Improved inverted bubble method for measuring small contact angles at crystal-solution-vapor interfaces.

We propose and evaluate an improvement of the inverted bubble method, originally proposed by McLachlan and Cox [Rev. Sci. Instrum. 46, 80 (1975)], a technique for measuring small contact angles at crystal-solution-vapor interfaces on a gas bubble under a solid immersed in a test solution. A simple experimental setup is used to evaluate the proposed method. We conclude that the method is suitable for measuring small contact angles with a minimum detectable angle of about 3 degrees . Improvements in instrument design are proposed to lower the detection limit to 0.5 degrees or below.