92168.pdf

154 The solid-liquid interface

Adhesional wetting

In adhesional wetting, a liquid which is not originally in contact with

the solid substrate makes contact and adheres to it. In contrast to

spreading wetting, the area of liquid-gas interface decreases. The

work (free energy) of adhesion is given by the Dupre" equation (see

equation (4.29) in the form

= TSG + TLG - TSL (6.7)

which, combined with Young's equation (6.2), gives the Young-

Dupr6 equation,

Polytetrafluoroathylene

(20°C)

1.0

0.8

0.6

0.4

0.2

0

-0.2

-0.4

Figure 6.2 Critical surface tension of polytetrafluoroethylene^78. •, n-alkanes; O,
other hydrocarbons; •, esters and ethers; a, halocarbons and halohydrocarbons; A,
miscellaneous liquids

15

30

45

60

75

1

90

105

10 20 30 40 50 60 70 80