Study of the Influence of SBS and APDDR on the Low-Temperature Properties of Road Bitumen

A comparative assessment of the effect of two modifiers on the low-temperature properties of BND 90/130 bitumen was investigated using Asphalt Binder Cracking Device (ABCD test) and Dynamic Shear Rheometer (DSR 4-mm test). These modifiers are styrene-butadiene-styrene block copolymer (SBS) and active powder of discretely devulcanized rubber (APDDR) - powder elastomeric modifier obtained by high-temperature shear grinding of waste tire crumb rubber. ABCD results of RTFO-aged samples showed clear and gradual decrease of the ABCD cracking temperature (improvement) for all BC as the modifier concentration increases. It is noteworthy that the Bitumen Composites (modified bitumens) were cracking at higher strain and fracture stress values compared to neat bitumen. Results of DSR-4 mm test showed a decrease in the complex shear modulus (G*), storage modulus (G¢) and loss modulus (G²) BC compared to the neat bitumen. It is shown that bituminous composites have no maximum on the Cole-Cole diagram (dynamic vitrification) at T = -28°C which is observed in the neat bitumen.

SYNTHESIS AND DIELECTRIC PROPERTIES OF La0.67LixTi1-xAlxO3 (0.15≤x≤0.3) CERAMICS

Solid solutions of Al-doped lithium lanthanum titanates La0.67LixTi1-xAlxO3 system (where 0.15 ≤ x ≤ 0.3) have been synthesized by solid-state reaction technique. Light optical microscopy has shown that the grain size of La0.67LixTi1-xAlxO3 ceramics insignificantly increases with an increase in lithium/aluminum concentration. The materials La0.67LixTi1-xAlxO3 show very high dielectric permittivity ε΄ 104 over a relatively wide frequency range (102 ≤ f ≤ 104 Hz) with no apparent dependence on the x. The impedance spectroscopy study indicates three semicircles on Cole-Cole diagram that can be attributed to electrically different areas of ceramic’s grain.

A study on the viscoelastic behavior of chitosan-polyvinyl alcohol-graphene oxide nanocomposite films as a wound dressing

The nanocomposites of Chitosan (CS)-poly vinyl alcohol (PVA) reinforced with graphene oxide (GO) were fabricated by casting in a mold. The nanocomposite films were characterized by various techniques. The viscoelastic properties of the wound dressings were evaluated by dynamic mechanical thermal analysis (DMTA) since the healing quality of a wound dressing depends on such properties. DMTA results also were modeled by the Cole-Cole diagram. Finally, the effects of GO on antimicrobial and biological properties of films were studied. It has been shown that nanocomposite films support the initial attachment, proliferation, and growth of mouse fibroblast cells.

Фазовый переход полупроводник--суперионик в пленках сульфида серебра

Frequency dependences of dielectric loss tangent tanδ (f) and Cole-Cole diagram of thin films of silver sulfide at various temperatures in the range 0-200 ° C were studied. A comparison of experimental data with the results of calculation of electrical circuit complex impedance of Ag2S samples is made. The comparison is made for temperatures before and after semiconductor-superionic phase transition. Based on the analysis of experimental results and literature data, a microscopic model of the phase transition in Ag2S is proposed.

Диэлектрическая спектроскопия и механизм фазового перехода полупроводник-металл в легированных пленках VO-=SUB=-2-=/SUB=-:Ge и VO-=SUB=-2-=/SUB=-:Mg

The frequency dependences of the dissipation factor tanδ( f ) and the Cole–Cole diagrams for germanium- and magnesium-doped vanadium-dioxide films in the range of 0.1–10^6 Hz are obtained. Measurements at temperatures between 173–373 K are performed. It is found that, at room temperature, an additional maximum in the tanδ( f ) dependence and an additional semicircle in the Cole–Cole diagram of the VO_2:Ge films as compared with those of undoped films appear at low frequencies. In the VO_2:Mg films, similar additional features in the dielectric spectra are observed at high frequencies. It is shown that the shape of the Cole – Cole diagrams for all the films is almost temperature independent in the mentioned temperature range, while the frequencies f _0 corresponding to the tanδ( f ) maxima increase with temperature. To interpret the dielectric spectroscopy data, a combined equivalent electrical circuit of the film sample is proposed. The mechanisms of the effect of Ge and Mg impurities on the characteristics of the complex Mott–Peierls semiconductor–metal phase transition are established.

Диэлектрическая спектроскопия пленок VO-=SUB=-2-=/SUB=-:Ge

The frequency dependencies of complex impedance $$\dot {Z}$$ , dielectric permittivity ε, and dielectric loss tangent tanδ of thin (1400 Å ) films V_1 –_ x Ge_ x O_2 (for x = 0 and 0.03) are studied in the frequency range of 10‒10^6 Hz at 300 K. It is found that, at x = 0, the frequency dependence of tanδ has a maximum at a frequency of 100 kHz, whereas at x = 0.03 an additional maximum in the region of 10 kHz is detected. Also, the Cole–Cole diagram of VO_2:Ge films acquires a feature in the form of an additional semicircle. Owing to the extremely high sensitivity of the dielectric spectroscopy method, the proposed equivalent circuit diagram of the sample allowed detecting the existence of two sets of VO_2 nanocrystallites in the V_0.97Ge_0.03O_2 film, including Ge-doped nanocrystallites and practically nondoped ones.

Диэлектрическая спектроскопия как метод исследования тонких пленок диоксида ванадия

The dielectric spectra of thin (1200 Å) vanadium dioxide films, a material with strong electron-electron correlations, were studied. Both the undoped and germanium-doped VO2: Ge films were studied. For the VO2: Ge, an additional maximum has been detected in the frequency of the dielectric loss spectrum. The fine structure of the spectra was investigated and the physical interpretation of two maxima in the frequency dependence of the tangent of the dielectric loss angle and of two semi-circles on the Cole-Cole diagram was performed. The results were analyzed on the basis of the equivalent electrical circuits of the samples: a single RC-circuit for the case of an undoped VO2 film and a double-circuit  for VO2: Ge. The numerical values of the parameters of the model schemes are determined. It has been established that the complicating of equivalent circuit for VO2: Ge compared to undoped VO2 is due to the complication of the electrical response of the doped film to the influence of an electromagnetic field. It is shown that this complication is associated with the acceptor properties of a Ge impurity, which is manifested when the strongly correlated material is doped with an isoelectronic impurity.

The Viscoelastic Characteristics of the Asphalt Concrete Modified with Different Synthetic Waxes Using a Modified Huet- Sayegh Model

The article presents the results of dynamic modulus tests carried on the asphalt concrete (AC16W). The sinusoidal load was applied to the samples in accordance with DTC-CY method. The neat bituminous binder (penetration grade 35/50) was modified by means two synthetic waxes, coming from the Fischer-Tropsch raction, with various molecular weights and softening point temperature results (hard and softer). The relaxation phenomenon in terms of changes in complex modulus and phase angle was evaluated using the modified Huet-Sayegh (2S2P1D). Estimated model parameters pointed out that the addition of the synthetic wax with the high (hard wax) and the low (softer wax) molecular weight raised the stiffness of the bituminous binder in relation to the reference bitumen 35/50. The application of the modified Huet-Sayegh model showed that the presence of the synthetic wax in the bitumen significantly affected the stiffness modulus of considered asphalt concretes. Basing analysis on Cole-Cole diagram it was found significant differences in the viscoelastic behaviour between the reference asphalt concrete and the asphalt concretes with synthetic waxes. In contrast, there were no significant differences between viscoelastic properties of tested asphalt concretes modified, used in the experiment, synthetic waxes. Furthermore, the sensitivity to the loading time of asphalt concretes containing both synthetic waxes was marginal.