Nanocomposites of poly (vinylidene fluoride), PVDF, and magnetite (Fe3O4) nanoparticles were prepared using the twin screw compounding method and the effect of filler concentration (5-15 wt%) on the thermal stability, dielectric properties and dielectric strength were investigated. It was observed that the dynamic characteristics of crystalline a c -relaxation peak remain almost constant for the composites studied; while the activation energy plots almost coincide indicating that the time scale of this relaxation process is independent of the Fe3O4 filler loading. Ferrite particles alter Maxwell-Wagner-Sillars (MWS) mechanism behaviour. In the isochronal diagrams of electric modulus dielectric function, at the lower ferrite concentration 5 wt% and the lowest frequency 0.1 Hz, two contributions to MWS process were clearly detected. For ferrite concentrations higher than 5 wt%, it seems that the contribution of amorphous-crystalline interfaces to the MWS relaxation drastically decreases and their effect is the broadening of the MWS peak at higher temperatures, while the effect of Fe3O4-PVDF matrix interfaces dominate in the formation of MWS relaxation. Herein, the nanocomposites dielectric strength performance was investigated by means of switching impulse high voltage stressing and AC (50 Hz) high voltage; from the results the nanocomposites demonstrated high levels of dielectrics strength accompanied with stable performance.

Polyvinyledene fluoride (PVDF) is a semi-crystalline thermoplastic polymer used in various technological applications because of its enhanced thermal stability and good chemical resistance. Polymer matrix nanocomposites represent a novel and rapidly growing field of engineering materials due to their improved thermomechanical, electrical and magnetic performance. In the present study the thermomechanical behaviour and dielectric response of Fe3O4/PVDF nanocomposites is investigated varying the content of the reinforcing phase.

. Composite systems of epoxy resin and barium ferrite nanoparticles have been prepared, and studied varying the content of the inclusions. Morphology of prepared samples has been examined via scanning electron microscopy and X-ray diffraction spectra, while electrical and magnetic properties were investigated by means of broadband dielectric spectroscopy, and magnetization tests respectively. Finally, water vapor sorption measurements were conducted in order to study the water sorption dynamics of the system. Electron microscopy images revealed the successful fabrication of nanocomposites. Dielectric permittivity increases with filler content, while three relaxation processes were detected in the relative spectra. These processes are attributed to interfacial polarization, glass to rubber transition of the matrix, and re-orientation of polar side groups of the polymer’s chain. Magnetization and magnetic saturation increase with magnetic nano-powder content. Nanocomposites absorb a small amount of water, not exceeding 1.7 wt%, regardless filler content, indicating their hydrophobic character.

Hybrid nanocomposites with barium ferrite and barium titanate nanoparticles embedded within an epoxy resin matrix, were prepared and studied, varying the fillers content. The morphology of the fabricated specimens was examined by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. Dielectric and magnetic properties of the nanocomposites were investigated via broadband dielectric spectroscopy and magnetization tests, respectively. Fine dispersions of nanofillers were detected via electron microscopy in all studied cases. Dielectric permittivity increases with diminishing frequency and increasing temperature and filler content. Recorded relaxation processes are attributed to interfacial polarization, between matrix and nanoparticles, glass to rubber transition of the polymer matrix (α-relaxation), and re-arrangement of polar-side groups of the main polymer chain (β-relaxation). Magnetization and magnetic saturation increase with the amount of barium ferrite nanoparticles.

Ternary nanocomposite systems of PVDF/Fe3O4/CNT and PVDF/Fe3O4/GN, prepared with twin screw compounding method, exhibit enhanced microwave absorption properties.

The dielectric and thermal response of epoxy resin (ER) based nanocomposites filled with semi-conductive zinc-oxide (ZnO) nanoparticles, were studied in the present work. Dielectric Relaxation Spectroscopy (DRS) technique was used, in the frequency range of 10(-1)-10(7) Hz and temperature range of 30-160 degrees C, for the investigation of the effect of ZnO nanoparticles on the dynamics of the molecular mobility of ER/ZnO system. On the other hand Differential Scanning Calorimetry (DSC) and Thermogravimetric/Differential Thermal Analysis (TGA/DTA) techniques have been used in order to examine the effect of ZnO nanoinclusions upon the molecular mobility, in relation to the thermal stability of the studied system. Four distinct relaxation mechanisms have been recorded in the spectra of all the systems under study. They were attributed to conductivity relaxation, interfacial polarization (IP), glass to rubber transition of the polymer matrix (alpha-relaxation) and re-orientation of polar side groups of the main polymer chain (beta-relaxation). Dielectric and thermal response could be interpreted by the simultaneous action of two opposite effects: (a) the addition of ZnO nanoparticles leads to a decreasing of the cross-linking density of the epoxy matrix which has as a result an increase of the fractional free volume and of the corresponding molecular mobility, and (b) the strong interactions between filler and epoxy matrix results to a reduction of the mobility of a fraction of the polymer chains at the interfaces of the constituents.

In the present study, the effect of nano magnetite (Fe3O4) content on structural, dielectric/electrical, magnetic and thermal properties of poly(vinylidene fluoride)/carbon nanotubes matrix, is investigated. Nanocomposite films of polyvinylidene fluoride, carbon nanotubes and Fe3O4 nanoparticles were prepared by the twin screw compounding method. Fe3O4, as magnetic inclusions was incorporated into the composites with carbon nanotubes loadings well above the percolation threshold, where conductive networks were formed. Magnetic characterization revealed the ferrimagnetic behavior of nanocomposites, with saturation magnetization values depending on magnetite content. Results obtained from the analysis of Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) techniques were very informative for the study of the polymorphism and crystallinity in PVDF. The incorporation of Fe3O4 inclusions in PVDF/CNT matrix, gradually increase both electrical conductivity and dielectric permittivity up to 10 wt% Fe3O4 content, while at the higher Fe3O4 content (15 wt%) reduced values were obtained. This behavior, at higher Fe3O4 content, should be possible related to the insulating and barrier role of Fe3O4 nanoparticles.

Polymer nanocomposite systems based on epoxy resin (ER), reinforced with amine-modified multi-walled carbon nanotubes (MWCNT) and/or nanoclays were studied by Dynamic Mechanical Analysis (DMA) and Thermogravimetric/Differential Thermal Analysis (TGA/DTA). For comparison, three different nanocomposite systems (ER/MWCNT ER/clay and ER/MWCNT+clay) were examined. The main aim of the present work is to investigate the effect of nanoclays incorporation on the degradation behaviour, thermal stability and thermomechanical properties of the nanocomposites. The addition of a small amount of nanoclays to ER/MWCNT composites enhances nanotubes dispersion without harming electrical conductivity or mechanical performance of the composites. Kissinger method was used to analyze the kinetics of decomposition mechanism. Apparent activation energies during the thermal degradation process were calculated.

In the present work the mechanical and thermal properties as well as the thermal stability of nanocomposite materials based on epoxy resin matrix reinforced with carbon black nanoparticles were investigated. For the preparation of the nanocomposites, diglycidyl ether of bisphenol A (DGEBA), triethylenetetramine (TETA) curing agent, and carbon black (CB) nanoparticles (25 to 75 nm in size) were used. Characterization was performed using Dynamic Mechanical Analysis (DMA), Thermogravimetric and Differential Thermal Analysis (TGA/DTA) and Differential Scanning Calorimetry (DSC) measurements. The addition of carbon nanofillers enhances, generally, the thermal behavior of the neat epoxy matrix. The dispersion of the nanoparticles and their interactions with the epoxy matrix play an important role on the thermal properties and molecular dynamics mechanisms, especially for higher filler concentrations. An increase in the activation energy (E-act) associated with the thermal degradation process and in the glass transition (T-g) values, is observed for CB weight content increasing up to 0.5% w/w. Composites with higher CB weight contents exhibit decrease in their E-act and T-g values. This discrete behavior below and above the critical value of 0.5% w/w is attributed to a well dispersed and to an agglomerated filler configuration, respectively. The results are explained in terms of changes in the free volume and conformational entropy of the composites.

SummaryHybrid composites consisted of an epoxy resin and BaTiO3 as well as ZnO particles were prepared and studied. Polymer composites with ferro‐ and/or piezo‐electric particles are expected to exhibit functional behaviour due to the varying polarization of the fillers. The BaTiO3 content was kept constant in all studied composites, while ZnO content varied from 0 to 50 particles per hundred resin per weight. Thermal properties of the systems were examined by means of Thermogravimetric/Differential Thermal Analysis technique. Decomposition temperature for all systems was found to lie in the range 385–395 °C, while residual weight for hybrids was significantly higher compared to epoxy resin. Dielectric response of the tested systems was determined via Dielectric Relaxation Spectroscopy.