## 2 Experimental Setup and Procedure  
The scheme of the experimental setup for measuring the instantaneous velocity field inside drop 2 and the temperature field \(T_{s}\) on the surface of the sessile drop is shown in Figure 1.  
During the experiment, the external pressure of 1 bar, relative humidity of 35-36%, and temperature of the external air of 21-22 \({}^{\circ}\)C were constant in the specified ranges throughout the experiment. Drop 2 with initial volume \(V_{02}\) = 40 \(\mu\)L (initial diameter of drop 2 was \(D_{02}\) = 7-7.5 mm, and the initial height \(h_{02}\) = 2.6 mm) was placed on a horizontal heated wall. Drops 1 and 2 were applied by dispensers, positioned perpendicular to the wall surface (Figure 1) (using a single-channel electronic pipette Finnpipette Novus (Thermo Fisher, Vantaa/Joensuu, Finland) with a step of the volume change of 0.1 \(\mu\)L). All the experiments were repeated four times, and the ranges of \(h_{02}\) and \(D_{02}\) are given taking into account repeated measurements of the geometric parameters of droplet 1. Droplet 1 (\(V_{01}\) = 2.5 \(\mu\)L, \(d_{01}\) = 0.8 mm) fell on drop 2 (Figure 1) (\(V_{02}\) = 40 \(\mu\)L). The height of the droplet 1 fall (\(H\)) measured from the edge of the dispenser to the top of the large drop 2 was 4-5 mm. The Weber number was \(We=(\rho{U_{01}}^{2}d_{01})/\sigma\) = 1-1.3, where \(\rho\) is the density of water and \(\sigma\) is the surface tension coefficient for water-air. The rate of droplet 1 falling just before the contact with the top surface of the sessile drop 2 was \(U_{01}\) = 0.32 m/s. This velocity was determined by high-speed shooting. Neither drop broke up, and at an impact on the liquid surface there was no spray. Droplet 1's impact did not lead to the formation of the crown, which was confirmed by the measurements by the high-speed camera. After droplet 1's fall, the diameter of the base of large drop 2 \(D_{02}\) did not change. After the interaction of droplets, a thermal wake remained on the free surface of drop 2. The substrate was made of copper (the substrate thickness was 5 mm and its diameter was 50 mm). After each experiment, the substrate was treated several times with alcohol and water, and then thoroughly dried. In addition, the wall roughness was periodically monitored by a profilometer, which showed the invariance of the mean square value of wall roughness. The substrate was placed on a hard table, located on a base that excluded vibrations of the table and the substrate. Squeezing out a large sessile drop was implemented rather slowly to maintain the constancy of the drop geometry for different experiments. The drop diameter and height for repeated experiments differed by no more than 3%. The static contact angle (\(\theta_{0}\)) for the sessile water drop 2 was 87-90\({}^{\circ}\) at a wall temperature under the sessile drop \(T_{w}\) = 79-81 \({}^{\circ}\)C. The optical system of plane-parallel light generation was used to provide a shadow image of drop 2 (Figure 1b). To obtain such light, the source (MI-150) and the telecentric backlight illuminator (62-760, Edmund Optics) were used together with the glass fiber optics cable (BX4 type Dolan-Jenner) and video camera (FastVideo 500 M) with the macro lens Sigma 105 mm f/2.8 G IF-ED AF-S. The initial static contact angles were determined using a tangential method. Figure 1: (a) Scheme of measuring \(T_{s}\) and the instantaneous velocity field inside drop 2 using PIV. PIV—Particle Image Velocimetry; TI—Thermal Imager. (b) The measurement scheme of drop 2 static contact angle: (1) the video camera; (2) the source of plane-parallel light; (3) the camera Nikon D750 (with micro lens); (4) drop 2; (5) a thermocouple for measuring the wall temperature (\(T_{w}\)). To minimize the measurement error of the contact angle, the experiments were repeated three times (under the same conditions). The average value of the contact angle was determined by the results of three experiments.