Stabilization of Apolar Nanoparticle Dispersions by Molecular Additives.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Alkanethiol-coated gold nanoparticles (AuNPs) exhibit limited colloidal stability in nonpolar solvents.
• Understanding factors influencing nanoparticle aggregation is crucial for their application in various fields.

Purpose of the Study:

• To investigate the impact of cyclic amine and sulfide additives on the colloidal stability of alkanethiol-coated gold nanoparticles.
• To elucidate the mechanism behind the observed stabilization effects using computational and experimental methods.

Main Methods:

• Small-angle X-ray scattering (SAXS) to determine agglomeration temperature (T_agglo).
• Molecular dynamics (MD) simulations to analyze ligand shell structure and additive interactions.
• Thermogravimetric analysis (TGA) to confirm ligand shell modifications.

Main Results:

• Tetrahydrothiophene reduced T_agglo by up to 29°C, significantly increasing colloidal stability.
• Amines showed a much weaker stabilizing effect (up to 2.5°C).
• An optimal concentration range for stabilization was observed, with higher concentrations having a detrimental effect.

Conclusions:

• Sulfide additives stabilize AuNPs by chemisorption, disrupting ligand ordering and lowering T_agglo.
• Smaller cyclic sulfides are more effective stabilizers due to reduced steric hindrance and stronger gold surface affinity.
• The study reveals that modifications to the nanoparticle ligand shell, rather than physisorbed additives, are responsible for enhanced colloidal stability.