Insights from theory and experiments on the dynamics of controlled in situ polymerization of pyrrole at the liquid–liquid interface

Abstract

The controlled diffusion and precise assembly of nanoparticles, polymers, and conventional surfactants at liquid–liquid (L–L) interfaces have significant potential in research domains such as oil recovery, electro-optics, and liquid electronics. Apart from this, L–L interfaces have been explored as a promising strategy to tune the nanostructure of conductive polymers and their hybrids in an in situ manner. The present work focuses on understanding the dynamics and molecular interactions between reactive intermediates and the solvent molecules at the interface to aid in optimizing the polymerization process. The molecular dynamics (MD) simulations and their experimental validation revealed the molecular interactions between the oligomeric/polymeric units of pyrrole and solvent molecules at the interface of chloroform and water. We focus on the polymer size and charge-to-size ratio in governing the confinement, interfacial coverage, and morphology during polypyrrole (PPy) formation under varying oxidant concentrations. The present results reveal that the charge-to-size ratio dictates the hydrophobic–amphiphilic–hydrophilic transition of PPy, which in turn controls the adsorption of the oligomers at the water–chloroform interface. Morphological characterizations such as FESEM, AFM, and HRTEM confirmed that at intermediate concentrations of oxidant, ammonium persulfate (APS), corresponding to the optimum charge-to-size ratio, well-defined two-dimensional PPy sheets form at the interface. The interfacial tension, density profiles, electrostatic potential, and hydrogen bonding interactions of reactive intermediates and the orientation of polymer units at the water–chloroform interface affirm the importance of the molecular interactions in controlling the in situ generation of conducting polymers at the L–L interface. The combined experimental and theoretical studies give profound insight into the mechanism of in situ interfacial polymerization and lay a foundation for controlled design of multifunctional polymer hybrids.