Mechanical Relaxation Spectroscopy Research Articles

Effect of UV Radiation on Dissipative Processes in Polyacrylates of Different Elasticities

Dynamic mechanical relaxation spectroscopy is used to study the relaxation behavior of elastic alkyl(met) polymers. The items of interest are acrylates on metal substrates before and after UV irradiation of different durations. Analysis is based on comparing the intensity of local dissipative relaxation in irradiated and non-irradiated polymers, along with their glass transition temperatures and elastic properties.

The Influence of a Metallic Filler on Relaxation Processes in Polyacrylates

The spectra of internal friction in elastic acrylic polymers are investigated by the method of dynamic mechanical relaxation spectroscopy in a wide temperature range in the absence and presence of a finely dispersed iron powder giving consideration to its distribution in the polymer film, which is analyzed using the atomic force and scanning electron microscopy methods. The study of the spectra is based on the analysis of the α, β, and μ relaxation processes occurring in unfilled and filled polymers. The spectra show an increase in the glass transition temperature of the polymer in the presence of a filler and a decrease in inelastic properties in the frequency–temperature dependence. The processing of internal friction spectra at temperatures below 0°C makes it possible to reveal µ processes that correspond to the formation of various forms of ice, destruction of the polymer structure upon freezing, and a decrease in elastic properties, which are most pronounced in systems with a filler. Identification of regions of polymer inelasticity is important for its operation at both the glass transition temperature and temperatures below 0°C.

Analyzing Dissipative Processes in a Filled Polymer Using Data from Mechanical Relaxation Spectroscopy

Dissipative processes that occur in a highly elastic acrylate polymer in the −150 to +100°C range of temperatures are studied via the differential processing of spectra of internal friction based on data from dynamic mechanical relaxation spectroscopy, allowing for the polymer’s filling with a highly disperse iron powder. Mathematical processing allows to determine the regions of relaxation activity in the filled and unfilled polymer and to evaluate the changes in the relaxation structure of the polymer after the introduction of a highly disperse filler.

Dissipative Processes in Irradiated Composite Polymers

The effect of ionizing irradiation on dissipative processes of α-, β-, and μ- relaxation in a polymer either filled or unfilled with highly dispersive iron powder considering the polymer structure has been investigated via the method of dynamic mechanical relaxation spectroscopy. The polymer structure has been analyzed on the basis of surface topography data obtained via atomic force microscopy. A correlation between the effect of irradiation on the temperature position of the maxima and the intensity of dissipative processes on the internal friction spectra, as well as on the temperature-frequency dependence with structural changes that have developed in cross linking and compaction of the polymer, have been demonstrated.

Effect of a Finely Dispersed Filler on the Relaxation Behavior of a Latex Polymer

The effect of finely dispersed iron powder on the relaxation behavior of highly elastic acrylate latex polymers was studied by dynamic mechanical relaxation spectroscopy. The introduction of a filler led to a decrease in the intensity of the maximum of dissipative losses of α relaxation and in the modulus defect of the polymer and to dissipative losses of β relaxation. Special attention was paid to relaxation effects at negative temperatures, which showed themselves as local dissipative processes of μ relaxation in the spectra of internal friction and on the temperature dependences of frequency.

The Effect of Phthalocyanine Modifiers on Local Dissipation Relaxation Processes in Latex Polymer at Negative Temperatures

Dynamic mechanical relaxation spectroscopy is used to study local dissipation processes of μ‑relaxation in a modified latex acrylate polymer in the negative temperature range taking into consideration their modification by different ionic phthalocyanines. Characteristic maxima of dissipation μ-relaxation losses due to a change in the polymer relaxation structure are observed.

Local Dissipation Relaxation Processes in Modified Latex Polymer under Negative Temperatures

Dynamic mechanical relaxation spectroscopy is used to study local dissipation processes of μ‑relaxation occurring in a modified latex polymer in the negative temperature range with account for their pretreatment in the freezing–thawing mode. The differential processing of temperature–frequency dependences is performed to identify the regions of their manifestation. The maximums of local dissipation processes due to the change in the relaxation structure and elastic properties of the polymer in the presence of the modifier are detected.

The Relaxation Behavior of Polymer Compounds Based on Latex Polymer and Water-Soluble Modifiers

The relaxation behavior of polymer compounds based on latex polymers and water-soluble modifiers with different chemical structures are studied by dynamic mechanical relaxation spectroscopy. The revealed changes in the intensity of dissipated losses of the α-relaxation process in the internal friction spectra of polymers depending on the modifier nature are compared with the Young’s modulus (the defect of the modulus) and the morphological features of the polymeric system. The phenomenological models are used to conduct a theoretical analysis of the association between frequency of the oscillatory process and the Young’s modulus of the polymer material, as well as to analyze the relaxation heterogeneity evaluated according to the width of the continuous spectrum of relaxation time in normalized coordinates λ/λmax versus {(Т – Тmax)/Тmax}.

Relaxation Behavior of Acrylic Latex Polymer Modified by Water-Soluble Dye. Freezing–Thawing Mode

The relaxation behavior of a styrene–acrylic latex polymer with a glass-transition temperature of ≤5°C and polymer composites on its basis modified by an indanthrene-type water-soluble dye was analyzed using the method of dynamic mechanical relaxation spectroscopy. The change in the intensity of maximum of dissipative losses of α-relaxation and also of the μ-process is found in polymer films in the negative-temperature range as dependent on the duration and number of their preliminary freezing–thawing cycles at‒30°C taking into account the modifier concentration, which is related to the change in Young’s modulus (modulus defect). Theoretical analysis is performed involving phenomenological model concepts as to the relationship between the vibration-process frequency and Young’s modulus of the polymer material.

Relaxation behavior of latex-polymers in frost-resistant aqueous-dispersion deep-penetration ground coats modified by water-soluble dye

The effect of a water-soluble indanthrene blue dye on the relaxation structure of styrene–acryl latex polymer with the glass-transition point below 5°C is studied in a frost-resistant aqueous-dispersion coat using the method of dynamic mechanical-relaxation spectroscopy. A significant difference is found between the change in the intensity of the maximum of α-relaxation dissipative losses of a latex-polymer binder in the ground coat and in free latex polymer when they are modified by a blue dye, which is due to the ground-coat composition. Special attention is paid to relaxation effects in the negative temperature range.

Relaxation behavior of latex polymers modified by water-soluble dyes. Negative temperature range

The effect of a water-soluble blue indanthrene-type dye on the relaxation structure of styrene–acryl latex with the glass transition point of ≤5°C is studied using the method of dynamic mechanical relaxation spectroscopy. Variation of intensity of the maximum of α-relaxation dissipation losses in the latex polymer is observed, same as its relationship to the mechanism of modification of the polymer film by a dye. Special attention is paid to relaxation effects in the negative temperature range.

The concept of fractal experiments: New possibilities in quantitative description of quasi-reproducible measurements

In this paper the authors suggest a new conception of the so-called fractal (self-similar) experiment. Under the fractal experiment (FE) one can imply a cycle of measurements that are subjected by the scaling transformations F(z)→F(zξm) in contrast with conventional scheme F(z)→F(z+mT) (m=0,1,…, M–1), where z defines the controllable (input) variable and can be associated with time, complex frequency, wavelength and etc., T – mean period of time between successive measurements and m defines a number of successive measurements. One can connect a fractal experiment with specific memory effect that arises between successive measurements. The general theory of experiment for quasi-periodic measurements proposed in [1] after some transformations can be applied for the set of the FE, as well. But attentive analysis shown in this paper allows generalizing the previous results for the case when the influence of uncontrollable factors becomes significant. The theory developed for this case allows to consider more real cases when the influence of dynamic (unstable) processes taking place during the cycle of measurements corresponding to some FE is becoming essential. These experiments we define as quasi-reproducible (QR) fractal experiments.The proposed concept opens new possibilities in theory of measurements and numerous applications, especially in different nanotechnologies, when the influence of the scaling factor plays the essential role. This concept allows also to introduce the so-called intermediate model (IM) which can serve as an unified platform for reconciliation of the proposed microscopic theory with reliable experiments “refined” from the influence of the random noise and apparatus function. We forced to consider a modified model experiment in order to demonstrate some common peculiarities that can be appeared in real cases. We know only couple of similar examples of experiments that are close to the proposed concept. Mechanical relaxation and dielectric spectroscopy (based on measurements of the complex susceptibility ε(jω)) represent the branches of physics related to consideration of mechanical and electric relaxation phenomena in different heterogeneous materials. The dielectric spectroscopy can be considered as an instructive example for better understanding of the proposed concept.In cases, when the microscopic model is absent the results of measurements can be expressed in terms of the fitting parameters associated with the generalized Prony spectrum (GPS) belonging to the IM. The authors do hope that this new approach will find an interesting continuation in various applications of different nanotechnologies.

Coupling of Caged Molecule Dynamics to JG β-Relaxation III: van der Waals Glasses.

In the first two papers separately on the polyalcohols and amorphous polymers of this series, we demonstrated that the fast dynamics observed in the glassy state at high frequencies above circa 1 GHz is the caged dynamics. We showed generally the intensity of the fast caged dynamics changes temperature dependence at a temperature THF nearly coincident with the secondary glass transition temperature Tgβ lower than the nominal glass transition temperature Tgα. The phenomenon is remarkable, since THF is determined from measurements of fast caged dynamics at short time scales typically in the ns to ps range, while Tgβ characterizes the secondary glass transition at which the Johari-Goldstein (JG) β-relaxation time τJG reaches a long time of ∼10(3) s, determined directly either by positronium annihilation lifetime spectroscopy, calorimetry, or low frequency dielectric and mechanical relaxation spectroscopy. The existence of the secondary glass transition originates from the dependence of τJG on density, previously proven by experiments performed at elevated pressure. The fact that THF ≈ Tgβ reflects the density dependence of the caged dynamics and coupling to the JG β-relaxation. The generality of the phenomenon and its theoretical rationalization implies the same should be observable in other classes of glass-formers. In this paper, III, we consider two archetypal small molecular van der Waals glass-formers, ortho-terphenyl and toluene. The experimental data show the same phenomenon. The present paper extends the generality of the phenomenon and explanation from the polyalcohols, a pharmaceutical, and many polymers to the small molecular van der Waals glass-formers.

Relaxation phenomena in latex polymer materials modified by ionic phthalocyanine

The relaxation structure of ionic phthalocyanine-unmodified and -modified latex styrenealkyl(meth)acrylate polymers formed using various methods of emulsion polymerization is studied by dynamic mechanical relaxation spectroscopy taking into account data on the modifier distribution in the polymer and polymer functionality. The relaxation homogeneity of the studied polymer is characterized on the basis of the results of relaxation studies.

Sub-Rouse Modes in Polymers Observed by Dielectric Spectroscopy

One of the characteristic features of polymer dynamics is the existence of additional relaxation processes that are related to connectivity of monomers in polymer chain and are absent in small molecular liquids. These processes are usually described as purely entropic Rouse modes and appear on time scales much longer than segmental (structural) relaxation in polymers. They are commonly observed by mechanical relaxation spectroscopy and are detected as normal modes in dielectric spectra of some polymers (where dipole moment accumulates along the chain). Here we present the evidence of additional modes that appear in dielectric relaxation spectra of some polymers between the segmental and Rouse modes. We identified these modes as sub-Rouse modes, the same as those previously found by mechanical spectroscopy. We also demonstrate that these modes are not detected in the dielectric loss spectra of many polymers. Moreover, existence of these modes does not correlate with the existence of dipole moment along the polymer chain. A possible explanation of this behavior is discussed.

Study of supercooled orientationally disordered binary solid solutions II: cyclohexyl derivatives, neopentanol and neopentylglycol

The main aim of the present investigation is to see how various relaxation processes including the chair-chair transformation (as found by earlier researchers at room temperature in mechanical relaxation spectroscopy) in cyclohexane derivatives evolve as the temperature is lowered. For this purpose, four remarkable (two-component) solid solutions that are orientationally disordered are investigated, where the first three systems are hydrogen (H-) bonded pairs, and the fourth is a non-H bonded pair. The former group is the two-component system of cyclohexanol (CHXOL) + 2,2-dimethyl-1-propanol or neopentanol (NPOL); cyclohexanol (CHXOL) + cycloheptanol (CHPOL) & neopentanol (NPOL) + neopentylglycol (NPGOL) systems, and the lone non H-bonded pair that has been studied is cyanocyclohexane (CNCH) and cyclohexylchloride (CHC). In all these cases, the liquid mixtures on cooling form orientationally disordered phases which are a solid solution of the corresponding pure phases. The feature is common to all the four systems studied here, but in CHXOL + CHPOL, the phase I of CHXOL beyond x(m) > or = 0.1 only forms a solid solution (designated as S(I')) with the phase I of CHPOL. In CNCH + CHC the solid phase is stable for the concentration range 0 < or = x(m) < or = 0.4 (without transition to any other phase). The above solid phase I (or I') has been investigated at low temperatures and for several concentrations, by means of dielectric spectroscopy and differential scanning calorimetry (DSC). Depending upon the concentration, this phase reveals a glass transition in the temperature range 116-150 K and associated with this is a pronounced relaxation process identifiable with the so called alpha-process. The dielectric spectra of this process is found to follow the Havriliak-Negami (HN) equation. In context of the binary system study here, the analysis of the various parameters obtained show an isomorphic relationship between the phases of the pure components through a continuous change of parameters. Another process of much smaller magnitude designated as the alpha'-process was also found in systems consisting of cyclohexyl derivatives above the glass transition temperature T(g) which kinetically freezes around 170 K. This process interestingly, is also non-Arrhenius in nature, becomes increasingly weaker with increase in the second component, and may be identified with (axial) chair-(equatorial) chair transformation. In addition in all these systems, a weak high-frequency process and a clear sub-T(g) process, are found which are designated as the beta- & gamma-processes respectively. The beta-process may be identified with Johari-Goldstein (JG) or beta(JG) process as it is found to follow the predictions of the coupling model proposed by Ngai. However, the identification of the gamma-process with internal degrees of freedom are fraught with some problems in the interpretation of the experimental data that are highlighted. The kinetic freezing of the various dielectric processes have been critically examined in relation to the T(g) found in the DSC experiments.

Effect of orientation and crystallization on dielectric and mechanical relaxations in uniaxially stretched poly(ethylene naphthalene 2,6 dicarboxylate)(PEN) films

Microstructural analysis (crystallinity, orientation) have been performed on stretched and isothermally crystallized poly(ethylene naphthalene 2,6 dicarboxylate)(PEN) films. The crystallinity ratios are higher at drawing temperatures below Tg than above Tg, and for similar draw ratios, a higher orientation can be obtained at drawing temperature below Tg than above Tg. The molecular mobility study by dielectric relaxation spectroscopy (DRS) and mechanical relaxation spectroscopy (MRS) was carried out as a function of draw ratio (λ) and drawing temperature (Tdraw). Drawing in glassy state apparently splits the α-relaxation into two components: an α-low component which exhibits a strongly accelerated dynamics but this relaxation process is masked by microstructural rearrangements occurring while heating followed by an α-high relaxation process. The two sub-glass processes (β and β∗) are influenced by the drawing in the glassy state. This can be observed from the increase of relaxation amplitudes and was related to a high disorder in the amorphous phase that is induced by drawing below glass transition temperature. Drawing at 160°C induces the opposite trend associated with crystallization and confinements effects. Differences in viscoelasticity behaviour were found by MRS in tensile mode parallel and perpendicular to stretching direction. As a result, when comparing oriented and crystallized samples with the same crystallinity ratios, a strong effect of morphology on the location and amplitude of the three relaxations of PEN can be found.

Influence of Phase Morphology on Molecular Mobility of Poly(propylene)‐(ethylene‐vinyl acetate) Copolymer Blends

AbstractThe dynamic mechanical and dielectric behaviours of Polypropylene (PP) and (Ethylene‐Vinyl Acetate) Copolymer (EVA) blends are reported as a function of the morphology. For EVA contents lower than 20%, blends show the two‐phase morphology characteristic of immiscible blends, with spherical EVA droplets finely dispersed in the PP matrix. After stretching in the molten state, the morphology of EVA fibers is observed. Mechanical Relaxation Spectroscopy display three relaxation processes: the EVA and PP α‐relaxations associated to the glass transitions and a β‐transition corresponding to a PP crystalline phase relaxation. The PP α‐relaxation shifts to higher temperatures when EVA presents a fiber morphology, corresponding to a decrease of PP chain mobility since it is hindered by the reinforcement effect of EVA fibers. Quite different results are obtained by DRS analysis. In blends containing EVA fibers, only one main relaxation associated to the EVA α‐transition is observed whereas one additional relaxation can be noticed in the blends containing EVA droplets. This new relaxation might be assigned to interfacial polarization effects, phenomena that are sometimes observed in heterogeneous polymer blends when a low content of one polar component is embedded in a non conductive matrix. In this case, the occurrence of a characteristic interfacial polarization relaxation appears to be correlated to the accessible experimental frequency.

Investigation of the Size Effect on the Giant Dielectric Constantof CaCu3Ti4O12 Ceramic

Cubic perovskite-related ceramic CaCu3Ti4O12 has avery high dielectric constant larger than 10000 in the kilohertzfrequency region. It is almost constant in the 100–600 K region. Theceramic compounds were prepared by conventional solid-state reaction atdifferent sintering temperatures 1040 degrees C(C04),1060 degrees C(C06), 1080 degrees C(C08), and 1100 degrees C(C10).Impedance spectroscopy on CaCusTi4O12 ceramicsdemonstrates that they are electrically heterogeneous and consist ofsemi-conducting grains with insulating grain boundaries. It is shownthat C06 is the most suitable one for device applications. Surfaceobservation and analysis of the grain-boundary-grained structure werecarried out by using scanning electron microscopy, which confirms thatthe samples have clearly different crystal grain sizes and C06 has alarger grain size of about 20 μm. Compared to the dielectric relaxationspectroscopy, the mechanical relaxation spectroscopy on C06 wasperformed and a mechanical loss peak was found, which was attributed tothe thermally activated behaviour being immanent in the grains.

Investigation of Size Effect on the Giant Dielectric CaCu3Ti4O12 Ceramic

CaCu3Ti4O12 ceramics were prepared by conventional solid-state reaction with dif-ferent sintering temperature. Impedance spectroscopy on CaCus Ti4O12 ceramics demonstrates that they are electrically heterogeneous and C06 (sintered in air at 1060C) is the most suitable for the device application. Surface observation and analysis of the grain-boundary-grained structure were proceeded by use of scan electronic microscopy, which confirms that the samples have surely different crystal grain sizes and C06 has bigger grain size of about 20 μm. The mechanical relaxation spectroscopy on C06 was also performed and a mechanical loss peak was found, which was attributed to the thermally activated behaviors of some units immanent in grains.