Fig. 4
From: Biomimetic coating-free surfaces for long-term entrapment of air under wetting liquids
Confocal microscopy images of silica surfaces with reentrant and doubly reentrant cavities immersed in water. a Mechanisms underlying the loss of air trapped in a hexagonal DRC on immersion in water and observed via confocal microscopy. The snapshots on top are the cross-sectional views of the top-views below at different times along the white dotted line. The light blue color in the images corresponds to the air-water interface on top that has been rendered partially transparent, while the dark blue color corresponds to the capillary condensed water at the bottom of the cavity. On immersion, the intruding water meniscus was stabilized at the doubly reentrant and reentrant edges. Over next 5–90 min, the capillary condensation of water inside the cavities led to the formation of small droplets that merged over time to form thick films. This volume of water displaced the trapped air causing upward bulging, which initiated the diffusion of trapped air in the water even before tfailing. Eventually the condensed water touched the primary meniscus on top and the cavity was invaded by water. b–e Computer-enhanced isometric reconstructions (center) along with cross-sectional views along the dotted lines (on either sides of the central image) of representative confocal images of water menisci after immersing silica surfaces with DRCs and RCs of circular and square shapes under a 5 mm high column of water. We observed that circular DRCs and RCs exhibited higher tfailing than square ones and DRCs outperformed RCs. (Scale bars: 200 µm)
