Effect of Hypergravity on the Dynamics of a Sessile Droplet on a flat solid surface

We present the experimental results on the behaviour of static and dynamic sessile drops under hypergravity (up to 19g), obtained at ESA Large Diameter Centrifuge (Noordwijk, The Netherlands). The goal of the experiment is to study the effect of the gravity on the shape of a static sessile drop and on the dynamic advancing contact angle in a growing sessile drop. Seven surfaces with micro- and nano- coatings are used, providing different contact angles (CA) and different contact angle hysteresis (CAH). Distilled deionized water is used as the working liquid. The main variable parameters are: gravity (1 - 19g); drop volume (1µl - 1ml); liquid flow rate (0.0625 - 64 ml/min); CA (30 - 130º). The drop shape is visualized from the side with the help of the Shadow Technique with a resolution of 10 µm/pixel. The results obtained during the experimental campaign show that for water sessile drops on hydrophilic surface, the advancing contact angle in the increased gravity environment is larger than that of the advancing CA in 1g (for example 10º for a PMMA-coated surface) for the same three-phase contact line advancing rates, while for water sessile drops on hydrophobic Teflon-coated surface (120° on-ground) the advancing contact angle decreases by 4°.