ABSTRACT
The correct values of the liquid-vapor interfacial tension and contact angle are necessary to analyze the wetting problems stated at the beginning of this section. Many methods have thus far been proposed for the measurement of these basic quantities. The methods may be classified into two categories, i.e., (1) methods of measuring the dynamic quantities and (2) methods of measuring the geometrical quantities. The Wilhelmy [22] and Du Noüy [23] methods for the measurement of liquid-vapor interfacial tension are typical examples of (1). In these methods, a clean glass plate or ring with zero contact angle is drawn from the liquid and the liquid-vapor interfacial tension acting on the periphery is measured directly using devices such as a microbalance. These methods may also be applied to the measurement of the contact angle by using a test plate, to which the test liquid attaches at certain contact angle, instead of a glass plate [24]. The maximum bubble pressure or drop weight method is another example of (1) for the measurement of interfacial tension [25, 26]. Both involve the use of force balance on the bubble or drop due to interfacial tension. The interfacial tension is calculated from the measurement of pressure inside the bubble in the former method and from the drop weight in the latter when it detaches from an orifice. Generally, the Wilhelmy, Du Noüy, and drop weight methods are widely used for the measurement of interfacial tension.
