De-wetting of evaporating drops on regular patterns of triangular posts.

Area of Science:

• Physics
• Materials Science
• Fluid Dynamics

Background:

• Directional liquid transport is crucial for various applications.
• Micro-patterned surfaces offer a method to control fluid behavior.
• Wetting films and contact line dynamics are key phenomena in liquid spreading.

Purpose of the Study:

• To investigate the formation and stability of wetting films during volatile liquid drop evaporation.
• To understand the influence of micro-pattern geometry on liquid drop behavior.
• To determine the factors controlling contact line mobility and film evolution.

Main Methods:

• Experimental observation of liquid drop evaporation on surfaces with triangular posts in a rectangular lattice.
• Systematic variation of post density and aspect ratio.
• Comparison with numerical energy minimization predictions.

Main Results:

• Observed two distinct drop behaviors: mobile three-phase contact lines (spherical-cap drops) and pinned contact lines (circular/angular drops).
• Drops with pinned contact lines evolved into a spreading liquid film and a shrinking cap-shaped drop.
• Drop evolution was governed by post density and aspect ratio, with post orientation having no evident effect on contact line mobility.

Conclusions:

• Micro-patterned surfaces with broken reflection symmetry can control liquid wicking and spreading.
• The density and aspect ratio of triangular posts are critical parameters for determining wetting film formation and stability.
• Spontaneous retraction of wicking liquid films is largely independent of the film edge orientation relative to the micro-pattern.