Measuring hydrophobicity

A water droplet beading up on the surface of a product is the iconic image for liquid repellency. The formation and structure of this droplet is fundamental in measuring the levels of hydrophobicity.

There are two main industry standards of measurement when it comes to determining how well a water repellent treatment is performing. The first involves taking a snapshot of the droplet of water and measuring the ‘contact angle’ between the surface of the product and the edge of the droplet (see picture). Hydrophobic surfaces have contact angles above 90°.

Another form of measurement uses standard water ratings with W0 being 100% water, with W10 being %100 Isopropanol. The incremental increase in isopropanol lowers the cohesive properties within the droplet and therefore making it susceptible to being absorbed into the material.

Did you know: A water droplet on a lotus leaf can produce a contact angle of 170° making it superhydrophobic.