Controlled droplet manipulation by light has tremendous technological potential. We report here a method based on photothermally induced pyroelectric effects that enables manipulation and maneuvering of a water droplet on a superhydrophobic surface fabricated on lithium tantalite (LiTaO3). In particular, we demonstrate that the pyroelectric charge distribution has an essential role in this process. Evenly distributed charges promote a rapid hydrophobic to hydrophilic transition featuring a very large water contact angle (WCA) change of ∼76.5° in air. This process becomes fully reversible in silicone oil. In contrast, the localized charge distribution induced by guided laser illumination leads to very different and versatile functionalities, including droplet shape control and motion manipulation. The influence of a saline solution is also investigated and compared to the deionized water droplet. The focusing effect of the water droplet, a phenomenon that widely exists in nature, is particularly of interest. Simple tuning of the laser incident angle results in droplet deformation, jetting, splitting, and guided motion. Potential applications, such as droplet pinning and transfer, are presented. This approach offers a wide range of versatile functionalities and ready controllability, including contactless, electrodeless, and precise spatial and fast temporal control, with tremendous potential for applications requiring remote droplet control.
Keywords: droplet deformation; droplet focusing effect; droplet lift-off; droplet manipulation; pyroelectric effect; wettability transition.