Poly-HEATLINE: Polymer HEAT Transfer by Learned INtermolecular Enhancement
Abstract
We seek to study the physics of thermal transport in polymers to identify mechanisms that enable both ultra-high thermal conductivity (k) and on-demand control of k by external stimuli. We hypothesize that the critical features needed to realize polymers with exceptionally-high k are (i) long-range crystallinity and (ii) enhanced intermolecular interactions that stiffen the system. This hypothesis, supported by our preliminary data, is based on the theoretical expectation that crystallinity and stiffness are key to achieving the long phonon mean free paths and high group velocities critical to realizing high k. Other than for mechanically-drawn polyethylene fibers, high polymer k has remained elusive to the siloed thermal community, which lacks access to chemists who can design and synthesize crystalline polymers. We will overcome this barrier by creating a unique multidisciplinary team that includes synthetic experts (Sumerlin, Evans) who have achieved major breakthroughs in creating crystalline polymers, multi-scale modelers (McGaughey, Jayaraman) with foremost expertise in modelling thermal transport and polymer structure using theory, simulation, and machine learning, and innovative experimentalists (Malen, Reddy) who have developed advanced tools to measure thermal transport across length scales from bulk plastics to single polymer chains. By carefully combining experiments and computations with machine learning, we will identify key design rules for achieving high and switchable k in polymers. Towards this goal, we will consider three broad classes of macromolecular systems that can be processed into highlycrystalline polymers with embedded stimuli-responsive motifs. 1) We will synthesize and process ultra-high molecular weight (UHMW) polymers into crystalline fibers and films. By introducing functional groups that undergo reversible chemical and structural transitions through optical and thermal stimuli, we will interrogate the limits to k switching. Laser and scanning probe measurements combined with multiscale molecular dynamics simulations will answer fundamental questions related to how features like monomer selection, chain conformation, intermolecular interactions, and switching moieties influence k. 2) We will leverage auto-templating approaches to produce crystalline two-dimensional polymers (2DPs), also known as covalent organic frameworks, that have unique potential for high in-plane k as identified by our experimental and theoretical work. Using laser measurements, microfabricated devices, and neutron spectroscopy along with phonon-level lattice dynamics calculations, we will achieve fundamental insights into how bonding anisotropy impacts anisotropy in k. Further, we will explore how the ultra-thin and porous nature of 2DPs can be used to switch k via electric-fields, light, and gas sorption. 3) We will embed Janus hydrogen-bonding moieties into block copolymers (BCP) to produce selfassembled structurally rigid monoliths. Our preliminary measurements demonstrate that one Janus BCP has k=2.7+/-0.6 Wm-1K-1, which is 10x higher than common polymers. Other BCPs, with structures controlled via systematic molecular engineering, will enable parametric investigations into thermal transport manipulation through designed supramolecular rigidification. Electrochemical stimuli and heat will modulate both the strength of the noncovalent interactions and phase segregation behavior, to switch mesoscale structure and k. Impact on DoD Capabilities: Polymers with high and switchable k will give our military competitive advantages as thermal cloaks that erase soldiers? thermal signatures and in active thermal management solutions for electronics and batteries. We will align with DoD interests through collaboration with the Army Research Laboratory, initially related to lightweight heat sinks and polymeric gas storage media suited for exothermic adsorption processes.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 01, 2023
- Source ID
- W911NF2310260
Entities
People
- Jonathan A Malen
Organizations
- Army Contracting Command
- Carnegie Mellon University
- United States Army