Effect of Grafting Density on the Two-dimensional Assembly of Nanoparticles

TL;DR

This study investigates how grafting density influences the two-dimensional assembly and stability of PEG-grafted silver and gold nanoparticles at interfaces, revealing structural differences based on chain length and nanoparticle type.

Contribution

It provides detailed insights into the structural behavior of PEG-grafted nanoparticles and how grafting density affects their assembly at interfaces, including binary mixtures.

Findings

PEG-grafted nanoparticles form stable hexagonal structures at interfaces.

Shorter PEG chains lead to dense, well-ordered films.

AuNPs exhibit higher grafting densities and more order than AgNPs.

Abstract

Employing grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR), we demonstrate that films composed of polyethylene glycol (PEG)-grafted silver nanoparticles (AgNP) and gold nanoparticles (AuNP), as well as their binary mixtures, form highly stable hexagonal structures at the vapor-liquid interface. These nanoparticles exhibit remarkable stability under varying environmental conditions, including changes in pH, mixing concentration, and PEG chain length. Short-chain PEG grafting produces dense, well-ordered films, while longer chains produce more complex, less dense quasi-bilayer structures. AuNPs exhibit higher grafting densities than AgNPs, leading to more ordered in-plane arrangements. In binary mixtures, AuNPs dominate the population at the surface, while AgNPs integrate into the system, expanding the lattice without forming a distinct binary superstructure. These results offer valuable insights into the structural behavior of PEG-grafted nanoparticles and provide a foundation for optimizing binary nanoparticle assemblies for advanced nanotechnology applications.