Colloidal monolayers with cell-like tessellations via interface assisted evaporative assembly

Area of Science:

• Colloid and Surface Science
• Materials Science
• Nanotechnology

Background:

• Evaporating sessile drops with surface-active colloids offer a route to self-assemble 2D nanostructures.
• Current methods often result in limited colloidal monolayer morphologies.
• The impact of evaporation kinetics on microstructure under controlled humidity remains under-explored.

Purpose of the Study:

• To experimentally investigate the evaporation-driven self-assembly of poly(N-isopropylacrylamide) (pNIPAM) microgel particles in sessile drops.
• To elucidate the role of controlled humidity on the microstructure at the liquid-vapor interface and the resulting colloidal monolayer morphology.
• To understand how evaporation kinetics influence the self-assembly of colloidal monolayers.

Main Methods:

• Utilized sessile drops containing surface-active pNIPAM microgel particles.
• Controlled evaporation kinetics by managing humidity levels.
• Analyzed the microstructure at the solvent-air interface and the morphology of the transferred colloidal monolayer on solid surfaces.
• Quantified structural evolution using Voronoi entropy analysis.

Main Results:

• Observed formation of particle-free and particle-rich regions at the water-vapor interface under saturated humidity.
• Demonstrated that interface shrinkage and increased particle density induce restructuring.
• Transferred de-wetting assisted patterns to the solid substrate upon solvent evaporation.
• Achieved enhanced crystalline order in microgel particle domains within the monolayer deposit.

Conclusions:

• Evaporation kinetics under controlled humidity significantly impact the self-assembly of colloidal monolayers from pNIPAM microgels.
• The study reveals a method to control microstructure and achieve ordered colloidal domains.
• Findings contribute to understanding bottom-up self-assembly techniques for nanostructure fabrication.