Electrowetting on superhydrophobic SU-8 patterned surfaces

Electrowetting on micro-patterned layers of SU-8 photoresist with an amorphous Teflon® coating has been observed. The cosine of the contact angle is shown to be proportional to the square of the applied voltage for increasing bias. However, this does not apply below 40 V and we suggest that this may be explained in terms of penetration of fluid into the pattern of the surface. Assuming that the initial application of a bias voltage converts the drop from Cassie-Baxter to Wenzel regime, we have used this as a technique to estimate the roughness factor of the surface.