Dynamics of electric charge transport and determination of the percolation insulator-to-metal transition in polyvinyl-pyrrolidone/nano-graphene platelet composites

Abstract

Polyvinyl-pyrrolidone (PVP) loaded with different fractions of dispersed nanographene platelets (NGP) were studied by Broadband Dielectric Spectroscopy in the frequency range from 1 mHz to 1 MHz. Complex permittivity and dynamic ac conductivity as a function of frequency, temperature and composition were explored. The concentration-dependent insulator-to-conductor transition was traced through dependence of the dc conductivity and the onset of the dispersive ac ac conductivity. The temperature evolution of the dielectric spectra, below and above the fractional threshold exhibits different dynamics and signs the critical percolation threshold. Percolation is dictated by quantum penetration of the effective potential barrier set by the polymer matrix operating in parallel with conduction along physical contact of NGP, in accordance with predictions for systems consisting of a semi-conducting matrix and dispersed conducting inclusions.* Corresponding author; e-mail address: antpapa@phys.uoa.gr 2 Functional polymers with dispersed nano-structures exhibit properties of significant technological importance, broad applicability and low production cost. Polyvinyl-pyrrolidone (PVP) is a polymer wide known for its pharmaceutical applications. It can be used as binder, coating and disintegrate for tablets stabilizer [1]. PVP is easily dissolved in water; both PVP and water are non-toxic, environmentally friendly and bio-compatible materials. Graphene is an excellent conductor of electricity and can be dispersed into water. Nano-graphene platelets combine the advantageous properties of graphene and the low production cost (e.g., in relation with single layered graphene). Thus, controlling the PVP/NGP composition, one can tune the properties of the composite, respectively, and achieve the desired optimum properties respectively. In this way, novel ambitious devices can be innovated. For example, water solutions PVP/ NGP composite can be used as bio-compatible link between electrodes and skin or tissues. As a result, various coated functional polymers with graphene [2, 3] have been prepared in order to analyse the mechanisms of charge transfer [4], to find the critical nanoparticle concentration to achieve percolation of electric charge carriers along the volume of the composite [5,6,7] and generally to inspect the electrical properties for those various matrices.Lastly, PVA (polyvinyl-alcohol) is a relevant material with polyvinyl-pyrrolidone that has been studied significantly [8]. In such studies, the dc conductivity vs composition is examined to find the percolation threshold. Standard percolation theories [9] assume that the host matrix is a perfect insulator, which is an abrupt assumption in many real systems. Recent progresses on percolation phenomena in systems with matrixes that can be penetrated by electron quantum mechanical tunneling [10] describe better PVP/NGP composites.Aqueous polymer solutions were formed by dissolving PVP K30 (ASG SCIENTIFICCAS 9003-39-8) in de-ionized doubly distilled water and aque...

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