Bouncing bubbles do not show water slip on smooth hydrophobic surfaces.

Hypothesis: The presence of hydrodynamic slip of water on smooth hydrophobic surfaces has been debated intensely over the last decades. In recent experiments, the stronger bounce of free-rising bubbles from smooth hydrophobic surfaces compared to smooth hydrophilic surfaces was interpreted as evidence for a significant water slip on smooth hydrophobic surfaces.

Experiments: To examine the possible water-slip effect, we conduct well-controlled experiments comparing the bouncing dynamics of millimeter-sized free-rising bubbles from smooth hydrophobic and hydrophilic surfaces.

Why Bubbles Coalesce Faster than Droplets: The Effects of Interface Mobility and Surface Charge.

Air bubbles in pure water appear to coalesce much faster compared to oil emulsion droplets at the same water solution conditions. The main factors explaining this difference in coalescence times could be interface mobility and/or pH-dependent surface charge at the water interface. To quantify the relative importance of these effects, we use high-speed imaging to monitor the coalescence of free-rising air bubbles with the water-air interface as well as free-falling fluorocarbon-oil emulsion droplets with a water-oil interface.

Flexible solar cells based on foldable silicon wafers with blunted edges.

Flexible solar cells have a lot of market potential for application in photovoltaics integrated into buildings and wearable electronics because they are lightweight, shockproof and self-powered. Silicon solar cells have been successfully used in large power plants. However, despite the efforts made for more than 50 years, there has been no notable progress in the development of flexible silicon solar cells because of their rigidity.