We have recently observed an interesting
phenomenon: even under
gravity, a microliter-scaled silicone oil drop was still able to run
upward between two nonparallel plates that were approximately vertically
placed. We also saw the same phenomenon in the case of isopropyl alcohol
(IPA) drops. In this work, we developed simple models to interpret
this phenomenon, followed by experimental validation. We demonstrated
that, by changing the locations of drops or tilt and opening angles
of plates, the moving directions of silicone oil, IPA, and water drops
could be controlled. In the cases of silicone oil and IPA, we also
found that the speed of a drop had a linear relation with the square
of the drop location when the drop was far away from the corner of
two nonparallel plates and that the drop moved faster as it became
closer to this corner
