Evolution of Electrosprayed Particles at a Static Air-Water Interface on Multiple Time Scales

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Nanotechnology

Background:

• Electrospray deposition is a field-driven technique for precise particle delivery to fluid interfaces.
• Colloidal particle arrangement at air-water interfaces depends on electrostatic repulsion, particle properties, and environmental factors.
• Non-equilibrium conditions allow observation of time-dependent colloidal transitions not seen in static systems.

Purpose of the Study:

• To investigate the long-term arrangement and dynamics of charged colloidal particles at air-water interfaces under non-equilibrium conditions.
• To explore the influence of electrostatic charge evolution, ionic strength, and surface contamination on colloidal assembly.
• To develop a platform for sustained observation of interfacial colloidal dynamics.

Main Methods:

• A custom fluidic device was engineered for stable air-water interface generation with feedback control.
• Electrospray deposition was utilized for targeted particle delivery to the interface.
• Sustained imaging captured particle motion over several hours, with modulated salt concentrations to study assembly regimes.

Main Results:

• Interfacial order degrades over time (>5h) due to charge relaxation, accelerated by ionization.
• Increased salt concentration initially enhances hexagonal ordering, demonstrating complex electrostatic screening effects.
• Heterogeneous particle diffusion was observed, linked to localized surface contamination.

Conclusions:

• Evolving electrostatic charge is a key driver of interfacial self-assembly and long-term colloidal dynamics.
• Environmental factors like ionic strength and contamination significantly modulate colloidal behavior at fluid interfaces.
• Non-equilibrium studies reveal dynamic processes crucial for understanding interfacial colloidal systems.