1 research outputs found
Thermal Conductance in Cross-linked Polymers: Effects of Non-Bonding Interactions
Weak interchain interactions have
been considered to be a bottleneck
for heat transfer in polymers, while covalent bonds are believed to
give a high thermal conductivity to polymer chains. For this reason,
cross-linkers have been explored as a means to enhance polymer thermal
conductivity; however, results have been inconsistent. Some studies
show an enhancement in the thermal conductivity for polymers upon
cross-linking, while others show the opposite trend. In this work
we study the mechanisms of heat transfer in cross-linked polymers
in order to understand the reasons for these discrepancies, in particular
examining the relative contributions of covalent (referred to here
as “bonding”) and nonbonding (e.g., van der Waals and
electrostatic) interactions. Our results indicate cross-linkers enhance
thermal conductivity primarily when they are short in length and thereby
bring polymer chains closer to each other, leading to increased interchain
heat transfer by enhanced nonbonding interactions between the chains
(nonbonding interactions being highly dependent on interchain distance).
This suggests that enhanced nonbonding interactions, rather than thermal
pathways through cross-linker covalent bonds, are the primary transport
mechanism by which thermal conductivity is increased. We further illustrate
this by showing that energy from THz acoustic waves travels significantly
faster in polymers when nonbonding interactions are included versus
when only covalent interactions are present. These results help to
explain prior studies that measure differing trends in thermal conductivity
for polymers upon cross-linking with various species