  We develop a model which predicts the contact angle hysteresis introduced by
smooth micropatterned defects. The defects are modeled by a smooth function and
the contact angle hysteresis 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. The defects are fabricated using a
photoresist and experimental results confirm the model. An important point is
that the model is scale-independent, i.e. the contact angle hysteresis is
dependent on the aspect ratio of the function, not on its absolute size; this
could have implications for natural surface defects.
