This work proposes a mechanism of deformation of an emulsion droplet upon collision with a wall, considering the vortex motion of a liquid inside the droplet. This motion leads to an increase in dissipative energy losses, affects spreading, corona splashing, and droplet relaxation at different liquid and wall temperatures, ranging from 20 °C to 80 °C, and influences the equilibrium shape of the drop during the liquid relaxation. For We = 100–900 and Re = 100–4000, a physical model is presented for the maximum spreading diameter of the emulsion droplet; it takes into account the heating of the boundary viscous layer and the development of temperature gradients along the droplet height, convective mixing of the liquid layers, and translational and vortex flow motion along the radius and height of the droplet. The process of corona splashing of the emulsion droplet has been studied, and the influence of the viscosity gradient due to the intermittent near-wall water film formation on the dynamics of the “corona” has been revealed. These differences led to the formation of an air gap, which in the case of an emulsion drop caused the development of a corona at lower We compared to homogeneous liquids. The duration of the liquid relaxation before capillary wetting was affected by the potential barrier of the contact line of the droplet, which depended on the vortex component of the velocity field as well as on the temperatures of the interacting media. Altering the initial thermal boundary conditions changed the relaxation time up to 60%.

Using the promising fuel microemulsions based on diesel fuel (29.41–95.33 vol. %) and the mixture of diesel fuel with the vegetable additive in the form of methyl esters of rapeseed oil (4.80–43.27 vol. %) stabilized by the nonionic surfactant, polyethylene glycol ester of isononylphenol, and the co-surfactant, 2-ethylhexanol (total emulsifier concentration of 2.72–41.18 vol.%), we investigated their thermal stability (up to 100–110 °C). Two methods to determine the thermal stability of the microemulsions are proposed, namely, the express thermostatting method and the long-term one. Based on the results obtained, the analysis of the influence of the microemulsion component composition on the range of their thermal stability is carried out. The introduction of the bioadditive is shown to result in a narrowing of the ranges of existence of the single-phase microemulsion by 10–15 °C. The temperature effect on the dynamic viscosity of the microemulsion systems in their single-phase region is investigated. Based on the fish-cut diagrams for the microemulsions in the coordinates “emulsifier content – temperature,” the color map diagrams are plotted, which show the dependence of the dynamic viscosity of the microemulsions on the specified parameters, namely, temperature, water fraction, and vegetable additive. The assumed regions of existence of microemulsions with a dispersed phase in the form of spherical aggregates are determined in the fish-cut diagrams. Graphical Abstract

The effect of coal hydrophilic particles in water-glycerol drops on the maximum diameter of spreading along a hydrophobic solid surface is experimentally studied by analyzing the velocity of internal flows by Particle Image Velocimetry (PIV). The grinding fineness of coal particles was 45–80 μm and 120–140 μm. Their concentration was 0.06 wt.% and 1 wt.%. The impact of particle-laden drops on a solid surface occurred at Weber numbers (We) from 30 to 120. It revealed the interrelated influence of We and the concentration of coal particles on changes in the maximum absolute velocity of internal flows in a drop within the kinetic and spreading phases of the drop-wall impact. It is explored the behavior of internal convective flows in the longitudinal section of a drop parallel to the plane of the solid wall. The kinetic energy of the translational motion of coal particles in a spreading drop compensates for the energy expended by the drop on sliding friction along the wall. At We = 120, the inertia-driven spreading of the particle-laden drop is mainly determined by the dynamics of the deformable Taylor rim. An increase in We contributes to more noticeable differences in the convection velocities in spreading drops. When the drop spreading diameter rises at the maximum velocity of internal flows, a growth of the maximum spreading diameter occurs. The presence of coal particles causes a general tendency to reduce drop spreading.

This study deals with the impact of a microgel particle-laden drop of the water–agar solution onto nanofiber mats of different wettability at Weber numbers in the range of 14–502 and initial velocities in the range of 0.32–1.83 m/s. We examined the effects of inertia and the competition between the wetting and antiwetting pressures within the liquid impalement on the hydrodynamic behavior of drops in the spreading and contraction phases. Hydrophilic mat representing a full water absorption coating is manufactured by electrospinning from a mixture of polycaprolactone and polyvinylpyrrolidone; hydrophobic—from polytetrafluoroethylene. The micro- and nanoscale characteristics of nanofiber mats are analyzed by scanning electron microscopy and atomic force microscopy, respectively. A physical model of liquid flow under an impacting microgel particle-laden drop along and inside the micro- and nanostructures of nanofiber mats is proposed. Empirical expressions for the prediction of drop impact hydrodynamics are derived. By introducing the impalement factor, which is physically close to the Euler number, they take into account the difference between wetting and anti-wetting pressures in addition to inertia. Microgel particle-laden drop deposition accounting for the effect of liquid impalement inside nanofiber materials with different wettability is expected to enhance the efficiency of bioprinting polymer layers in tissue engineering.