## 3 Results and Discussion  
### Morphology and Regime Map of Different Impact Behaviors  
Figures 2 and 3 demonstrate the typical impact behavior of ethanol/propanol binary droplets and ethanol/water binary droplets on the heated wall for different liquid components and surface temperatures, respectively. For an ethanol/propanol binary droplet, when \(T_{\text{s}}=100\)\({}^{\circ}\)C, the droplet is in the film evaporation state and continues to evaporate throughout the entire process. No bubble rupture or generation of secondary droplets occurs, although occasional bubbles are observed inside the droplet. When \(T_{\text{s}}=120\)\({}^{\circ}\)C, the droplet is in the nuclear boiling state, and more bubbles and satellite droplets (\(D_{\text{s}}<0.3\) mm) with smaller diameters are generated. When \(T_{\text{s}}=150\)\({}^{\circ}\)C, the droplet is in the transition boiling state. At the initial stage, the droplet is in the nuclear boiling state and produces a large number of satellite droplets. With the increase in vapor production, the droplet gradually retracts, detaches from the wall, and eventually rebounds. When \(T_{\text{s}}=180\)\({}^{\circ}\)C, the droplet transitions to the Leidenfrost state. Compared to the ethanol/propanol binary droplets, the impact behavior of the ethanol/water binary droplets is more diverse, as shown in Figure 3. When \(T_{\text{s}}=120\)\({}^{\circ}\)C, the ethanol/water binary droplet is in the nucleation boiling state, and a large number of bubbles as well as secondary droplets are generated. Due to the high surface tension of water, the generation of bubbles with large diameters can be observed during the boiling process of ethanol/water binary droplets, which has not been observed in ethanol/propanol binary droplets. This will be discussed in further detail later. With the gradual increase in surface temperature, droplets reach the transition boiling state, and the impact behaviors become more diverse. Besides producing satellite droplets, the ethanol/water binary droplet also generates fragment droplets (\(D_{\text{s}}>0.3\) mm) through the breakup of the parent droplet. This unique parent droplet breakup phenomenon has not been observed in the impact of the ethanol/propanol binary droplets or pure droplets on the smooth heated surface. The transitional boiling behaviors of ethanol/water binary droplets are investigated in more detail in another work [38] involving a rougher surface (\(R_{a}=15\) nm), which is not the focus of the current study. Finally, as the surface temperature increases further, the ethanol/water binary droplet gradually reaches the Leidenfrost state. Figure 4 illustrates the impact behavior regime map for the two kinds of binary droplets. The ethanol/water binary droplets significantly broaden the transition boiling region and have higher Leidenfrost temperatures compared to the ethanol/propanol binary droplets. Moreover, the Leidenfrost temperature of ethanol/propanol binary droplets remained essentially constant with increasing ethanol content, but the Leidenfrost temperature of ethanol/water binary droplets decreased significantly with increasing ethanol content. According to the previous work of [PERSON] et al. [17] and [PERSON] et al. [39], Leidenfrost temperature depends on the boiling point of the liquid, the latent heat, and the specific heat of gas. The latter two physical parameters need to take into account the effect of temperature, and the values at saturation temperature are used; these are obtained from NIST's REFPROP V8.0 software [34] as shown in Table 3. In this work, the Leidenfrost temperature for pure liquids is calculated using the relation given by [PERSON] et al. [39]: \(\theta_{\text{L}}=1.17\theta_{\text{b}}+0.05\), where \(\theta_{\text{L}}=T_{\text{L}}\text{c}_{\text{P},\text{g}}/h_{\text{fg}}\), \(\theta_{\text{b}}=T_{b}\text{c}_{\text{P},\text{g}}/h_{\text{fg}}\). Figure 3: Snapshots of the impact behaviors of ethanol/water binary droplets with various liquid components and surface temperatures.