# Influence of Multiple Factors on the Wettability and Surface Free Energy of Leaf Surface
## 3 Results and Discussion  
### The Comparison of Surface Free Energy on Rice and Rape Leaf  
The measurements of probe liquids on rice and rape leaves both on the adaxial and abaxial surfaces are given in Table 3. When deionized water, formamide, and ethylene glycol were used as test liquids, respectively, the contact angles on rice and leaf surface showed the same variation tendency. The contact angles of both formamide and ethylene glycol were smaller than that of deionized water due to a lower surface tension. In addition, the contact angle of rice adaxial surface was higher than that of the abaxial surface, which is consistent with the new leaf of rape, while the contact angle of the adaxial surface of rape old leaf was lower than that of the abaxial surface. Figure 3: The collision process of between falling droplet and solid surface in five platforms. The results of the effect of crop type, rape leaf status, leaf surface, and probe liquid on contact angles using ANOVA were given in Tables 4 and 5. We found that the crop type (rice and rape), leaf surface (adaxial and abaxial surface), and probe liquids (deionized water, formamide, and ethylene glycol) have significant difference (P < 0.001) on contact angles. While there was no practical difference between the contact angles and rape leaf status (P = 0.416), indicating that the difference between new leaf and old leaf of rape had less influence on leaf surface wettability compared with the factors of crop type, leaf surface, and probe liquid, and the influence of probe liquid could also be found in [PERSON]'s research [3]. The SFE of rice and rape leaves as well as its dispersive and polar components was calculated based on the OWRK method. In general, the SFE of 0-20 mJ/m\({}^{2}\) is considered to be highly hydrophobic while the SFE of 20-40 mJ/m\({}^{2}\) is considered to be hydrophobic [3]. The surface shows hydrophilicity when the polar component is dominant, while it shows hydrophobicity when the dispersive component is dominant [36]. According to Figure 3, all of the tested leaves of rice and rape (two growth platforms), in two statuses for each, adaxial and abaxial, performed with high hydrophobicity (SFE < 20 mJ/m\({}^{2}\)) from the perspective of SFE value. The dispersion components of all leave statuses accounted for a larger proportion than polar component. Except for the abaxial surface of rape old leaves (68.50%), the dispersive components of the remaining rice and leaves accounted for more than 90%. Besides this, there was a great difference in the SFE between rice and rape leaves, where the hydrophobicity of rice leaves is stronger than that of rape leaves based on the values of contact angle and SFE. On one hand, the SFE of rape new leaves is higher than that of old leaves, and the SFE of the adaxial surface is a little lower than that of the abaxial surface in rape new leaves while the SFE of the adaxial surface is much higher than that of the abaxial surface in rape old leaves. It is indicated that the wettability of adaxial surface is generally better than that of the abaxial surface, except for the decaying leaves, which is correlated with the stomatal distribution of the leaf [17]. On the other hand, the SFE of the adaxial \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Source**} & \multicolumn{2}{c}{**Type III Sum**} & \multirow{2}{*}{**DF**} & \multirow{2}{*}{**MS**} & \multirow{2}{*}{**F**} & \multirow{2}{*}{**P-Value**} \\  & **of Squares** & & & & & \\ \hline crop type & 4893.393 & 1 & 4893.393 & 390.432 & \textless{}0.001 \\ leaf surface 1  & 238.052 & 1 & 238.052 & 18.994 & \textless{}0.001 \\ probe liquid & 1784.951 & 2 & 892.476 & 71.209 & \textless{}0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Effect of crop type, leaf surface, and probe liquid on contact angles.