How to calculate the polar and dispersive surface tension components of a liquid?
by JikanGroup
There are two methods for calculating the polar and dispersive surface tension components of a liquid:
 pendant drop method (preferred).
 sessile drop method.
1. The pendant drop method for measuring the surface tension components of a liquid
Using the OWRK (OwensWendtRabelKaelble) or geometric mean method, the surface tension between test and reference liquids (also known as the interfacial tension) is calculated as:

(1) 
where γ_lr is the interfacial (surface) tension between test and reference liquids, γ_l and γ_r are the surface tensions of test and reference liquids, accordingly, p and d superscripts show the polar and dispersive surface tension components.
For a strictly dispersive reference liquid, i.e. γ_{r}=γ_{r}^{d}, Eq. 1 becomes:

(2) 
And γ_{l}^{p} can be found using Eq. 3.

(3) 
If using the OWRK method, the value of γ_{l}^{p} was found negative, Wu method (harmonic mean) should be used as follows:

(4) 
For a strictly dispersive reference, i.e. γ_{r}=γ_{r}^{d}, Eq. 4 becomes:

(5) 
And γ_{l}^{p} can be found using Eq. 3.
The reference liquid shall be:
 immiscible and be able to form a meniscus.
 chemically homogenous.
 strictly dispersive (and free from polar contaminations)
 colourless with a melting point lower than 20°C.
Suggested reference liquids:
Preferably use liquid hydrocarbons (e.g. ndecane, ndodecane, ntetradecane and nhexadecane) but if the test liquid is soluble to hydrocarbon, use perfluorohydrocarbons (e.g. nperfluorohexane and nperfluorooctane).
Cleaning of reference liquids:
Hydrocarbon:
 distillation
 chromatography columns with a minimum length of 60 cm filled with silica gel (e.g. particle size mesh 60). The silica gel with polar surfaces absorbs the polar contaminations (e.g. ketones).
Perfluorohydrocarbon:
 does not need cleaning.
After cleaning, for the hydrocarbon and perfluorohydrocarbon, the measurable interfacial tension compared to water shall be at least 52 mN/m and 54 mN/m at 23°C, accordingly.
Storage of reference liquids:
The cleaned nalkanes shall be stored in lightproof glass bottles in the refrigerator at a maximum temperature of 4°C.
2. The sessile drop method for measuring the surface tension components of liquids
Using the OWRK method (geometric mean), on a pure dispersive solid surface, the relation between contact angle (θ) and surface tension components of the test liquid is:

(6) 
Using the Wu method (harmonic mean), on a pure dispersive solid surface, the relation between contact angle and surface tension components of the test liquid is:

(7) 
The polar component of the test liquid surface tension is found using Eq. 3.
Note: For γ_{s} > 20 mN/m use Eq. 6 otherwise use Eq.7:
The reference solid shall be:
 Sufficiently, chemically and topologically homogenous.
 Dispersive, e.g. made of paraffin (25.5 ± 0.5 mN/m) or PTFE (18.5 ± 0.5 mN/m).
 Where γ_{s}^{p} < 0.5 mN/m
 Mean roughness value R_{a} < 0.3 μm