Nanoscale conformational ordering in polyanilines investigated by SAXS and AFM

• Published in: Journal of colloid and interface science 2007-12, Vol.316 (2), p.376-387
• Main Authors: Leite, Fabio L., de Oliveira Neto, Mario, Paterno, Leonardo G., Ballestero, Michel R.M., Polikarpov, Igor, Mascarenhas, Yvonne P., Herrmann, Paulo S.P., Mattoso, Luiz H.C., Oliveira, Osvaldo N.
• Format: Article
• Language: English
• Subjects: Adsorption; Adsorption and conformation; AFM; Aniline Compounds - chemistry; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Microscopy, Atomic Force - methods; Models, Molecular; Molecular Structure; Nanostructures; Nanostructures - chemistry; Nanotechnology - methods; PANI; Particle Size; Quantum Theory; SAXS; Scattering, Small Angle; Self-assembly; Solutions - chemistry; Surface physical chemistry; Surface Properties; TEM; Thin films; X-Ray Diffraction
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2007.08.069

Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly( o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology—seen with atomic force microscopy and transmission electron microscopy—that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids. The polyaniline molecules in solution present a coiled structure (less-packed) when in pH 3, which indicates a more extended structure, while at pH 10 blobs are formed. The figures show the low-resolution particles shape determined from the experimental data using the ab initio procedure.