Contact angle measurements using the Wilhelmy balance for asymmetrically treated samples

The Wilhelmy balance technique can be used to assess the wettability of rectangular samples with two differently treated faces. The contact angle on the treated face can be reliably deduced, provided that a consistent value for the contact an le on the untreated face has been obtained. As an example, a hydrophobic plate with various serrations on one face only is examined in detail. The agreement between the experimentally determined contact angles and the angles predicted by the Cassie equation is very good. We demonstrate that there are no methodological reasons to reject the use of the Wilhemy technique for samples which have received different physical or chemical treatments on the two faces.