Nanofibrous materials for passive thermal control on earth and in space

Abstract

Nanofibrous materials and their fabrication by electrospinning are disclosed for passive temperature control on earth and in outer space. The materials combine high solar reflectivity with high thermal emittance in the infrared region, including in the long wavelength atmospheric window region between 8 μm and 13 μm. The materials include nanofibrous PTFE/PEO and silica materials. The physical properties of the materials are suitable for extraterrestrial as well as terrestrial applications.

What is claimed is: 
     
         1 . A temperature-regulating material comprising:
 nanofibers having an average diameter of between about 200 nm and about 1500 nm, wherein the material has:
 a thickness of greater than about 400 μm; 
 an average solar absorptance (<a s >) of less than about 0.1, the average solar absorptance being determined over the range from 0.3 μm to 2.5 μm; 
 an average thermal emittance (<ε IR >) of greater than about 0.75 at 300 K, the average thermal emittance being determined over the range from 2.5 μm to 15 μm; and 
   a figure of merit greater than about 20, the figure of merit being the ratio <ε IR >/<a s >.   
     
     
         2 . The temperature-regulating material of  claim 1 , wherein the figure of merit of the material is greater than about 500. 
     
     
         3 . The temperature-regulating material of  claim 1 , wherein the <a s > of the material is less than about 0.05. 
     
     
         4 . The temperature-regulating material of  claim 1 , wherein the <a s > of the material is less than about 0.005. 
     
     
         5 . The temperature-regulating material of  claim 1 , wherein the nanofibers are silica-based nanofibers. 
     
     
         6 . The temperature-regulating material of  claim 1 , wherein the nanofibers comprise a water soluble polymer, and nanobeads of a fluoropolymer, the nanobeads of the fluoropolymer being attached to surfaces of the water soluble polymer. 
     
     
         7 . The temperature-regulating material of  claim 6 , wherein the water soluble polymer is selected from the group consisting of polyethylene oxide, polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, and carboxymethylcellulose. 
     
     
         8 . The temperature-regulating material of  claim 6 , wherein the fluoropolymer is selected from the group consisting of polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PDVF-HFP), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), and combinations thereof. 
     
     
         9 . The temperature-regulating material of  claim 1 , wherein the nanofibers comprise polyethylene oxide (PEO) nanofibers, the material further comprising polytetrafluoroethylene (PTFE) nanobeads,
 wherein the PTFE nanobeads are disposed on surfaces of the PEO nanofibers,   wherein the weight ratio of PTFE to PEO is between about 75:25 and about 95:5.   
     
     
         10 . The temperature-regulating material of  claim 6 , wherein the material has a figure of merit greater than about 800. 
     
     
         11 . The temperature-regulating material of  claim 9 , wherein the PTFE nanobeads have an average diameter of between about 150 nm and about 300 nm. 
     
     
         12 . The temperature-regulating material of  claim 9 , wherein the material has a figure of merit greater than about 800. 
     
     
         13 . The temperature-regulating material of  claim 1 , wherein the material has porosity of greater than about 0.5. 
     
     
         14 . The temperature-regulating material of  claim 1 , wherein the temperature-regulating material is obtained by a process of electrospinning. 
     
     
         15 . The temperature-regulating material of  claim 5 , wherein the temperature-regulating material is obtained by a process of electrospinning. 
     
     
         16 . A method of obtaining a temperature-regulating material, the method comprising:
 dissolving a water soluble polymer in water to form a water soluble polymer solution;   adding fluoropolymer nanobeads to the water soluble polymer solution to form a mixture of fluoropolymer nanobeads and water soluble polymer in water, the weight ratio of fluoropolymer to water soluble polymer being between about 75:25 and about 95:5, the fluoropolymer nanobeads having an average diameter of between about 150 nm and about 300 nm; and   electrospinning the mixture of fluoropolymer nanobeads and water soluble polymer in water to obtain the temperature-regulating material of  claim 6 .   
     
     
         17 . A method of obtaining a temperature-regulating material, the method comprising:
 dissolving PEO in water to form a PEO solution;   adding PTFE nanobeads dispersed in water to the PEO solution to form a mixture of PTFE nanobeads and PEO in water, the weight ratio of PTFE to PEO being between about 75:25 and about 95:5, the PTFE nanobeads having an average diameter of between about 150 nm and about 300 nm; and   electrospinning the mixture of PTFE nanobeads and PEO in water to obtain the temperature-regulating material of  claim 9 .   
     
     
         18 . The method of  claim 17 , wherein the ratio of PTFE to PEO is about 90:10. 
     
     
         19 . A method of obtaining a temperature-regulating material, the method comprising:
 mixing together a tetraalkyl orthosilicate, an alcohol, water, and a strong acid to form a mixture;   stirring the mixture; and   electrospinning the mixture to obtain the temperature-regulating material of  claim 5 .   
     
     
         20 . The method of  claim 19 , wherein the tetraalkyl orthosilicate is tetraethyl orthosilicate, the alcohol is ethanol, and the strong acid is hydrochloric acid.