SELF-ASSEMBLY OF THE ELECTROACTIVE COMPLEXES OF POLYANILINE AND SURFACTANT

An electroactive material with remarkable solubility, processibility a s well as mechanical properties has been developed by complexation (th ermal doping) of polyaniline (PANi) emeraldine base with dodecylbenzen esulfonic acid (DBSA) in the solid state. Isothermal treatment of such a mixture was found to promote the complex formation. Optimum conditi ons of complexation were established with respect to the formation of layered structure, electrical conductivity and solubility. The optimal temperature for the doping process was found to be in a range of 100- 120 degrees C while the best ratio of DBSA to PANi was between 3:1 and 4:1 by weight, a nearly stoichiometric equivalence of aniline repeat units and DBSA molecules. The time of isothermal treatment should be c ontrolled within 30 min. Thermal doping induced orientation to polymer chains in a layered structure, whereby the hydrophobic tails of the s urfactants function as spacers between parallel stacks of the main cha ins. This anisotropy was achieved by the self-assembly during the ther mal doping rather than ordinary drawing or stretching of the polymers. A unique liquid crystalline mesophase with a smectic-like optical tex ture was observed for the soluble portions of some specimens. The exce ss DBSA in the samples is considered to function as a solvent and to g ive rise to the liquid crystalline fluidity of the phase. The scanning tunneling microscopy (STM) image 5000 x 5000 Angstrom on a submicrome ter scale obtained from a PANi/DBSA thin film exhibits a surface morph ology with a granular size of 200-300 Angstrom. The image of 150 x 150 Angstrom on a molecular scale obtained from multilayer PANi/DBSA depo sited on a highly oriented pyrolytic graphite (HOPG) surface provides a direct observation of a self-assembled structure and close layer pac king of the polymer backbone with dimensions in accord with the result s found by X-ray diffraction. Our results indicate that the thermal do ping process of polyaniline by DBSA offers new possibilities to obtain optimal structures through a self-assembly.