The surface microstructures on ray florets of 62 species were characterized and compared with modern phylogenetic data of species affiliation in Asteraceae to determine sculptural patterns and their occurrence in the tribes of Asteraceae. Their wettability was studied to identify structural-induced droplet adhesion, which can be used for the development of artificial surfaces for water harvesting and passive surface water transport. The wettability was characterized by contact angle (CA) and tilt angle measurements, performed on fresh ray florets and their epoxy resin replica. The CAs on ray florets varied between 104° and 156°, but water droplets did not roll off when surface was tilted at 90°. Elongated cell structures and cuticle folding orientated in the same direction as the cell elongation caused capillary forces, leading to anisotropic wetting, with extension of water droplets along the length axis of epidermis cells. The strongest elongation of the droplets was also supported by a parallel, cell-overlapping cuticle striation. In artificial surfaces made of epoxy replica of ray florets, this effect was enhanced. The distribution of the identified four structural types exhibits a strong phylogenetic signal and allows the inference of an evolutionary trend in the modification of floret epidermal cells.
In this contribution, we discuss wrinkling as a process resulting in well‐defined periodic micron‐sized structures, as known from the interface of several plant cells. We show possible pathways to transfer this principle to artificial materials such as epoxy resins or polymers. While topographical structuring of surfaces by wrinkling is meanwhile well established for elastomers like poly (dimethyl siloxane), so far the step towards other classes of materials has not been taken. This puts several limitations to potential applications of artificial wrinkled structures, as elastomers show poor dimensional stability, low optical quality, and tend to swell in organic solvents. As well, artificial structures formed by wrinkling are not tension‐free on the microscopic level, which makes them metastable. Residual mechanical tensions can affect dimensional stability on long timescales. We introduce two processes, micro thermoforming and molding, as means to overcome these restrictions and to pattern non‐elastomeric materials by using wrinkled elastomers as templates. The two approaches allow the formation of negative and positive replicas and allow the transfer of sub‐micron features with high fidelity.magnified image
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