Nematic Ordering via Vertical Stratification in Drying Clay Nanotube Suspensions

Area of Science:

• Materials Science
• Nanotechnology
• Colloid Science

Background:

• Evaporative self-assembly is a cost-effective method for nanostructured materials.
• Achieving tunable and ordered assemblies from polydisperse nanoparticles is challenging.

Purpose of the Study:

• To present a physical protocol for achieving high orientational ordering in dried deposits of rod-like halloysite nanotubes.
• To overcome challenges associated with nanoparticle polydispersity in self-assembly.

Main Methods:

• Utilizing a sessile droplet on a heated substrate (50 °C) to induce self-healing Marangoni flows.
• Controlling evaporation to suppress the coffee-ring effect and promote uniform deposition.
• Leveraging vertical stratification for particle segregation based on aspect ratio.

Main Results:

• Suppression of the coffee-ring effect led to uniform deposition of colloidal rods.
• Vertical stratification segregated particles by aspect ratio, with longer rods (aspect ratio ≥ 6.5) migrating to top layers.
• The top layer exhibited a high degree of orientational order over millimeter-scale areas.

Conclusions:

• A robust strategy for engineering ordered structures from disordered colloidal suspensions was developed.
• The protocol effectively manages nanoparticle polydispersity to achieve desired material properties.
• This method offers a pathway for creating functional nanostructured materials with controlled orientational order.