Effect of low concentrations of carbon nanotubes on electric dipole relaxation in a polyurethane elastomer

Abstract

The effect of small (up to 0.018 wt %) additions of single-walled carbon nanotubes (SWNTs) on the complex electric modulus M*= M′ - jM″ and the spectrum of the relaxation times G(τ) of a cross-linked polyurethane elastomer containing ∼10 vol % of polyamide-6 dispersed in the polyurethane matrix and incompatible with it was studied. The measurements were conducted in the range of electric field frequencies 10⁻³–10⁵ Hz at temperatures from 133 to 413 K. Based on the shape analysis of the M″(M′) diagrams, the contributions of electric conductivity and dielectric relaxation to complex dielectric permittivity ɛ* = ɛ′ - jɛ″ were separated and the effect of additions on α and β relaxation for both polyurethane and polyamide phases was analyzed in accordance with the peculiarities of phase-separated systems. The introduction of SWNTs in the composite affected the dielectric properties of the material; the maximum effect was observed at concentrations of 0.002–0.008 wt %; at higher SWNT concentrations, the scatter of data increased and did not allow us to evaluate the effect. The effect of SWNTs on G(τ) in the main phase was opposite to that in the polyamide phase. In the temperature range of α relaxation of the polyurethane phase, the relaxation times increased after the introduction of SWNTs evidently because of the decrease in the free volume that determines the α relaxation times of polyurethane. In contrast, for the polyamide phase in the range of α relaxation, the relaxation times decreased after the introduction of SWNTs. The results agree with the literature data on the effect of ultrasmall SWNT concentrations on the physicomechanical characteristics of the polyurethane elastomer and its electric conductivity.