Experimental Investigation Of Droplet Impact On Pillar-arrayed PDMS Surfaces

When a droplet impacts on a solid surface,it usually appears the phenomena of deposition,rebound,partial rebound and so on.The study of the mechanical mechanism of the droplet impacts on the wall has practical significance in industrial and agricultural applications,such as inkjet printing,spray cooling,material waterproof,pesticide spraying,etc.During years of research,the relevant scientific researchers had gained a certain understanding of the impact mechanism on the surface of hard materials.In order to further improve the acknowledge of droplets impact on solid surface and expand the application of flexible materials,this paper carried out the experiments of droplets impact on the polydimethylsiloxane(PDMS)surface with micro-pillar array.The main research results were as follows:(1)The behavior of spherical pure water and sodium dodecyl sulfate(SDS)droplets impact on the PDMS surface of the micro-pillar array with solid fractions of0.50,0.20,and 0.06 were studied.The results showed that the droplets would rebound completely within a certain Weber number interval,and the upper and lower limits of the intervals were affected by the substrate morphology and the surface tension of droplets.(2)According to the analysis of the rebound interval,it was found that when the Weber number was larger than the upper limit of the interval,the droplets had a transition from Cassie-Baxter wetting state to Wenzel wetting state,and a theoretical model to calculate the upper limit of droplets impact velocity was proposed.(3)The contact time of droplets rebound decreased with the decrease of solid fraction.When the Weber number was large,the pinning and contact time of SDS droplets were generally longer than that of pure water droplets.Meanwhile,with the increase of solid fraction,the contact time of SDS droplets changed more obviously with the Weber number.