Molecular junctions for thermal transport between graphene nanoribbons: covalent bonding vs. interdigitated chains

TL;DR

This study uses molecular dynamics to compare thermal conductance of covalent and Van der Waals chains between graphene nanoribbons, revealing how chain length, density, and bonding type affect heat transfer efficiency.

Contribution

It provides a systematic analysis of how molecular junction design influences thermal conductance in graphene contacts, highlighting the importance of covalent bonding for heat management applications.

Findings

Longer chains reduce conductance

Lower grafting density decreases conductance

Covalent chains outperform Van der Waals chains in heat transfer

Abstract

Proper design and manufacturing thermal bridges based on molecular junctions at the contact between graphene platelets or other thermally conductive nanoparticles would provide a fascinating way to produce efficient heat transport networks for the exploitation in heat management applications. In this work, using Non Equilibrium Molecular Dynamics, we calculated thermal conductance of alkyl chains used as molecular junctions between two graphene nanoribbons, both as covalently bound and Van der Waals interdigitated chains. Effect of chain length, grafting density, temperature and chain interdigitation were systematically studied. A clear reduction of conductivity was found with increasing chain length and decreasing grafting density, while lower conductivity was observed for Van der Waals interdigitated chains compared to covalently bound ones. The importance of molecular junctions in enhancing thermal conductance at graphene nanoribbons contacts was further evidenced by calculating the conductance equivalence between a single chain and an overlapping of un-functionalized graphene sheets. As an example, one single pentyl covalently bound chain was found to have a conductance equivalent to the overlapping of an area corresponding to about 152 carbon atoms. These results contribute to the understanding of thermal phenomena occurring within networks of thermally conductive nanoparticles, including graphene nanopapers and graphene-based polymer nanocomposites, which are or high interest for the heat management application in electronics and generally in low-temperature heat exchange and recovery.