Bulk Relaxation Processes Research Articles

Exploring temperature effects on raw polysaccharide in semi-diluted solution using complex conductivity: Correlation analysis of activation energies

The evolution of the complex conductivity of raw polysaccharides extracted from Cystoseira myriophyloides algae exhibited significant temperature dependence in an aqueous solution. An analysis of the complex conductivity versus frequency was conducted using an appropriate electrical circuit based on our theoretical approach. This facilitated the generation of analytical functions representing the relaxation processes occurring at different temperatures. Subsequently, extrapolation and deconvolution procedures were employed to further investigate and identify all relaxation processes and their origins. These approaches revealed the presence of three relaxation processes. The first relaxation, observed at low frequency, is attributed to interfacial polarization between the electrode and the solution. The second and third relaxations, observed at medium and high frequencies, are attributed to bulk relaxation processes. Then, subtracting the low-frequency process clarified the bulk relaxation processes. Both relaxations are described by the Cole-Cole relaxation, which effectively models the well-known Maxwell-Wagner-Sillars (MWS) phenomenon typically observed in polyelectrolyte solutions. This relaxation is typically caused by interfacial polarization between molecular chains and counterions in the sample. Both relaxations were found to be thermally activated. The temperature dependence of useful parameters extracted from each relaxation, such as relaxation time (τσ) and conductivity (σdc) and (σ∞), followed Arrhenius law behavior. Furthermore, activation energy values for each relaxation process were determined, establishing a linear correlation between activation energy values related to relaxation time (τσ) and both conductivities (σdc) and (σ∞). These results confirm the origin of bulk relaxations and demonstrate a strong link between relaxation and conduction mechanisms.

The electro-mechanical tensile properties of an engineered cementitious composite

The influence of ongoing cement hydration and multiple microcrack formation on the electrical impedance of an engineered cementitious composite (ECC) is presented. Impedance measurements were obtained over the frequency range 20 Hz–1 MHz and displayed in the Nyquist format. In addition, the permittivity and conductivity were de-embedded from the measured impedance and presented in both time and frequency domains to elucidate the nature of conduction and polarisation processes. It was found that, over a curing period of 90 days, the ECC displayed a classic impedance response. Both conductivity and relative permittivity were found to be frequency dependent due to bulk relaxation processes operating within the composite. Tensile straining was shown to result in a detectable change in the impedance response, but retained a similar overall profile. When presented in the frequency domain, a downward displacement in both conductivity and relative permittivity profiles was evident with increasing tensile strain. It is shown that the relative permittivity at the high-frequency end could be exploited as a potentially useful indicator for strain/damage detection. The influence of microcracking on the piezo-resistive response of the composite is discussed based on crack patterns obtained from both visual observations and digital image correlation.

Lampert triangle formation and relaxation behavior in doped poly(3,4-ethylenedioxythiophene) devices

The current density–voltage (J–V) characteristics in stainless steel/poly(3,4-ethylenedioxythiophene)/Ag devices show the formation of the complete Lampert triangle (ΔABC) bounded by three limiting curves: Ohmic, trap-limited/filling space charge limited conduction, and trap-free/trap-filled space charge limited conduction. From the analysis of the Lampert triangle, values for carrier density (p0) ∼ 0.72 × 1013/cm3, mobility (μp) ∼ 77.47 × 10−4 cm2/V s, and transit time (tt) ∼ 10−12 s are obtained and also the transition voltages for different conduction mechanisms are estimated. The relaxation processes in bulk and interface are observed to be different from temperature-dependent impedance measurements. Estimated values of relaxation times are interface (τ1) ∼ 10−3 s and bulk (τ2) ∼ 10−6 s. Two parallel RQ (Q: constant phase element) circuits in series are used to fit the impedance data; however, the model varies for data at 110 and 120 K (two parallel CQ circuits in series). Since the samples have doped carriers, the activation energies are low (< 70 meV), and relaxation times follow Arrhenius behavior.

Relaxing nonequilibrated polymers in thin films at temperatures slightly above the glass transition

ABSTRACTWe have studied the dewetting process of thin polystyrene films on nonwettable substrates in the viscoelastic regime slightly above the glass transition temperature. The evolution of the shape of the dewetting rim for varying film thickness, molecular weights and dewetting temperatures allowed us to determine the relaxation rates of residual stresses, which originated from nonequilibrated polymer chain conformations formed during film preparation by spin‐coating. For long chain polymers, we found rates notably faster than the longest bulk relaxation processes, highly independent of molecular weight and temperature. Our study demonstrates that dewetting is a powerful tool for sensitive characterization of nonequilibrium properties of thin polymer films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2017,55, 515–523

Preparation and characterization of Li 1 + x Al ySc x − y Ti 2 − x (PO 4) 3 (x = 0.3, y = 0.1, 0.15, 0.2) ceramics

The powder of Li 1 + x Al ySc x − y Ti 2 − x (PO 4) 3 with x = 0.3 and y = 0.1, 0.15, 0.2 has been prepared by solid state reaction and the ceramics have been sintered. The results of X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and impedance spectroscopy up to 10 9 Hz are presented. At room temperature the compounds belong to the rhombohedral symmetry (space group R3̅ c). Ti 2p, P 2p, O 1s, Sc 2p, Al 2p, and Li 1s core level XP spectra's were fitted. The values of binding energies of core level XP spectra's, splitting energies of Ti 2p 3/2–Ti 2p 1/2, Sc 2p 3/2–Sc 2p 1/2, P2p 3/2–P2p 1/2 spin-orbit doublets, and amount of the elements with different binding energies were found to be dependent on stoichiometric factor y. The elemental compositions are defined by EDX. Impedance spectroscopy study in the frequency range 10 Hz–3 GHz have shown three relaxation dispersion regions of electrical properties and the processes are thermally activated. The high frequency dispersion region may be attributed to the relaxation processes in bulk, while lower dispersion regions are related to the processes in grain boundaries and blocking Pt electrodes.

High signal to noise ratio THz spectroscopy with ASOPS and signal processing schemes for mapping and controlling molecular and bulk relaxation processes

Asynchronous Optical Sampling has the potential to improve signal to noise ratio in THz transient sperctrometry. The design of an inexpensive control scheme for synchronising two femtosecond pulse frequency comb generators at an offset frequency of 20 kHz is discussed. The suitability of a range of signal processing schemes adopted from the Systems Identification and Control Theory community for further processing recorded THz transients in the time and frequency domain are outlined. Finally, possibilities for femtosecond pulse shaping using genetic algorithms are mentioned.

On the influence of cylindrical sub-micrometer confinement on heptyloxycyanobiphenyl (7OCB). A dynamic dielectric study

Broadband dielectric spectroscopy (10 2 Hz to 1.8 × 10 9 Hz) was used to perform a study of the molecular dynamics of the liquid crystal heptyloxycyanobiphenyl (7OCB) in the bulk as well as confined to 0.2 μm diameter parallel cylindrical pores of Anopore ® membranes in the isotropic and nematic phases. In bulk samples, two orientations (parallel and perpendicular) of the molecular director with regard to the probe electric field were investigated. In confined samples, untreated and HTBA-treated membranes were considered to obtain axial and radial confinements, respectively. The different molecular relaxation processes in bulk and confined samples were identified as well as discussed and compared.

A master equation study of vibration-dissociation coupling in shock-heated oxygen molecules

The vibration-dissociation coupling phenomena in shock-heated oxygen molecules highly dilute in an argon heat-bath have been studied numerically. State-to-state transition rate coefficients were evaluated by using relatively simple models developed through the information theoretical approach. The master equation was solved by numerical integration to obtain time-resolved vibrational population distributions. The results of the master equation analysis are compared with those obtained by using a widely-used phenomenological vibration-dissociation coupling model. The results show that during the relaxation process the depletion of high-lying vibrational energy levels is severe and significantly affects bulk properties related to dissociation and that the phenomenological model can reproduce qualitatively the bulk relaxation process found in the master equation analysis.

VISUALIZATION OF SPATIALLY INHOMOGENEOUS SPIN RELAXATION PHENOMENA IN LIQUID 3HE-4HE MIXTURES

By using the Magnetic Resonance Imaging (MRI) technique, we studied the spatial recovery of the longitudinal magnetization of liquid 3 He- 4 He mixtures in a 2mm × 2mm × 20mm rectangular parallelepiped sample cell below 1 K. We applied saturation pulses to destroy the magnetization and took two-dimensional pictures of the recovery of the magnetization in three orthogonal planes by the MRI as a function of waiting times. We found from the MRI pictures that the bulk relaxation process was so slow that the surface relaxation and the subsequent diffusion process were dominant mechanisms for the 3He spin relaxation. When the mixture was phase-separated, the magnetization in the concentrated side recovered much faster than that in the diluted side. It was also shown that there was no extra magnetization recovery at the phase boundary. As a result, the magnetization diffused from the concentrated side, flowed through the phase boundary into the diluted side and caused a magnetization recovery in the diluted side.

Electrical Behaviour of Finely Divided Ice

AbstractThe electrical behaviour of ice which has been finely ground and compressed was investigated during ageing in air and over a range of temperatures. The dielectric behaviour may be accurately represented as the sum of two elliptical relaxation spectra. The behaviour eventually stabilizes with similar activation energies for the mean relaxation time of each spectrum c. 0.25 eV, and the ratio of the relaxation times is ten in samples of density c. 0.42 Mg m-3. Arguments are presented on whether the higher-frequency dispersion is a consequence of the heterogeneous nature of the samples or is a bulk relaxation process. The similarities between the behaviour of such finely ground ice and of deposited snow and polar glacier ice are discussed. The extent to which the results may be attributed to surface adsorption of CO2 are examined by reference to measurements of the CO2 content of finely divided ice and ice from polar regions.

Electrical Behaviour of Finely Divided Ice

Abstract The electrical behaviour of ice which has been finely ground and compressed was investigated during ageing in air and over a range of temperatures. The dielectric behaviour may be accurately represented as the sum of two elliptical relaxation spectra. The behaviour eventually stabilizes with similar activation energies for the mean relaxation time of each spectrum c. 0.25 eV, and the ratio of the relaxation times is ten in samples of density c. 0.42 Mg m-3. Arguments are presented on whether the higher-frequency dispersion is a consequence of the heterogeneous nature of the samples or is a bulk relaxation process. The similarities between the behaviour of such finely ground ice and of deposited snow and polar glacier ice are discussed. The extent to which the results may be attributed to surface adsorption of CO2 are examined by reference to measurements of the CO2 content of finely divided ice and ice from polar regions.

Brillouin Scattering in Multiply Relaxing Liquids

The spectral distribution of scattered light is calculated for the model of a liquid in which the bulk and shear relaxation processes are each characterized by a multiplicity, or a continuous set, of relaxation times. The treatment is a generalization of that given by the authors previously [Phys. Rev. 173, 231 (1968)] in which bulk relaxation was ascribed to the relaxation of a thermodynamic order parameter relaxing with a single relaxation time. It is found that, in general, one has to introduce two independent distribution functions associated with the bulk relaxation times. Only when all the bulk relaxation processes are of the same type (pressure induced, temperature induced, etc.), does the expression for the spectral function contain just one distribution for bulk relaxations. This is in contrast to the results obtained by previous workers and may have significance in relation to a reported discrepancy in interpreting (in terms of a single distribution function for bulk relaxation) experimental data on Brillouin scattering and ultrasonic absorption in glycerine.

Brillouin Scattering in Liquids of High Viscosity

The spectral distribution of scattered light is calculated for the model of a liquid in which the shear and bulk relaxation processes are each characterized by a continuous set of relaxation times. The treatment is a generalization of that given by the authors previously [Phys. Rev. 173, 231 (1968)] in which bulk relaxation was ascribed to the relaxation of a thermodynamic order parameter relaxing with a single relaxation time. It is found that, in general, one has to introduce two independent distribution functions associated with the bulk relaxation times. Only when all the bulk relaxation processes are of the same types (pressure induced or temperature induced, etc.) does the expression for the spectral function contain just one distribution function, say gd(τ), for bulk relaxations. In contrast, the bulk relaxation in ultrasonic work can always be characterized by just gd(τ). The significance of these reuslts in relation to experimental data on Brillouin scattering and ultrasonic absorption in glycerine are discussed.