On the maximum spreading of liquid droplets impacting on soft surfaces

With the method of the high-speed camera and image recognition, the spreading procedure of the liquid droplet impacting on the surface of Polydimethylsiloxane (PDMS) with different thickness and different modulus is obtained. The variation curves of between the spread factor with time are also plotted. Compared with the total energy of the system, the viscous energy dissipation caused by the compression deformation of the PDMS substrate is too small to affect the spreading procedure. In the case of lower impact velocity, the viscoelastic energy dissipation caused by the wetting ridge, which is formed on the surface of PDMS, is the major component of the total energy dissipation of the system. It increases with the decrease of the modulus of flexible materials. For this reason, the spread factor shows a decrease trend with the decrement of the modulus of PDMS. When the impact velocity increases, the viscous energy dissipation becomes the major component of the total energy dissipation and the spread factor remains unchanged with the change of the modulus of the flexible material.