Title

Improving conducting polymer electrochromic speeds and depositing aligned polymeric nanofibers by electrospinning process

Date of Completion

January 2009

Keywords

Chemistry, Polymer|Nanoscience|Nanotechnology

Degree

Ph.D.

Abstract

The effects of film thickness and porosity on electrochromic switching time of conducting polymers was pursued to determine the morphology influence on ions transport during oxidation step of the redox process, affording sub-second or seconds switching times. ^ Electrospinning technique provided non-woven nanofiber mats, while spin coating and electropolymerization of monomer (N3T) provided films. Porosity decreased as depositing method changed from electrospinning to spin coating. In electrochemical oxidation, the electrons leave the polymer at the metal electrode-polymer film interface, and counter ions arrive at the polaron-bipolaron sites left in the polymer, through polymer-electrolyte interface. Counter ion diffusion in conducting polymers are film thickness limited at increasing thickness and inability of ions to reach holes sites on the oxidizing polymer accounts for long switching speeds, introducing extensive and micro pores and high surface areas should lead to decreasing electrochromic switching speed to single digit time in seconds (for display and vision applications), while increasing the maximum optical switching contrast due to increased fiber mat thicknesses. ^ Photolithographic patterning of nanofiber mats of the conducting polymer precursor having photo cross-linking unit was also explored. The photo-crosslinkable polymer was prepared by including norborene methacrylate (NMA) units to the polymer backbone during precursor polymerization, yielding a terpolymer poly(N3T-NA-NMA). The influence of photo crosslinking on electrochemical switching in conducting polymer nanofibers, and effect of developing parameters (solvent and time) on pattern transfer to the nanofiber mat was investigated and showed no influence on the electrochemical redox of the polymer. Solvents suitable for dissolving the polymer were investigated as developers with results showing non-differentiable pattern transfer for all suitable solvents, and no net preference to solvent choice. ^ Lastly, the alignment of electrospun nanofibers during electrospinning was investigated to prepare composites of aligned nanofiber mats on macro-mesh fabric, and control alignment by non-conventional methods. Nanofibers produced during electrospinning are usually collected as non-woven randomly oriented fibers, but by manipulating the electric field at the collector, aligned nanofibers were obtained. Further modifications using a mesh fabric as collector, or using non-conventional conductive surfaces, deposition of continuous and aligned nanofibers of poly lactic acid was achieved. ^