Morphological Transition and Associated Conductivity Shift in Emeraldine Polyaniline: Unraveling the Urbach Tail Analysis

Abstract

The conducting polymer, polyaniline (PANI), was synthesized in its emeraldine salt (ES) and emeraldine base (EB) forms by the method of chemical oxidative polymerization using hydrochloric acid (HCl) as the dopant. Characterization of these samples was carried out by UV–Visible spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDX) and two probe conductivity measurements. It was observed that the electrical conductivity of the ES form of PANI had a six-order increase when compared to its EB form. This result was correlated with the morphological switch-over from granular to coral-reef structure of the PANI. Optical properties of the two forms were compared using Tauc plots and Urbach tail analyses. This article emphasizes a thorough investigation of the relatable features of the ES and EB forms of PANI toward tuning its d.c. conductivity. The study places a strong emphasis on the use of characterization techniques as an effective tool for characterizing the electrical properties of PANI. The tailoring of these properties of the two forms of PANI can empower the applicability of this class of conducting polymers in various state-of-the art devices.

Keywords:

• Conducting polymers
• polyaniline
• emeraldine salt-base
• Urbach tail
• electron microscopy
• two-probe conductivity

Acknowledgement

The authors acknowledge the Department of Science and Technology(DST), Government of India; the University Grants Commission (UGC) and the Centre of Excellence (CoE) Project, Government of Kerala for funding the work. The authors also acknowledge the DST-SAIF, Sophisticated Test and Instrumentation Centre (STIC), Cochin University of Science & Technology Campus for optical, structural and thermal studies; the Central Laboratory for Instrumentation and Facilitation (CLIF), University of Kerala for structural studies and the Materials for Energy Storage and Optoelectronic Devices Group, Department of Physics, Sanatana Dharma College, Alappuzha for conductivity studies.

Authors’ Contribution

K. S. Mary Linsa: Conceptualization, Methodology, Sample preparation, Formal analysis, Resources, Writing - original draft, Writing - review & editing. Roshila K. Pavithran: Sample preparation. Roshan Joseph Mathew: Writing - review & editing. Parvathy Radhakrishnan: Writing - review & editing. R. Pragash: Writing - review & editing. U. S. Sajeev: Formal analysis, Writing - review & editing, Validation, Supervision.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Department of Science and Technology(DST), Government of India under a FIST 0-Level Grant [SR/FST/COLLEGE-206/2014]; by the University Grants Commission (UGC) under a Major Research Project (F No. 42.895/2012 (SR)); and by the Government of Kerala under the Center of Excellence (CoE) Project [A3-1307/2018/Plan 18-19].