Dynamic Dielectric Behaviour Research Articles

A structurally modified 85SiO2–9P2O5–6TiO2 system and its dynamic dielectric behavior–a starting point for hydrogen detection

Novel proton conducting materials with composition 85SiO2–9P2O5–6TiO2, modified by addition of liquid xH3PO4 in different amounts xH3PO4 = 0; 17; 35; 52 mmol, were synthesized via sol–gel route. XRD patterns show amorphous nature for “pure” (xH3PO4 = 0 mmol) sample and crystalline for all H3PO4-doped samples. FTIR and SEM analysis revealed that this modification led to appreciable structural changes on molecular level and morphology, which, heavily impacts the water intake ability, impedance behavior as well as the dielectric parameters. The detailed impedance examination showed distinct response of changing parameters such as relative humidity and temperature, while the dielectric parameters derived from the impedance spectra, provide in-depth understanding of proton conduction dynamic. Based on these observations different models were proposed gathering proton transfer in humid and dry atmospheres. The enhanced proton conduction is a basic requirement for successful usage of the material for hydrogen gas detection.

Digital Memory Characteristics of Aromatic Polyimides Based on Pyridine and Its Derivatives.

Soluble aromatic polyimides and polyvinyls were prepared by incorporating pyridine moiety and its derivatives in the backbone and the side groups, respectively: 6F-Py-i polymers based on the polyimide backbone (6F-Py-1 to 6F-Py-7) and PVPy-i polymers based on the polyvinyl backbone (PVPy-1 to PVPy-4). All polymers were found to be amorphous. The 6F-Py-i polymers were thermally stable up to 511–545 °C; the PVPy-i polymers were stable up to 362–376 °C. Their glass transitions, thin film densities, molecular orbitals, and band gaps were determined. The electrical devices fabricated with the polymers in an electrode/polymer/electrode structure revealed p-type unipolar write-once-read-many times (namely, permanent) or dynamic random access memory or dielectric behavior, depending on the substituents of the pyridine unit and the film thicknesses. In particular, such digital memory characteristics were found to originate from the pyridine moieties possessing a high charge affinity in the polymers. However, the pyridine moieties were found to still need at least two or more aromatic substituents to get enough power to stabilize charges via utilizing the resonance effects provided by the substituents. Overall, this study demonstrated that the pyridine unit conjugated with two or more aromatic substituents is a very useful component to design and synthesize digital memory materials based on thermally stable polyimides and other high performance polymers. The 6F-Py-i polymers have potential for the low-cost mass production of high-performance programmable unipolar permanent memory devices with very low power consumption.

Dielectric response of transformer oil based ferrofluid in low frequency range

In this article, our experimental study of the dynamic dielectric behaviour of transformer oil-based ferrofluid with magnetite nanoparticles is presented. Frequency-dependent dielectric permittivity and dissipation factor were measured within the frequency range from 20 Hz to 2 MHz by a capacitance method. The ferrofluid samples were placed in a liquid crystal cell, and experiments were carried out in an electromagnetically anechoic chamber. Two polarization processes and corresponding relaxations were revealed within the applied frequency range. Schwarz theory of electric double layer polarization is used to explain the low frequency relaxation maximum. Moreover, the shift of the maximum position towards higher frequencies is observed as the magnetic volume fraction in the ferrofluid increases. The related decrease in relaxation time due to higher counterion mobility is analysed. Reduced electric field intensity due to depolarization field, which is dependent on the particle concentration, is proposed as the reason for the maxima shift. This assumption is wholly supported by a complementary experiment.

Dynamic Mechanical and Dielectric Relaxation Behavior of Chitosan Films: Influence of Water Content

AbstractThe dynamic mechanical dielectric behavior of neutralized chitosan films has been investigated as a function of water content and temperature. Chitosan films exhibit three relaxation processes in the low frequency range: the first one between 86–102 °C, it corresponds to the α‐relaxation process and shifts to higher temperatures with decreasing water content; a second relaxation was observed from 80 °C to the onset of thermal degradation (240 °C) and it is identified as the σ‐relaxation often associated with proton mobility; and a third relaxation process in the 240–300 °C temperature range that corresponds to chitosan thermal degradation.

Dynamic Mechanical and Dielectric Behavior of Banana-Glass Hybrid Fiber Reinforced Polyester Composites

Hybrid composites of glass and banana fiber (obtained from the pseudo stem of Musa sapientum) in polyester matrix, are subjected to dynamic mechanical analysis over a range of temperature and three different frequencies. The effect of temperature on the storage modulus (E′), loss modulus (E′′), and loss factor or damping efficiency (tan δ) is determined. All the properties are compared with those of the neat polyester samples and the un-hybridized composites. The effects of the layering pattern of the two fibers on the ultimate viscoelastic behavior of the composites are also investigated. Composites are prepared with banana as the surface layer and glass as the surface layer and also as an intimate mixture of glass and banana. At temperatures above T g,, the storage modulus values are found to decrease even with the addition of glass fiber for the geometry where glass is the core material. The value of the storage modulus of the composites with the above mentioned geometry is found to be different, above and below Tg, the value above Tg being lower than that below Tg unlike in unhybridized composite. The loss modulus curves and the damping peaks are found to be flattened by the addition of glass. Layering pattern or the geometry of the composites is found to have a profound effect on the dynamic properties of the composite. An intimately mixed composite is found to have the highest storage modulus values in all compositions. The values are consistent with the results of tensile strength. The tan δ curve is found to be affected by the layering pattern followed and gives insight into the interaction in the material. The dielectric behavior of the composites are also found to be dependent on the glass fiber volume fraction as well as the layering pattern employed.

Hydrogen-related dynamic dielectric behavior of barium titanate single crystals

Barium titanate single crystals had been placed in 0.01M NaOH solution to deposit hydrogen on their electrodes through the electrolysis of water. Two kinds of time-dependent changes in dielectric properties of the single crystals were observed: One occurred in the course of hydrogen deposition and the other lasted for a long period of time after the deposition. The diffusion of hydrogen and in and out of the single crystals may be the cause for the changes. This hydrogen-related dynamic dielectric behavior clearly shows that hydrogen is an important mobile ion other than oxygen vacancy in perovskite-type lattice. Extra attention should be paid to the role of hydrogen in time-dependent property changes, including resistance degradation and ferroelectric aging, of perovskite-type ferroelectric titanates.

Static and dynamic dielectric behavior of mesogenic compounds of different polarity in the vicinity of the isotropic to nematic phase transition.

Mesogenic compounds belonging to the two well-known -cyanophenyl, and -isothiocyanatophenyl homologous series, which distinctly differ in the molecular polarity (-C identical with N, 5D; -N=C=S, 2.5D), show an essential difference in the pretransitional dielectric behavior in the vicinity of the isotropic to nematic (I-N) phase transition. Taking into account the results presented in Phys. Rev. E 67, 041705 (2003), the features of the I-N transition observed for the less polar mesogens are characteristic for the first order phase transition, whereas in the case of the strongly polar ones, the I-N transition is undoubtedly close to the second order.

Semi‐interpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. II. Dielectric relaxation and thermal behaviour

AbstractSemi‐interpenetrating polymer networks (semi‐IPNs) based on crosslinked polyurethane (PU) and linear polyvinylpyrrolidone (PVP) were synthezised, and their thermal and dynamic mechanical properties and dielectric relaxation behavior were studied to provide insight into their structure, especially according to their composition. The differential scanning calorimetry results showed the glass transitions of the pure components: one glass‐transition temperature (Tg) for PU and two transitions for PVP. Such glass transitions were also present in the semi‐IPNs, whatever their composition. The viscoelastic properties of the semi‐IPNs reflected their thermal behavior; it was shown that the semi‐IPNs presented three distinct dynamic mechanical relaxations related to these three Tg values. Although the temperature position of the PU maximum tan δ of the α‐relaxation was invariable, on the contrary the situation for the two maxima observed for PVP was more complex. Only the maximum of the highest temperature relaxation was shifted to lower temperatures with decreasing PVP content in the semi‐IPNs. In this study, we investigated the molecular mobility of the IPNs by means of dielectric relaxation spectroscopy; six relaxation processes were observed and indexed according the increase in the temperature range: the secondary β‐relaxations related to PU and PVP chains, an α‐relaxation due to the glass–rubber transition of the PU component, two α‐relaxations associated to the glass–rubber transitions of the PVP material, and an ionic conductivity relaxation due to the space charge polarization of PU. The temperature position of the α‐relaxation of PU was invariable in semi‐IPNs, as observed dynamic mechanical analysis measurements. However, the upper α‐relaxation process of PVP shifted to higher temperatures with increasing PVP content in the semi‐IPNs. We concluded that the investigated semi‐IPNs were two‐phase systems with incomplete phase separation and that the content of PVP in the IPNs governed the structure and corresponding properties of such systems through physical interactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1191–1201, 2003

On the Dynamic Dielectric Behaviour of (CH3NH3)3Sb2Br9(MABA)

The complex electric permittivity of ferroelectric (CH3NH3)3Sb2Br9 (MABA) single crystals has been measured in the frequency range 1 kHz - 3 GHz between 15 and 300 K. The dynamic dielectric behaviour of MABA is determined by the properties of high frequency relaxation of Cole-Cole type. It is thermally activated and characterised by a relatively small activation energy. The phase transitions at 168 and 134 K influence the amplitude of the relaxation (Δε) without any important changes in the relaxation frequency.

Dynamic mechanical and dielectric relaxation behaviour of poly(methacrylate)s containing saturated rings with seven and eight members in the side‐chains

AbstractDynamic mechanical and dielectric behaviour of poly(cycloheptyl methacrylate), poly(cycloheptylmethyl methacrylate) and poly(cyclooctyl methacrylate) have been investigated. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity ϵ*. Results are discussed in terms of the effect of the size and structure of the side ring. The saturated ring group shows mechanical and dielectric activity at low temperature that is analyzed in terms of the Fuoss–Kirkwood equation. The free volume for the three polymers was determined. The conductive and interfacial phenomena were studied by MacDonald and Coelho models, where the dipolar contribution was introduced.© 2002 Society of Chemical Industry

New polymer mortars containing polymeric wastes. Part 2. Dynamic mechanical and dielectric behaviour

Abstract A promising application for polymer mortars and concretes is for machine tool structures: for this purpose, composite materials with good mechanical properties and high damping characteristics are required. Accordingly, four recycled fillers (powdered rubber, tyre rubber, micronized tyre fibres and milled electrical cable waste) have been used to formulate new polymer mortars. The internal energy dissipation and relaxation processes of the different materials, studied by the combined use of both dynamic mechanical and dielectric analysis, are compared thus showing the effect of the powdered rubber based filler as a damping promoter. The use of silane coupling agents has also been investigated and its effect in leading to stiffer materials is reported and discussed.

Dynamic Mechanical and Dielectric Relaxational Behavior of Poly(cyclohexylalkyl methacrylate)s

The dynamic mechanical and dielectric behavior of three poly(cyclohexylalkyl methacrylate)s with different spacer groups has been studied. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity ε*. Results are discussed in terms of the effect of the side chain structure and the insertion of flexible spacer groups. Molecular dynamic calculations for the repeating unit of the polymers under study are analyzed. Close to room temperature the interconversion between axial and equatorial conformations is not observed whitin the total time of 5 ns. The analysis was then performed from 1000 to 1500 K, and the results were extrapolated to lower temperatures. By this way the fraction of axial and equatorial conformations was calculated. The free energy change against the number of carbon atoms in the side chain is in excellent agreement with the experimental data. This means that the γ relaxation associated with the chair-to-chair conformational change in the cyclohexyl group is also influenced by the length of the spacer group. The molecular dynamics approach allows to observe the relative incidence of the two conformations of the cyclohexyl group which can be related to the motions responsible for the γ relaxation.

Dynamic mechanical and dielectric characterisation of amylose–glycerol films

The dynamic mechanical, dielectric and calorimetric behaviour of amylose films, plasticised with glycerol, was examined as a function of temperature and glycerol content. Two separate relaxation processes were observed. Whereas the temperature of the lower temperature transition, in the vicinity of −50°C, showed a weak dependence on composition, the temperature of the upper transition, in the range 150–50°C, decreased with increasing glycerol content. The activation energy of the lower temperature transition, obtained from the dependence of the frequency of the relaxation peak upon temperature, was typical of a primary α-relaxation or glass transition process. This indicated that although glycerol was an effective plasticiser of amylose, amylose–glycerol mixtures are only partially miscible.

Structure and dynamic dielectric behaviour of ferroelectric[NH2(CH3)2]3Sb2Br9 (DMABA)

The crystal structure of DMABA has been determined at 293 and 180 K. Itcrystallizes in the monoclinic P21/c space group. The structure was refinedto R1 = 0.0466 for 1269 independent reflections at 293 K and R1 = 0.038 for1728 reflections at 180 K. DMABA is isomorphous with the chlorine analogue,DMACA. Its anionic sublattice forms corrugated two-dimensional layers in thebc plane. There are two crystallographically independent, disordereddimethylammonium cations in the crystal structure. One of them occupiescavities inside the polyanionic layers; the other is located between thelayers. The temperature dependence of lattice parameters has been determinedbetween 100 and 290 K. The presence of the ferro-paraelectric phasetransition at 164 K has been confirmed. The complex dielectric permittivity ofDMABA single crystals in the frequency range 100 Hz-10 GHz between 10 K and300 K has been measured. The dynamic dielectric behaviour of DMABA is found tobe determined by the properties of two independent relaxators: a low frequencyone (~1 MHz at Tc) with a critical slowing down of its dynamics anda high frequency one (~5 GHz), which is thermally activated andcontributes to the electric permittivity at least from about 80 K.

Relaxation behaviour in blends of PEEK and PEI

Blends of poly(ether ether ketone) and poly(ether imide) have been produced in the composition range 2–20 wt% poly(ether ether ketone) and dynamic mechanical and dielectric behaviour of these materials have been investigated. A composition dependent α process was observed using both techniques, the temperature of which increased with increasing poly(ether imide) content. The low temperature relaxation behaviour of poly(ether imide) and the dielectric relaxation time in the glass transition region was found to be affected by the addition of poly(ether ether ketone). The variation of loss and storage permittivities showed that the asymmetric broadening was strongly dependent on the blend composition, indicating a high degree of interaction between the components.

Dynamic mechanical and dielectric relaxations in poly(dibenzyl itaconate) and poly(diethylphenyl itaconate)

Dynamic mechanical and dielectric behaviour of poly(dibenzyl itaconate), and poly(diethylphenyl itaconate) were studied. The study was performed by determining the components of the complex relaxation modulus E∗ and the complex dielectric permittivity ε∗. The results are compared with those previously reported for poly(benzyl methacrylate), poly(monobenzyl itaconate) and poly(monoethylphenyl itaconate). The results are discussed in terms of the effect of flexible spacer groups and of the different steric hindrance between mono and disubstituted polymers.

Dielectric behaviour of some monohydric alcohols and their mixtures on dilution by cyclohexane

Abstract Results of static and dynamic dielectric measurements up to 36 GHz are reported for the 1-alkanols C 6 , C 9 and C 12 and the isomers 4-methyl-2-pentanol ( cf. C 6 ) and 5-nonanol ( cf. C 9 ), moreover of mixtures of two or three of these alcohols, all studied in mixtures with cyclohexane over the whole alcohol concentration range at 20, 30 and 40 °C. The apparent dipole moments and the relaxation parameters from a three Debye term analysis of the spectra are discussed. Most of the systems behave qualitatively similar, except those with the two isomers. In particular the behaviour of 5-nonanol is remarkable, which exhibits a rather weak tendency towards self-association in its static as well as dynamic dielectric behaviour, obviously due to steric conditions, but seems to contribute considerably to hetero-association.

On the dynamic dielectric behaviour of (CH 3NH 3) 3Sb 2I 9 (MAIA) single crystals

The dielectric permittivity of (CH 3NH 3) 3Sb 2I 9 (MAIA) single crystals has been measured in frequency range from 100 Hz to 10 GHz and in the temperature range from 10 K to 300 K. The low frequency dielectric relaxation found in the range from 40 to 60 K has very similar properties as the high frequency relaxation observed in the 100 MHz–10 GHz range near and above the 147 K phase transition. Both are of Cole–Cole type and thermally activated with an activation energy of 0.06 eV and 0.095 eV below and above the phase transition, respectively, without a critical behaviour at the transition temperature. The relaxation observed in the low temperature phase is not associated with the mechanism of the phase transition.

Dynamic mechanical and dielectric relaxations in poly(monoethylphenyl itaconate)

Dynamic mechanical and dielectric relaxational behavior of poly(monoethylphenyl itaconate) at different frequencies and temperatures was studied. Three relaxation zones are found. The dynamic mechanical response is dominated by a relaxation peak at room temperature, labeled β relaxation. Two prominent shoulders labelled as γ and α relaxations are observed. Because of the overlapping of the α and γ with the β relaxation, a deconvolution method to improve the understanding of these phenomena is proposed. In spite of the complexity of the experimental spectra, the proposed deconvolution method seems to be a convenient approach to interpret the relaxational behavior of this polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2749–2756, 1997

Dynamic mechanical and dielectric behavior of erucamide (13-cis-docosenamide), isotactic poly(propylene), and their blends

Blends of erucamide (13-cis-docosenamide) and isotactic poly(propylene) were analyzed by means of dynamic mechanical (at 3, 10, and 30 Hz) and dielectric (at 1, 6, and 20 kHz) techniques. The dependence of tan δ with temperature for each one of the blends has been fitted to Gaussian functions in order to deconvolute the overlapped relaxations. Three relaxations for i-PP, αi-PP, βi-PP, γi-PP, three for erucamide, αERU, βERU, and γERU, and five for their blends have been observed and assigned. They do not vary appreciably with composition, suggesting that the components are incompatible either as globules in the matrix or in the amorphous regions of the spherulites, and/or in their surroundings. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1473–1482, 1997