Polymer-based nanostructured materials with tunable properties and methods of making thereof
Nano structured surfaces and bulk composite materials which exhibit tunable surface morphology, wettability, thermal conductivity, and total thermal resistance properties, and methods of fabrication and uses thereof are described herein. Arrays of vertically-aligned nanostructures produced via a template assisted fabrication approach using nanoporous templates, or alternatively, via an electropolymerization process are described. As a result, control over the surface morphology and wettability can be achieved using the selective template etching process. The composite materials also demonstrate tunable thermal and electrical properties based on the methods of their fabrication. The arrays of polymeric nanostructures are chemically, mechanically, and thermally robust and can serve as soft substrates with heat dissipation capability for use in the fabrication of thermal management materials, tunable wetting for microfluidic applications, and for use in heterojunction organic photovoltaic cells.
1. An array comprising:
a plurality of rows of vertically aligned polymeric nanostructures, each of the nanostructures having a base and an end tip,
wherein the plurality of rows of vertically aligned polymeric nanostructures are embedded in a template and one or more surfaces of the template have been etched for a period of time of between about four to about twelve minutes to at least expose the end tips of the plurality of rows of vertically aligned polymeric nanostructures from the template,
at least two of the end tips of the nanostructures are in contact to form a bundle having a tip, and
wherein at least the tips of two bundles are in contact to form a ridge,
wherein the array comprises a plurality of ridges, at least two ridges being interconnected and each ridge having a constant width (W) along the ridge, and
wherein the array has a surface fraction, the ratio of the total surface area to the surface area in contact with the nanostructures, of between about 0.01 and about 0.30.
2. The array of claim 1 , wherein a spacing (S) between the ridges is uniform.
3. The array of claim 1 , wherein the plurality of vertically aligned polymeric nanostructures comprises polythiophene.
4. The array of claim 1 , wherein at least a portion of the plurality of polymeric nanostructures are polymer nanotubes, nanofibers, nanowires, or combinations thereof.
5. The array of claim 4 , wherein the nanotubes or nanofibers are formed of a conjugated polymer.
6. The array of claim 5 , wherein the conjugated polymer is regioregular poly(3-hexylthiophene).
7. The array of claim 1 , where the template is a nanoporous anodic alumina template.
8. The array of claim 1 , wherein the width (W) is between about 0.5 μm and about 2.5 μm.
9. The array of claim 2 , wherein the spacing (S) is between about 5 μm and about 30 μm.
10. The array of claim 1 , wherein one or more surfaces of the array have a contact angle between 90 and 170°.
11. The array of claim 1 , wherein the one or more surfaces are superhydrophobic and have a contact angle greater than about 150°.
12. The array of claim 1 , wherein the array has a thermal contact resistance between about 15 and about 45 mm 2 ·K W −1 .
13. The array of claim 1 , wherein the array has a thermal conductivity between about 0.1 and about 5 W m −1 K −1 .
14. The array of claim 1 , wherein the template was etched for a period of time of about 6, 8, 10, or 12 minutes.
15. The array of claim 1 , wherein the template was etched for a period of time of between about 6 and 12 minutes.
16. A method of fabrication of a nanostructured polymer-based array comprising the steps of:
a) wetting a template comprising vertical nanotunnels with a polymer solution to form vertically aligned polymeric nanostructures in the vertical nanotunnels;
b) applying an etching solution to one or more surfaces of the template for a period of time of between about four to about twelve minutes to etch the template and at least expose end tips of the plurality of polymeric nanostructures from the template; and
c) applying a thermal treatment to the array;
wherein the at least partially exposed polymeric nanostructures have end tips, at least two of the end tips of the nanostructures are in contact to form a bundle having tips wherein at least the tips of two bundles are in contact to form a ridge,
wherein the array comprises a plurality of ridges,
wherein at least two ridges are interconnected,
wherein each ridge has a constant width (W) along the ridge, and
wherein the array has a surface fraction, the ratio of the total surface area to the surface area in contact with the nanostructures, of between about 0.01 and about 0.30.
17. The method of fabrication of claim 16 , where the period of time is about 6, 8, 10, or 12.
18. The method of fabrication of claim 16 , where the period of time is between about 6 and 12 minutes.
19. The method of fabrication of claim 16 , wherein at least a portion of the plurality of polymeric nanostructures are polymer nanotubes, nanofibers, nanowires, or combinations thereof.
20. The method of fabrication of claim 16 , wherein the nanostructures are formed of a conjugated polymer.
21. The method of fabrication of claim 20 , wherein the conjugated polymer is regioregular poly(3-hexylthiophene).
22. The method of fabrication of claim 16 , wherein a spacing (S) between the ridges is uniform.
23. The method of fabrication of claim 16 , wherein the width (W) is between about 0.5 μm and about 2.5 μm.
24. The method of fabrication of claim 16 , wherein the spacing (S) is between about 5 μm and about 30 μm.
25. The method of fabrication of claim 16 , wherein the etching solution comprises potassium hydroxide.