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John O | February 2018

Nanostructure of silk fibers could lead to better understanding of heat transfer


by josh perry, editor
jperry@coolingzone.com

 

according to a report on the purdue university website, researchers have discovered that the nanostructure of silkworm fibers causes anderson localization of light, which confines light due to scattering and defects, and could help develop synthetic materials with the same properties.

 


fibers from a silkworm’s cocoon may represent natural metamaterials. (purdue university)

 

the light confinement in natural tissue was unexpected, according to researchers, and shows that silk fibers may be natural metamaterials and natural metastructures.

 

“various research groups have created synthetic ‘metamaterials’ capable of the ultra-efficient control of light,” the article explained. “because silk’s nano-architecture is ‘disordered’ instead of meticulously designed periodic structures, the findings suggest a strategy to produce metamaterials that are less expensive to fabricate and manufacture and easier to scale up for industry.”

 

the silk fibers in the study were 10-20 microns in diameter and are composed of thousands of nanofibrils around 100 nanometers wide. the anderson localization of light is caused by the fibers the scattering and interference of light waves, which could destroy the light or intensify it.

 

“the small size and roughly parallel arrangement of the nanofibrils are conducive to the effect,” the article added. “the scattering power is maximized when there are many scattering centers and when their size is comparable to the wavelength of the light, both criteria found in the silk fibers.”

 

in addition to its relation to the optics industry, researchers believe that this discovery will have an impact on the study of heat transfer.

 

the article said, “the silk has a high emissivity for infrared light, meaning it readily radiates heat, or infrared radiation, while at the same time being a good reflector of solar light. because the strong reflectivity from anderson localization is combined with the high emissivity of the biomolecules in infrared radiation, silk radiates more heat than it absorbs, making it ideal for passive, or ‘self-cooling.’”

 

the research was recently published in nature communications. the abstract stated:

 

“light in biological media is known as freely diffusing because interference is negligible. here, we show anderson light localization in quasi-two-dimensional protein nanostructures produced by silkworms (bombyx mori). for transmission channels in native silk, the light flux is governed by a few localized modes. relative spatial fluctuations in transmission quantities are proximal to the anderson regime.

 

“the sizes of passive cavities (smaller than a single fibre) and the statistics of modes (decomposed from excitation at the gain–loss equilibrium) differentiate silk from other diffusive structures sharing microscopic morphological similarity.

 

“because the strong reflectivity from anderson localization is combined with the high emissivity of the biomolecules in infra-red radiation, silk radiates heat more than it absorbs for passive cooling.

 

“this collective evidence explains how a silkworm designs a nanoarchitectured optical window of resonant tunnelling in the physically closed structures, while suppressing most of transmission in the visible spectrum and emitting thermal radiation.”

 

learn more about this discovery in the video below: 

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