Elsevier

Synthetic Metals

Volume 145, Issues 2–3, 21 September 2004, Pages 265-270
Synthetic Metals

Synthesis of polyaniline–montmorillonite nanocomposites by the mechanochemical intercalation method

https://doi.org/10.1016/j.synthmet.2004.05.011Get rights and content

Abstract

Nanocomposites consisting of conducting polyaniline (PANI) and montmorillonite (MMT) were synthesized by the mechanochemical intercalation method. The mixtures of sodium MMT and anilinium chloride were mechanochemically ground in a mortar. X-ray diffraction (XRD) analysis confirmed that anilinium cations, which are the monomer of PANI, were intercalated into MMT by a cation-exchange reaction between the sodium cations of MMT and the anilinium cations of anilinium chloride. The basal spacing of the anilinium–MMT intercalation compound significantly expanded from 0.96 to 2.47 nm by adding an excess amount of anilinium chloride. After polymerization by the mechanochemical grinding with ammonium peroxodisulfate in a mortar, a decrease in the basal spacing to 1.33 nm was observed, indicating that PANI was synthesized between the interlayer spaces of MMT. It was further characterized by Fourier transform infrared (FT-IR) spectroscopy. The result of thermogravimetric analysis showed the improved thermal stability of PANI due to modification of the incorporated MMT.

Introduction

Recently, organic–inorganic nanocomposites have received considerable attention because of the intriguing properties and unique structure, and many hybrid composite materials have been synthesized and studied [1]. The intercalation of organic guest species into inorganic materials is a way to construct an ordered organic–inorganic assembly [2]. Polymer intercalation nanocomposites prepared by using layered materials are expected to lead to a high degree of polymer ordering and exhibit advanced gas barrier, thermal stability and enhanced mechanical properties compared to pristine polymers [3]. On the other hand, electrically conducting polymers have also attracted much interest because of the many promising technological applications such as microelectronic devices, electroluminescence devices, corrosion inhibitors, electrochemomechanical devices and chemical sensors [4]. Among the conducting polymers, polyaniline (PANI) is the most promising polymer due to its simple synthesis, high conductivity, and excellent environment stability. However, the poor thermal stability and difficult processability of PANI should be overcome for the application of this electrically conducting polymer. Therefore, there are many published reports focusing on the preparation and new property studies of novel nanocomposites consisting of PANI with various layered materials, such as FeOCl [5], MoO3 [6], V2O5 [7] and clay minerals [8], [9], [10], [11]. The encapsulated conducting polymers in the interlayer spaces of layered materials may provide different characteristics, which cannot be attained from a pristine polymer. Among the many layered materials, clay minerals (e.g., montmorillonite (MMT)) have been extensively investigated because they are natural, abundant and inexpensive. Furthermore, they provide attractive features, such as a large surface area and ion-exchange properties. Polyaniline–clay nanocomposites are usually prepared from the mixtures of aniline and clays in an aqueous solution. Wu et al. [8] studied the intercalative polymerization of aniline into sodium MMT. Kim et al. [9], synthesized dodecylbenzensulfonic acid-doped PANI–MMT nanocomposites using an emulsion polymerization method. Yang and Chen [10] and Jia et al. [11] synthesized PANI–MMT nanocomposites with organically modified clays. However, there have been few reports on the preparation of nanocomposites of PANI with MMT by a mechanochemical reaction. A mechanochemical reaction, which is a solid-state reaction, has been mainly employed in the study of metals and alloys. It has obvious advantages such as a simple process, high capacity and relatively low cost. Furthermore, mechanochemical reactions are environmentally benign reactions without using any solvents. Ogawa et al. [12], [13], reported that solid–solid reactions are useful ways to introduce organic guest species into the interlayer spaces of clay minerals. They succeeded in the solid-state intercalation of organic compounds into MMT by both a cation-exchange reaction and adsorption of polar molecules.

In this paper, we report the results of the preparation of PANI–MMT nanocomposites using the mechanochemical intercalation method that is an effective solid-state reaction for the fabrication of intercalation compounds. The synthesized nanocomposites were characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetry-differential thermal analysis (TG-DTA).

Section snippets

Materials

The clay used in this study as the host material was sodium MMT (Kunipia F) purchased from Kunimine Ind. Co., Japan. Its cation-exchange capacity (CEC) value is 115 meq/100 g clay. As the guest molecule, anilinium chloride was obtained from WAKO Pure Chemical Ind. Co. Hydrochloric acid (HCl), ammonium peroxodisulfate ((NH4)2S2O8) and other chemicals used in this experiment were obtained from WAKO Pure Chemical Ind. Co., as extra pure grade. These reagents were used without further purification.

Preparation of PANI–MMT nanocomposites

Characterization of anilinium–MMT intercalation compounds

The intercalation of anilinium chloride into MMT by the mechanochemical grinding proceeds with a color change from the pristine MMT color to red. Fig. 1 shows the XRD patterns of the product obtained by grinding sodium MMT and anilinium chloride with the added amount of 1.15 mmol/1 g of MMT, together with those of pristine MMT and anilinium chloride. Hereafter, the products prepared from the mixtures of sodium MMT and anilinium chloride are denoted as Ani–MMT (n), where n indicates the amount of

Conclusions

We synthesized nanocomposites consisting of PANI and MMT by the mechanochemical intercalation method. The amount of anilinium incorporated into MMT by the mechanochemical intercalation method was much greater than that by a conventional solution method. That is, the mechanochemical intercalation method enables one to intercalate the anilinium that cannot be intercalated by a conventional solution method. The XRD analysis confirmed that PANI was also synthesized between the interlayer spaces of

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    However, in these examples, the driving force for intercalation of the organic molecule was the formation of a coordination complex with the preexisting interlayer cations. A mechanochemical route to the interlayer polymerization of polyaniline and polypyrrole in montmorillonite has also been proposed (Yoshimoto et al., 2004a,b, 2005a,b,c), but there are few data regarding non-polymerizing solid-state intercalation of surfactants. OMt was prepared by heating the mixture of Mt., cetyl trimethyl ammonium bromide (CTAB) and silane coupling agent with vigorous stirring (Ge and Jia, 2008, 2009).

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