Page 87 - Handbook of Adhesives and Sealants

Theories of Adhesion 55

1.0 0

15

c
0.9
30
Cosine θ 0.8 Contact angle θ (degrees)

45
0.7

14 18 22 26 30
Surface tension (dynes/cm) at 20°C
Figure 2.3 Zisman plot for determining critical surface tension of polytetrafluoroethylene.
Test liquids are n-alkanes. 5

Substitution of the Young equation into the Dupre equation results in
the Young-Dupre equation that states:

W (1 cos ).
A LV
This equation relates a thermodynamic parameter, W , to two easily
A
determinable quantities: the contact angle and the liquid-vapor sur-
face tension. For conditions of perfect wetting (cos 1):

W 2 LV W C
A

2.2.4 Bond failure energy
Bond failure energy is composed of two parts: a reversible work of
adhesion and an irreversible work of adhesive deformation. Thus, the
strength of styrene-butadiene rubber adhesive depends on two com-
ponents: a viscoelastic energy dissipation term, which is a function of
test rate and temperature, and the intrinsic failure energy which
agrees closely with the work of adhesion, W , when bond failure is
A
apparently interfacial.