Summary and Final Remarks

Abstract

Many believe that the concept of wetting begins with the Young’s equation. Although the Young’s equation is very simple, it has been a source of arguments over the last two centuries because the equation comprises four quantities of which two of them cannot be measured reliably. Moreover, researchers did express frustration in their inability to measure the Young’s angle consistently, at least a century ago. This chapter provides a brief overview of the history and the source of some of the misconceptions. Fundamental concepts that have been clarified in recent years, including (1) the recognition of the fact that it is the contact line, not the contact area, that determines the contact angle; (2) advancing and receding contact angles are the most important contact angles, and they measure wettability and adhesion respectively, and surface stickiness can be predicted from the sliding angle; and (3) hydrophilicity and hydrophobicity should be defined by the receding contact angle, not the static contact angle. In answering Good’s calling for standardization of measurement protocols for contact angle measurements, a set of guidelines for determining static contact angle, advancing/receding contact angle, and sliding angle are provided. We hope that these guidelines will benefit the community in the near term and serve as a springboard for the development of standardized procedures by the “authority” or leaders in this field in the near future.