Highly anisotropic conductivity of tablets pressed from polyaniline-montmorillonite nanocomposite

Highlights

• Montmorillonite (MMT) can be intercalated with polyaniline (PANI) chains.

• Tablets pressed from PANI/MMT exhibit high anisotropy in electrical conductivity.

• Pressure 28MPa is sufficient to reach the anisotropy.

• Tablets pressed from pure PANI also exhibit anisotropy in electrical conductivity.

Abstract

Polyaniline-montmorillonite nanocomposite was prepared from anilinium sulfate (precursor) and ammonium peroxodisulfate (oxidizing agent) using simple one-step method. The resulting nanocomposite obtained in powder form has been pressed into tablets using various compression pressures (28–400 MPa). Electrical conductivities of tablets in two perpendicular directions, i.e. direction parallel with the main surface of tablet (σ=) and in orthogonal direction (σ⊥), and corresponding anisotropy factors (i.e., the ratio σ=/σ⊥) have been studied in dependence on compression pressure used during the preparation. Polyaniline-montmorillonite nanocomposite was characterized using X-ray diffraction analysis, raman spectroscopy, transmission electron microscopy, thermogravimetric analysis and molecular modeling which led to the understanding of the internal structure. Measurement of hardness performed on pressed tablets has been also involved. Taking into account the highest value of anisotropy factor reached (σ=/σ⊥ = 490), present study shows a chance to design conductors with nearly two-dimensional conductivity.

Introduction

In conducting polymer systems the nanostructure and chains alignment are the crucial factors affecting their properties. Ordering of polymer chains can be achieved by various methods such as mechanical orientation of polyaniline (PANI) chains using blends with insulating polymers, using electric field or high pressure [1], [2], [3]. Hybrid PANI/phyllosilicate nanocomposites offer the promising way of PANI chains alignment due to the inclusion of phyllosilicate particles into polymeric matrix and due to the intercalation of polymeric chains into the phyllosilicate layered structure. In addition, the interaction of PANI chains with phyllosilicate structure leads to improved thermal, mechanical and anticorrosive properties [4], [5], [6]. Among various phyllosilicates the montmorillonite (MMT) represents the most convenient layered structure suitable as a matrix for conducting polymers because (1) MMT structure is easily expandable (i.e., able to accommodate polymeric chains in the interlayer space) and (2) thanks to a low layer charge of MMT layers the conductivity of PANI chains is not significantly reduced in PANI/MMT nanocomposite.

Dependence of conductivity on pressure for PANI and its derivatives has been investigated by several authors [7], [8], [9]. Results obtained in these studies showed that the dependence can be strongly affected by many factors, like acid doping of PANI, the synthesis pathway, and use of PANI derivatives. In spite of many studies focused on conductivity of PANI/phyllosilicate nanocomposites [4], [5], [6], [10], [11], [12], [13], [14], [15], the dependence of conductivity on compression pressure used for the preparation of tablets from these materials has not been studied yet. In present work we investigate how various compression pressures (28–400 MPa) affect the electrical conductivity of tablets prepared from PANI/MMT nanocomposite. Also, the internal structure of PANI/MMT nanocomposite is studied using combination of X-ray diffraction analysis, thermogravimetric analysis, transmission electron microscopy, raman spectroscopy, and molecular modeling. The main aim of our work is reaching very high anisotropy in order to obtain the two-dimensional conductivity.