Advancing and Receding Angle

When we place a liquid drop on a clean, planar, solid surface, we can observe a contact angle which is precisely the angle contained in Young s 

FIGURE 3.1. (a) Advancing angle when the drop is inflated (b) receding angle when the drop is deflated. 

FIGURE 3.2. Liquid column trapped in a vertical capillary tube. 

For an equilibrium to exist, the upper line must be able to resist a receding movement, which implies 0i Or and cos0i cos07. Similarly, the lower line must resist an advancing movement, which means O2 0a and cos 02 cos0. Consequently, equilibrium is possible only if 

Without hysteresis Or = 0 ), there can be no equilibrium (this is Bertrand s theorem, cited by Bouasse). 

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Both the advancing and receding angles can be observed with one drop when the substrate is tilted [5]. 

We shall now review some of these techniques, more or less in order of increasing complexity. Regarding the ycosa methods frequent reference will be made to chapter 1. Strictly speaking, a measurement is incomplete unless both the advancing and receding angle are obtained. By this strict criterion, the literature does not contain many complete measurements. According to Marmur (see below), the drop volume is also an Important parameter. 

Maximum Possible Hysteresis. The maximum possible angle, receding angles, it is improbable that [Pg.113]

Hysteresis - f r Qualitatively, fact that hiany different contact angles can be observed for a given liquid on a given surface. Quantitatively, difference between advancing and receding angles... 

The alkane partially wets the teflon. For each alkane, measure the advancing and receding angles by examining the capillary rise. 

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