## 2 Materials and Methods  
Figure 1 presents a detailed schematic of the experimental apparatus, which comprises a droplet generation device, a heating device, and an imaging system. The droplet is extruded at a controlled flow rate of 30 \(\mu\)L/min by a syringe pump from a needle that has an external diameter of 0.8 mm and an internal diameter of 0.51 mm. A droplet forms at the tip of the needle and detaches when gravity overcomes the surface tension, of which the volume is around 6 \(\mu\)L. The primary focus of this study is to investigate the effects of surface temperature and droplet component while maintaining a constant needle height, thereby ensuring a uniform droplet impact speed of 0.7 m/s. The research fluids employed in this study are the ethanol/propanol mixture and the ethanol/water mixture, both of which contain three mixing contents: 25 vol.%, 50 vol.%, and 75 vol.%. Table 1 displays the physical parameters of the pure liquids, which are obtained from NIST's REFPROP V8.0 software [34]. Table 2 displays the specific mixture ratio of binary droplets and the corresponding physical parameters. The density, specific heat, and latent heat of the mixture are calculated using the recommended mixing rules [9;35]: \(\rho_{1}=(y_{1}/\rho_{11}+y_{2}/\rho_{12})^{-1}\), \(c_{\text{p,l}}=y_{1}c_{\text{p,l1}}+y_{2}c_{\text{p,l2}}\), \(h_{\text{fg}}=y_{1}h_{\text{fg1}}+y_{2}h_{\text{fg2}}\). The saturation temperature of the binary mixture liquid is calculated by the Aspen Plus Simulator V11.0. The surface tension of the ethanol/water mixture is obtained from the database [36]. The difference in surface tension between ethanol and propanol is modest, and the surface tension of the mixture is calculated by mole fraction weighted averaging: \(\sigma=x_{1}\sigma_{1}+x_{2}\sigma_{2}\). The target substrate used for this study is a finely polished 6061 aluminum alloy plate of circular shape, 80 mm diameter, and 2 mm thickness. The surface roughness (\(R_{\mathrm{d}}\)) is about 7 nm, which is measured by a 3D profiler (KLA-Tencor P7, KLA, Milpitas, CA, USA). The plate is heated by a CNC heating platform (400 W) that has a temperature control range of 30 \({}^{\circ}\)C to 400 \({}^{\circ}\)C with a precision of less than 1%. The surface temperature is maintained between 100 \({}^{\circ}\)C and 400 \({}^{\circ}\)C. A K-type thermocouple, located at the center of the plate, is used to measure the surface temperature before the droplet impact and is subsequently removed during the impact process. To mitigate any potential cooling effect from previous droplet impacts on the surface temperature, a designated minimum time gap of 3 min is imposed between sequential trials. The droplet impact process is captured using a high-speed camera (Phantom V2012, Vision Research, Inc., Wayne, NJ, USA) operating at 3000 frames per second with an \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Properties** & **Ethanol** & **Propanol** & **Water** \\ \hline \(\rho_{\mathrm{l}}\) [kg/m\({}^{3}\)] & 785.92 & 799.8 & 997.07 \\ \(c_{\mathrm{p1}}\) [KJ/(kg\({}^{\circ}\)C)] & 2.439 & 2.678 & 4.184 \\ \(h_{\mathrm{fg}}\) [KJ/kg] & 922.79 & 765.68 & 2435.12 \\ \(T_{\mathrm{b}}\) [\({}^{\circ}\)C] & 78.31 & 97.15 & 100.02 \\ \(\sigma\) [mN] & 21.7 & 26.3 & 72.1 \\ \(\mu\) [mPa s] & 1.077 & 1.89 & 0.9125 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Pure liquid properties at room temperature. Figure 1: Schematic diagram of the experimental setup. \begin{table}