Characterization of drops with non circular footprints

P. D. RAVAZZOLI; J. A. DIEZ; A. G. GONZÁLEZ

Tandil

Conferencia; FLUIDOS 2014 - XIII Meeting on Recent Advances in Physics of Fluids and its Applications; 2014

We study experimental and theoretically the shapes and contact angles of sessile drops (of some microliters) of polydimethilsiloxane (PDMS) with non circular footprint on glass substrates under partial wetting conditions. The drops are generated as consequence of the breakup of a PDMS filament, which is unstable and breaks up spontaneously on the substrate. Thus, the drop formation process involves both wetting and dewetting dynamics. By means of a shadowgraph technique we obtain the shape of the footprint as well as of the thickness profiles along both the longitudinal and transversal directions of the original filament. This technique also allows us to measure the contact angles in both directions. On the other hand, by using an additional refractive technique we measure the azimuthal distribution of contact angles along the periphery of the footprint. These experimental results are compared with an analytical solution obtained within the framework of the lubrication approximation, which gives the thickness of the drop at all points of the footprint. The comparison shows an excellent agreement for the thickness profiles, the shape of the footprint, and the contact angles in the longitudinal direction, while the contact angles in the transverse direction are a bit smaller than the measured ones.