Electrospinning of fine hollow fibers
A method for electrospinning nanofibers having a core-sheath, tubular, or composite structure is disclosed. The process uses a spinneret having first and second capillaries that channel first and second fluids in the spinneret, the second capillary surrounding the first. A high voltage is applied between the spinneret and a spaced conductive collector. In one embodiment, the first fluid is a mineral oil and the second fluid is a polymeric solution that may include a polymer, a catalyst, a solvent, and a sol-gel precursor. The as-spun nanofiber includes an oil core and a composite sheath. The oil may be removed to produce a composite tubular fiber or the polymer and oil may be removed by calcination to produce a ceramic tubular fiber. In other embodiments, miscible fluids are used to produce porous nanofibers, selected additives functionalize the surfaces of the nanofibers and/or conjugated polymers are used.
1. A method for electrospinning a nanofiber comprising:
providing a spinneret having a needle defining a bore, the needle fluidly connected to a first liquid comprising a spinnable polymeric solution, and a capillary having a proximal end connected to a second liquid and a distal end disposed in the needle bore such that an annular aperture is defined between the needle and the capillary;
providing a conducting collector disposed a distance from the needle;
applying a voltage between the needle and the conducting collector; and
feeding the polymeric solution through the needle and feeding the second liquid through the capillary;
wherein the applied voltage is sufficiently high to induce a jet made of the polymeric solution and the second liquid to travel from the spinneret to the collector to form a composite nanofiber.
2. The method of claim 1 , wherein the needle is a conductive metal.
3. The method of claim 2 , wherein the capillary is a polymer-coated silica capillary.
4. The method of claim 3 , wherein the needle and capillary are substantially axisymmetrically disposed.
5. The method of claim 1 , wherein the polymeric solution includes a polymer and a sol-gel precursor.
6. The method of claim 5 , wherein the sol-gel precursor is a metal alkoxide.
7. The method of claim 5 , wherein the polymer is poly(vinyl pyrrolidone).
8. The method of claim 5 , wherein the polymeric solution further comprises an acid stabilizer and a solvent.
9. The method of claim 8 , wherein the acid stabilizer is acetic acid and the solvent is ethanol.
10. The method of claim 5 , wherein the polymeric solution and the second fluid are immiscible.
11. The method of claim 1 , wherein the second fluid comprises an oil.
12. The method of claim 11 , wherein the second fluid further comprises an additive selected from a molecular species soluble in the oil or nanoparticles that form a stable dispersion in the oil.
13. The method of claim 12 , wherein the additive is selected from an oil-based ferrofluid and tin isopropoxide.
14. The method of claim 12 , wherein the additive is a long-chain silane.
15. The method of claim 12 , wherein the additive is a hydrophobic substance.
16. The method of claim 1 , wherein the second fluid comprises a conjugated polymer solution.
17. The method of claim 1 , wherein the conjugated polymer solution comprises MEH-PPV and chloroform.
18. The method of claim 1 , wherein the conjugated polymer solution comprises a blend of conjugated polymers and a solvent.
19. The method of claim 18 , wherein the blend of conjugated polymers comprises MEH-PPV and PHT, and chloroform.
20. The method of Claim 11 , further comprising the step of soaking the composite nanofiber in a solvent to remove the second liquid such that a hollow nanofiber remains.
21. The method of claim 20 , wherein the solvent is an alkane.
22. The method of claim 11 , further comprising the step of calcining the composite nanofiber such that a hollow ceramic fiber remains.
23. The method of claim 22 , wherein the calcination temperature is about 500° C.