Comment on "Patterns in Drying Drops Dictated by Curvature-Driven Particle Transport"

Area of Science:

• Colloid and Surface Science
• Fluid Dynamics
• Nanomaterials

Background:

• Drying of colloidal droplets can form distinct deposit patterns like coffee rings and coffee-eyes.
• Previous research proposed particle adsorption at the interface for coffee-eye formation in pendent droplets.
• The established coffee-ring model attributes pattern formation to internal radial flow in sessile droplets.

Purpose of the Study:

• To investigate an alternative mechanism for coffee-eye formation in pendent nanofluid droplets.
• To challenge the necessity of particle adsorption for coffee-eye formation.
• To explore the role of nanoparticle size and colloidal stability in deposit patterns.

Main Methods:

• Experimental observation of coffee-eye formation from pendent droplets of nanofluids.
• Systematic variation of nanoparticle size within the colloidal liquid.
• Analysis of droplet drying dynamics and particle distribution.

Main Results:

• Coffee-eye patterns were successfully generated from pendent droplets by increasing nanoparticle size.
• Destabilization of the colloidal liquid led to nanoparticle accumulation at the droplet apex.
• This accumulation occurred without evidence of particle adsorption at the liquid-air interface.

Conclusions:

• Coffee-eye formation in pendent droplets can be achieved by increasing nanoparticle size to destabilize the nanofluid.
• Particle adsorption at the interface is not the sole mechanism for coffee-eye formation.
• Colloidal liquid destabilization offers a new route to control deposit patterns in drying droplets.