Directional Templating Mechanisms of Anisotropic Nanoparticles Using Poly(pyromellitic dianhydride‑p‑phenylenediamine)

This study reports for the first time the use of poly­(pyromellitic dianhydride-p-phenylenediamine) (PPDD) as a reducing and stabilizing agent, immobilization matrix, and directional template for the synthesis of anisotropic silver nanoparticles (AgNPs). The work also provides a new physical insight into the mechanisms of directional templating of anisotropic nanoparticles based on diffusion-limited aggregate model and coalescence growth mechanism. Molecular dynamics simulations and density functional theory calculations were performed to provide insight into possible conformations of the PPDD monomer. Anisotropic (nonspherical) peanut-shaped nanorods and dendritic nanostructures were prepared in situ using varying concentrations of precursors from 0.1 to 1.0% w/v within PPDD matrix. The PPDD served as the reducing and directional template, thus enforcing preferential orientation. The mechanism of formation and growth of the polymer-mediated anisotropic nanoparticles was confirmed using transmission electron microscopy, UV–vis near-infrared absorption spectra (UV–vis-NIR), and X-ray diffraction. The size distribution of the nanoparticles was found to be 6–10 (0.1% w/v), 20 (0.2% w/v), and 70–100 nm (0.5% w/v). The UV–vis-NIR spectra confirmed the existence of transverse and longitudinal surface plasmon resonance according to Mie theory. The anisotropic growth of dendritic/nanorods AgNPs could be attributed to diffusion-limited aggregate model and coalescence growth mechanism. 111 planes were the most predominant structures, indicating inhibition of growth along the perpendicular axis by PPDD, thus conferring the preferred coalescence orientation of nanoparticle parallel on the film.