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DESIGN INFORMATION AND DATA
8.13. SURFACE TENSION
It is usually difficult to find experimental values for surface tension for any but the more
commonly used liquids. A useful compilation of experimental values is that by Jasper
(1972), which covers over 2000 pure liquids. Othmer et al. (1968) give a nomograph
covering about 100 compounds.
If reliable values of the liquid and vapour density are available, the surface tension can
be estimated from the Sugden parachor; which can be estimated by a group contribution
method, Sugden (1924).
4
P ch L v 12

D ð 10 8.23
M
2
where D surface tension, mJ/m (dyne/cm),
P ch D Sugden’s parachor,
3
L D liquid density, kg/m ,
3
v D density of the saturated vapour, kg/m ,
M D molecular mass.
, L , v evaluated at the system temperature.
The vapour density can be neglected when it is small compared with the liquid density.
The parachor can be calculated using the group contributions given in Table 8.7. The
method is illustrated in Example 8.13.

Table 8.7. Contribution to Sugdens’s parachor for organic compounds (Sugden, 1924)
Atom, group or bond Contribution Atom, group or bond Contribution
C 4.8 Si 25.0
H 17.1 Al 38.6
H in (OH) 11.3 Sn 57.9
O 20.0 As 50.1
O 2 in esters, acids 60.0 Double bond: terminal
N 12.5 2,3-position 23.2
S 48.2 3,4-position
P 37.7 Triple bond 46.6
F 25.7 Rings
Cl 54.3 3-membered 16.7
Br 68.0 4-membered 11.6
I 91.0 5-membered 8.5
Se 62.5 6-membered 6.1

8.13.1. Mixtures
The surface tension of a mixture is rarely a simple function of composition. However,
for hydrocarbons a rough value can be calculated by assuming a linear relationship.

m D 1 x 1 C 2 x 2 .. . 8.24
where m D surface tension of mixture,
1 , 2 D surface tension of components,
x 1 ,x 2 D component mol fractions.