Electrophoretic Integration of Polyaniline on NIST Microhotplate for Gas Sensing
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Electrophoretic Integration of Polyaniline on NIST Microhotplate for Gas Sensing Guofeng Li*,†,‡ and Steve Semancik† †
Chemical Science and Technology Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899-8362, USA
‡
Research and Development Center, GEO-CENTERS Inc., 9460 Innovation Drive, Manassas, VA 20110, USA
ABSTRACT We present a method for controlled deposition of polyaniline from a colloidal suspension. Stable suspensions of polyaniline colloids were formed by dispersing polyaniline/formic-acid solutions into acetonitrile. It is demonstrated that the positively charged polyaniline colloids can be electrophoretically patterned onto microfabricated device features with great precision and control. Futhermore, the electrophoretically deposited polyaniline films reveal a nanoporous morphology, which greatly enhances the gas diffusion that leads to improved sensor performance.
INTRODUCTION Like many electrically conducting polymers, polyaniline is difficult to process due to its insolubility in common solvents. Despite all the progress, polyaniline’s limitation in processibility persists, preventing it from fully reaching its practical potential. Especially for device applications, delivering small amounts of materials onto miniaturized device features is not a trivial task. With features increasingly going down in size, there is a pressing need for a practical method capable of reproducibly integrating polyaniline onto selected device structures with precision and control. The formation of polyaniline dispersions has been exploited as an effective method of circumventing the limitations of processability for this material. In previous work, the colloidal suspensions of polyaniline have been mostly produced by a process that is referred to as dispersion polymerization [1]. The dispersion polymerization of polyaniline is carried out in an aqueous mixture containing aniline monomers and oxidants with the presence of a suitable steric stabilizer. As the aniline monomers polymerize, a surface layer of a steric stabilizer attaches to the precipitates of polyaniline particles, not only preventing further polymerization of aniline monomers onto the particles, but also protecting the particles from aggregation. Hence, a stable dispersion of polyaniline colloidal particles can be obtained. Although a polyaniline chain in its emeraldine salt form is a polymeric cation, the charge-stabilization contribution from the core is secondary to the steric stabilization that originates from the shell. One drawback of preparing *
Corresponding authors: Guofeng Li, Email: [email protected]; Phone: 301-975-4782; Mailing address: NIST, 100 Bureau Drive, MS 8362, Gaithersburg, MD 20899-8362, USA
Mater. Res. Soc. Symp. Proc. Vol. 876E © 2005 Materials Research Society
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polyaniline colloidal suspensions through dispersion polymerization is that the processibility is gained through compromising the purity of the polyaniline. Additionally, having a layer of insulating polymer or ox
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