Effect of graphene nanoplatelets on the dielectric permittivity and segmental motions of electrospun poly(ethylene-co-vinyl alcohol) nanofibers

The influence of the addition of graphene nanoplatelets (GNPs) on the intra/inter - molecular segmental motions of poly(ethylene-co-vinyl alcohol) (EVOH) was assessed by means of dielectric thermal analysis (DETA). The relaxation spectra were studied in terms of the dielectric permittivity (epsilon') and the dielectric loss tangent (tan delta) at wide ranges of frequency (from 10(-2) to 10(7) Hz) and temperature (from -150 to 140 degrees C). Two relaxation zones were disthinguished. Below the glass transition temperature (T-g), two beta-relaxations were observed, which are characteristic local modes of mobility of the EVOH side groups, and related to the influence of the different surroundings of ethylene or vinyl alcohol units. At higher temperatures, the dielectric alpha-relaxation in the vicinities of the glass transition of EVOH was determined. The thermal activation of the beta-relaxations was explained by an Arrhenius model, and showed activation energies (E-a) around 55 and 80 kJ.mol(-1). The alpha-relaxation was explained by the Vogel-Fulcher-Tammann-Hesse (VFTH) model. The study of the segmental dynamics showed an increase in the dynamic fragility parameters with the addition of GNPs. The permittivity was increased at preferential concentrations of GNPs. In particular, the addition of GNPs up to 0.5 wt% increased the dielectric permittivity of the electrospun EVOH/GNPs nanocomposite fibers, specially at low frequencies. (C) 2020 Elsevier Ltd. All rights reserved.