Exploring the structural properties and enhancement of Opto-electrical investigations for the synthesized epoxy based polymers with local nanoscale structures

Epoxy networks of the diglycidyl ether of bisphenol A (DGEBA) were prepared using 4, 4′-diaminodiphenyl (44′DDS) and 3, 3′-diaminodiphenyl (33′DDS) sulfone diamines crosslinking hardeners. The structural, linear optical and mechanical properties of the investigated sample were analysed. Dynamic Mechanical Thermal Analysis and wide-angle x-ray diffraction were conducted to select a candidate presenting interesting thermo-mechanical properties and particular nanostructures embedded in an amorphous matrix. Our choice is therefore focused on DGEBA/33′DDS polymer for which, rocking curve measurements revealed the existence of two principal reflecting planes inclined to each other by about 0.27°. To highlight the potential effect of these interfaces, Thermally Stimulated Depolarization Current (TSDC) and Time Domain Spectroscopy measurements have been carried out. The application of the windowing polarization TSDC technique, in DGEBA/33′DDS polymer sample, gives an almost linear variation of the activation energies in the range between 3.65 and 4.09 eV. To our knowledge, this is the first study concerning epoxy polymers in which activation energies associated to ρ interfacial charge relaxations are calculated. To study the effect of the interfaces and trapped charge carriers, correlated by the angle x-ray diffraction measurements, the optical parameters were investigated. Our contribution will open a new avenue for developing the DGEBA/33′DDS polymer sustainable candidate in optoelectronic engineering applications

Optical, Dielectric Properties and Energy Storage Efficiency of ZnO/Epoxy Nanocomposites

International audienceZnO/epoxy nanocomposites were prepared in five different contents (0.25–3.0 wt%). Optical, thermal and dielectric properties have been examined as a function of ZnO nanoparticles. The absorption optical spectra exhibit a broad intense peak assigned to the n–π* (HOMO–LUMO) transitions. Nanocomposite with 3.0 wt% ZnO sample completely blocks UV-light radiations in the region from 300 to 480 nm, which allowed that the prepared material to be used for UV-Shielding devices. The optical band gap is found to decrease with increasing filler ZnO concentrations. This might be due to increasing the density of defect states. Permittivity and electric modulus formalisms are used to analyze and interpret the experimental data. γ relaxation is observed in the low temperature region, which is attributed to the rearrangement of small parts of the polymeric chains. The α relaxation and the Maxwell–Wagner–Sillars (MWS) effect, attributed to the glass rubber transition of the polymeric matrix and the interfacial polarization phenomena respectively, are observed in the high temperature region. Using Havriliak–Negami approach, the temperature dependence of relaxation time for MWS and γ relaxations follows an Arrhenius behavior while the α relaxation time is well described by the Vogel–Fulcher–Tamann behavior. The activation energies of all relaxation modes were calculated and discussed. The energy density of the investigated samples is significantly enhanced. It is about 2 × 10−6 J/m3 for nanocomposite with 3.0 wt% ZnO at 20 °C.These results indicate that the effect of ZnO nanoparticles makes the proposed materials suitable candidates for energy storage applications

Dielectric characterization of epoxy resin based polymer

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A comparative study of structural and dielectric properties of diglycidyl ether of bisphenol A (DGEBA) cured with aromatic or aliphatic hardeners

International audienceThis study aims to present structural and dielectric comparisons between two epoxy polymers. These polymers are realized by curing diglycidyl ether of bisphenol A (DGEBA) resin with either aliphatic 1,3-diaminopropane (PDA) or aromatic 4,4′-diaminodiphenyl sulfone (DDS) hardeners. They are called DGEBA/PDA and DGEBA/DDS. Several complementary techniques have been used in the present study. The structural analysis was performed using grazing incidence X-ray reflectometry. It reveals the presence of a locally ordered nanostructure in the DGEBA/DDS polymer and an amorphous character for the DGEBA/PDA one. Dielectric characterization was carried by means of dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC) and time domain spectroscopy (TDS). DRS measurements performed over wide ranges of temperature (−80 to 160 °C) and frequency (10−1–106 Hz) showed the presence of dipolar γ and α relaxations in both polymers. Nevertheless, the interfacial Maxwell–Wagner–Sillars (MWS) relaxation appeared only in DGEBA/DDS. This can be related to the local nanostructure within this polymer, which can give rise to interfaces. Relaxation parameters were deduced from the best fits of experimental data with the Havriliak–Negami model. The calculated fragility index indicates that DGEBA/DDS is more fragile than DGEBA/PDA. The loss factor ε′′(f) was calculated from the isothermal discharging current measurements, using Hamon approximation. Thanks to this ε′′ calculation an interfacial relaxation was revealed in the frequency range of 10−3–10−1 Hz for each investigated polymer

Effects of curing agent on conductivity, structural and dielectric properties of an epoxy polymer

International audienceTwo epoxy polymers were prepared by curing the diglycidyl ether of bisphenol A (DGEBA) epoxy resin with two hardeners: the ethylenediamine (EDA) and the 3,3′-diaminodiphenyl sulfone (33′DDS) which are respectively aliphatic and aromatic. Structural properties of DGEBA/EDA and DGEBA/33′DDS polymers were investigated by means of grazing incidence X-ray reflectometry. Their dielectric properties were studied using the dielectric relaxation spectroscopy (DRS) over wide ranges of temperature (from −80 to 200 °C) and frequency (from 10−1–106 Hz), and thermally stimulated depolarization current (TSDC) technique. X-ray data revealed the presence of a locally periodic nanostructure in polymer cured with the aromatic hardener (DGEBA/33′DDS). γ and α dipolar relaxations were highlighted for the two polymers while the Maxwell–Wagner–Sillars (MWS) relaxation appears only in the DGEBA/33′DDS. The electric modulus data were fitted using Havriliak–Negami approch. Conductive properties of epoxies were investigated. Ac conductivity data reveal that DGEBA/EDA is more conductive than the DGEBA/33′DDS

Study of AC electrical conduction mechanisms in an epoxy polymer

International audienceThe AC conductivity of an epoxy resin was investigated in the frequency range 10−1−106 Hz at temperatures ranging from -100 to 120 °C. The frequency dependence of σac was described by the law: σac=ωε0ε′′HN+Aωs. The study of temperature variation of the exponent (s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the small polaron tunneling mechanism (SPTM) at low temperature (-100 -60 °C) and the correlated barrier hopping (CHB) model at high temperature (80-120 °C)

Exploring the optical and dielectric properties of bifunctional and trifunctional epoxy polymers

Two polymers were prepared from diglycidyl ether of bisphenol A (DGEBA) and triglycidyl p-aminophenol (TGAP) epoxy resins, using the same hardener diethylenetriamine (DETA). The obtained polymers were compared in terms of structural, optical, mechanical, thermal and dielectric properties. Dielectric spectroscopy and dynamic mechanical analysis indicated the presence of dipolar dielectric relaxations in both polymers, and interfacial one only for TGAP/DETA, which is consistent with XRD findings. Different approaches were considered to fit electrical modulus and conductivity and to estimate the relaxation times and activation energies according to temperature. For optical measures, a novel result processing approach is proposed for an accurate determination of the polymers bandgap and for highlighting the existence of additional energy transition level for TGAP. Results indicate that this polymer could be a potential candidate for use as a protective film and as UV/blue-light filter for screens and window