Intramolecular Entropy and Size-Dependent Solution Properties of Nanocrystal–Ligands Complexes

CdSe–stearates nanocrystal–ligands complex as a whole possess strongly temperature- and size-dependent yet well-defined solubility in small organic solvents, which shows little solvent effects as long as the complexes remained intact. A quantitative thermodynamic model is developed to describe such solubility behavior, which differs fundamentally from conventional models for micron colloids. The model reveals that the conformation entropy of the n-alkanoate chain released in dissolution greatly stabilize the colloidal solution but the strong chain–chain interdigitation between adjacent particles in solid diminishes the solubility. These understandings result in "entropic ligands" (see full disclosure in another report (10.1021/acs.nanolett.6b00730)) as the universal means to battle processability challenges of colloidal nanocrystals.