Excluded volume effect of surfactant ligands on the shape of nascent nanocrystal

TL;DR

This study models how the physical size of surfactant ligands influences the shape of nascent nanocrystals, revealing that ligand interactions restrict shape diversity without favoring specific forms.

Contribution

It introduces a theoretical and simulation framework to understand how ligand excluded volume effects determine nanocrystal shapes during synthesis.

Findings

Ligand excluded volume constrains nanocrystal conformations.

Shape states include nanoplates and nanorods.

Higher ligand density reduces conformational diversity.

Abstract

We investigate the effect of the excluded volume of surfactant ligands on the shape of incipient quantum dots (QDs) to which they are attached. We consider a model in which ligands are represented by hard-sphere particles that are bound to the surface of a nanoparticle (NC) that is cast in the shape of a prism. It is found in Monte Carlo simulations that the ensemble of relevant NC conformations consists of a small number of specific states that take on the form of nanoplates and nanorods. The shape of these states can be well described by the derived theoretical models. At increasing ligand density, the free energy of different states is seen to be approximately the same, suggesting that excluded volume interactions among ligands acts to narrow down the conformational space accessible to an NC without creating a statistical preference for any particular configuration.