Swift Heavy Ion Irradiation Effects on the Properties of Conducting Polymer Nanostructures

Abstract

This chapter presents the basic concepts of conducting or π-conjugated polymers and their different nanostructures and physico-chemical properties, which ushered in a new era of functional organic materials with potential applications. Most importantly, they can replace the traditional metallic conductors owing to their excellent properties of high conductivity, thermal stability, light weight, low corrosion, high flexibility, ease of synthesis and low cost. The first studied conducting polymer was polyacetylene, and in the last two decades, the most extensively studied conducting polymers are polyaniline (PAni), polypyrrole (PPy) and polythiophine (PTh) and their derivatives owing to their interesting physico-chemical properties. Irradiation on polymers with energetic heavy ions is used to tailor their different physico-chemical properties. The energetic heavy ion irradiation-induced modifications on various properties of polymers depends on various parameters viz. type of energy transferred (i.e., nuclear or electronic) to the target, species of ion and ion fluences. The ion-matter interaction with low energy (eV to keV) range causes implantation of the ions, while ions with high energy (keV to MeV) interaction cause irreversible structural modification along the cylindrical ion track, which is of the order of few nanometers in diameter. The fundamental aspects of ion-solid interaction, different related parameters and models governing the ion-solid interaction have been described in details in this chapter. PPy nanotubes, potential candidate of highly conducting π-conjugated polymers, have been chosen for irradiation at different ion fluences to enhance their structural, morphological, electrical, optical and thermal properties. Room temperature swift heavy ion (SHI) irradiation on thin PPy films (thickness ~30–35 µm) was investigated under high vacuum (~10−5 Torr) condition by 160 MeV Ni12+ SHI using various irradiation fluences such as 1010, 5 × 1010, 1011, 5 × 1011 and 1012 ions/cm2. High-resolution transmission electron microscopy (HRTEM) was used to investigate the morphological changes of SHI-irradiated PPy nanotubes. The irradiated nanotubes exhibit denser structure, and density is highest at 5 × 1011 ions/cm2 irradiation fluence. However, on irradiation with the highest ion fluence of 1012 ions/cm2, the density of irradiated PPy nanotubes is decreased. Up to the ion fluence of 5 × 1011 ions/cm2, reduction in optical band gap energy (Eg) of irradiated PPy nanotubes is observed; however, at the investigated highest irradiation fluence of 1012 ions/cm2, value of Eg is found to be higher as compared to the unirradiated PPy nanotubes. Micro-Raman studies exhibit that upon SHI irradiation up to the ion fluence of 5 × 1011 ions/cm2, the π-conjugation length and crystallinity of PPy nanotubes are increased. Thermogravimetric analysis (TGA) shows enhanced thermal stability of irradiated PPy nanotubes with increasing ion fluence, while thermal stability of PPy nanotubes decreases at the highest irradiation fluence. The current-voltage (I-V) characteristics for the irradiated PPy nanotubes get enhanced with increasing ion fluence, while their I-V characteristics decrease at the highest irradiation fluence of 1012 ions/cm2. The scaling of modulus spectra of irradiated PPy nanotubes at different irradiation fluences depicts irradiation fluence-independent relaxation dynamics of charge carriers. At the end of the chapter, the challenges in the field of ion-matter interaction in pre-/post-irradiation as well as the processing, characterization and application of the target materials have been discussed.