Special WFU Chemistry & Physics Colloquium

TITLE: Synthesis and Applications of Conducting Polymer Nanofibers

SPEAKER: Professor Richard B. Kaner ,

TIME: Wednesday Jan. 23, 2008 at 11:15 AM

PLACE: Room 103 in Olin Physical Laboratory

By using either interfacial polymerization or rapidly mixing aniline, oxidant and acid, pure nanofibers of polyaniline can be produced.^[1,2,3] The key to forming nanofibers is to suppress secondary growth that results in the agglomerated particles found in conventional polyaniline synthesis.^[4] Not shaking or stirring the solutions after the initial reaction is also important.^[5] Our methods are template-free and readily scalable. Stable and processable colloids are now available.^[6] The synthesis of nanofibers of polyaniline derivatives has recently been accomplished by adding appropriate initiators.^[7] The applicability of these ideas to form nanostructures of polypyrrole and polythiophene will be discussed.

Polyaniline nanofibers exhibit an exceptional photothermal effect in which they instantaneously melt and cross-link upon exposure to a camera flash.^[8] This novel flash welding technique can be used to form patterned nanofiber films, create polymer based nanocomposites and make asymmetric polymer membranes. These asymmetric structures can act as mechanical actuators (artificial muscles) when exposed to strong acids. Polyaniline nanofibers are useful in many applications such as resistive-type sensors where their high surface area enable very rapid response times often less than two seconds.^[9,10] Polyaniline nanofibers can be modified to respond to many different vapors including toxic agents such as hydrogen sulfide. Th key is using a metal salt such as CuCl₂ that reacts with H₂S to produce CuS and HCl. This process converts a weak acid (H₂S) into a strong acid (HCl) that in turn can be readily detected at very low concentrations. Polyaniline nanofibers can be decorated with metal nanoparticles which not only can enhance sensor response, but also leads to molecular memory devices.^[11]

Some references:

1. Huang, J.; Virji, S.; Weiller, B.H.; Kaner, R.B. J. Am. Chem. Soc. 2003, 125, 314.
2. Huang, J.; Kaner, R.B. J. Am. Chem. Soc. 2004, 126, 851.
3. Huang, J.; Kaner R.B. Angew. Chem. Inter. Edition 2004, 43, 5817.
4. Huang, J.; Kaner, R.B. Chem. Commun. 2006, 367.
5. Li, D.; Kaner, R.B. J. Am. Chem. Soc. 2006, 128, 968; J. Mater. Chem., 2007, 17, 2279.
6. Li, D.; Kaner, R.B. Chem. Commun. 2005, 3286.
7. Tran, H.; Kaner, R.B. Chem. Commun. 2006, 3915.
8. Huang, J.; Kaner, R.B. Nature Mater. 2004, 3, 783.
9. Virji, S.; Fowler, J.D.; Baker, C.O.; Huang, J.; Kaner, R.B.; Weiller, B.H.; Small 2005, 1, 624.
10. Virji, S.; Huang, J.; Kaner, R.B.; Weiller, B.H.; Nano Lett. 2004, 4, 491.
11. Tseng, R.J.; Huang, J.; Ouyang, J.; Kaner, R.B.; Yang, Y.; Nano Lett. 2005, 5, 1077; Appl. Phys. Lett., 2007, 90, 53101.

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