Influence of Micropillar Height Modulation on Droplet Evaporation and Wetting State Transitions

Controlling droplet evaporation dynamics is critical for numerous applications across physical, chemical, and biological sciences. This study investigates the effect of micropillar arrays with triangular height variations on the evaporation behavior of sessile droplets while maintaining a constant solid area fraction and similar superhydrophobic wetting properties. All fabricated substrates exhibited high static contact angles, consistent with the Cassie–Baxter wetting regime. However, evaporation behavior differed noticeably with changes in the amplitude and wavelength of the height variation patterns. Arrays with higher amplitudes and shorter wavelengths promoted a prolonged Cassie–Baxter state, allowing the droplet to retain a nearly constant contact angle over a longer duration. In contrast, substrates with lower amplitude and longer wavelengths induced a gradual transition from the Cassie–Baxter to the Wenzel state, leading to early contact line pinning and a constant contact line evaporation mode. Height variation patterns also impacted the effective water evaporation rate, independent of contact angle and droplet shape. These findings show that by adjusting height variation patterns, it is possible to manipulate evaporation dynamics while preserving overall wetting behavior. Tailoring micropillar height profiles enables precise control of evaporation while maintaining superhydrophobicity, offering new design pathways for surface engineering in droplet‐based technologies.