Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Surface wettability, a property that governs the interaction between the solid and liquid phases, is central in various biological systems and technological applications. A typical approach to assess the wetting interaction is based on the sessile droplet contact angle. Despite its experimental simplicity, caution is required in the measurement and interpretation of the sessile contact angle as a wettability metric. In this work, the major challenges related to the use of the sessile droplet contact angle for characterizing surface wetting behavior are reviewed. The complexity of interpreting surface wettability using the contact angle value arising from the following factors is discussed: the role of solid-liquid interfacial area and three-phase contact line, the existence of multiple metastable states with a range of contact angle values, and the droplet size dependence of contact angles. An overview of the emerging alternative wetting evaluation techniques and parameters that can complement the sessile contact angle measurement is outlined.