Unusual Dielectric Properties of Electrochromic Polydipyridinium Triflate Composites with Carbon Nanotubes
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ICS OF CONDENSED STATE OF MATTER
Unusual Dielectric Properties of Electrochromic Polydipyridinium Triflate Composites with Carbon Nanotubes I. A. Malyshkina1* , E. E. Makhaeva1** , and R. D. Pichugov1*** 1
Department of Physics, Moscow State University, 119991, Moscow, Russia Received November 25, 2019; revised January 22, 2020; accepted January 23, 2020
Abstract—The dielectric properties of electrochromic composite material based on poly[4,4’-(1,4phenylene)bis(2,6-diphenylpyridinium)triflate] (PV) and multi-wall carbon nanotubes (MWCNTs) have been studied. Negative permittivity was registered at low frequencies of the alternating electric field (10−1 −103 Hz) in the PV/MWCNT nanocomposites of different composition. The frequency of transition from negative to positive permittivity, as well as the values of conductivity, increased in the case of application of direct-current (dc) voltage. The physical mechanism responsible for the unusual properties appears to be related to the delocalized charges located at the multiple insulator–conductor interfaces. Keywords: electrochromic polymers, carbon nanotubes, nanocomposites, negative permittivity, conductivity. DOI: 10.3103/S0027134920020071
INTRODUCTION Polymer composite materials are progressively gaining ground and being developed. Polymer composites are widely used in different areas, from building to airspace engineering. Inclusion of nanoscale fillers to polymers may lead to a significant enhancement of some physical properties in comparison with the initial material. Even at low concentrations of nanofillers, one can achieve a considerable improvement of their properties due to their high surface area to volume ratio. Carbon nanotubes (CNTs) are used as fillers for the production of a new class of polymeric heterostructures. They are of great interest due to their nano-scale dimensions and significant shape anisotropy, as well as their unique mechanical, thermal, and electrical properties [1, 2]. Polymer-CNT composites combine the unique characteristics and functionality of components, which is reflected in the physical-chemical and exploitation properties of materials [3–7]. The macroscopic specimens of singlewall CNTs in the form of randomly oriented fibers of nanotubes form a pseudo-metal with a conductivity of approximately 103 S/cm [8]. *
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The main aspect associated with the conductivity properties of a composite is the relationship between its conductivity and number of particles. When the volume concentration of the filler particles reaches some critical value, the properties abruptly change from dielectric to conductive. Such a behavior is related to formation of an interconnected net of conducting particles; the corresponding critical volume fraction of particles is called the percolation threshold [9]. The electric percolation threshold depends on both the material of the matrix and the process of specimen preparation [10]. Even for a polymer such as polyethy
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