The influence of key factors on the movement of a crystal and a non-crystalline particle on a free droplet surface

Experimental studies on non-isothermal crystallization on the free surface of a drop of NaCl salt solution have been carried out. The article compares the behavior of the motion of aluminum particle and NaCl crystal on the surface of a drop of an aqueous salt solution. In addition, there is a comparison of the character of the crystal motion at room temperature of 21 °C and at high heat flux when the temperature on the droplet surface is 85 °C. For the first time it is shown that the crystal motion for all these cases is qualitatively and quantitatively different and is determined by the simultaneous influence of several key factors: (1) the surface tension gradient to the left and right of the particle (crystal); (2) the curvature radius and (3) the Marangoni force. Depending on the size of each of these factors, the motion can be directed both to the center of the drop and to its edge (to the contact line). Previously, it was believed that a particle can only move to the center of the drop.