Calculating Surface Tension Using Contact Angle

Surface tension is important to know when you are trying to determine the wettability of a material, whether its corrugated paper or a solar cell.   

The contact angle of a droplet can be used to determine the surface tension of a droplet, offering a fast and non-intrusive testing solution for determining the spreadability of absorption of a liquid on a surface.  

Dive in for more essential knowledge about using the contact angle method to measure surface tension.  

The contact angle method for measuring surface tension

The contact angle is the angle where a liquid droplet meets a solid surface. It is usually measured through the shape of the liquid.  

Different surface tensions create different shaped water droplets. The cohesive forces of the surface layer typically pull droplets of water into a spherical shape. However, droplets are also easily deformed and studying these deformations reveals information about the surface tension. Liquids with low surface tension tend to evaporate quickly while high surface tension liquids will evaporate more slowly.  

Formula for the contact angle method

The formula that is used to measure contact angle of a liquid on a solid substrate is the well-known Young’s equation: 

γLV Cosqe = γSV – γSL  

In this formula, γSL, γSV,  and γLV are solid-liquid, solid-vapor and liquid-vapor interfacial tensions which measure the free energy (per unit area) and qe is the equilibrium contact angle. 

Determining surface tension with a goniometer 

The surface tension of a liquid droplet can be measured with a goniometer, a fast and accurate tool that tests in a non-destructive way.  

The Fibro PGX+ Pocket Goniometer from our specialist testing brand TQC Sheen is an excellent example of a portable and precise tool. It can be placed directly on the surface sample and provides a mini test environment. It can take up to 80 pictures per second and connects to a PC, so that the images and data can be analyzed quickly and easily. This gives you accurate measurements of surface tension and surface free energy (SFE) in a short amount of time. 

Find out more about how goniometers work and their applications in our guide to goniometers.  

Measuring surface tension with Industrial Physics

Surface tension is an important test for everything from determining the wettability of paper to how likely a liquid is to evaporate, making it a staple in coating and ink testing. At Industrial Physics, we know just how important it is to have testing equipment that meets not only your individual needs but also the industry standards of your sector. That’s why we create testing and measurement solutions you can rely on, including those in our specialist paint and coatings brand TQC Sheen.