A study on measurement of solid-liquid contact angles.

A new measuring method of solid-liquid contact angles is proposed. The well-known phenomena that the liquid meniscus formed under a downward solid surface spontaneously falls down at a certain height of the solid is applied to the measurement of the contact angles. The relation between the contact angle and the critical height of the solid surface at which the instability occurs was theoretically obtained considering the solid-liquid wetting behavior from a thermodynamic view-point. Applying the theoretical results, the contact angles can be obtained by measuring the critical height of the solid. The validity and the usefulness of the method were experimentally confirmed for various solid surfaces and test liquids.