Captive bubble method
The captive bubble (sessile bubble) method is a special arrangement for measuring the contact angle between a liquid and a solid using drop shape analysis. Instead of placing a drop on the solid as in the case of the sessile drop, a bubble of air is injected beneath a solid, the surface of which is located in the liquid.
The method is particularly suitable for solids with high surface free energy on which liquids spread out. Hydrogels, such as soft contact lenses for example, are likewise inaccessible for the standard arrangement; the captive bubble method is also used in such cases.