Nanopipette dynamic microscopy unveils nano coffee ring

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Liquid-phase electron microscopy (LP-EM) is crucial for understanding nanosynthesis and assembly.
• Existing closed-geometry LP-EM cells limit the study of open systems, like evaporation-driven phenomena.
• The nanoscale coffee-ring phenomenon, vital in materials science, has lacked experimental observation tools.

Purpose of the Study:

• To introduce a novel quartz nanopipette liquid cell for observing nanoscale phenomena in open systems.
• To enable the study of the coffee-ring phenomenon at the nanoscale.
• To investigate nanoparticle assembly and dynamics during droplet evaporation.

Main Methods:

• Development of a quartz nanopipette liquid cell with tunable dimensions compatible with standard microscopes.
• Utilizing the nanopipette's open geometry to image evaporation-induced pattern formation in nanodroplets.
• Tracking individual nanoparticles within evaporating nanodroplets to analyze assembly dynamics and movement.

Main Results:

• Successfully observed the nano coffee-ring phenomenon by tracking nanoparticles in evaporating nanodroplets.
• Demonstrated that nanoflows, driven by surface effects, govern nanoparticle assembly and ring pattern disruption.
• Observed nanoparticle trajectories ('drunken man trajectory') where nanoflows dominate over thermal fluctuations at the nanoscale.

Conclusions:

• The quartz nanopipette liquid cell provides a versatile platform for studying nanoscale phenomena in open systems.
• This method allows unprecedented observation of the coffee-ring effect at the nanoscale.
• Nanoflows play a dominant role in nanoparticle assembly and dynamics, overriding thermal effects at small scales.