DaveO Posted May 20, 2019 Share Posted May 20, 2019 I was searching for UV patterns and came across this gem which pins down something that I think Birna and Andrea have long suspected: Open access Ultraviolet patterns of flowers revealed in polymer replica - caused by surface architecturehttps://www.beilstein-journals.org/bjnano/articles/10/45 ConclusionIn this study we provided experimental data relating the structuraldifference of the UV-reflecting and UV-absorbing areaswithin flower petals. Furthermore, we provided the first quantitativemeasurements of these structural differences and their influenceon the reflectivity and the scattering properties of lighton the petal surface. We showed that the structures in theUV-absorbing area are higher in all three model plants and thatthey possess smaller tip angles than in the UV-reflecting areas.Using petal replicas, we separated this surface architecture fromthe cell pigments and thereby eliminated their influence on theUV-patterns. This procedure provides the first proof that theUV-patterns in flowers are not just pigment-based, but alsostructurally determined. Through this, differences in UV-reflectivitybetween the absorbing and reflecting areas of almost 50%have been found, which is new for the UV-regime. Theseresults are important from a biological point of view as they arethe first debatable measurements of the structural influence onUV-patterns and they show strong differences even within justthe three model plants. From a technical point of view, theseresults are promising and important for different types of applicationsgiven that the optical properties of surfaces arebecoming more relevant, for example, for hierarchically structuredsolar panels, biomimetic antireflective or absorbing coatings,lenses and many more. Link to comment
Andy Perrin Posted May 20, 2019 Share Posted May 20, 2019 Oh, that is a nifty experiment. It looks pretty definitive. So the UV patterns (at least on those flowers) are structural coloring. That explains also why they vanish in IR — the spacing is wrong to get absorption in IR. Link to comment
colinbm Posted May 23, 2019 Share Posted May 23, 2019 Thanks DaveThat is some amazing research.CheersCol Link to comment
DaveO Posted May 23, 2019 Author Share Posted May 23, 2019 Thanks Col,This has been one of those niggling questions that we have come up against for some time. I think it isn't the whole answer. If we consider a typical anti-reflective coating as used on lenses, they typically use destructive interference with a layer a quarter of a wavelength thick. So for 360 nm UV we have a thickness of about 90 nm, which is about a thousand times smaller than the structures shown in the SEMs in the paper with a scale of 20 micro-metres. So the structures which lead to the UV-absorbing effect may be hidden within the details of the hairs or fibres seen on the sides of the conical cells in the SEM photos. A similar principle applies in the acoustic field where anechoic wedges work best around quarter wave heights. It would be nice to see SEMs in the nm range.Dave (Probably wrong as usual) Link to comment
Andy Perrin Posted May 23, 2019 Share Posted May 23, 2019 So for 360 nm UV we have a thickness of about 90 nm, which is about a thousand times smaller than the structures shown in the SEMs in the paper with a scale of 20 micro-metres.Yeah, they need to be looking on a different scale. Even with multilayer coatings, usually each layer is a quarter wavelength, where "wavelength" in this case is the wavelength INSIDE the material, which is different from the 360nm value in air by a factor of the refractive index. (i.e. if n=1.5, wavelength is 360nm/1.5=240nm inside the material). Link to comment
Guest Posted May 25, 2019 Share Posted May 25, 2019 Does anyone have any info on the transmission spectrums for the IR neutralization and UV transmission filters they used in the study (NG, and SP2 400UV,respectively)? Link to comment
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