## 1 Introduction  
Investigating the patterns of the interaction of liquid droplets with solid surfaces as illustrated by substrates and particles is of special importance. Several numerical and experimental studies on the interaction of droplets of water [1], solutions [1, 2], emulsions [3] and slurries [4, 5, 6] with substrates and particles from different materials, such as steel [3, 7] and glass [8, 9], have been published. The considerable interest in these processes is conditioned by a wide range of their applications in, e.g., chemical and heat exchange technologies [10, 11, 12], pharmaceutical industry [13, 14], food industry [15, 16], firefighting [17, 18], thermal treatment of water [19, 20], spraying technologies [21, 22], etc. Experimental research into the collisions of liquid droplets with solid particles is carried out using several approaches [23]. The most popular approaches involve the generation of a droplet in free fall on a fixed particle [24, 25, 26], simultaneous movement of droplets and particles [27, 28] and identification of the interaction of droplets with particles in two- and multiphase flows. To date, the effect of a group of factors and parameters on the regimes and outcomes of the interaction of liquid droplets with solid particles has been experimentally studied [23, 28, 29] using the above approaches. These parameters include the sizes, velocities, impact angles and surface properties (wettability, roughness) of particles and substrates [30]. The following regimes of droplet-particle interaction are usually distinguished [23]: agglomeration, stretching separation and stretching separation with the formation of a different number of satellite droplets of varying sizes. Theoretical studies made it possible to establish the effect of such major parameters as surface wettability [31; 32], Weber number [31; 33; 34; 35], Reynolds number [36], droplet-to-particle size ratio [31], surface curvature [35; 37], droplet diameter and liquid viscosity [8] on the outcomes of the droplet-particle interaction. The present-day ideas of the patterns of interaction of liquid droplets with solid particles are shaped by the experimental and theoretical studies such as [35; 38; 39]. They present typical collision regime maps for liquid droplets and solid particles. The critical Weber, Reynolds, Ohnesorge and capillary numbers were shown, at which a collision regime changes. Among the key parameters affecting the droplet-particle interaction, the properties of liquid (its viscosity, density, surface and interfacial tension) are especially interesting to explore in the context of their effect on the interaction. This is because the multicomponent liquids used in technical applications vary greatly in their viscosity, surface and interfacial tension. Thus, e.g., research findings [8; 40; 41] substantiate the crucial role of liquid properties in the characteristics of the interaction of droplets with solid surfaces. Thus, for instance, a lower viscosity of liquid in the collision of a free-falling droplet with a substrate leads to a significant reduction in the size of child droplets [42; 43; 44]. Lower surface tension increases the time taken to break up the liquid bridge between particles, which, in turn, has a considerable influence on the impact dynamics and characteristics of droplet spreading over a solid surface [8]. Such effects help promote cost reduction in liquid spraying due to a decrease in the critical Weber number and consequently relative droplet velocities. The joint contribution of different liquid properties is generally described using dimensionless similarity criteria (the Weber, Ohnesorge, Reynolds and capillary numbers). The critical values of these criteria were determined [45] for the regime transition boundaries of droplet-droplet interaction. To supplement the study [45], it is instructive to evaluate the effect of liquid properties on the characteristics of collisions between droplets and solid particles of comparable sizes.