Determination of Contact Angle Hysteresis and Characterization of Hydrophobic Properties of a Solid Surface

The tilting stage method is to slowly tilt a contact angle sample until the sessile drop on it begins to move in the downhill direction. At that time of “incipient motion”, the downhill contact angle is the advancing angle and the uphill angle the receding contact angle. (Strictly speaking, only droplet images immediately before actual motion takes place should be used for determination, because once motion starts, the system is no longer in thermodynamic equilibrium).

The principal alternative to the tilting stage method is having the dispense needle remain embedded in the sessile drop and pumping in until the drop expands in base area and pumping out until the drop contracts in base area. The tilting stage method has two comparative advantages:

1)?? there is no problem of the dispense needle distorting the drop shape, and
2)?? both the advancing and receding angles are obtained at the same time, and from the very same droplet and on the very same surface location

Furthermore, two of the most important parameters which can be used for characterizing the
(super-) hydrophobic or water repellent properties of a sample surface, contact angle hysteresis and the droplet moving force (related to the droplet volume and roll-off angle), can be determined straightforward by using a tilting stage.