Wetting on smooth micropatterned defects

Abstract

We develop a 2D model which predicts the contact angle hysteresis (CAH) introduced by smooth micropatterned defects. The defects are modeled by a smooth function, and the CAH is explained using a tangent line solution. When the liquid micro-meniscus touches both sides of the defect simultaneously, depinning of the contact line occurs and the droplet pops-up. The defects are fabricated using the photoresist SU-8. The experimental results, using common liquids (water, isopropyl alcohol, and ethylene glycol), agree well with the predictions of the model. The profile of the defect has a large influence on the CAH. © 2011 American Institute of Physics.