Hierarchical structures for superhydrophobic surfaces and methods of making

Abstract

Embodiments of a superhydrophobic structure comprise a substrate and a hierarchical surface structure disposed on at least one surface of the substrate, wherein the hierarchical surface structure comprises a microstructure comprising a plurality of microasperities disposed in a spaced geometric pattern on at least one surface of the substrate. The fraction of the surface area of the substrate covered by the microasperities is from between about 0.1 to about 1. The hierarchical structure comprises a nanostructure comprising a plurality of nanoasperities disposed on at least one surface of the microstructure.

1 . A superhydrophobic structure comprising a substrate and a hierarchical surface structure disposed on at least one surface of the substrate, the hierarchical surface structure comprising:
 a microstructure comprising a plurality of microasperities disposed in a spaced geometric pattern on at least one surface of the substrate, wherein the fraction of the surface area of the substrate covered by the microasperities is from between about 0.1 to about 1; and   a nanostructure comprising a plurality of nanoasperities disposed on at least one surface of the microstructure.   
   
   
       2 . The superhydrophobic structure of  claim 1  wherein the plurality of nanoasperities are arranged in a geometric pattern, a random pattern, or combinations thereof. 
   
   
       3 . The superhydrophobic structure of  claim 1  wherein the nanoasperities comprise tubules, platelets, or combinations thereof. 
   
   
       4 . The superhydrophobic structure of  claim 1  wherein the plurality of nanoasperities are disposed on the microasperities, on the substrate in the spacing between adjacent microasperities, or combinations thereof. 
   
   
       5 . The superhydrophobic structure of  claim 1  wherein the plurality of microasperities comprise a height H of between about 1 to about 100 μm, a diameter D of between about 1 to about 50 μm, and a pitch P of the microasperities is between 1 and 500 μm, and the plurality of nanoasperities comprise a height h of between about 1 to about 100 nm and a diameter d of between about 1 to about 300 nm. 
   
   
       6 . The superhydrophobic structure of  claim 1  wherein the arrangement of microasperities on the microstructure defines the following relationship (√{square root over (2)}P−D) 2 /R<H. 
   
   
       7 . The superhydrophobic structure of  claim 1  wherein the fraction of the surface area of the substrate covered by the microasperities is from between about 0.5 to about 1. 
   
   
       8 . The superhydrophobic structure of  claim 1  wherein the fraction of the surface area of the substrate covered by the microasperities is from between about 0.8 to about 1 
   
   
       9 . The superhydrophobic structure of  claim 1  wherein the superhydrophobic structure comprises a contact angle of between about 150° to about 180°. 
   
   
       10 . The superhydrophobic structure of  claim 1  wherein the superhydrophobic structure comprises a contact angle of between about 165° to about 180°. 
   
   
       11 . The superhydrophobic structure of  claim 1  wherein the superhydrophobic structure comprises a contact angle hysteresis of between about 0° to about 10°. 
   
   
       12 . The superhydrophobic structure of  claim 1  wherein the superhydrophobic structure defines a contact angle hysteresis of between about 0° to about 5°. 
   
   
       13 . The superhydrophobic structure of  claim 1  wherein the microasperities comprise epoxy resin, silicon, or combinations thereof. 
   
   
       14 . The superhydrophobic structure of  claim 1  wherein the nanoasperities comprise  tropaeolum  wax,  leymus  wax, n-hexatriacontane, or combinations thereof. 
   
   
       15 . A method of making hierarchical structures comprising:
 depositing a polymer mold onto a silicon surface comprising a plurality of microasperities;   removing the polymer mold after the polymer mold has hardened;   depositing a liquid epoxy resin into the polymer mold;   forming a microstructure with a plurality of microasperities by separating the epoxy resin from the mold after the epoxy resin has solidified; and   forming a nanostructure by depositing alkanes on the microstructure in the presence of solvent vapor.   
   
   
       16 . The method of  claim 15  wherein the alkanes are n-hexatriacontane, alkanes of  tropaeolum  wax, alkanes of  leymus  wax, or combinations thereof. 
   
   
       17 . The method of  claim 15  wherein  leymus  wax is deposited in the presence of a solvent vapor comprising chloroform. 
   
   
       18 . The method of  claim 15  wherein the  tropaeolum  wax is deposited in the presence of a solvent vapor comprising ethanol. 
   
   
       19 . The method of  claim 1  wherein the microasperities comprise epoxy resin, silicon, or combinations thereof. 
   
   
       20 . The method of  claim 1  wherein the nanoasperities comprise tubules, platelets, or combinations thereof.