  Polyvinyl-pyrrolidone (PVP) loaded with different fractions of dispersed
nano-graphene 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.
