Characteristics of drops on flat microplating surfaces from controlled upward longitudinal impact

Abstract

Sessile drops, based on water–glycerol mixtures at 40μL, deposited on solid substrates were studied as they were accelerated upwards and then stopped suddenly to create an upward longitudinal impact effect. By varying the initial start positions of the platform in the setup, controlled impact momentums of up to 4.31×10−3 Ns could be attained. Three categories of drop behavior, labeled I to III, were uncovered. On the non-scribed substrate types I and II drop behavior were found, whereas all types of demeanor were exhibited by the scribed surface. On the scribed surface, the contact angle is able to recede more (by 20̊) than on the non-scribed surface (by 15̊). This is primarily due to the strong contact line pinning offered by the parapet and steep scarp formed around the groove. Since the liquid body is able to attain a lower receding contact angle on the scribed surface, this will allow higher adhesion effect of its lower portion even as the upper portion seeks to separate. This manifests in a greater propensity for the liquid body to neck and thus for separation to occur. Numerical simulations reveal the tendency of the separated drops to develop circulations that change direction as they coalesce. There is therefore potential for increased mixing using this mode.