Original Entry: Tom Dimiduk APPHY 225 Fall 2010
Editing Development of color-producing beta-keratin nanostructures in avian feather barbs
Self Assembly, Phase Separation, Spinodal Decomposition, Nucleation, Coffee Stain Effect, Photonic Structures
Figure 2a: "Adult blue-and-yellow macaw. This paper investigates the formation of the photonic nanostructures which give this bird its color."
Many organisms owe their color to coherent light scattering from wavelength sized nanostructures. In many many arthropods, these are are believed to be generated by sophisticated biochemical synthesis. The authors propose that in the case of many bird feathers, these structures are created through a self-assembly process involving phase separation. They show evidence that some feathers use spinodal decomposition and others use a nucleation-growth process. They provide evidence for their conclusions in the form of electron micrographs of fully developed feather structures compared simple physical structures known to be caused by spinodal decomposition and nucleation-growth. They also show micrographs of development and propose explanations of the feater growth process in the context of their hypothesis.
Figure 1: "Electron micrographs of (a,b) channel type feather barbs, (c,d) sphere type feather barbs, (e) Spinodal Decomposition of an Ag-Au alloy, (f) Carbon dioxide bubbles formed by nucleation and growth in beer."
Figure 3: "Phase diagram. The tan region is that where the mixed state is not thermodynamically unstable. Inside the dotted line the mixture will phase separate by spinodal decomposition, between the dotted and solid lines there is a kinetic barrier, and it will decompose by nucleation and growth."
Figure 1: "Spatial frequency spectrum of (a) channel type feathers and (b) sphere type feathers. The colored dots are from feathers, the solid lines are for a polymer spinodal decomposition."