Dry under water: air retaining properties of large-scale elastomer foils covered with mushroom-shaped surface microstructures

Matthias Mail; Stefan Walheim; Thomas Schimmel; Wilhelm Barthlott; Stanislav N Gorb; Lars Heepe

doi:10.3762/bjnano.13.113

Dry under water: air retaining properties of large-scale elastomer foils covered with mushroom-shaped surface microstructures

Beilstein J Nanotechnol. 2022 Nov 21:13:1370-1379. doi: 10.3762/bjnano.13.113. eCollection 2022.

Authors

Matthias Mail^{1

2}, Stefan Walheim², Thomas Schimmel², Wilhelm Barthlott¹, Stanislav N Gorb³, Lars Heepe^{3

4}

Affiliations

¹ Nees Institute for Biodiversity of Plants, University of Bonn, Venusbergweg 22, D-53115 Bonn, Germany.
² Institute of Nanotechnology (INT) and Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.
³ Department of Functional Morphology and Biomechanics, Institute of Zoology, Christian-Albrechts-University of Kiel, Am Botanischen Garten 1-9, D-24118 Kiel, Germany.
⁴ Gottlieb Binder GmbH & Co KG, Bahnhofstr. 19, D-71088 Holzgerlingen, Germany.

Abstract

Superhydrophobic surfaces are well known for most different functions in plants, animals, and thus for biomimetic technical applications. Beside the Lotus Effect, one of their features with great technical, economic and ecologic potential is the Salvinia Effect, the capability to keep a stable air layer when submerged under water. Such air layers are of great importance, e.g., for drag reduction (passive air lubrication), antifouling, sensor applications or oil-water separation. Some biological models, e.g., the floating fern Salvinia or the backswimmer Notonecta, show long term stable air retention even under hydrodynamic conditions. Therefore, they are ideal models for the development of technical biomimetic air retaining surfaces. Up to now, several prototypes of such surfaces have been developed, but none provides both, stable air retention and cost effective large scale production. Meanwhile, a novel biomimetic surface is commercially available and produced on a large scale: an adhesive elastomeric film with mushroom-shaped surface microstructures that mimic the adhesion system of animals. In this study, we show that these films, which have been initially developed for a different purpose, due to their specific geometry at the microscale, are capable of stable air retention under water. We present first results concerning the capabilities of mushroom-shaped surface microstructures and show that this elastomer foil is able to stabilize a permanent air layer under water for more than two weeks. Further, the stability of the air layer under pressure was investigated and these results are compared with the predicted theoretical values for air retention of microstructured surfaces. Here, we could show that they fit to the theoretical predictions and that the biomimetic elastomer foil is a promising base for the development of an economically and efficient biomimetic air retaining surface for a broad range of technical applications.

Keywords: Salvinia effect; adhesive tape; air layer; air retention; bionics; fouling; gecko tape; mushroom structures; passive air lubrication; superhydrophobicity.

Grants and funding

Funding of the work presented in this paper was provided by the Federal Ministry for Education (BMBF) in the joint research project ARES (Air REtaining Surfaces, grant 03V0752) in the VIP program. Furhter, funding was prvided by the Deutsche Forschungsgemeinschaft (DFG) within the Graduiertenkolleg ‘Bionik - Interaktion über Grenzflächen zur Außenwelt’ (GRK1572) and within the project ‘Grundprinzipien der Gasretention an Oberflächen unter Wasser: Ein materialorientierter Ansatz auf Basis von Kohlenstoffnanoröhren Architekturen‘ (MA8804/2-1).