Fish and flowers inspire diving goggle material

says an article in Chemistry World. 

First, the fish.  Fish repel oil by trapping water within their scales to create a self-cleaning, oil-repellent coat.

And in the other corner, this little flower, Diphylleia grayi, – also known as the skeleton flower – which has the property that when rained on, its petals turn transparent, becoming white again on drying out.

(Source of picture.)   It comes from mountainous regions in Japan and north China.

Chen Feng (surname first!) of the Xi’an Jiaotong University (yes, the city of the terracotta warriors), has used this property of the flowers (left, wet, right, dry) to create a fish-scale like surface.



They took glass and treated it with femtosecond laser blasts (in this case a pulse time of 0•000,000,000,000,050 seconds, see the five clusters, “femto‑” being derived from the Norwegian word for “five”) to produce a surface with texture that acts like a fish scale, being microporous on the nanoscale after nanoregions of glass have been blasted away.  (That’s called bioinspired fabrication).  This produces a surface which is very non-reflective underwater since the soggy fishy-scale layer acts like an antireflection coating on a lens.  The surface is also superoleophobic and anti-oil (how horrible it is, trying to wash greasy glass plates, and even worse in the case of chemical glassware coated in silicone oil.)

Ideal for diving goggles.  But perhaps one might find fish bumping into one’s mask, unaware of the surface like a bird flying into a window.

This reminded me of something I read in Letters on England, by Voltaire:

LETTER XVI. — ON SIR ISAAC NEWTON’S OPTICS

From what cause, therefore, do colours arise in Nature? It is nothing but the disposition of bodies to reflect the rays of a certain order and to absorb all the rest.

What, then, is this secret disposition? Sir Isaac Newton demonstrates that it is nothing more than the density of the small constituent particles of which a body is composed. And how is this reflection performed? It was supposed to arise from the rebounding of the rays, in the same manner as a ball on the surface of a solid body. But this is a mistake, for Sir Isaac taught the astonished philosophers that bodies are opaque for no other reason but because their pores are large, that light reflects on our eyes from the very bosom of those pores, that the smaller the pores of a body are the more such a body is transparent. Thus paper, which reflects the light when dry, transmits it when oiled, because the oil, by filling its pores, makes them much smaller.

The bold part is quite correct, but not so the origin of colour.  Where does the misunderstanding in the first part arise — was it simply speculation on the part of Sir Isaac, who would need to wait for another couple of centuries or so of chemistry to know the answer in any depth?  Or is it Voltaire getting hold of the wrong end of the stick?  Je ne sais pas.

Even so, the part in bold impressed me very much when I read it.  Have you ever tried asking a physics student why paper is white instead of transparent?