Splashing of a Newtonian drop impacted onto a solid substrate coated by a thin soft layer

Abstract

For many industrial applications it is important to control the outcome of drop impact. One of the means of passive control for such processes is in the application of smart, deformable, rheologically complex surfaces. In this experimental work an impact of a viscous Newtonian drop onto a substrate coated by a thin visco-elastic layer is investigated. The elastic and viscous properties of the layer are varied in a wide range. It is shown that the properties of the substrate only slightly influence the spreading of the drop after collision, but significantly influence the rate of the receding.It has been shown that the deposition/splashing threshold for smaller Reynolds numbers, Re, is determined by a critical Weber number, We. This result is in agreement with the existing recent theories for splashing threshold which account for the aerodynamic affects in the spreading wedge near the contact line. However, for higher Reynolds numbers the threshold is described well by a new splashing parameter L = WeRe−2/5, obtained from the balance of the inertial and surface tension forces in the spreading lamella. The critical L number is higher on the deformable surfaces than on dry solid substrates, which is caused by dumping of some part of the kinetic energy of impact by the deformable layer. It is interesting that the critical L number does not depend on the rheological properties of the deformable layer.