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In this study, series of nanocomposites consisting of an epoxy matrix and different carbon nanoinclusions (Carbon Black, Multiwall Carbon Nanotubes (MWCNT), Graphene nanoplatelets (GnP) and nanodiamonds) were developed, and their electrical response was examined in wide frequency and temperature ranges. Depending on the filler type and concentration, nanocomposites exhibited either insulator to conductor transitions or dielectric relaxation phenomena. Recorded relaxations were attributed to interfacial polarization, glass to rubber transition and motion of polar side groups. Nanocomposites integrating carbon black or MWCNTs exhibit an abrupt increase in permittivity and conductivity at a critical concentration (or percolation threshold). The insulator to conductor transition is described by means of percolation theory and critical concentration and exponent are determined. Conductance mechanisms are investigated in all sets of nanocomposites, by accounting the influence of temperature on conductivity and by applying the Variable Range Hopping model. Further, analysis reveals hopping conductivity as the main charge migration process below critical concentration, while hopping and metallic-like conduction coexist above it.

The temperature- and frequency-dependent relaxation processes in films of a polymeric blend comprising a polyvinyl alcohol (PVA)/polyvinyl acetate (PVAc) co-polymer blended with polyvinyl pyrrolidone (PVP) in equal proportion by weight, and doped with an inorganic metallic salt, cadmium chloride ( CdCl 2 ) , at 0.0 wt% and 10.2 wt% doping levels (DLs), have been studied using dielectric relaxation spectroscopy (DRS). The frequency response of dielectric parameters for these samples has been studied with variation in temperature, from 303 up to 373 K, at different fixed frequencies (from 12 Hz up to 200 kHz). Study of Cole–Cole plots reveals a decrease in bulk resistivity of the samples with increase in temperature, which is attributed to thermally induced increase in the mobility of polymer chains. A 10-fold increase in bulk conductivity is observed for doped films with a DL of 10.2 wt%, when compared with the bulk conductivity of the un-doped (0.0 wt% DL) sample. The temperature dependence of dielectric parameters at different frequencies has been studied and the activation energy has been calculated. The relaxation time is found to be of the order of a few milliseconds, which implies that electrical conduction in CdCl 2 -doped PVA/PVAc–PVP blend films is predominantly due to the migration of ions. The variation of AC conductivity with frequency is in agreement with Jonscher’s universal power law. AC conductivity of the sample is found to increase significantly with an increase in temperature of the sample. Frequency-dependent dielectric properties of CdCl 2 -doped PVA/PVAc–PVP blend films, for various DLs, are also studied at room temperature.

Dielectric measurements performed on vinyl resin (VR) matrix and its composites reinforced with microcrystalline cellulose (MCC) and multi-wall carbon nanotubes (MWCNT) focus on the effect of the reinforcement weight fraction variation on its electrical properties in the frequency and temperature ranges 0.1 Hz–1 MHz and 30–130 °C, respectively. The relative volume fraction ratio of the MCC/MWCNT multi-scale reinforcement is of 9:1. In this analytical study, three reinforcement weight fractions of 2%, 4% and 6% are undertaken. The dielectric analysis reveals the presence of two dielectric relaxations for the VR matrix at temperatures above the glass transition temperature. The first one appearing at lower temperatures and higher frequencies is associated with the α relaxation originating from the glass rubbery transition of the terpolymer. Whereas the second one appearing at higher temperatures and lower frequencies is attributed to α′ relaxation due to more repeat units compared to α relaxation. An additional dielectric phenomenon originating from the interfacial polarization effect occurred at the reinforcement/matrix interfaces is identified for the composites. All these dielectric features are taken into account in the complex impedance analysis in order to probe their effects on the improvement of AC conductivity. Furthermore, the AC conductivity analysis using the developed Jonscher law allows determining the associated conduction mechanisms. Hence, changes of the electrical properties may be related to different reinforcement/matrix interactions and to the semi-crystalline character variation of the terpolymer shown by the thermal and structural analyses based on the differential scanning calorimeter and X-ray diffraction, respectively.

Water molecules near cellulose nanocrystals (CNCs; produced via the sulfuric acid-catalyzed hydrolysis of wood pulp) are believed to relax slower than those in the bulk liquid, which may result in unique properties of CNC aqueous dispersions. This study analyzed the polarization behavior of water molecules in CNC aqueous dispersions and other reference samples using a dielectric relaxation spectroscopy (DRS) technique in the microwave frequency range (0.2–20 GHz). As the CNC concentration increases, two slow relaxation components become prominent. The comparison with DRS data of aqueous dispersions of nanoporous silica, polyvinyl alcohol (PVA), and hairy CNC (HCNC) with amorphous chains protruding from both ends suggested that these slow relaxation modes of water near CNC surfaces cannot be attributed to direct hydrogen bonding interactions with the hydroxyl (OH) groups exposed and immobilized at the solid surface. Instead, they are similar to the water molecules interacting with OH groups attached to flexible polymer chains. Molecular dynamics (MD) simulations of the polarization behavior of water near the (110) facet of cellulose Iβ crystals confirmed that the interactions of water molecules with the cellulose crystal surface do not cause slower relaxations in the frequency range studied via the DRS. These results indicated that the CNC surface cannot be depicted with the crystallographic facets of cellulose Iβ; instead, it resembles a polymer-brush surface on which the short glucan residues or fragments of the strong acid-catalyzed hydrolysis process are swollen and extended into the aqueous phase.

Tire production shows a high annual growth followed by approximately the same increase in waste generation. Because used tires present an insignificant degree of natural degradation, having high strength, elasticity and long life time, a series of new technologies for tire waste processing were developed. A new method may consist of the using of tires as raw materials in the obtaining of composites for house and industrial applications. Such composites may be obtained from rubber powder of tires, fabrics from used textiles and rubber solutions. These composites can be characterized in terms of thermal characteristics with the aid of thermogravimetric analysis (TGA) connected with simultaneous FT-IR/MS analysis and with dielectric relaxation spectroscopy. With Netzsch “Thermokinetics-3” software it was demonstrated that the thermal degradation is complicated and takes place in several stages. Through FT-IR and MS analysis of the products released during thermal degradation it has been established that the main gases are CO, CO 2 , methane, ethane, ethene, propane propene, butane, butene, C5 fractions, unsaturated and higher saturated hydrocarbons and aromatic products.

Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using dielectric relaxation spectroscopy. The analysis of the CHW effect on the molecular mobility at the glass transition, Tg, indicates that non-attractive intermolecular interactions between KCg and CHW occur. The fragility index increased upon CHW incorporation, due to a reduction in the polymer chains mobility produced by the CHW confinement of the KCg network. The apparent activation energy associated with the relaxation dynamics of the chains at Tg slightly increased with the CHW content. The filler nature effect, CHW or montmorillonite (MMT), on the dynamic mobility of the composites was analyzed by comparing the dynamic behavior of both carrageenan-based composites (KCg/xCHW, KCg/xMMT).

The dielectric spectra and conductivity properties of neat poly(epichlorohydrin-co-ethylene oxide)(PECH-co-EO) copolymer and two modified copolymers with a 20% or 40% of dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate units were analysed. A process of thermal orientation was applied to the copolymers to fine-tune the molecular motion of the side chains and determine their validity for cation transport materials. The study was conducted using Dielectric Thermal Analysis (DETA). The spectra of the modified unoriented and oriented copolymers consisted of five dielectric relaxations (δ, γ, β, αTg, and αmelting). The analysis of the relaxations processes shows that as the grafting with the dendron units increases, both the lateral and main chains have a greater difficulty moving. The thermal orientation induces in the main chain partial crystallization, including the polyether segments, and modifies the cooperative motion of the main chain associated with the glass transition (αTg). A deep analysis of the electrical loss modulus revealed that the degree of modification only modifies the temperature peak of each relaxation, and this effect is more perceived if the dendron unit content is higher (40%). The thermal orientation process seems equal to the spectra of CP20-O and CP40-O to the point that the degree of modification does not matter. Nevertheless, the fragility index denotes the differences in the molecular motion between both copolymers (40% and 20%) due to the thermal orientation. The study of the electric conductivity showed that the ideal long-range pathways were being altered by neither the thermal orientation process nor the addition of dendrimers. The analysis of the through-plane proton conductivity confirmed that the oriented copolymer with the highest concentration of dendrimers was the best performer and the most suitable copolymer for proton transport materials.

The principal objective is to determine and study the dielectric relaxation characteristics of primary and secondary acetates such as Methyl Acetate, Ethyl Acetate, Isopropyl Acetate, n-Butyl Acetate and Amyl Acetate with complex permittivity spectra (CPS), which has been measured in 0.1 < ν/GHz < 50 frequency range using Time Domain Reflectometry and fitted to Debye model. Static dielectric permittivity, relaxation time and Kirkwood correlation factor have been determined using non-linear least squares fit method. Association of molecule and chain length affects on dielectric relaxation process in esters. The Arrhenius behavior has been revealed by means of temperature dependent value of relaxation time.