Title

Enhanced processibility of conductive polymers via solid-state oxidative cross-linking

Date of Completion

January 2004

Keywords

Chemistry, Polymer

Degree

Ph.D.

Abstract

Intrinsically conducting polymers (ICP) have received great attention due to their potential use in applications such as electrochromic devices, protective coatings, organic light emitting diodes (LED), solar cell, energy storage batteries, volatile gas sensors, nonlinear optics, charge dissipating films, and molecular-scale electronics. Typically ICPs are prepared from monomer solution by chemical/electrochemical means and the polymers thus produced are intractable possessing processing difficulty. ^ In this work, a novel technique, “Solid-state Oxidative Crosslinking (SOC)”, addresses making electrochemical polymerization more practical and provides a way to make ICPs in different form factors, is demonstrated. Utilizing this technique, ICPs were prepared via conversion of their insulating precursor polymers in the solid-state to conducting polymers in nearly quantitative yield. Conventional solution-processing techniques can be used to process the precursor polymers and the SOC conversion to ICPs is performed without perturbation of the precursor polymer shapes. Furthermore, this SOC technique can be used to precisely control the conversion of insulating polymers to conducting polymers in micron and nano-scale. ^ Direct writing of intrinsically conducting polymers in nanoscale regimes is shown using “Electrochemical Oxidative Nanolithography (ECON)”, SOC coupled with electrochemical atomic force microscopy (ECAFM). Conducting polymer nanolines of 45 nm width were successfully written via contact and tapping mode. The line width was successfully controlled between 45 nm to 240 nm depending upon the writing speed, writing mode, and applied potential. This technique was found to be >1,500 times faster than other existing atomic force microscopy (AFM) based lithographic techniques known to produce nanometer sized conducting polymer lines. Furthermore, in ECON, no restriction in the choice of substrate was found thus far, envisioning the feasibility to the application to plastic nanoelectronics. ^ A simple method of preparing conductive polymer nanofibers was demonstrated via electrospinning of precursor polymer solutions followed by SOC. Polythiophene nanofibers having diameter of 90–180 nm were successfully obtained using this technique and no significant perturbation of the nanofibers morphology during SOC was found. Furthermore, a large red shift in the absorption spectra of the polythiophene nanofibers compared to the corresponding films suggests a possible increase in the effective conjugation length of the conjugated thiophene polymers due to extension of the precursor polymer chains during spinning. ^