title: Reliable measurement of the receding contact angle.
abstract: Surface wettability is usually evaluated by the contact angle between the perimeter of a water drop and the surface. However, this single measurement is not enough for proper characterization, and the so-called advancing and receding contact angles also need to be measured. Measuring the receding contact angle can be challenging, especially for extremely hydrophobic surfaces. We demonstrate a reliable procedure by using the common needle-in-the-sessile-drop method. Generally, the contact line movement needs to be followed, and true receding movement has to be distinguished from "pseudo-movement" occurring before the receding angle is reached. Depending on the contact angle hysteresis, the initial size of the drop may need to be surprisingly large to achieve a reliable result. Although our motivation for this work was the characterization of superhydrophobic surfaces, we also show that this method works universally ranging from hydrophilic to superhydrophobic surfaces.
authors: Molecular Materials, Department of Applied Physics, Aalto University School of Science (former Helsinki University of Technology), Espoo, Finland.
authors: Juuso T
authors: JT
authors: Korhonen
authors: Tommi
authors: T
authors: Huhtamäki
authors: Olli
authors: O
authors: Ikkala
authors: Robin H A
authors: RH
authors: Ras