Solvent Effects in Ligand Stripping Behavior of Colloidal Nanoparticles

Inorganiccolloidal nanoparticle (NP) properties can be tuned bystripping stabilizing ligands using a poor solvent. However, the mechanismbehind ligand stripping is poorly understood, in part because in situ measurements of ligand stripping are challengingat the nanoscale. Here, we investigate ethanol solvent-mediated oleylamineligand stripping from magnetite (Fe3O4) NPsin different compositions of ethanol/hexane mixtures using atomisticmolecular dynamics (MD) simulations and thermogravimetric analysis(TGA). Our study elucidates a complex interplay of ethanol interactionswith system components and indicates the existence of a thresholdconcentration of similar to 34 vol % ethanol, above which ligand strippingsaturates. Moreover, hydrogen bonding between ethanol and strippedligands inhibits subsequent readsorption of the ligands on the NPsurface. A proposed modification of the Langmuir isotherm explainsthe role of the enthalpy of mixing of the ligands and solvents onthe ligand stripping mechanism. A good agreement between the MD predictionsand TGA measurements of ligand stripping from Fe3O4 NPs validates the simulation observations. Our findings demonstratethat the ligand coverage of NPs can be controlled by using a poorsolvent below the threshold concentration and highlight the importanceof ligand-solvent interactions that modulate the propertiesof colloidal NPs. The study also provides an approach for a detailed in silico study of ligand stripping and exchange from colloidalNPs that are crucial for applications of NPs spanning self-assembly,optoelectronics, nanomedicine, and catalysis.