Abstract
Kapton is widely used in microelectronics, optoelectronics, composites, and optics because of its high heat resistance, high mechanical strength, and good dielectric properties. However, this material has a low surface energy, and therefore poor wettability and low adhesion that limits its use in certain applications.
In this work, the effect of DBD on the Kapton surface was studied. The main attention was devoted to the investigation of changes in surface hydrophilicity, surface composition and surface morphology induced by the atmospheric pressure air plasma treatment as well as to the temporal stability of such changes.
The filamentary plasma was generated between two parallel planar electrodes, one conductive and the other covered with dielectric. Samples were placed on the lower electrode.
The upper, moveable electrode was operated at 30 W. The scanning speed was selected so that the processing time when passing in one direction and back corresponded to 1 second.
The number of scans ranged from 1 to 20 scans. It was found that the Kapton film exhibited already after 1 second of plasma treatmentmuch higher hydrophilicity (water contact angle close to 20o) as compared to untreated film (water contact angle ~ 80o).
Such noticeable change in wettability was found to beconnected predominantly with the surface oxidation and formation of new oxygen containing functional groups on the Kapton surface as witnessed by XPS. Furthermore, the plasma treatment caused not only dramatic changes in wettability of Kapton films,but influenced also the dynamics of water droplet drying: whereas for the untreated Kapton three phases drying with significant constant contact angle (CCA) phase was observed, the CCA phase was absent on plasma treated films.
Regarding the ageing, the wettability of Kapton films was found to increase with the storage time and saturated at the value 55+-5o two weeks after the treatment.