Time-Resolved Analysis of the Structural Dynamics of Assembling Gold Nanoparticles

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Hydrophobic collapse is a key structural transition for polymer chains in poor solvents.
• This event is crucial for polymer-stabilized nanoparticle clustering but has not been observed in real-time.
• Understanding this process is vital for controlling nanoparticle assembly and material properties.

Purpose of the Study:

• To investigate the real-time dynamics of hydrophobic collapse in polymer-stabilized nanoparticles during early-stage clustering.
• To determine the relationship between solvent conditions and the rate of polymer shell collapse.
• To establish the temporal sequence of polymer shell collapse relative to nanoparticle aggregation.

Main Methods:

• Utilized a microfluidic 3D-flow-focusing mixing reactor for precise control over solvent mixing.
• Employed in situ small-angle X-ray scattering (SAXS) for real-time analysis of polymer shell structure.
• Integrated UV-vis-NIR spectroscopy and numerical simulations to map solvent composition and particle interactions.

Main Results:

• Successfully mapped particle interaction energies at 30 ms after solvent mixing.
• Quantified the rate of hydrophobic collapse, finding it ranges from 100 to 500 nm/s and is dependent on water concentration.
• Provided direct evidence that the polymer shell undergoes collapse before nanoparticle clustering initiates.

Conclusions:

• The study provides the first real-time observation of hydrophobic collapse in polymer-stabilized nanoparticles.
• The findings highlight the critical role of polymer shell dynamics in the initial stages of nanoparticle assembly.
• This research offers new insights into controlling nanoparticle aggregation through solvent manipulation and understanding polymer behavior.