Self-Cleaning and Superhydrophobic Surfaces Based on TIO2 Nanotubes

Abstract

A method for producing a superhydrophobic coating with self-cleaning properties on a metallic substrate involves providing a metallic substrate that titanium and an electrolyte solution that includes a fluoride salt. At least part of a surface of the metallic substrate is contacted with the electrolyte solution. The metallic substrate is anodized in order to produce a nanoporous layer having nanotubes including titanium dioxide on the metallic substrate. A superhydrophobising coating is applied onto the nanoporous layer comprising nanotubes including titanium dioxide, wherein the electrolyte solution includes a further water-soluble salt selected from the group comprising ammonium sulphate, sodium sulphate, sodium bisulphate, potassium sulphate, potassium bisulphate and mixtures thereof.

1 - 15 . (canceled) 
     
     
         16 . A method for producing a superhydrophobic coating with self-cleaning properties on a metallic substrate, the method comprising:
 a) providing a metallic substrate comprising titanium;   b) providing an electrolyte solution comprising a fluoride salt;   c) contacting at least part of a surface of the metallic substrate with the electrolyte solution from step b);   d) anodizing the metallic substrate from step c) in order to produce a nanoporous layer comprising nanotubes including titanium dioxide on the metallic substrate; and   e) applying a superhydrophobising coating onto the nanoporous layer comprising nanotubes including titanium dioxide, wherein the electrolyte solution comprises a further water-soluble salt selected from the group comprising ammonium sulphate, sodium sulphate, sodium bisulphate, potassium sulphate, potassium bisulphate and mixtures thereof.   
     
     
         17 . The method of  claim 16 , wherein the metallic substrate is a titanium alloy and the alloy additionally comprises at least one further metal selected from the group comprising V, Fe, Sn, Ni, Nb, Mo, Zr, Y, Hf, Ta, Ce, Tb, Nd, Gd, Dy, Ho and Er, or in addition at least one further element selected from the group comprising Zn, Mn, Ag, Li, Cu, Si, Al or Ca. 
     
     
         18 . The method of  claim 16 , wherein the metallic substrate additionally comprises Al and V. 
     
     
         19 . The method of  claim 16 , wherein the fluoride salt is selected from the group comprising ammonium fluoride, ammonium bifluoride, potassium fluoride, sodium fluoride, calcium fluoride, magnesium fluoride and mixtures thereof. 
     
     
         20 . The method of  claim 19 , the fluoride salt is ammonium fluoride. 
     
     
         21 . The method of  claim 16 , wherein the further water-soluble salt is ammonium sulphate. 
     
     
         22 . The method of  claim 16 , wherein the anodization of the metallic substrate in an electrolyte solution comprising 50 to 250 g/l and 0.5 to 10 g/l of ammonium fluoride is carried out at a temperature in a range of 10 to 60° C. and a voltage of 2 to 50 volt for 5 to 480 minutes. 
     
     
         23 . The method of  claim 16 , wherein the anodization of the metallic substrate in an electrolyte solution comprising 120 to 140 g/l of ammonium sulphate and 4 to 6 g/l of ammonium fluoride is carried out at a temperature in a range of 20 to 30° C. and a voltage of 10 to 20 volt for 20 to 40 minutes. 
     
     
         24 . The method of  claim 16 , wherein the nanotubes including titanium dioxide have a diameter in a range of 10 to 300 nm. 
     
     
         25 . The method of  claim 16 , wherein the nanotubes including titanium dioxide have a diameter in a range of 30 to 140 nm. 
     
     
         26 . The method of  claim 16 , wherein the nanotubes including titanium dioxide have a diameter in a range of 30 to 100 nm. 
     
     
         27 . The method of  claim 16 , wherein the superhydrophobic coating with self-cleaning properties on the metallic substrate has a layer thickness between 100 nm and 10 μm. 
     
     
         28 . The method of  claim 16 , wherein the superhydrophobic coating with self-cleaning properties on the metallic substrate has a layer thickness between 280 nm and 600 nm. 
     
     
         29 . The method of  claim 16 , wherein the superhydrophobic coating with self-cleaning properties on the metallic substrate has a layer thickness between 300 nm and 500 nm. 
     
     
         30 . The method of  claim 16 , wherein the superhydrophobising coating comprises a fluoroalkyl functional silane. 
     
     
         31 . The method of  claim 16 , wherein the contacting of the metallic substrate surface with the electrolyte solution or the application of the superhydrophobising coating on the nanoporous layer is carried out by dipping, spinning, flooding, brushing or spraying. 
     
     
         32 . A metallic substrate having a superhydrophobic coating and self-cleaning properties, which is obtain by:
 a) providing a metallic substrate comprising titanium;   b) providing an electrolyte solution comprising a fluoride salt;   c) contacting at least part of a surface of the metallic substrate with the electrolyte solution from step b);   d) anodizing the metallic substrate from step c) in order to produce a nanoporous layer comprising nanotubes including titanium dioxide on the metallic substrate; and   e) applying a superhydrophobising coating onto the nanoporous layer comprising nanotubes including titanium dioxide, wherein the electrolyte solution comprises a further water-soluble salt selected from the group comprising ammonium sulphate, sodium sulphate, sodium bisulphate, potassium sulphate, potassium bisulphate and mixtures thereof.   
     
     
         33 . The metallic substrate as claimed in  claim 32 , wherein the surface of the substrate with a superhydrophobic coating and self-cleaning properties has a contact angle to water of more than 140°.