Search

This article presents a general introduction to the thermophysical and dynamical properties of supercritical fluids. It is organized in two parts: in a first section, the nature of the critical point is discussed and its influence on the properties of supercritical fluids is presented; in a second section, we then examine the dynamic processes induced by these peculiar properties, concentrating on heat and mass transfer and more generally on relaxation phenomena.

Phonon relaxation and internal friction in kaolin-and bentonite-filled PVC composites are studied. By varying the temperature and/or content of the ultrafine mineral filler in the PVC, one can control the contribution from phonon viscosity, damping force, and the effect of viscosity into the energy dissipation of ultrasonic oscillations in the MHz frequency interval. The dynamic character of the measurements makes it possible to differentiate between relaxation phenomena in the composites and to suggest methods for their controlled changes.

In this thesis an attempt is made to demonstrate in accordance with known physical principles that significant changes in the macroscopic equilibrium of the earth can be attributed to rate processes which do not call upon the existence of macroscopic gradients and disturbances in the earth. Such processes and their relation to known mechanisms of plastic deformation and to the experimentally established behavior of materials under high pressures are critically evaluated. This evaluation is carried out in the light of some well-established concepts of statistical mechanics and modern physics. In so doing specific methods for producing seismic disturbances which are based upon known mechanisms of plastic deformation and rupture become indicated. It is also shown that under very high pressures, pressure and temperature can complement each other in producing disturbances associated with polymorphic transitions of materials leading to a reduction in symmetry of their lattice structure. A specific mechanism for producing and repeating earth­quakes at shallow and intermediate depths is proposed. This mechanism is based upon the existence of a visco-elastic surface layer supported by a plastic material embodied with stress relaxing properties. The effect of such a configuration upon the propagation of Love Waves is investigated quantitatively. This investigation shows that the plastic sub-layer would explain the observed selection of the period of Love Waves.

Electron spin resonance spectrometry of the γ-irradiated fresh papayas followed by freeze-drying and powderization was performed. We found a strong single peak in the flesh was observed at g = 2.004 and attributed to organic free radicals. Using the method of Lund et al., relaxation times of the peak from 0 to 14 days-stored samples after γ-irradiation were calculated. T2 showed a dose response, while T1 kept almost constant by the increment of doses. The γ-radiation-induced radicals showing progressive saturation behaviors can be caused through a different pathway from indirect effects by the low LET radiations.

The decrease of initial relative permeability at 103-106Hz is observed in MgCuZn or MnMgCuZn ferrites. By measuring the temperature dependence of loss factor, the gradual deterioration of initial relative permeability is attributed to a relaxation phenomenon. The relaxation phenomena of MnMgCuZn ferrites occur in the condition of the stoichiometoric composition and the higher sintering temperatures. The activation energies of the relaxation phenomena are calculated to be 0.3-1.0eV. The relaxation times at infinite temperature are calculated to be 10-12-10-16 second. The initial relative permeability of MgCuZn or MnMgCuZn ferrites with the relaxation phenomena is higher than the value calculated from the resonance frequency and Snoek’s limit law.

The low-temperature dynamics of ultraviscous liquids hold the key to understanding the nature of glass transition and relaxation phenomena, including the potential existence of an ideal thermodynamic glass transition. Unfortunately, existing viscosity models, such as the Vogel–Fulcher–Tammann (VFT) and Avramov–Milchev (AM) equations, exhibit systematic error when extrapolating to low temperatures. We present a model offering an improved description of the viscosity–temperature relationship for both inorganic and organic liquids using the same number of parameters as VFT and AM. The model has a clear physical foundation based on the temperature dependence of configurational entropy, and it offers an accurate prediction of low-temperature isokoms without any singularity at finite temperature. Our results cast doubt on the existence of a Kauzmann entropy catastrophe and associated ideal glass transition.

Using the γ-irradiated fresh mangoes followed by freeze-drying and powderization, electron spin resonance spectrometry of specimens was performed. As a result, a strong single peak in the flesh, the pericarp and the seed was observed at g=2.004 and attributed to organic free radicals. When relaxation times of the peak was calculated using the method of Lund et al., T2 showed dose responses according to increasing doses while T1 was almost constant. Dose responsibility of the relaxation time T2 obtained from flesh specimens of the mangoes could be measured regardless of the preservation period of 1 to 9 days following γ-irradiation. Therefore, there might be possible to detect the irradiation treatment of fresh mangoes using relaxation time T2.

We have reported that the magnetic power losses per magnetizing cycle change with the magnetization pausing time in a constant rate of magnetization change and some relaxation phenomena exist in the magnetization pausing period. We discuss the influence of the relaxation phenomena on the dynamic magnetic power losses and suggest that the relaxation phenomena seems to be causes of the frequency dependence of the magnetic losses and of the variation of losses that cannot be expressed only by magnetization speed dependence of losses.

The relaxation phenomena arising from both the static-constrained stress and the cyclic variation of atmospheric temperature of Fe59Mn30Si6Cr5 shape memory alloy were studied. Experimental results show that the amount of relaxation decreases with increasing initial compressive loading. The cyclic variation of atmospheric temperature has a smaller effect on the relaxation than the static-constrained stress does. The relaxation phenomenon is more obvious both in the earlier cycles and at higher cyclic heating temperatures. The static-constrained stress relaxation is ascribed to the combination and rearrangement of the stress-induced thin platelets of ɛ martensite. The contribution of cyclic heating on the stress relaxation originates from the formation of new-oriented ɛ martensite. The ɛ ↔ γ transformation, thermal stress and shape-recovery stress during the thermal cycling are considered to have significant influences on the formation of new-oriented ɛ martensite.

An exact solution has been obtained for numbers and densities of vibrational states of the system of “truncated” harmonic oscillators. Simple formulas that present these results in an analytical form have been derived. The model is applied to harmonic oscillators with a cutoff for several molecules for which a close agreement with the exact results is obtained.

Low temperature Mossbauer and AC susceptibility have been used to study relaxation phenomena in nano-sized particles of Cr0.25Co0.25Zn0.5Fe2O4. From these studies, the energy density constant for this system has been estimated to be 4 x 106 erg/cm3. Cation distribution has also been determined and the observed results are correlated to calculated relaxation times.

The frequency dependences of dielectric constant (er′) for 8 mol% Y2O3 stabilized ZrO2 (8YSZ) with two kinds of electrodes, Pt and La0.6Ca0.4MnO3 (LCM), were successfully explained by the superposition of both electrolyte-electrode interfacial polarizations and Debye-type polarizations due to dopant-vacancy associates. The different behaviors in the frequency dependence of er′ for 8YSZ having the different electrodes were ascribed to the dopant-vacancy associates, (YZr′–VO••) and (YZr′–VO••–YZr′), which were very large for 8YSZ with Pt electrode, but almost disappeared for 8YSZ with LCM electrode. The frequency dependences of the ac conductivity (σac) were also explained by the relaxation phenomena of the dopant-vacancy associates, suggesting that the dispersion of σac can not be ascribed to grain boundary effect of electrolyte.

Polycrystalline samples La 0.7− x Nd x Sr 0.3 Mn 0.7 Ti 0.3 O 3 ( x =0.10; 0.20 and 0.30) were prepared by a high-temperature solid-state reaction technique. The X-ray diffraction shows that all the samples crystallize in the orthorhombic structure, Pbnm space group, with presence of a minor unreacted Nd 2 O 3 . The electrical response was studied by impedance complex spectroscopy over a broad frequency range (40–100 MHz) at room temperature. The values of ac conductivity for all samples were fitted by the Jonscher law σ ( ω ) = σ dc + A ω s . For x =0.10 and 0.20, hopping occurs between neighboring sites, whereas for x =0.30 the hopping process occurs through longer distance. Complex impedance plots exhibit semicircular arcs described by an electrical equivalent circuit, which indicates that the Nd-doped compounds obey a non-Debye relaxation process.

A theoretical model explaining the CO 2 sensing mechanism of BaTiO 3 –CuO thin-films is presented. This model is based on the work function variations of the p–n heterojunction that exists between BaTiO 3 (n-type) and CuO (p-type). Impedance measurements are carried out at different carbon dioxide concentrations in order to check the theory exposed and also to show that the Ag as an additive improves the sensor response because a metal–semiconductor junction appears between the silver and the sensing material. Response to CO 2 at different working frequencies and the relation between response and the spatial-charge and relaxation phenomena are also presented.

Combining atomic force microscopy (AFM) and in situ grazing incidence X-ray diffraction (GIXD) we study the morphology and in-plane structure of diindenoperylene (DIP) on SiO 2 in the early stages of the growth. We unravel noticeable strain relaxation phenomena in the in-plane structure during the growth of the first layers, concomitant with a transition from layer-by-layer growth to rapid roughening at a certain critical thickness of about five monolayers.

In this paper a thermomechanical model for viscoanelastic media, proposed by one of us (VC), is combined with the linear response theory in which a harmonic shear deformation is assumed as cause and the relative stress as effect. The phenomenological coefficients that occur in the mathematical description of the model are calculated as functions of frequency and their numerical values are obtained. It is also shown that, in linear response, the analytical expressions of the coefficients satisfy the inequalities that play an important rule in the entropy production. Finally, the results are applied to a polymeric material (poly-isobutilene) for the sake of testing the applicability of the model.

A theory of the relaxation phenomena associated with the molecular motion in polymer crystals (the so-called crystalline relaxation) developed by the author is outlined. These relaxation phenomena are considered to arise from the viscous interaction between polymer chains in crystals due to the incoherent lattice vibrations. Based upon the equilibrium theory of the stability of polymer crystals developed by Peterlin et al., a semi-quantitative theory of crystalline relaxation is given. The main conclusion reached is that the relaxation strength and the relaxation times depend strongly upon the thickness of platelike single crystals or lamellae. The experimental facts known so far agree, al least qualitatively, with the theory.

Stress relaxation following small tensile strain was measured for samples of normal, bleached, and permanent-waved hair immersed in water. The measurements covered up to six decades of log time and were carried out at temperatures from 30 to 85°C. Approximation to the distributions of mechanical relaxation times show a good deal of partially resolvable fine structure. Some of the experimental distributions can be approximated by a small number of Maxwell models in parallel. The different modes of relaxation in a given sample appear to have different temperature shift factors and hence different energy requirements. The effects of bleaching are quite easily seen from the relaxation spectra, whereas the effects of permanent waving, although noticeable, are not as pronounced- Proposals for the mechanism of some of the modes of relaxation involve backbone conformational changes of amino acid residues. A large-scale relaxation is found in bleached hair at temperatures from 60 to 85°C. Perhaps this involves an extensive helix-coil transformation.

Temperature dependence of viscosity of title glasses (x=0, 2, 4, 6, 8, 10, abbreviated as M0, M2, M4, M6, M8, and M10, respectively) was measured by rotational viscometry (high temperature region: 102−106.5 dPas) and thermomechanical analysis (low temperature region: 108.5−1011.5 dPas) and described by the Vogel-Fulcher-Tammann equation. The MgO/CaO equimolar substitution (i.e. the increasing x value) smoothly shifts the high temperature viscosity to higher values.

We report results from a heterodyne-detected transient grating experiment on a three-component microemulsion system, consisting of water-AOT-decane. We studied the microemulsion characterized by a water-to-AOT ratio of X = 40.8 and a volume fraction phi = 0.50, in a temperature range around the percolation threshold. The measurements have been performed with two exchanged momenta q approximate to 1 and 2 mu m(-1) corresponding to sound frequencies around NO and 420 MHz. The Measured Sound velocities show small but significant evidence of the percolation transition in the temperature domain.

We show a method to measure experimentally the phenomenological coefficients and to verify some inequalities which occur in a thermodynamical model for dielectric relaxation proposed by one of us in some previous papers. Assuming a sinusoidal form for induction vector D (extensive variable: cause), the electric field (intensive variable: effect) inside the system which depends on unknown phenomenological coefficients, has been obtained by integration. Then we compare it with a similar form of the electric field obtained by experimental considerations, where well known experimentally determinable coefficients appear. The comparison of these two forms, together with the introduction of an experimentally determinable relaxation time, allows us to determine univocally the above-mentioned phenomenological coefficients as functions of experimentally determinable coefficients only. This allows us to verify the aforementioned inequalities. Moreover, a condition for the applicability of Kluitenberg–Ciancio theory is determined. Finally we carry out dielectric measurements on PMMA and PVC at different frequencies and fixed temperature in order to obtain the phenomenological coefficients as functions of the frequency.

This report describes a study of the effect of SiO2 nanopowders on the mechanism of ionic motion and interactions taking place in hybrid inorganic-organic membranes based on Nafion. Five nanocomposite membranes of the formula [Nafion/(SiO2)x] with SiO2 ranging from 0 to 15 wt % were prepared by a solvent casting procedure. TG measurements demonstrated that the membranes are thermally stable up to 170 degrees C but with the loss water it changes the cluster environments and changes the conductivity properties. MDSC investigations in the 90-300 degrees C temperature range revealed the presence of three intense overlapping endothermal peaks indicated as I, II, and III. Peak I measures the order-disorder molecular rearrangement in hydrophilic polar clusters, II corresponds to the endothermic decomposition of -SO3 groups, and III describes the melting process in microcrystalline regions of hydrophobic fluorocarbon domains of the Nafion moiety. ESEM with EDAX measurements revealed that the membranes are homogeneous materials with smooth surfaces. DMA studies allowed us to measure two relaxation modes. The mechanical relaxation detected at ca. 100 degrees C is attributed to the motion of cluster aggregates of side chains and is diagnostic for R-SO3H...SiO2 nanocluster interactions. DMA disclosed that at SiO2/-SO3H (psi) molar ratios lower than 1.9, the oxoclusters act to restrict chain mobility of hydrophobic domains of Nafion and the dynamics inside polar cages of [Nafion/(SiO2)x] systems; at psi higher than 1.9, the oxoclusters reduce the cohesiveness of hydrophilic polar domains owing to a reduction in the density of cross-links. FT-IR and FT-Raman studies of the [Nafion/(SiO2)x] membranes indicated that the fluorocarbon chains of Nafion hydrophobic domains assume the typical helical conformation structure with a D(14pi/15) symmetry. These analyses revealed four different species of water domains embedded inside polar cages and their interconnecting channels: (a) bulk water [(H2O)n]; (b) water solvating the oxonium ions directly interacting with sulfonic acid groups [H3O+...SO3(-)-].(H2O)n; (c) water aggregates associated with H3O+ ions [H3O+.(H2O)n]; and (d) low associated water species in dimer form [(H2O)2]. The conductivity mechanism and relaxation events were investigated by broadband dielectric spectroscopy (BDS). [Nafion/(SiO2)x] nanocomposite membranes were found to possess two different molecular relaxation phenomena which are associated with the alpha-relaxation mode of PTFE-like fluorocarbon domains and the beta-relaxation mode of acid side groups of the Nafion component. Owing to their strong coupling, both these relaxation modes are diagnostic for the interactions between the polar groups of the Nafion host polymer and the (SiO2)x oxoclusters and play a determining role in the conductivity mechanism of the membranes. The studies support the proposal that long-range proton charge transfer in [Nafion/(SiO2)x] composites takes place due to a mechanism involving exchange of the proton between the four water domains. This latter proton transfer occurs owing to a subsequent combination of domain intersections resulting from the water domain fluctuations induced by the molecular relaxation events of host Nafion polymer.

Investigations on diffusion in systems with memory [I.V.L. Costa, R. Morgado, M.V.B.T. Lima, F.A. Oliveira, Europhys. Lett. 63 (2003) 173] have established a hierarchical connection between mixing, ergodicity, and the fluctuation-dissipation theorem (FDT). This hierarchy means that ergodicity is a necessary condition for the validity of the FDT, and mixing is a necessary condition for ergodicity. In this work, we compare those results with recent investigations using the Lee recurrence relations method [M.H. Lee, Phys. Rev. B 26 (1982) 2547; M.H. Lee, Phys. Rev. Lett. 87 (2001) 250601; M.H. Lee, J. Phys. A: Math. Gen. 39 (2006) 4651]. Lee shows that ergodicity is violated in the dynamics of the electron gas [M.H. Lee, J. Phys. A: Math. Gen. 39 (2006) 4651]. This reinforces both works and implies that the results of [I.V.L. Costa, R. Morgado, M.V.B.T. Lima, F.A. Oliveira, Europhys. Lett. 63 (2003) 173] are more general than the framework in which they were obtained. Some applications to slow relaxation phenomena are discussed., Comment: 6 pages, 1 figure. Corrected last citation. Proceedings of LAWNP05

Methyl groups are most outstanding quantum systems due to their inherent symmetry properties which cannot be destroyed by any kind of lattice disorder. We show how optical hole-burning techniques can be employed to measure rotational tunneling relaxation processes. Since the tunneling parameters are extremely sensitive to changes in the host lattice, there is a rich variety of relaxation phenomena that can be observed. Hole-burning techniques have the capability of measuring not only extremely slow processes with high precision but also rather fast processes. We exploit this possibility to show that the relaxation times at 2K change by 14 orders of magnitude if the permutation symmetry of the methyl group is destroyed by asymmetric deuterium substitution.

The use of mechanical spectroscopy to characterize the quasicrystalline state of solid matter is reviewed. After a general, chronological survey of existing mechanical spectroscopy studies, which include elastic properties as well as various relaxation phenomena between lowtemperature tunneling processes and high-temperature background damping, three subjects are considered in more detail: (i) the nature of intrinsic relaxation phenomena, including relaxation peaks in Al-Pd-Mn single quasicrystals, (ii) hydrogen-induced loss peaks in Zr/Ti-based quasicrystals and their use as a probe, and (iii) the study of nano-quasicrystalline structures and amorphousquasicrystalline transitions. It is shown that by combined studies of different elastic and anelastic phenomena, mechanical spectroscopy can be a valuable tool to obtain information about the nature and motion of defects, about the type of local atomic order, and about phase transformations and different processes leading to the formation of quasicrystalline order.

A list of monographs on internal friction, anelasticity, ultrasonic attenuation, relaxation phenomena in solids, and mechanical spectroscopy published in Soviet Union, Russia, and Ukraine is provided. A complete list of proceedings from international and Russian conferences is also given. This work is a valuable supplement to the Mechanical Spectroscopy - Suggested Reading Series.

Mechanical spectroscopy and relaxation phenomena in solids are briefly discussed from the viewpoint of generalized susceptibility and linear response theory. Comparison of mechanical spectroscopy with other spectroscopic techniques is provided in the endeavour to formulate a multidisciplinary approach to selected relaxation phenomena in solids.

We study some of the basic properties of a generalized Cauchy process indexed by two parameters. The application of the Lamperti transformation to the generalized Cauchy process leads to a self-similar process which preserves the long-range dependence. The asymptotic properties of spectral density of the process are derived. Possible application of this process to model relaxation phenomena is considered.

The hyperelastic constitutive model of cardiac muscle is developed based on the animal surgical operation and mechanical experiments from the heart of the dogs, and the relaxation phenomena is also studied based on the Hill three elements model which is viscoelastic. Some numerical simulations are presented by finite element for the cardiac pacing/defibrillation lead interaction with muscles of the heart.

The relaxation behavior of the spin- 3 / 2 Ising model Hamiltonian with bilinear and biquadratic interactions near the second-order phase transition temperature or critical temperature is studied by means of the Onsager's theory of irreversible thermodynamics or the Onsager reciprocity theorem (ORT). First, we give the equilibrium case briefly within the molecular-field approximation in order to study the relaxation behavior by using the ORT. Then, the ORT is applied to the model and the kinetic equations are obtained. By solving these equations, three relaxation times are calculated and examined for temperatures near the second-order phase transition temperature. It is found that one of the relaxation times goes to infinity near the critical temperature on either side, the second relaxation time makes a cusp at the critical temperature and third one behaves very differently in which it terminates at the critical temperature while approaching it, then showing a “flatness” property and then decreases. We also study the influences of the Onsager rate coefficients on the relaxation times. The behavior of these relaxation times is discussed and compared with the spin- 1 / 2 and spin-1 Ising systems.

Surface area exclusion chromatography (SAEC) was employed to determine the stability characteristics of saturated homogeneous layers when interfacial exchange or transfer of molecules was promoted. In these experiments, the first polymer layer was established by elution of a column composed of stacked glass-fiber filters with one polymer. Then, after displacement of the void by water, the second polymer was subsequently injected under the same elution conditions. The experiments combine polymers of equal or different molecular weight and/or hydrolysis grade. Histograms of SAEC experiments demonstrate the great stability of the initially adsorbed layer. Domains of high and low adsorption values were determined to exist along the chromatography column after injection of the first polymer sample. The polymer injected second slightly modifies the initial adsorption histogram and mainly overadsorbs on the low adsorption domain of the first polymer. The major result relates to the relaxation phenomenon affecting or not the second adsorbed polymer when it adsorbs on filters belonging to the low adsorption domain of the polymer first injected. The relaxation is impeded when the relaxation of the first polymer is of great amplitude, whereas it occurs when the relaxation of the first polymer is small.

A survey is given on some applications of broadband acoustical spectrometry of liquids, with particular emphasis on aqueous systems. Various relaxation phenomena occurring in the frequency range between about 10 kHz and 10 GHz are discussed in the light of elementary molecular processes, including thermoelastic and viscoinertial effects, conformational isomerizations, associations, ion-molecule complexations, and precritical concentration fluctuations.

Dielectric properties and relaxation phenomena of composite materials (epoxy resin - barium titanate) were studied as a function of ceramic content. The composites were prepared mixing both components and pouring them into suitable moulds. Some composites were made using tetrahydrofuran (THF) because it helped to reduce matrix viscosity, facilitating the system mixture. Dielectric measurements showed that dielectric constant of composites depended on the filler amount, the temperature and the frequency. Dielectric losses also were influenced by the temperature and by the frequency through relaxation process, even though volume fractions did not have influence on losses. Fil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Reboredo, Maria Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

Dielectric properties of material mixtures are of importance in diagnostics, characterization and design of systems in various engineering fields. In this Letter, we propose a peculiar dielectric mixture expression, which is based on the dielectric relaxation phenomena and the spectral density representation [E. Tuncer J. Phys. Condens. Matter 17(12) L125 (2005)]. The expression is tested on several composite systems. Results illustrate that the proposed expression can be used to obtain valuable structural informations in composites, even for highly filled, bi-percolating, systems. Lastly, the proposed expression is an alternative to other existing homogenization formulas in the literature.

PurposeIn this paper, special attention is focused on the study of the relaxation phenomena of fabrics containing elastane yarn.Design/methodology/approachFor this purpose, the relaxation phenomena of wound fabric under constant deformation, as the consequence of accumulated stress during winding, were analysed. Maxwell's model and the modified standard linear solid model are used for explaining the relaxation.FindingsThe results of the study of the relaxation phenomena of fabrics containing elastane yarn show a close connection between stress relaxation under constant deformation in the fabric roll and the degree of deformation with manual unwinding. Expert knowledge of the relaxation phenomena in fabrics containing elastane yarns has a big influence on explaining the problem of dimensional changes and instability in such fabrics.Originality/valueA better understanding of the relaxation phenomena in fabrics containing elastane yarns.

The thermal properties of the solid and liquid bismuth–lead eutectic (44.6 wt.% Pb) have been investigated by a γ-ray attenuation technique over the temperature range from 293 to 750 K. New data on the temperature dependences of the solid and the melt densities have been obtained. The density change during the solid–liquid transition has been directly measured for the first time. The effect of the solid density relaxation has been detected and studied. A model has been proposed, which explains the observed phenomenon.

The dynamic mechanical thermal properties of a family of poly(-alkyl ,l-aspartate)s bearing various cyclic, linear, and branched alkoxycarbonyl groups in the side chain were studied. The measurements carried out by dynamic mechanical thermal analysis (DMTA) revealed the significant influence of the constitution of the side chain on mechanical relaxation phenomena. Three relaxations were observed, which are referred to as , , and , in increasing order of temperature. The first two, and , are related to the local and global motions of the side chain, respectively. Relaxation is related to the motion of the main chain. Relaxation , which is associated with the rotation of the side chain, is the most intense. The magnitude and temper- ature at which this relaxation occurs depends on the volume, the length, and the degree of branching of the ester group of the side chain. A comparison between the dynamic mechan- ical properties of poly(,l-aspartate)s and poly(,l-gluta- mate)s revealed that the two methylene groups spacing the ester group from the main chain provides the poly(-l- glutamate)s with greater mobility, and thus, relaxations and occur at lower temperatures. © 2005 Wiley Periodicals

The results of studying the isothermal polarization of thin polymer films of an azomethine compound (Schiff base) with varying polarization field intensity are described. Intense relaxation processes induced by space-charge accumulation in the metal-polymer near-contact zone are revealed in the studied samples. Experimental data are analyzed in terms of the relay mechanism of charge transfer in the conduction band involving deep local levels. Values of the microparameters characterizing the observed relaxation phenomena are determined.

Non-destructive electromagnetic wave-based techniques have been used for over a century to gain insight into the behaviour of geomaterials. The technique used in this study is a high frequency [Formula: see text] open-ended coaxial probe measurement system. This study highlights the importance of knowing the limitations of the measurement system. The specimens that are tested are aqueous solutions of NaCl, [Formula: see text], and [Formula: see text] with conductivities ranging from approximately [Formula: see text]. Real permittivity data of the high conductivity specimens show a relaxation phenomena at MHz frequencies where none exists, indicating that electrode polarization is occurring. The frequency at which electrode polarization begins to manifest (e.g., limiting frequency) increases as the specimen conductivity increases. An empirical relationship between the limiting frequency and specimen conductivity is presented and is applied to three kaolinite-NaCl slurries. Additional problems associated with measuring high conductivity specimens using this equipment may arise since the model for the aperture admittance was optimized using low conductivity materials. Previous studies have shown that measurement errors at low frequencies are reduced if the system is calibrated using a material of similar electrical properties to the test specimen.

The use of perfluorinated anionic carboxylic acids (PFCAs) as surfactants is common and widespread. Investigations of PFCAs have shown that their physical properties and toxicological aspects are dependent upon the carbon chain length. The magnitude of these properties is not a linear function of chain length and as yet no explanation of these unique observations has been made. Their environmental dissemination is expected to be nonproportional to the PFCAs chain length. An understanding of the fundamental underlying reason for this novel physical property, chain length trend, would aid further investigators' interpretation of their environmental and toxicological observations. In this study we have utilized 19F NMR techniques, such as, chemical shift, spin−lattice (T1), and spin−spin (T2) relaxation phenomena, coupling constants, and variable-temperature NMR to furnish a qualitative explanation of why increasing the carbon chain length causes unexpected intrinsic property changes within this group of che...

Some results on the relaxation processes (Glauber dynamics) obtained in the last decade are presented. This article is intended to be a short guided tour through these results for readers without prior knowledge of rigorous statistical mechanics or stochastic processes.

Through photocopolymerisation of the cluster Zr4O2(OMc)(12) bearing 12 polymerisable groups with methylmethacrylate in a monomer:cluster molar ratio of 50, a novel inorganic-organic hybrid thin film was obtained. The prepared thin film, having a thickness of about 70 mum, was characterised through dielectric spectroscopy. The dielectric spectra of the film were measured at different temperatures (20-73.4 degreesC) and in the frequency range 20 Hz-1 MHz. The alpha and beta relaxations typical of polyalkylmethacrylate polymers were detected and the electric response mechanisms were investigated by analysing the dielectric spectra in terms of the Davidson-Cole phenomenological equation. Finally, a dielectric constant of 1.93 at 25 degreesC and 1 kHz was determined. This value classifies this system as a promising dielectric material for the development of electronic devices, such as polymer based field effect transistors.

In this paper we are concerned with adsorption, structure, morphology, and dynamic properties of food dairy proteins (β-casein, caseinate, and whey protein isolate (WPI)) and water-insoluble lipids (monopalmitin and monoolein) at the air-water and oil-water interfaces. Combined surface chemistry (surface film balance and dynamic tensiometry) and microscopy (Brewster angle microscopy (BAM)) techniques have been used to determine the adsorption, structure, morphology, relative film thickness, relaxation phenomena, and dilatational rheological characteristics of emulsifiers (proteins and lipids) at fluid-fluid interfaces, including the effect of temperature. The derived information shows that protein and lipid type and temperature affect the interfacial characteristics. The nature of emulsifier (protein or lipid) interactions at the interface has an important role in their physicochemical characteristics. Important functional differences have been established between proteins and lipids, and between globular...

I reviewed the recent studies of rubbery materials, especially which deal with relaxation phenomena. The NMR relaxations for rubbers have been widely investigated before developing the high-resolution solid-state NMR technique in early 1980s. Before starting review of the recent works, I touched upon the utilized formulae for NMR relaxation very simply because some admirable reviews about NMR relaxation have already been recently published. In the past 15 years, supreme pulse techniques and analysis methods were developed and applied to elastomers and rubbers to elucidate the network structure and the polymer chain dynamics. I focused on such research works in this review, namely NMR relaxation feature under strain, degradation and aging process, cross-link density, interaction with fillers and its interface structure, network structure and defects, polymer chain dynamics, and so on. Finally, I concisely summarized the applications of the inverse Laplace transform, which facilitates visual analysis and recognition, to reveal dynamics and cross-link density of elastomers and rubbers.

Recent developments in experimental techniques of dielectric spectroscopy are based on the new concept of broadband dynamics observed by using a broadband dielectric spectroscopy (BDS ) measuring system. BDS techniques are particularly effective for studying water structures in biological systems. Water molecules interacting with biomolecules show various behaviors of collective modes, and these behaviors are closely related to the macroscopic and microscopic properties and functions of biomaterials. This chapter discusses the basic concept of the dynamic behaviors of water structures obtained from experimental and analytical methods based on BDS. Observation techniques based on BDS solve some of the problem s of observing dynamics. The physical picture of water structures and the interpretation of relaxation phenomena are suggested from dynamic hydrogen bonding (HB) networks, and the dynamic properties are also explained on the basis of the fractal concept. Although this concept is not perfect, it is a suitable approach for characterizing the dynamic behaviors of HB networks . Although the fractal approach has been applied to complex materials using various techniques, this approach also suggests the existence of a problem related to length scales in the observation of dynamic behaviors. Complementary approaches with various observation techniques will be very effective for solving such problems and for suggesting future applications.

The aim of this paper is to investigate the influence of HNT on the dielectric properties of LLDPE (linear low density polyethylene) nanocomposite compounds in the different level of fulfillment (0, 1, 3, 7 wt%). The utilization of these HNT/LLDPE nanocomposite compounds can be seen in the cable industry, where the dielectric properties are essential. Used experimental compounds have been prepared in the laboratory blades mixer Brabender W50 EHT and the plasticorder Brabender PLE 651. Immediately after mixing, the molten compounds were removed from the mixer, inserted into the spacer, and pressed into films of 0.25 mm thickness. Dielectric properties in the DC field (polarization current, reading of polarization index, volume resistivity) of the individual samples were measured and the temperature and frequency range by Broadband dielectric spectroscopy Alpha-A (Novocontrol) were investigated. Samples have been subjected to the dielectric strength test according to standards. As results showed, experimental samples were affected by HNT, especially in the dielectric relaxation phenomena, when during the increment of the level of fulfilment occurred the increasing of the nearly lossless dielectric relaxations. The volume resistivity of the samples was affected in the range of one magnitude.