# Experimental Investigation into the Influence of Plasma Technology on Seed Surface Wettability
## 4 Discussion  
Based on the results above, some crucial outcomes for APD treatment could be highlighted. It has a small and rather negative effect on all seeds. It seems inappropriate because the seed surface is hydrophobized, and the contact angle is increased--by up to 9% for peaks, 11% for wheat, and 38% for sunflower. A short treatment of peas for 10 s at a flow rate of 30 SCFH is the only exception, where a statistically significant decrease of 6% in the value of the contact angle was achieved. However, more prolonged treatment has negligible or even negative effects. This negative effect is more pronounced for higher airflow. Furthermore, it seems that there is no causation between the APD process parameters and the apparent water contact angle of the wheat and sunflower seed surfaces. Therefore, it could be stated that concerning the relatively high carrier gas temperature [22] used in the treatment, the APD treatment is utterly unsuitable for seed surface wettability improvement in general. LPMD treatment seems much more effective in this area, but it depends on the type of seed. It positively affects the wettability of the pea and wheat seed surfaces at various process parameters. It could be concluded that the power of 800 W seems to be ideal for improving the wettability of these seeds. The contact angle can decrease by up to 50% for the pea seed or by 40% for the wheat seed. Completely different outcomes were achieved for sunflower seeds. A short treatment of sunflower seeds increases the water contact angle by up to 15%, and only the more prolonged treatment to 60 s leads to an improvement in wettability. LPMD treatment does not even have to positively affect the seeds, which could be due to the relatively good wettability of the untreated variant. This plasma treatment probably has no significant effect on changes in the apparent water contact angle. It can even worsen the seed wettability of sunflower (as a representative of oilseed). The observed adverse effect could be related to the composition of the seed, where the fat content of the sunflower seed is significantly (minimum of 20 times) higher than that of the wheat or pea seed. Due to the high fat content, sunflower seeds could also be more sensitive to the higher temperature of the working gas [27]. This can cause undesirable changes on the seeds' surface or even damage them. In order to maintain the Gliding Arc discharge, it is necessary to supply a large amount of energy, which is manifested by the higher temperature of the carrier gas. The temperature decreases with increasing distance from the active area of the discharge [22]. Therefore, it is crucial to place the substrate at a greater distance from the electrodes than is usual for other atmospheric discharges to avoid unwanted thermal damage. In addition, the mean free path of the particles under atmospheric pressure is very low compared to low pressure processes. For this reason, the probability of impact of active particles generated by APD is significantly lower than that of LPMD, leading to the low wettability of the seeds. Some authors previously reported similar results of their experiments. [PERSON] et al. used RF plasma to treat mung bean seeds and observed a 57% lower contact angle of the water droplet on the seed surface exposed to the plasma [18]. [PERSON] et al. used the same plasma type and observed a decrease in the contact angle from 113\({}^{\circ}\) to 74\({}^{\circ}\) for wheat seeds [19]. This phenomenon was the result of exposure of the seeds to plasma discharge for 300 s. The DBD type atmospheric plasma discharge in terms of the wettability change was used in [15; 16; 17]. The discharges differed only in excitation frequency. [PERSON] et al. was able to improve the wettability of wild _Mimosa_ with this type of discharge. [PERSON] et al. treated _Erythrina velutina_ seeds and observed an increase in water absorption and, at the same time, a lower contact angle of the water droplet on the seed surface (48%) [15]. [PERSON] et al.