Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Polyaniline/clay nanocomposites. A comparative approach on the doping acid and the clay spacing technique Claudia María De León-Almazan a , Iván Alziri Estrada-Moreno b , Ulises Páramo-García a , José Luis Rivera-Armenta a, ⁎ a Centro de Investigación en Petroquímica, Instituto Tecnológico de Ciudad Madero, Prol. Bahía de Aldair y Ave. de las Bahías, Parque de la Pequeña y Mediana Industria, Altamira, Tams., 89600, México b CONACyT – Centro de Investigación en Materiales Avanzados, S.C., Centro de Investigación en Materiales Avanzados, S.C., Miguel de Cervantes 120, Chihuahua, Chih., 31136, Mexico ARTICLE INFO Keywords: Polyaniline Clay Nanocomposites ABSTRACT Polyaniline/clay nanocomposites (PCNs) have been synthesized by oxidative polymerization of aniline by using two different clay treatment techniques (mechanical agitation and ultrasonication), as well as two different doping acids (hydrochloric acid – HCl – and dodecylbenzene sulfonic acid – DBSA –). The effect of both con- ditions on their chemical nature, structure and morphology has been studied by Raman spectroscopy, X-ray Diffraction (DRX), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). PCNs electrical conductivity was measured by the 4-probe technique. The results reveal that the type of clay treatment shows no impact on the PCNs morphology, but it does determine their final structure – either intercalation or exfoliation – which has a remarkable effect on the electrical conductivity. Moreover, the doping acid presented a strong influence on both morphology and electrical conductivity of the prepared PCNs. In this work, HCl doping and ultrasonication are highlighted as the optimal PCN synthesis conditions, since the highest electrical con- ductivity is reached with less time and energy consumption. 1. Introduction Since the early 90s, the study of conducting polymers (CPs) has attracted the attention of the scientific community due to their singular electrical, optical and optoelectronic properties [1,2]. Polyaniline (PAni) ranks as one of the most studied CP because of its high electrical conductivity, ease of preparation, low cost, environmental stability and non-toxicity [1–5]. These remarkable features have taken this peculiar polymer to several interesting applications such as electrostatic charge dissipation, touch control switches, electromagnetic interference shielding, pressure sensor, electrochromic equipment, photochemical cells, rechargeable batteries, separation membranes, sensors and an- ticorrosive coatings [2–4,6]. However, in spite of its multiple advantages, PAni cannot be easily used as filler due to its poor mechanical and thermal stability [6]. For this reason, the control and improvement of PAni properties have be- come one of the most significant challenges of PAni research [7]. The formation of PAni composites with inorganic materials has opened a new approach to get synergistic properties with respect to their pristine constituents [1,8]. Recently, there is a growing interest on the development of PAni nanocomposites with increased electrical, thermal and mechanical stabilities [1,7,9]. Since chain alignment is a very important factor in CP systems, the exploitation of PAni properties can be achieved by the inclusion of plate-like inorganic structures to raise the ordering degree of PAni chains as a result of their non-bond interaction with the inorganic surface. This phenomenon leads to a reduced percolation threshold – i.e. the minimum concentration of conductive filler required to build a conductive network – and thus, enhanced electrical conductivity [7,9,10]. Over the last decade, the interest has been oriented to polymer/clay composites, aiming at a strengthening of their original properties [11,12]. Layered phyllosilicates, such as smectite clays, stand out as the most commonly used materials to get PAni/clay nanocomposites (PCNs), being montmorillonite (MMT) the most popular one because of its small particle size, large surface area, cation exchange properties and swelling capability [7,8] and also due to its attractive inexpen- siveness and natural abundance [5,11]. Nevertheless, clays show hy- drophilic nature, hindering their compatibility with polymers. There- fore, compatibilizing agents – usually quaternary alkylammonium salts – are used to shift clays polarity and hence, to increase their affinity to https://doi.org/10.1016/j.synthmet.2018.01.006 Received 26 October 2017; Received in revised form 23 December 2017; Accepted 14 January 2018 ⁎ Corresponding author. E-mail address: jlriveraarmenta@itcm.edu.mx (J.L. Rivera-Armenta). Synthetic Metals 236 (2018) 61–67 0379-6779/ © 2018 Elsevier B.V. All rights reserved. T