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Tunable contact angle hysteresis on micropatterned surfaces

Micropatterned surfaces composed of concentric circular defects having a smooth trench-like profile are formed using a photoresist (SU-8). When an evaporating droplet encounters the micropatterned surface an evaporation phase is observed consisting of distinct discontinuities and steps in the droplet wetting contact angle and base radius respectively. The addition of gaps into the circular defects enables tuning of the contact angle hysteresis; the receding contact angle of fluorocarbon coated SU-8 can be tuned between 34.6° and 89.1° and that of SU-8 surfaces from 5.6° to 43.3° depending on the gap length. In addition, a model is developed which accurately predicts the observed behavior.