Cremaschini S. et al.
https://pubs.acs.org/doi/10.1021/acsami.3c16573
A collaboration between research groups belonging to the Department of Physics and Astronomy of the University of Padova has experimentally observed for the first time and explained theoretically with simulations the splitting of water droplets placed on engineered surfaces with a light beam.
The work has been published in the prestigious scientific journal ACS Applied Materials & Interfaces: https://pubs.acs.org/doi/10.1021/acsami.3c16573.
Prof. Giampaolo Mistura explains: “Nowadays, the manipulation of fluids in the form of droplets on surfaces has important applications in industrial fields and medicine. The precise control of the motion of droplets can be obtained by exploiting the peculiar properties of specific materials, which are characterized by properly engineered surfaces to reduce the friction effect.
In a previously published work in 2022, we were able to manipulate water droplets exploiting the photovoltaic effect of Lithium Niobate (LiNbO3) and achieving a “liquid coating” named LIS on its surface to reduce friction. In that work, we were also able to observe the splitting of water droplets, but the preliminary results were not very reproducible”.
“Lithium Niobate”- Dr. Annamaria Zaltron says,- “is a particular material, where surface charge accumulations occur after the illumination with a proper light beam (e.g. a laser in the visible range). These charge accumulations behave like “virtual reconfigurable electrodes”, which could be exploited both for water droplet manipulation through the dielectrophoretic force and for droplet splitting. In particular, by joining my knowledge of the material and the expertise of Prof. Mistura group in wetting, we were able to obtain droplet splitting in a controlled way, and we noticed that a part of the mother droplet remains trapped in the charged region, while a second fragment moves along three preferential directions related to the crystallographic properties of LiNbO3”.
“This experimental phenomenon”- Prof. Paolo Umari concludes - “ has been explained by numerical simulations. In particular, we found that the splitting phenomenon is the synergic result of the photovoltaic effect combined with the thermal effects induced by the heating of the material with a laser beam: the photovoltaic effect determines droplet splitting, while the pyroelectric effect explains why a fragment moves along three specific directions after the splitting of the mother droplet”.
