Role of Anionic Micellar Template on the Morphology, Solid-State Ordering, and Unusual Conductivity Trend in Poly(aniline-co-pyrrole) Nanomaterials

Abstract

Here, we report three structurally different anionic amphiphilic dopant micellar templates for the development of poly(aniline-co-pyrrole) copolymer nanomaterials and investigating the role of dopant on the morphology, solid-state ordering, and unusual bulk conductivity trend in conducting nanostructures. All three amphiphilic dopants possessed identical azobenzene sulfonic acid as polar head but vary in their hydrophobic alkyl tails. Dynamic light scattering analysis confirmed the formation of 4.3 and 100 nm micelles by the single tail and double tail amphiphiles in water, respectively. Upon adding aniline or pyrrole (or mixture of both), the dopant micelles produce a thick white emulsion containing micrometer size larger aggregates, which template for nanomaterial. The copolymer nanomaterials were synthesized by varying the amount of aniline and pyrrole in the feed from 0 to 100 mol % under identical emulsion polymerization routes. Electron microscopic analysis (SEM and TEM) revealed that the morphology of the copolymer nanomaterials transformed from nanofiber to nanospheres via nanorods upon increasing the composition of pyrrole in the feed. Four probe bulk conductivities of the nanomaterials, which were produced on the basis of single tail dopant (or no tail dopant), showed unusual nonlinear trend over the pyrrole composition. Because all three copolymers series showed similar morphology evolution, the influence of morphology transformation on the unusual trend in the bulk conductivities was ruled out. The percent crystallinity of the samples obtained from WXRD spectra provides direct evidence that the bulk conductivity of the copolymer conducting nanomaterials is primarily influenced by their three-dimensional solid-state ordering rather than other factors such as morphology transformation. The structure of the dopant plays major roles in arranging the polymer-dopant complexes in highly ordered forms, which contribute to their bulk conductivity behaviors in the solid state.