Ligand Desorption and Surface Oxidation Drive Nanoparticle Coalescence in Diffusion-Limited Aggregation

Area of Science:

• Nanomaterials Science
• Surface Chemistry
• Chemical Engineering

Background:

• Peptides were previously shown to drive diffusion-limited aggregation (DLA) of silver nanoparticles (AgNPs).
• The underlying mechanism of peptide-mediated AgNP fractal assembly remained unclear.
• Understanding ligand effects is crucial for controlling nanomaterial self-assembly.

Purpose of the Study:

• To elucidate the mechanism by which surface ligand chemistry governs the DLA of AgNPs.
• To investigate how different ligand classes (phosphine, thiolate, polyphenol) influence aggregation dynamics and structural outcomes.
• To establish a framework for chemically directed DLA for creating hierarchical nanomaterials.

Main Methods:

• Systematic examination of nine different ligands with varying chemical properties.
• Characterization of aggregation dynamics, redox behavior, and structural transformations using techniques like zeta potential measurements, X-ray photoelectron spectroscopy (XPS), and electron microscopy.
• Analysis of light scattering, elemental composition, and ligand distribution.

Main Results:

• Aromatic phosphine ligands, particularly bis(p-sulfonatophenyl)phenylphosphine (BSPP), uniquely promote DLA.
• BSPP facilitates partial ligand desorption and silver surface oxidation, enabling nanoparticle coalescence and recrystallization into fractal architectures.
• Thiol and polyphenol ligands do not support the necessary restructuring for fractal formation.
• Evidence includes charge neutralization, oxidized silver species, enhanced light scattering, and validated fractal structures.

Conclusions:

• Ligand chemistry dictates AgNP fractal assembly not just through interactions but by inducing core structural transformations.
• Aromatic phosphines enable DLA via oxidation-driven restructuring, leading to micron-scale fractal architectures.
• This work provides a mechanistic understanding and a tunable strategy for synthesizing hierarchical nanomaterials for applications in biosensing, catalysis, and soft matter engineering.