Thermally assisted mobility of nanodroplets on surfaces with weak defects

Imaging electrochemically regulated water-air nanointerfaces with single-molecule fluorescence

Water-air nanointerfaces are essential components of multiphase electrochemical processes in various energy-related applications, including water electrolysis, hydrogen fuel cells, and CO2 electrochemical reduction. Deep insights into the critical properties of the interfaces are much sought after but very challenging to obtain due to their highly dynamic, transparent, and nanoscopic nature. A new approach has been proposed for constructing stable water-air nanointerfaces using FIB-fabricated Janus nanopore electrodes. The curvature of the nanointerfaces can be controlled electrochemically, ranging from positive (nanodroplets) to negative (nanoconcaves/nanobubbles) ones. The morphologies of different nanointerfaces were fully characterized with AFM. Single-molecule collision events of charged dye molecules, recorded with fluorescence imaging, were used to probe the intrinsic properties of the nanointerfaces. A unique phenomenon of charged dye rejection was discovered for isoelectric nanointerfaces. The role of surface curvature in the collision frequency was also elucidated. We believe that using this platform could be highly beneficial for deepening our understanding of the interfaces, thus guiding the rational design of various energy-related systems.

Liquid droplet impact on a sonically excited thin membrane

The characteristics of droplet impact on hydrophobic surfaces can be altered by introducing surface oscillations. The contact duration, spreading, retraction, and rebounding behaviors of the impacting water droplet are examined at various sonic excitation frequencies of the hydrophobic membrane. Membrane oscillation and droplet behavior are analyzed by utilizing a high-speed camera. The restitution coefficient and membrane dynamics are formulated and the findings are compared with those of the experiments. It is found that the mode of membrane oscillation changes as the sonic excitation frequency is changed. The droplet spreading and retraction rates reduce while the rebound height and restitution coefficient increase at a sonic excitation frequency of 75 Hz. However, further increase of the excitation frequency results in reduced rebound height because of the increased energy dissipation on the impacted surface. The droplet contact (transition time) duration reduces as the excitation frequency increases. Increasing droplet Weber number enhances the droplet contact period on the membrane, which becomes more apparent at low frequencies of sonic excitation.