Infrared-pump, electronic-probe (IPEP) spectroscopy is
used to
measure heat flow into and out of CdSe nanocrystals suspended in an
organic solvent, where the surface ligands are initially excited with
an infrared pump pulse. Subsequently, the heat is transferred from
the excited ligands to the nanocrystals and in parallel to the solvent.
Parallel heat transfer in opposite directions uniquely enables us
to differentiate the thermal conductances at the nanocrystal/ligand
and ligand/solvent interfaces. Using a novel solution to the heat
diffusion equation, we fit the IPEP data to find that the nanocrystal/ligand
conductances range from 88 to 135 MW m–2K–1and are approximately 1 order of magnitude higher than the ligand/solvent
conductances, which range from 7 to 26 MW m–2K–1. Transient nonequilibrium molecular dynamics (MD)
simulations of nanocrystal suspensions agree with IPEP data and show
that ligands bound to the nanocrystal by bidentate bonds have more
than twice the per-ligand conductance as those bound by monodentate
bonds.