Well-controlled electrospun nanostructures and methods thereof

Abstract

Electrospun films of nonwoven silk nanofibers, when appropriately structured, can surpass Cyphochilus scales in scattering strength for the entire visible spectrum. Detailed modeling studies demonstrate how the key structural parameters affect scattering properties in the electrospun films. An electrospun film with the similar characteristic structural parameters as those in Cyphochilus scales provides two resonance peaks in the visible reflectance spectrum in the limit of a uniform fiber diameter. As the distribution of diameter increases appreciably to experimentally achievable degrees, the resonance peaks broaden and the reflectance spectrum becomes relatively flat with stronger scattering in shorter wavelengths, resulting in disappearance of the structural color. This supports the concept that controllable fibrous nanostructures that exceed the exceptionally strong broadband optical scattering found among living organisms can be volume-produced.

1 .- 18 . (canceled) 
     
     
         19 . A fibrous network film comprising a plurality of electrospun fibers, wherein:
 the plurality of electrospun fibers comprise fiber diameter values such that a relative standard deviation σ of fiber diameter values for the plurality of electrospun fibers is approximately 0.32;   the plurality of electrospun fibers, taken together, comprise a mean fiber diameter value that is from about 0.20 μm to about 0.32 μm; and   the plurality of electrospun fibers in the fibrous network film comprise a filling fraction from about 10% to about 60%.   
     
     
         20 . The fibrous network film of  claim 19 , wherein the filling fraction is from about 31% to about 45%. 
     
     
         21 . The fibrous network film of  claim 19 , wherein the filling fraction is about 38%. 
     
     
         22 . A fibrous network film consisting of a plurality of electrospun fibers, wherein:
 the plurality of electrospun fibers comprise fiber diameter values such that a relative standard deviation σ of fiber diameter values for the plurality of electrospun fibers is approximately 0.35 μm;   the plurality of electrospun fibers, taken together, comprise a mean fiber diameter value that is approximately 0.20 μm to about 0.30 μm;   the plurality of electrospun fibers in the fibrous network film comprise a filling fraction from approximately 10% to approximately 60%; and   the fibrous network comprises fibroin.   
     
     
         23 . The fibrous network film of  claim 22 , wherein the filling fraction is from about 31 to about 45%. 
     
     
         24 .- 26 . (canceled) 
     
     
         27 . A method of generating a fibrous network film, the method comprising:
 preparing a fibroin solution;   loading the fibroin solution into a syringe with a conductive needle or nozzle:   applying a high voltage to the conductive needle or nozzle and grounding a conductive surface of a collector; and   electrospinning the fibroin solution from the syringe or nozzle with the conductive needle or nozzle to the grounded conductive surface of the collector to generate the fibrous network film, wherein the fibrous network film comprises one or more pluralities of electrospun fibers, on the grounded conductive surface; and wherein:
 the pluralities of electrospun fibers comprise fiber diameter values such that a relative standard deviation (σ) of fiber diameter values for each of the pluralities of electrospun fibers is from about 0.32 μm to about 0.35 μm; 
 the pluralities of electrospun fibers, taken together, comprise a mean fiber diameter value that is from about 0.20 μm to about 0.32 μm; and 
 the pluralities of electrospun fibers in the fibrous network film comprise a filling fraction from about 10% to about 60%. 
   
     
     
         28 . (canceled) 
     
     
         29 . The method of  claim 27 , wherein:
 an index of refraction of the fibrous network film is from about 1.4 to about 1.6; and   the fibrous network film comprises a plurality of electrospun polymer fibers.   
     
     
         30 . The fibrous network film of  claim 19 , wherein the fibrous network film comprises fibroin. 
     
     
         31 . The fibrous network film of  claim 19 , wherein an index of refraction of the fibrous network film is from about 1.4 to about 1.6. 
     
     
         32 . An optical film comprising the fibrous network film of  claim 19 . 
     
     
         33 . A clothing item comprising the fibrous network film of  claim 19 . 
     
     
         34 . The fibrous network film of  claim 23 , wherein the filling fraction is about 38%. 
     
     
         35 . The fibrous network film of  claim 22 , wherein an index of refraction of the fibrous network film is from about 1.4 to about 1.6. 
     
     
         36 . The method of  claim 27 , wherein an index of refraction of the fibrous network film is from about 1.4 to about 1.6. 
     
     
         37 . The method of  claim 27 , wherein the mean fiber diameter value is about 0.32 μm and the filling fraction is about 38%. 
     
     
         38 . The method of  claim 27 , wherein the collector moves in lateral motion relative to the conductive needle during the electrospinning. 
     
     
         39 . The method of  claim 27 , wherein:
 the collector is rotated; and   the conductive needle is a 21-gauge stainless-steel needle.   
     
     
         40 . The method of  claim 27 , wherein the collector is drum-shaped with a diameter of about 1 cm to about 40 cm and the grounded conductive surface comprises stainless steel. 
     
     
         41 . The method of  claim 40 , wherein the collector is rotated about an axis at a speed of about 20 to about 45 rpm during the electrospinning. 
     
     
         42 . The method of  claim 27 , wherein:
 a distance between a tip of the conductive needle and the grounded conductive surface is 15 cm; and   the high voltage is about 21 kV.