Coalescence-induced droplet jumping on superhydrophobic surfaces have recently received significant attention owing to their potential in a variety of applications. Previous studies demonstrated that the self-jumping process is inherently inefficient, with an energy conversion efficiency η ≤ 6% and dimensionless jumping velocity V j* ≤ 0.23. To realize a quick removal of droplets, increasing effort has been devoted to breaking the jumping velocity limit and inducing droplets sweeping. In this work, we used superhydrophobic surfaces with an asymmetric V-groove to experimentally achieve an enhanced coalescence-induced jumping velocity V j* ≈ 0.61, i.e., more than 700% increase in energy conversion efficiency compared with droplets jumping on flat superhydrophobic surfaces, which is the highest efficiency reported thus far. Moreover, the enhanced jumping direction shows a deviation as high as 60° from the substrate normal. The induced in-plane motion is conducive to remove a considerable number of droplets along the sweeping path and significantly increase the speed of droplet removal. Numerical simulation indicated that the jumping enhancement is a joint effect resulting from the impact of the liquid bridge on the corner of the V-groove and the suppression of droplet expansion by the sidewall of the V-groove. The transient variation of the droplet velocity and the driving force of the coalescing droplets on a surface with and without the asymmetric V-groove were revealed and discussed. Furthermore, effects of groove angle, droplet pair positions, and size mismatches on the jumping velocity and direction have been studied. The novel mechanism of simultaneously increasing the coalescence-induced droplet jumping velocity and changing the jumping direction can be further studied to enhance the efficiency of various applications.

When two or more droplets coalesce on a superhydrophobic surface, the merged droplet can jump spontaneously from the surface without requiring any external energy. This phenomenon is defined as coalescence-induced droplet jumping and has received significant attention due to its potential applications in a variety of self-cleaning, anti-icing, antifrosting, and condensation heat-transfer enhancement uses. This article reviews the research and applications of coalescence-induced droplet jumping behavior in recent years, including the influence of droplet parameters on coalescence-induced droplet jumping, such as the droplet size, number, and initial velocity, to name a few. The main structure types and influence mechanism of the superhydrophobic substrates for coalescence-induced droplet jumping are described, and the potential application areas of coalescence-induced droplet jumping are summarized and forecasted.

Coalescence-induced droplet jumping has received considerable attention owing to its potential to enhance performance in various applications. However, the energy conversion efficiency of droplet coalescence jumping is very low and the jumping direction is uncontrollable, which vastly limits the application of droplet coalescence jumping. In this work, we used superhydrophobic surfaces with a U-groove to experimentally achieve a high dimensionless jumping velocity V j * ≈ 0.70, with an energy conversion efficiency η ≈ 43%, about a 900% increase in energy conversion efficiency compared to droplet coalescence jumping on flat superhydrophobic surfaces. Numerical simulation and experimental data indicated that a higher jumping velocity arises from the redirection of in-plane velocity vectors to out-of-plane velocity vectors, which is a joint effect resulting from the redirection of velocity vectors in the coalescence direction and the redirection of velocity vectors of the liquid bridge by limiting maximum deformation of the liquid bridge. Furthermore, the jumping direction of merged droplets could be easily controlled ranging from 17 to 90°by adjusting the opening direction of the U-groove, with a jumping velocity V j * ≥ 0.70. When the opening direction is 60°, the jumping direction shows a deviation as low as 17°from the horizontal surface with a jumping velocity V j * ≈ 0.73 and corresponding energy conversion efficiency η ≈ 46%. This work not only improves jumping velocity and energy conversion efficiency but also demonstrates the effect of the U-groove on coalescence dynamics and demonstrates a method to further control the droplet jumping direction for enhanced performance in applications.

The retinoblastoma gene product (RB protein) plays a key role in the progression of the cell cycle from G1 to S phase in normal and neoplastic cells. The activity of RB is regulated by phosphorylation and dephosphorylation with cell-cycle-dependent protein kinases. We investigated the effect of the protein kinase inhibitors, staurosporine and 7-hydroxy-staurosporine (UCN-01), on RB protein expression of N417 small cell lung cancer cells (absent RB), H209 small cell lung cancer cells (mutant RB), and Ma-31 non-small cell lung cancer cells (wild-type RB), using immunologic blotting. Staurosporine and UCN-01 each suppressed the growth of N417, H209 and Ma-31 cells in a dose-dependent manner in MTT assay. IC50 values of staurosporine for N417, H209 and Ma-31 cells were 54, 29 and 602 nM, respectively. IC50 values of UCN-01 for N417, H209 and Ma-31 cells were 737,181 and 2,197 nM, respectively. Exposure to staurosporine and UCN-01 for 72 h each suppressed the level of expression and altered the ratio of phosphorylated/dephosphorylated RB protein (ppRB/pRB) of Ma-31 cells. Conversely, these agents increased the expression level of RB protein at concentrations less than IC50, and did not change phosphorylation status of mutant RB protein of H209 cells at the concentrations studied. A time course study demonstrated that exposure to the IC50 concentration of staurosporine for 48–72 h increased the ratio of ppRB/ pRB of Ma-31 cells, while exposure to the IC50 concentration of UCN-01 decreased that ratio. UCN-01 increased % cells in G2+M phase and decreased % cells in S phase, while staurosporine increased % cells in G1 phase and decreased % cells in G2+M phase. UCN-01 did not induce apoptosis (DNA content < 2N) of Ma-31 cells, but staurosporine induced it. These findings suggest that the differing effects of staurosporine and UCN-01 on RB protein expression and cell cycle phases of lung cancer cells may explain their differing in vivo antitumor effect of staurosporine and UCN-01 despite their similar chemical structures.

Calibration of the stiffness of atomic force microscope (AFM) cantilevers is critical for industry and academic research. The multi-position calibration method for AFM cantilevers based on vibration is investigated. The position providing minimum uncertainty is deduced. The validity of the multi-position approach is shown via theoretical and experimental means. We applied it to the recently developed vibration method using an AFM cantilever with a normal stiffness of 0.1 N m−1. The standard deviation of the measured stiffness is 0.002 N m−1 with a mean value of 0.189 N m−1 and the relative combined uncertainty is approximately 7%, which is better than the approach using the single position at the tip of the cantilever.