The Study of Droplet Impact Behavior on Flat Surface with Different Surface Properties

The impact behavior of a liquid droplet on solid surface is a complex phenomenon and yet is a basic component of various industrial processes particularly in the pharmaceutical industry. In this industry, film coating technique is used in tablet coating, in which coating uniformity is important especially if the coating is for functional purposes. Coating uniformity on a tablet could be affected by several factors, one of which is the impingements of droplets on its surface. In this work, the maximum spreading diameter and the initial impact behavior of a single droplet on pharmaceutical tablet surfaces and metal surfaces having different surface properties are investigated. A Charged-Coupled-Device (CCD) high-speed camera with framing rate of 2,000, attached to a 10X microscope, was used to capture the phenomena. The results show that the initial impact behavior of a droplet is not affected by the porosity of a surface. The results on the pharmaceutical tablets, stainless steel and etched silicon surfaces show that the rougher the surface the lower the spreading factor. The droplets on all surfaces demonstrate that a droplet that produces higher spreading factor gives a lower bouncing factor.