Springtails (Collembola) are wingless arthropods adapted to cutaneous respiration in temporarily rain-flooded habitats. They immediately form a plastron, protecting them against suffocation upon immersion into water and even low-surface-tension liquids such as alkanes. Recent experimental studies revealed a high-pressure resistance of such plastrons against collapse. In this work, skin sections of Orthonychiurus stachianus are studied by transmission electron microscopy. The micrographs reveal cavity side-wall profiles with characteristic overhangs. These were fitted by polynomials to allow access for analytical and numerical calculations of the breakthrough pressure, that is, the barrier against plastron collapse. Furthermore, model profiles with well-defined geometries were used to set the obtained results into context and to develop a general design principle for the most robust surface structures. Our results indicate the decisive role of the sectional profile of overhanging structures to form a robust heterogeneous wetting state for low-surface-tension liquids that enables the omniphobicity. Furthermore, the design principles of mushroom and serif T structures pave the way for omniphobic surfaces with a high-pressure resistance irrespective of solid surface chemistry.

Springtail skin morphology is translated into robust omniphobic polymer membranes by reverse imprint lithography. The combination of overhanging cross-sections and their arrangement in a self-supporting comblike pattern are crucial for mechanically stable coatings that can be even applied to curved surfaces.

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groups. However, the methanol permeability value did not differ greatly. This is because CLPE or PI substrates have a mechanically strong matrix, as shown in Figures 2a,b, and the swelling of the PATBS was effectively suppressed. The methanol permeability through the pore-filling membranes showed lower values compared to the Nafion 117 or Nafion 112 membrane. The substrate matrix effectively suppressed the membrane swelling, and resulted in a lower methanol permeation value.If we employed a single polyelectrolyte as the filling polymer with different substrate and pore-filling ratios, then the relationship between the proton conductivity and the inverse of the methanol permeability would lie on a single line. Assuming that this line is straight, then the order of performance was: PAA < PAAVS < PATBS as shown in Figure 4, and this order corresponds to the sulfonic acid content. Thus, we can obtain better performance membranes by combining a filling polymer having a high strong acid group content with a mechanically strong matrix to suppress the swelling. At the same time, it is possible to achieve a balance in the methanol permeability and proton conductivity that is suitable for realizing a DMFC application by controlling the substrate strength and the filling ratio.In summary, the CLPE and PI substrates can suppress membrane swelling, and the change in membrane area between the dry and swollen states is negligible for pore-filling membranes containing those substrates. An ATBS filling polymer having a high sulfonic acid content shows a high proton conductivity of 0.15 S cm ±1 at 25 C. The relationship between the proton conductivity and the methanol permeability of a single pore-filling polymer can be controlled by changing the substrate strength and pore-filling ratio. This enables us to control the membrane performance for a given fuel cell application. ExperimentalMembrane Preparation: Porous cross-linked high-density polyethylene (CLPE), polyimide (PI), and PTFE were employed as substrates. The CLPE substrates were supplied by the Nitto Denko Co Ltd., and the PI substrates were supplied by the Ube Industry Co. Ltd. The CLPE and PI substrates had thicknesses of 27 and 30 lm, pore diameters of 100 and 300 nm, and porosities of 47 % and 40 %, respectively. The PTFE substrates were supplied by the Nitto Denko Co. Ltd., and had a thickness of 83 lm, a pore diameter of 50 nm, and a porosity of 52 %. The acrylamide-tert-butyl sulfonate sodium salt (ATBS-Na) used was supplied by the Toa Gosei Co Ltd. The ATBS-Na and the methylenebis-acrylamide cross-linker were used as received. In addition, a water-soluble azo initiator, 2,2¢-azobis(2-methylpropionamidine) dihydrochloride (V-50), was also employed in the reaction. The monomer impregnation polymerization method was used to prepare the pore-filling electrolyte membrane. The details of this process are described elsewhere [17]. After the reaction, the sample was placed in an oven and kept at 50 C for 1 h to complete the polymerization reaction. The prepared membrane w...

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