Geometry-Encoded Droplet Evaporation on Rectangular Micropillared Surfaces: From Wetting-State Transitions to Programmable Colloidal Deposit Morphology

For representative micropillared surfaces with <i>P</i> = 60 μm, classical destabilization criteria are not satisfied; instead, evaporation-induced vapour confinement promoting wetting-film growth and sidewall advancement is proposed as the physically plausible mechanism dictating transition. For <i>P</i> = 80 μm, transition onset is governed by pressure-driven capillary entry. Post-transition CL evolution in Wenzel state is shown, in a hitherto unreported mechanistic framework, to be governed by geometry-imposed constraints on CL motion, wherein interpillar gap geometry and lattice symmetry drive anisotropic meniscus-mediated spreading and discrete micropillar-row anchoring.

These dynamics prescribe octagonal, rectangular, hexagonal, and square morphologies with anisotropy factors of 1.10–1.50. Colloidal particles suppress transition-induced spreading through enhanced pinning, whereas substrate heating promotes meniscus-mediated secondary spreading, enabling coupled control of deposit size and shape. These findings establish a physically interpretable, multidimensional design space for programmable evaporation-driven microscale deposition, advancing the rational engineering of surface-texture-directed patterning for these applications.