Experimental Investigation of Dynamic and Metastable Contact Angles

Abstract

Contact angle phenomena are complicated. There exist many experimental contact angles and many researchers employed them widely in Young's equation for the determination of solid surface tensions. This thesis examined the thermodynamics status of contact angles and experimentally determined the various metastable contact angles. Experimental setup for metastable contact angles was designed by carefully controlling the vibration amplitude via loudspeakers. It has been demonstrated that only the advancing contact angle on smooth surfaces are compatible with Young's equation. Attempts in the literature to determine the true equilibrium contact angle are meaningless in terms of Young's equation. Only the advancing angle on smooth and heterogeneous surfaces is a good approximation of the contact angle in Young's equation. A new model to determine the maximum and minimum spreading ratio of droplets impacting onto smooth surfaces was also established. Good agreement was found between the predicted and experimental values. Impacting droplet experiments were also employed to examine carbon/polymer surfaces as a new way of characterizing such surfaces.