OWRK procedure

The OWRK method , named after Owens, Wendt, Rabel and Kaelble, is a method for determining the polar and disperse fractions of the surface energy of solids . In order to be able to use the method, it is necessary to determine the contact angle of at least two test liquids on the sample to be measured.

Necessary data

For the calculation, knowledge of the polar and disperse fractions of the surface tension of the test liquid is required. Furthermore, the static contact angle between two test liquids and the surface to be measured must be determined. ${\displaystyle \Theta }$

Table of values ​​for the surface tension at 25 ° C

liquid	Surface tension ( ) ${\displaystyle \sigma _{l}}$ in mN / m = 10 −3  N / m	Disperse parts ( ) ${\displaystyle \sigma _{l}^{d}}$ in mN / m = 10 −3  N / m	Polar parts ( ) ${\displaystyle \sigma _{l}^{p}}$ in mN / m = 10 −3  N / m
water	72.8	21.8	51.0
Diiodomethane	50.8	50.8	0.0
Ethylene glycol	47.7	30.9	16.8
Glycerin	63.4	37.0	26.4
Hexadecane	27.6	27.6	0.0
1-bromonaphthalene	44.6	44.6	0.0
Benzyl alcohol	38.9	29.0	9.9
Decalin (mixture of isomers)	30.6	30.6	0.0
cis-decalin	32.2	32.2	0.0
trans-decalin	29.9	29.9	0.0

Action

First, the equation found by Owens and Wendt must be linearized, which results in the following form:

${\displaystyle {\frac {\sigma _{l}(1+\cos(\Theta ))}{2{\sqrt {\sigma _{l}^{d}}}}}={\sqrt {\sigma _{s}^{d}}}+{\sqrt {\sigma _{s}^{p}}}{\sqrt {\frac {\sigma _{l}^{p}}{\sigma _{l}^{d}}}}}$

Now a coordinate system is plotted on the Y-axis . In contrast, it is plotted on the X axis. If you now insert the corresponding values ​​and carry out a linear regression , the polar and disperse fractions of the surface energy can be calculated from the Y-axis intercept and slope. The Y-axis intercept corresponds to the root of the disperse fractions of the surface energy. The slope corresponds to the root of the polar components of the surface energy. The total surface energy of the solid is calculated as the sum of polar and disperse fractions. ${\displaystyle {\frac {\sigma _{l}(1+\cos(\Theta ))}{2{\sqrt {\sigma _{l}^{d}}}}}}$ ${\displaystyle {\sqrt {\frac {\sigma _{l}^{p}}{\sigma _{l}^{d}}}}}$ ${\displaystyle (={\sqrt {\sigma _{s}^{d}}})}$ ${\displaystyle (={\sqrt {\sigma _{s}^{p}}})}$

See also

• Surface tension
• Contact angle

Individual evidence

1. ↑ Krüss: Method according to Owens, Wendt, Rabel and Kaelble (OWRK). Krüss, accessed on June 30, 2019 . 
2. ↑ ^{a b} German Institute for Standardization e. V. (Ed.): DIN 55660-2 Determination of the surface free energy of solid surfaces by measuring the contact angle . Beuth Verlag, Berlin December 2011.
3. ↑ DK Owens, RC Wendt: Estimation of the Surface Free Energy of Polymers . In: Journal of Applied Polymer Science . tape 13 , 1969, p. 1743 .