Modulating thermal conductance at ligand/nanocrystal interfaces via oxygen-coordinated ligands

The interfacial thermal conductance (h_lig-NC) between a cadmium selenide (CdSe) nanocrystal (NC) and three related organic ligands-olealdehyde, oleyl alcohol, and oleic acid-was investigated computationally. These ligands have the same carbon backbone but differ in the number and type of oxygen-coordinated headgroups (carbonyl and/or hydroxyl), leading to distinct bonding geometries involving monodentate and bidentate bonds. For a fully encapsulated NC, h_lig-NC increases in the order of olealdehyde, oleic acid, and oleyl alcohol ligands. To isolate the contributions of h_lig-NC from each headgroup type, the distinct bonding geometries were analyzed. Aldehyde and alcohol ligands, each featuring a single oxygen headgroup (carbonyl or hydroxyl), exhibit similar O-Cd separations and nearly identical h_lig-NC per ligand at full surface coverage. However, the hydroxyl group in the alcohol ligand enables a higher ligand grafting density on the NC surface, resulting in a greater overall h_lig-NC than the aldehyde-grafted NCs. In contrast, the oleic acid ligand forms multidentate bonds with the NC, leading to a shorter average O-Cd separation and a higher h_lig-NC per ligand compared to monodentate bonds. Nevertheless, steric hindrance from the acid ligand's larger headgroup reduces its grafting density relative to alcohol ligands, ultimately resulting in a lower overall h_lig-NC.