What does the Surface Energy Calculator do?

By measuring the contact angles of 2 or 3 specially chosen liquids on the surface of interest it is possible to gain greater insight into the surface energy properties. SEC takes the inputs (white backgrounds) and calculates the outputs (light blue backgrounds) each time you change an input value.

Dispersion and Polar

If you just put a drop of water onto a surface you get a contact angle, and nothing much else. If, however, you also measure the contact angle with an Apolar liquid and enter both angles into SEC you start to get some insights into the surface energy.

The two classic Apolar liquids used are Di-Iodo and Bromo-Naphthalene. The surface tensions of both these liquids are provided and shown when you select either of them

Water has (till we get on to Lewis Acid/Base) two components - the Total surface tension (the familiar value of 72.8 dynes/cm) and the Dispersion component (Van der Waals) which is 21.8.

Using the single (Dispersion) value for the Apolar liquid and the two values for water it is possible to calculate the Dispersion, Polar and Total values of the surface energy, based on the respective contact angles.

The calculation can be made via two methods: Owens-Wendt and Wu. Very often their values are similar, in which case it doesn't matter which you choose. Other times you just have to reach your own conclusion about which to believe - there are arguments for and against each of them.

Lewis Acid/Base

If the contact angle of a third, Polar, liquid is included (there is a choice of three Polar liquids) then it is possible to take the Acid/Base values for water and the polar liquid (the second pair of values) and compute the Dispersion, Acid/Base, Acid, Base and Total values for the surface. Whether these values are worth the effort of measuring them is up to you.

© Copyright 2012 Steven Abbott TCNF www.stevenabbott.co.uk