The captive bubble method is used to determine specific contact angles. It enables the contact angle on a solid surface in a surrounding liquid to be examined and can be used for surfaces that are very easy to wet. A contact angle meter is required for practical implementation.

What is the captive bubble method and what is it used for?

The captive bubble method is a special method for measuring the contact angle. It is closely related to the sessile drop method. Using the sessile drop method, a drop of liquid rests on a solid surface in a gas phase (usually air). Using captive bubble method, on the other hand, the solid surface is surrounded by a liquid. A gas bubble or a drop of a second liquid is deposited on the solid surface.

A key advantage of the captive bubble method is that it allows investigation under liquid conditions. This makes it particularly suitable for biological surfaces, hydrophilic materials or coated substrates that would be unstable in the gas phase.

Another advantage is that samples that are very easily wettable can be tested. During a contact angle measurement using the sessile drop method, a drop of liquid would spread completely on such surfaces, making it impossible to determine the contact angle accurately. The captive bubble method provides more accurate results for these samples.

Fundamentals of the captive bubble method: contact angle measurement

In materials science, the determination of contact angles and the surface energy of solids plays a crucial role in understanding the interactions between solid surfaces and liquids.

The contact angle describes the angle formed by a drop of liquid on a solid surface and provides information about the wetting behaviour of this liquid-solid combination. Measuring the contact angle of a liquid on a solid provides information about the wetting behaviour of this combination. At a contact angle of 0°, the drop is completely spread out on the solid surface. At a contact angle of 180°, the drop lies on the surface in a spherical shape and only touches the solid at one point. In practice, the contact angle is usually between these two extreme values.