Surface cleanliness
Susanna Laurén Apr 12, ’22 ~ 4 min

How to evaluate surface cleanliness through contact angle measurements?

Surface cleanliness is an important topic in many industrial areas. It is especially needed in applications like coating, painting, or printing where something is added on top of the other material. If the surface where the coating is applied is not clean, the adhesion between the coating and the substrate is typically poor. There are many different ways to ensure surface cleanliness in industrial settings, such as intensive washing cycles or plasma cleaning. But how can you be sure that the cleaning process has been effective? Or maybe you are spending too much time to ensure surface cleanliness when less would be enough. Contact angle measurements offer a fast and sensitive way to evaluate the effectiveness of different cleaning processes. It can also be used as a tool for quality control to ensure suitable surface properties.

Using contact angle to evaluate the cleanliness of metal surfaces

Clean metal surfaces have high surface free energies which can be seen as low water contact angles. Native metal surfaces have in theory extremely high surface free energy, even over 1000 mN/m, which is due to strong metallic bonds that hold the metal atoms together. However, as the surface energy is so high, in practice, a completely clean metal will immediately react with the molecules in the air and the surface is instantly contaminated. Thus theoretical surface free energy values are never measured in practice but there is still a clear difference between the clean and clearly contaminated surface.

Before adding a coating on metal, it needs to be cleaned to remove grease or other contaminants. In the table below [1], the water contact angle on a copper and nickel surface is measured before any cleaning procedure and immediately after. Most of the contamination is already removed after ultrasonic cleaning in soap solution but the contact angle can be further reduced with additional cleaning steps.

Cleaning of metal

Using contact angle to evaluate the cleanliness of polymer surfaces

For polymers, using water contact angle measurements is not as straightforward. This is because the water contact angle on a clean polymer surface is often fairly high. If looking at the table above, the water contact angle on a contaminated Teflon is lower than what you would assume for a native Teflon surface (120 ° is a typical value reported). The last cleaning step is plaining with the razor blade which seems to increase the contact angle even higher but that is due to the added roughness rather than increased surface cleanliness.

To evaluate cleanliness on polymer surfaces, measurement of advancing and receding contact angles can be useful. From the data below, it can be especially seen that there is a clear difference in the receding contact angle before and after cleaning in all samples.

Before and after cleaning contact angles

If you want to hear more about how contact angle measurements can be used to predict adhesion, please watch the webinar through the link below.

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Webinar

Contact angle measurement to predict adhesion

Watch  the Webinar
  1. Horsthemke and J.J. Schröder, “The wettability of industrial surface: contact angle measurements and thermodynamic analysis”, Chemical Engineering and Processing: Process Intensification 19 (1985) 277

Related products

   Theta Flow Premium contact angle meter suitable for demanding surface research and  quality control.
   Theta Flex Contact angle meter for all your measurement needs. Theta Flex is designed to  fit both research and quality control.
   Theta Lite Contact angle meter for simple and precise measurements. Clean and compact  instrument with user-friendly design.

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