"Nanotechnology and nanomaterials"

The dielectric spectroscopy of epoxy composites with unoxidized graphene nanoplates
Gorb A.M.1, Gorelov B.M.2, Polovina O.I.1, Shulga S.V.2, Czapla Z.3, Kostrzewa M.3, Ingram A.3, Wacke S.3
1 Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska Str., Kyiv-01601, Ukraine, Ukraine. 
E-mail: g_alla@ukr.net
2 Chuiko Institute of Surface Chemistry of the NAS of Ukraine, 17 General Naumov Str., Kyiv-03164, Ukraine.
3 Department of Physics, Opole University of Technology, Ozimska 75, 45-370 Opole, Poland.

The purpose of this work was to establish a correlation between the behavior of the real and imaginary parts of the permittivity ε* = ε1 + iε2 with structural changes in epoxy composites upon loading epoxy with unoxidized multilayer graphene. The graphene particles had a base surface size of 55 μm, the average particle thickness was 50 nm, and the number of layers was about 100. The complex permeability was measured in the frequency range 4 – 8106 Hz and temperature range 77 – 350 K using the computer-controlled impedance meter Hioki IM3536 General Purpose LCR Meter.
It was found, the growth in the dielectric permittivity ε1 upon loading with graphene is related to the formation of interfacial regions having more disordered and rigid polymer structure. The relation between the dielectric permittivity of composites and structural changes can be described by the expression ε1(C) ~ [1-μ(C)]ε1e + μ(C)ε1i, where ε1e and ε1i are dielectric permittivity of epoxy and interface regions, relatively, and μ is a factor reflecting the content of interfacial regions. The rise in dielectric losses ε2 correlates with reduction of the free volume in the polymer matrix with increasing graphene content.
It is shown that the dielectric response of the matrix monotonously reduces over the entire frequency range with increasing frequency. This behavior is related to the energy exchange between resonant dipoles and their dipole environment. In addition, the dielectric losses increase no monotonously with a maximum at the relaxation β-resonance frequency fβ. The ε2(f) no monotonous dependence is associated with the prevalence of different loss mechanisms at frequencies lower and higher than fβ. In the low-frequency range, losses related to the spatial factor prevail, while in the high-frequency range, losses associated with the transfer of energy from temperature vibrating dipoles to resonant dipoles prevail.