Unlike the standard setup in which we use syringe to create and drop the liquid onto the surface, this unique instrument can be used to create two independent droplets inside a liquid bath. The droplet surface can be visualized from bottom and side-ways using a unique camera setup.
In the pendant drop deposition technique, a needle containing the drop at its end is brought near the surface. On touching the surface the drop spreads and attains equilibrium and in the process the drop gets detached from the needle spontaneously.
This mechanism inevitably requires the condition that the drop-substrate surface energy is larger than the drop needle surface energy. Hence for surfaces, for which the corresponding drop-substrate surface energy is much smaller than the drop-needle surface energy, such simple steps, as discussed above, do not occur.
Using our instrument, one can generate a drop at the tip of a needle inserted inside the liquid bath, where the low energy substrate is present. Instead of bringing the drop closer to the substrate as we do our standard contact angle meter, we take it away from the substrate so that the drop needle entity hits the liquid–fluid interface. Here this fluid can be air, or some other liquid whose film has been deliberately created on the liquid surface. The moment the drop-needle combination hits the liquid–fluid interface, the drop and the needle are subjected to different surface tension forces, thereby allowing them to get detached from each other. Consequently, the needle goes out of the liquid bath, whereas the drop remains at the interface.