of the 2DP. To ensure the consistency of measurements on the polymer thin film, which has a roughness of approximately 10 µm, we applied a systematic scanning method, covering an 11 × 11 grid within a 300 µm × 300 µm area. Each discrete point in this grid underwent an individual measurement using FDTR, yielding an average to 𝑘 = 0.20 ± 0.1 W/mK. Comparing to the in-plane thermal conductivity measured by suspended platform, which is 0.52W/mK, high anisotropy is shown. Measurements are also taken over a range of temperatures from 77K to 400K and are compared to molecular dynamics simulations to understand the underlying heat transfer mechanism.

 

Presenting Author: Yuxing Liang Carnegie Mellon University

Presenting Author Biography: Yuxing Liang is a fifth year PhD student in mechanical engineering department of Carnegie Mellon University working with Prof. Jonathan Malen in the field of nanoscale heat transfer.

Authors:

Yuxing Liang Carnegie Mellon University
Kiana Treaster University of Florida
Manoj Settipalli Carnegie Mellon University
Ayan Majumder University of Michigan
Shravan Godse Carnegie Mellon University
Rupam Roy University of Florida
Kanishka Panda University of Michigan
Alan Mcgaughey Carnegie Mellon University
Pramod Reddy University of Michigan
Austin Evans University of Florida
Jonathan Malen Carnegie Mellon University