Tuning evaporation driven deposition in sessile drops via electrostatic hetero-aggregation

Area of Science:

• Colloid science
• Materials science
• Surface chemistry

Background:

• The coffee-ring effect, a common phenomenon in drying colloidal drops, leads to uneven particle deposition.
• This effect is driven by outward capillary flow during evaporation.
• Controlling deposit morphology is crucial for various applications.

Purpose of the Study:

• To investigate the use of oppositely charged species mixtures in colloidal drops to control drying patterns.
• To demonstrate the suppression of the coffee-ring effect and engineer diverse deposit morphologies.
• To explore the fundamental mechanisms governing drying patterns in these systems.

Main Methods:

• Video microscopy
• Electrophoretic measurements
• Particle tracking microrheology
• Bulk rheology

Main Results:

• A tunable method for controlling dried deposit morphology by adjusting mixing fraction (ωf) and total particle concentration (CT).
• Complete suppression of the coffee-ring effect was achieved.
• The interplay of sedimentation, capillary flow, and gelation dictates the observed drying patterns.

Conclusions:

• Mixing oppositely charged colloidal species offers a universal approach to engineer deposit patterns and suppress the coffee-ring effect.
• Fundamental insights into colloidal drying dynamics were elucidated.
• The findings were successfully applied to achieve uniform micronutrient deposition on leaf surfaces.