Kerberos: A three camera headed centrifugal/tilting device for studying wetting/dewetting under the influence of controlled body forces

- Description of a new device for studying droplet spreading and sliding.
- Simultaneous droplet rotation and tilting allow fine applied force control.
- A two-dimensional linearized equilibrium model supports the experiment design.

Despite the significant effort spent over the years to study wetting and dewetting phenomena of droplets on solid substrates under applied forces, there are still many unresolved issues. To name a few, a concise theory for the two dimensional contact line is missing. Also, a controversy has recently arisen for the effect of droplet size on the tangential force required for the inception of sliding. It is clear that to resolve such issues and to better understand the underlying processes a new generation of experimental techniques and results are needed. In this spirit, a novel device, Kerberos, is proposed and constructed here. Kerberos offers two major innovative features compared to prior techniques: (a) it allows simultaneous rotation and tilting of the droplet supporting plate (these mechanisms have been employed separately in the past) and (b) three Wi-Fi cameras (viewing the droplet from X-Y-Z directions) follow the rotation/tilting motion. The above features permit on one hand the independent control of normal and tangential forces applied to the droplet and, on the other, allow real time 3D impressions of the droplet shape. Indicative results manifest the wealth of new experimental data accessible by Kerberos which were out of reach by other techniques. The theoretical background of droplet behavior in the new device is discussed, making assumptions that lead to closed form solutions. Such a model is useful for the design of experiments with the new device.

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