Contact angle measurements to evaluate plasma treatment efficiency

Plasma treatment is a common process for treating various materials prior to coating, printing or gluing. One of the main purposes of the plasma treatment is to improve the wettability of the material as good wettability is required in all the aforementioned processes. As more products rely on plastics, from medical devices to automobile bumpers, this concept has grown more important since plastics generally exhibit poor wettability for many liquids. This is due to the low surface free energy of many plastics. Plasma treatment is a safe and effective technique for increasing the wettability without harmful gases or high temperatures, and complex geometries can be easily treated.

Contact angles are used to detect the effect of the plasma treatment

In a plasma treatment process, the surface is placed in a chamber under vacuum and bombarded by ionized gas. The ionized gas will induce chemical reactions at the surface of the material being treated, changing its surface energy. Contact angle measurements are used to analyze the surface after plasma treatment. Contact angle is used since it is very sensitive to the changes occurring at the surface monolayer. A water contact angle alone will give indication of the effectiveness of the plasma treatment as the low water contact angle indicates better wettability of the surface. To further analyze the effect of plasma treatment, surface free energy of the surface can be calculated by performing contact angle measurements with two or more probe liquids.

Several parameters affect the plasma treatment, including gas type, process pressure as well as plasma power and time. All of these parameters need to be optimized. This is typically done by using contact angle measurements. 

To read how optimum plasma treatment time of polypropylene can be evaluated, please download the case study through the link below.