The Salvinia Paradox: Superhydrophobic Surfaces with Hydrophilic Pins for Air Retention Under Water

Abstract

A novel mechanism for long‐term air retention under water is found in the sophisticated surface design of the water fern Salvinia. Its floating leaves are evenly covered with complex hydrophobic hairs retaining a layer of air when submerged under water. Surprisingly the terminal cells of the hairs are hydrophilic. These hydrophilic patches stabilize the air layer by pinning the air–water interface. This “Salvinia Effect” provides an innovative concept to develop biomimetic surfaces with long‐term air‐retention capabilities for under water applications. © Martin Oeggerli / www.Micronaut.ch, original SEM scan by Prof. Barthlott.

Superwettability of Gas Bubbles and Its Application: From Bioinspiration to Advanced Materials

“…Reproduced with permission. [30] Copyright 2010, Wiley-VCH. e) The steady pinning effect of air bubbles (i.e., aerophobicity and high adhesion property) on a rose petal interface with a combination of micropapillae and nanofolds.…”

“…The patches (with high interface energy) at the tips of the hairs presumably stabilize the air film against pressure fluctuations (Figure 1d). [30] The steady pinning effect of air bubbles with a final spherical shape is observed on a rose petal, i.e., aerophobicity. This novel phenomenon is attributed to the micro/nanohierarchical rough structures (microscaled papillae and nanofolds).…”

Unraveling the Salvinia Paradox: Design Principles for Submerged Superhydrophobicity

“…[ 1 ] Moving toward submerged applications requires a new inspiration: a promising candidate is the Salvinia molesta (Figure 1 a), because of its superior gas trapping capabilities. [ 6,[18][19][20] The gas entrapped within surface asperities can be either air or the vapor phase coexisting with the liquid: albeit the partial pressure of the other gases stabilizes the Cassie state, their presence is not a requirement for (meta)stable superhydrophobicity [ 21 ] (see the Supporting Information for additional details on the role of dissolved gases). The entrapped gas may be lost through different mechanisms, analyzed in detail below, determining the failure of superhydrophobicity:…”

The superhydrophobicity of polymer surfaces: Recent developments

“…In a type of water weed hydrophilic patches at the tips of the REVIEW structures add to this effect. 92 The flexibility of the hairs absorbs any pulses of pressure preventing loss of gas from the features of the surface, particularly when the tops of the hairs are hydrophilic. 86 This reduces the tendency for the gas film to lose volume and eventually collapse.…”