# Influence of Multiple Factors on the Wettability and Surface Free Energy of Leaf Surface
## 3 Results and Discussion
### The Influence of PPP Concentration on Wettability  
In order to investigate the effect of the PPP concentration on the wettability of rape leaves, 20% wettable powder tricyclazole, 40% wettable powder dimethachlon, and 25% suspending agent iprodione were divided into different concentration gradients according to the agrochemical label recommended dosage. The contact angle varies with the concentration of three PPPs was shown in Figure 9.  
Wettable powder is one of the earliest and most commonly used PPP reagents, while the biggest problem while using is that the poor solubility of the wettable powder results in the precipitate of the particles. Thus, the wettable powder solution needs to be stirred frequently during the spraying process to ensure its uniformity. Comparing to wettable powder, the particle size of suspending agent is smaller and the suspension rate is higher, thus it is not easy to precipitate and the stability of suspending agent is better as well. In this experiment, three kinds of PPP with different formulation were used.  
According to Figure 9, tricyclazole is a kind of protective fungicide with strong internal absorption, whose contact angle fluctuates between 42\({}^{\circ}\) and 50\({}^{\circ}\) along with a slow decreasing trend as the concentration increases. In general, the variation of contact angle with tricyclazole concentration is almost negligible and a possible explanation is that the solubility of 20% wettable powder tricyclazole is poor, as a lot of sediments were found in the bottom of test tube. Although the shaking treatment was done before the test, the effective components of tricyclazole in the solution may have reached the saturation degree. In addition, dimethachlon is a potent fungicide, which is the most commonly used towards rape among three PPP. Dimethachlon showed the largest decrease in contact angle with the increase of dimethachlon concentration, and the wettability of rape leaves was almost not improved when the concentration was at a low level, which was close to the contact angle between water and rape leaves (96.56\({}^{\circ}\)). With the continuous increase of dimethachlon concentration, the wettability of rape leaves increased significantly and the contact angle decreased to about 80\({}^{\circ}\) when the concentration reached 10 g/L. Besides this, iprodione is a kind of contact fungicide with broad range and high  
Figure 9: The variation of contact angle with the variation of PPP concentration.  
efficiency, whose contact angle decreases gradually with the increase of iprodione concentration and it also fluctuates in a wide range between 63\({}^{\circ}\) and 86\({}^{\circ}\). The reason might be that the solution has reached its saturated state when the concentration is high, and the bubble and sediment in the solution might also affect the measurement of contact angle to some extent. In general, with the increase of PPP concentration, the wettability increased differently depending on the formulation of PPP, and the wettability of microemulsion is better than that of suspending agent and wettable powder.