Photo-induced synthesis of polypyrrole-silver nanocomposite films on N-(3-trimethoxysilylpropyl)pyrrole-modified biaxially oriented polyethylene terephthalate flexible substrates

Abstract

Polypyrrole-silver (PPy–Ag) nanocomposite films were prepared on a N-(3-trimethoxysilylpropyl)pyrrole modified biaxially oriented polyethylene terephthalate (BOPET) substrate by photopolymerisation of pyrrole using AgNO₃ as a photo-initiator. The films were prepared for a fixed molar concentration of pyrrole (0.5 M), varying molar concentrations of AgNO₃ (0.05–0.7 M) and different UV exposure times (15 min–180 min). With increasing AgNO₃ concentration or with increasing polymerisation time, the film morphology shows a transition from two dimensional lamellar to granular structures. The films are adherent, flexible and exhibit a maximum room temperature electrical conductivity of ∼15 S cm⁻¹ (for AgNO₃ ∼ 0.5 M, 120 min of UV exposure). However, the films directly prepared on pristine BOPET show granular morphology and their conductivity value is ∼0.5 S cm⁻¹. The high conductivity of PPy–Ag films is attributed to the high conjugation length, the incorporation of Ag nano-particles between the polypyrrole chains and the ordered structure due to the templating effect of the silanised pyrrole layer, as confirmed by GIXRD, FTIR, Raman and temperature dependent conductivity measurements. The metallic state of the embedded Ag nano-particles in the polypyrrole matrix is confirmed by XRD and XPS. The films with the least amount of Ag (AgNO₃ ∼ 0.1 M) only show a reversible conductivity change in the opposite manner on exposure to ppm levels of H₂S and NH₃ gases. The mechanism has been proposed to explain these antagonistic responses for reducing gases.