Wetting analysis using the captive bubble technique


© Fraunhofer IKTS
Konventionelle Kontaktwinkelmessung mittels Sessile-Drop-Technik (»liegender Tropfen«).
© Fraunhofer IKTS
Kontaktwinkelmessung mittels Captive-Bubble-Technik (»gefangene Blase«) als spezielle Methode für Oberflächen mit hoher freier Oberflächenenergie, auf denen Flüssigkeiten spreiten.

The captive bubble technique uses a special setup that allows contact angle measurement even when the conventional "lying drop" method (sessile drop technique) does not work.

The contact angle formed by a drop of liquid on a solid surface provides information about the wettability of the surface with this liquid. Small contact angles (< 90°) correspond to high wettability and large contact angles (> 90°) to poor wettability. The contact angle is influenced by both the surface tension of the liquid and the chemical and physical properties of the solid. Contact angle values can be used to determine its surface free energy and its disperse and polar fractions.

Typically, the contact angle is determined using the horizontal drop method, in which drops are placed on the solid surface from above. However, this method is not suitable for surfaces with high surface free energy on which liquids spread. For this purpose, Fraunhofer IKTS uses the captive bubble technique. The solid surface is completely immersed in the liquid and an air bubble is dispensed below the surface. "Trapped" at the surface, the contact angle is formed at the three-phase point between solid, liquid and air bubble.

This technique can be particularly advantageous for strongly hydrophilic surfaces, because here hydration under water is complete and thus defined. Measuring the contact angle under water is also useful if the surface to be tested is intended for use in water. Then we can study processes at the interface, for example the fouling of a solid surface with a biofilm.

Application examples


1.       Wetting tests on ceramic membranes for the purification of liquids.

Due to their highly hydrophilic surface, the wet membranes can be examined very well with the captive bubble technique. The composition of the test liquid can be adapted to the specific application.


2.       Wetting tests on coatings for antifouling use

Antifouling coatings can have a porous surface with great roughness. The captive bubble technique can also be used advantageously for this application. Once a biofilm has grown, the surface becomes more hydrophilic and can best be characterized when it is fully hydrated. This is the case with the captive bubble arrangement under water. The test liquid can be adapted to the application. Natural or artificial seawater are possible.


3.       Adsorption tests on implant surfaces

Protein adsorption and cell attachment and spreading are determined by the physicochemical properties of medical surfaces. Surface energy is an important indicator of biomolecule adsorption. For wetting measurements to investigate hydrophilicity and derive surface energy, the captive bubble technique is suitable because it allows working in the natural, aqueous environment.


Services offered


Determination of contact angles using the captive bubble technique on different surfaces:

  • Highly hydrophilic surfaces with contact angles less than 10°
  • Ceramic membranes
  • Antifouling coatings for maritime applications
  • Surfaces for medical technology (e.g. implants)
  • Polymer surfaces
  • Hydrogels
  • Porous surfaces