Molecular Tilt on Monolayer-Protected Nanoparticles

TL;DR

This paper models the tilted phase of monolayer-protected nanoparticles using a Ginzburg-Landau approach, revealing phase transitions and defect structures that influence functionalization and assembly.

Contribution

It introduces a simple theoretical model to analyze tilt phases and defect configurations on different nanoparticle geometries.

Findings

Transition from tilted to normal alignment on spherical particles.

Presence of six topological defects on octahedral particles.

Defects serve as sites for chemical functionalization.

Abstract

The structure of the tilted phase of monolayer-protected nanoparticles is investigated by means of a simple Ginzburg-Landau model. The theory contains two dimensionless parameters representing the preferential tilt angle and the ratio epsilon between the energy cost due to spatial variations in the tilt of the coating molecules and that of the van der Waals interactions which favors uniform tilt. We analyze the model for both spherical and octahedral particles. On spherical particles, we find a transition from a tilted phase, at small epsilon, to a phase where the molecules spontaneously align along the surface normal and tilt disappears. Octahedral particles have an additional phase at small epsilon characterized by the presence of six topological defects. These defective configurations provide preferred sites for the chemical functionalization of monolayer-protected nanoparticles via place-exchange reactions and their consequent linking to form molecules and bulk materials.