Contact angle indicates the tendency of a liquid drop to spread out and adhere to the surface of materials, reflecting its wettability and hydrophilicity
[5][6]. The higher the contact angle values, the higher the tendency of the surface to repel water. In general, the application of cold plasma onto film surfaces decreases the contact angle values indicating an increase in the hydrophilicity and the wettability of the films. Application of cold plasma onto the film surface generates reactive species and free radicals resulting in the amplification of several polar groups like -COOH, -OH, and CO leading to increased polarity, surface tension, and surface free energy, eventually increasing the hydrophilicity and wettability of the film surface
[4][7][8]. Another probable reason is the surface roughness caused by the etching effect that aids in the spreading of liquid onto the surface
[9][7][10]. As reported in the published literature, the water contact angle is the function of plasma treatment time and voltage. Plasma treatment at higher voltages and with longer exposure times increases the surface roughness and polar groups, resulting in hydrophobicity and wettability of the film surface. In contrast to the general trend where the application of cold plasma decreases contact angle, DBD plasma-treated starch film showed an increase in the contact angle values. This could be due to the oxidation of the hydroxyl group into carbonyl groups, resulting in the formation of the new hydrogen bonds. These hydrogen bonds may have decreased the availability of polar groups on the surface, leading to the enhancement in hydrophobicity of the film surface
[11]. Similarly, contact angle values increased for corn starch thermoplastic films treated with SF
6 plasma
[12]. Overall, it can be concluded that the contact angle is a factor of plasma gas composition, as well as voltage and exposure time. The contact angle of a film is an important criterion to decide its suitability in packaging applications
[13][14]. The wettability of a film affects the coating, printing, absorbance, adhesion, and frictional properties of the film surface
[14][15].