This document specifies evaluation methods for surface tension of ultrafine bubble (UFB) dispersion in water.

Three test methods, Wilhelmy, du Noüy and the pendant drop method, are adopted because of their advantages to detect small change in surface tension by UFB dispersion in water and the high accessibility to commercially available instruments.

This document can be used to measure the surface tension of liquid containing UFB dispersion in dilute surfactant water solution such as detergent or machining coolant as well as UFB dispersion in water.

NOTE            Measurement data of liquid containing UFB dispersion in dilute surfactant water solution are summarized in Annex D.