Design and Fabrication of Molecular Assemblies of Conductive Polymers

Two new methods of fabricating multilayer Langmuir -Blodgett (LB) thin films of electrically conductive polyaniline and a novel method of constructing molecular assemblies of polyaniline via the spontaneous adsorption (SA) technique were developed. Quantitative transmission/reflection Fourier transform infrared spectroscopy, polarized ultraviolet -visible spectroscopy and X-ray diffraction techniques were used to examine the structure and composition of multilayer thin films. In the structural study of LB films fabricated from 3-octadecyl pyrrole (3-ODP), 3-octadecanoyl pyrrole (3-ODOP) and polypyrrole/3-ODOP (PPY/3-ODOP), the level of order and orientation were found to be affected by the intermolecular and intramolecular interactions between molecules. For the manipulation of polyaniline using the LB technique, stable and easily transferrable LB monolayers were formed at the air-water interface by mixing polyaniline in its emeraldine-base form (PANb) with two processing aids. Films fabricated from the PANb/StA mixture were found to be phase separated with domains of polyaniline and stearic acid while those from the PANb/PI blend were found to be miscible. Both polyaniline LB films were rendered conductive by doping with 1 M HCl or HCl vapor. Multilayer polyaniline films were also constructed via a SA process. The multilayer buildup of doped polyaniline and sulfonated polystyrene (PANi/SPS) is facilitated by the electrostatic attraction between the delocalized positive -charged defects along the PANi backbone and the negative charges present in the ionizable pendant sulfonic acid groups of the SPS. Uniform multilayer thin films with thicknesses between 20 A and 100 A were constructed on different surfaces with complex topologies. Conductivities in the level of 0.1-1 S/cm were achieved by doping the multilayer PANi/SPS films with 1 M HCl. This level of conductivity was achieved by films with as few as 4 layers of PANi/SPS, that is, films with thicknesses of about 200 A. The lower conductivities attained by thinner films were attributed to the lack of formation of continuous conductive PANi pathways. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.).