## 3 Results and Discussion
### Contact Angle of Bifenthrin Droplets with Adjuvants on Tea Leaves  
The images of the pure water droplet deposited on the surfaces of the fresh bud and young leaf of tea photographed by the optical contact angle measuring device (\(\theta_{1}\) = 108.649\({}^{\circ}\), \(\theta_{2}\) = 93.791\({}^{\circ}\)) are shown in Figure 4. The steady state of the droplet could be due to the equilibrium of three interfacial tensions (\(\gamma_{sl}\), \(\gamma_{lg}\), \(\gamma_{sg}\)) at the junction of solid, liquid, and gas phases. The surface of the fresh bud was more hydrophobic with poorer wettability than the young leaf. Although the pure water droplets on the surface of the young leaf could not easily roll off, the contact area was not large enough to achieve a good wetting effect. This was due to the difference in the shape and thickness of wax on the surface of tea leaves of different ages. The thick and smooth hydrophobic waxy layer on the fresh bud increased the contact angle of pure water droplets on the surface. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Concentration (\%)**} & \multicolumn{4}{c}{**Viscosity (mpa-s) a**} \\ \cline{2-5}  & \multicolumn{4}{c}{**Adjuvants**} \\ \cline{2-5}  & **Silwet L-77** & **6501** & **Greenwet 720** & **JFC** \\ \hline
0 & 0.982 (\(\pm\)0.007) ab & 0.982 (\(\pm\)0.007) b & 0.982 (\(\pm\)0.007) a & 0.982 (\(\pm\)0.007) a \\
0.01 & 0.956 (\(\pm\)0.014) c & 0.954 (\(\pm\)0.016) c & 0.956 (\(\pm\)0.010) b & 0.976 (\(\pm\)0.008) ab \\
0.05 & 0.968 (\(\pm\)0.012) bc & 0.926 (\(\pm\)0.008) d & 0.976 (\(\pm\)0.010) a & 0.978 (\(\pm\)0.010) ab \\
0.1 & 0.974 (\(\pm\)0.010) bc & 0.928 (\(\pm\)0.007) d & 0.948 (\(\pm\)0.007) b & 0.958 (\(\pm\)0.012) bc \\
0.2 & 1.003 (\(\pm\)0.006) a & 0.998 (\(\pm\)0.011) a & 0.982 (\(\pm\)0.009) a & 0.946 (\(\pm\)0.010) c \\ \hline F b  & 10.385 & 41.484 & 11.981 & 10.051 \\ DF & 4 & 4 & 4 & 4 \\ \(p\)-value & 0.000102 & \textless{}0.0001 & \textless{}0.0001 & 0.000126 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Viscosity of bifenthrin diluent mixed with adjuvants in different concentrations. The changing trends of the contact angle of pesticide droplets on the surfaces of the fresh bud (a, c, e, g) and young leaf (b, d, f, h) with different concentrations and types of adjuvants over time are shown in Figure 5, with pure water as the control. The contact angle of the pure water droplet was significantly reduced by a 3000 times solution of 10% bifenthrin EC. Different types of adjuvants can further reduce the contact angle and accelerate the diffusion of droplets on the surface of tea leaves. The two columns in Figure 5 show that the contact angle of the young leaf was smaller than that of the fresh bud for each adjuvant at different concentrations. The hydrophobic waxy layer gradually fell off with the growth of fresh buds, making it easy for adjuvant droplets to wet the surfaces. Moreover, with the increase in solid-liquid area under the droplet and around the contact line, the influence of adjuvant adsorption on the contact angle increased. Since the contact area between the adjuvant droplets and the rough leaf surface was larger than that of the smooth bud surface, the amplification effect of adjuvants on the wetting of young leaves was greater. Previous studies have also shown that the surface morphology of target leaves was an important factor in wetting behaviors of pesticides by changing the rebound of droplets and spray run-off. [PERSON] and [PERSON] (2007) assessed the superhydrophobic and superhydrophobic surfaces of plants and pointed out that cell sculptures and fine surface structure, such as folding of the cuticle or epicuticular waxes, can influence the wetting of plants. [PERSON] et al. (2017) investigated two surface states based on the diversity of phenotypic genes in different leaves: wax deposition without hairs and hairy surface. The microroughness increased with increasing glandular trichomes, and then caused the wide spread of droplets.