Dielectric relaxation processes in epoxy resin—ZnO composites

Abstract

Polymer matrix‐ZnO microcomposites were prepared in different filler concentrations. The electrical relaxation dynamics of all samples was examined by means of broadband dielectric spectroscopy (BDS) over a wide temperature range. Two relaxation modes (namely β and γ), observed in the low temperature region, are attributed to the reorientation of small polar groups of the polymer matrix. Glass‐rubber transition (α‐mode) of the polymeric matrix and interfacial polarization phenomena are considered as responsible for the recorded relaxation processes in the high temperature region. An additional relaxation mode, named intermediate dipolar effect (IDE), is recorded at temperatures higher than −30 °C in all composites. Its occurrence and dynamics are related to the presence and concentration of the filler. IDE and α‐relaxation are observed in the same frequency and temperature range, leading to a mutual superposition. The two processes were distinguished following a simulation procedure employing the simultaneous fitting of two Havrilliak‐Negami terms and a third term describing the contribution of DC conductivity to dielectric losses. The temperature dependence of relaxation times for α‐mode follows the Vogel‐Tamann‐Fulcher equation, whereas IDE relaxation times follow unusual temperature dependence. The latter is discussed under the assumption of intrinsic interfacial polarization phenomena within ZnO crystal domains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 445–454, 2009

Dielectric relaxations in polyoxymethylene and in related nanocomposites: Identification and molecular dynamics

“…Similar relaxation mechanisms have been previously reported for polymer matrix / inorganic filler composites and have been attributed to polarization phenomena taking place within the reinforcing phase [24][25]27]. Since this relaxation is attributed to the layered silicate itself, its analysis is beyond the scopes of the current work.…”

“…For that reason this process can be initially attributed to the alumina filler itself. Such intermediate mechanisms have been observed in polymer matrix/ ceramic filler composites and are attributed to polarization phenomena that take place within the reinforcing phase [24][25]27]. On the other hand, previous studies by us on alumina containing composites embedded in a PU polymer matrix (PU/alumina composites) [28], do not reveal the existence of such mechanism that can be attributed to polarization within the alumina filler.…”

“…In the same frequency and temperature region a steep increase of the real part of the permittivity (not shown here), is recorded. This is characteristic of the presence of interfacial phenomena such as interfacial and/or electrode polarization, due to accumulation of charges, as well as increased conductivity [5,[23][24][25]. This low frequency-high temperature response should be attributed, in the systems under study, to interfacial polarization phenomena rather than increased conductivity.…”

Electrical response and functionality of polymer matrix-titanium carbide composites

“…Because of the frequency and temperature superposition, loss peaks shift to higher frequencies when temperature is raised (Figures 3 and 4). However, peak shift rate varies from process to process, although in some cases this rate is constant and the relative process appears to be temperature independent [23]. Interfacial polarization follows Arrhenius type behaviour, described by Equation (2): (2) where E A is the activation energy of the process, f 0 pre-exponential factor, k B the Boltzmann constant and T the absolute temperature.…”

Re-examination of the dielectric spectra of epoxy resins: bulk charge transport and interfacial polarization peaks

“…Here we point out that the same power law behaviour at low frequencies can be produced by a bulk QDC transport process that has fractal transport features [16]. We will also show that loss peak dispersions observed in materials dominated by ion transport cannot be necessarily associated with bulk molecular relaxation mechanisms [28][29][30] as these dispersions are shown to be caused here by interface effects.…”