Tunable contact angle hysteresis by micropatterning surfaces

Lithography is used to form circular micropatterns which govern the evaporation of a water droplet. The surfaces are composed of concentric circular defects having a smooth indentation profile. When a droplet encounters a micropattern, evaporation occurs with distinct discontinuities in the droplet wetting contact angle and base radius. The addition of gaps into the patterns enables modification of the contact angle hysteresis; the receding angle of fluorocarbon coated SU-8 can be tuned between 34.6° and 89.1° and that of SU-8 from 5.6° to 43.3° depending on the gap length. A model is developed which accurately predicts the observed behavior.