The measurement of water contact Angle is the most widely used method to evaluate the hydrophilicity of thin films.

Hydrophilic membrane

The water drops on the surface of the solid film. The Angle between the solid-liquid interface and the liquid-gas interface is the contact Angle of the water drops on the material surface, that is, the water contact Angle. The international standard ISO 15989 specifies the measurement of water contact angles on thin film surfaces. According to the provisions of ISO 15989, surface water contact Angle test method is: using syringe will be 1 ~ 2 mu L distilled water or ultrapure water injection and hung to needles, upward adjustment sample set, make water droplets in contact with the surface of the sample under test, and then down to adjust the sample units, moving water droplets to the surface of sample under test, and then using contact Angle meter test water droplets on the surface of the sample, contact Angle, and selected 10 points on the surface, in turn, testing, calculating the average of 10 points as the final sample surface contact Angle values. The international standard, ISO 27448-2009, also contains detailed requirements for self-cleaning evaluation of photocatalytic materials - methods for testing water contact angles.