Direct Observation of Interactions between Nanoparticles and Nanoparticle Self-Assembly in Solution

Area of Science:

• Materials Science and Nanotechnology
• Physical Chemistry
• Surface Science

Background:

• Hierarchically organized nanoparticles (NPs) are crucial for advanced applications.
• Current understanding of NP self-assembly mechanisms is limited by indirect characterization methods.
• Theoretical models are often restricted to small systems or short timescales.

Purpose of the Study:

• To investigate NP self-assembly processes in solution using real-time imaging.
• To elucidate the fundamental interactions governing NP assembly at different length scales.
• To identify previously unknown intermediate stages in NP formation and assembly.

Main Methods:

• In situ liquid cell transmission electron microscopy (LC-TEM) with subnanometer resolution.
• Real-time observation of atom-to-NP transformation, NP interactions, and NP assembly dynamics.
• Analysis of nucleation, solvation forces, linker-mediated assembly, and directed assembly.

Main Results:

• Identified three distinct steps in nanocrystal nucleation: spinodal decomposition, amorphous cluster nucleation, and crystallization.
• Demonstrated that hydration layers mediate NP interactions, with attachment occurring upon water drainage.
• Observed concentration-dependent assembly of NPs and nanorods into linear chains or side-to-side configurations, and nanoring formation directed by nanodroplets.

Conclusions:

• LC-TEM provides unprecedented insights into the real-time mechanisms of NP self-assembly.
• Understanding nanoscale interactions, including solvation forces and linker effects, is key to controlling hierarchical nanostructures.
• This approach enables quantitative descriptions of nanoscale object interactions in solution.