(Invited) The Role of Ligand Characteristics in Modulating the Size, Size Distribution, and Alloy Formation in Metal Nanoparticle Systems

The transformation of the intert noble metals into functional materials not only involves their preparation at nanometer scale but also their surface functionalization with appropriate molecules. Such surface functionalization assumes significance not just for their stability in diverse solvent media but defines the way nanoparticles interact either with themselves or with the environment/biological systems. In general, organic molecules/ligands which have at least one functional group are known to act as stabilizing agents. Apart from this ligands also play a key role in nanoparticle formation in many aspects viz. controlling their size, morphology and their dispersional stability in a given medium. This talk briefly reviews the role of molecules/ligands as tools for controlling nanoparticle size, morphology and dispersion stability in solvent media. In particular we will introduce “Digestive Ripening” (DR), a post-synthetic size modification process as a reliable and reproducible method offering great control over size and size distribution of NCs. DR is known for converting a polydisperse NC system, post synthesis to nearly monodisperse NCs with the help of surface active organic molecules/ligands. Some of the recent results that we obtained helped unravel the dependency of DR process on the final size distribution dependency on the ligand chain length, the liagnd head group-NC binding strength, the ligand-solvent compatibility etc. Based on the understanding gained from this work we also try to provide some guidelines on how DR could be effectively used to make alloy NCs from a physical mixture of NC dispersions. The specific details of the above mentioned parameters will be disussed during the talk.