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This work reports the dielectric behavior of the biopolymer ethyl cellulose (EC) observed from transient currents experiments under the action of a direct current (DC) electric field (~107 V/m) under vacuum conditions. The viscoelastic response of the EC was evaluated using dynamic mechanical analysis (DMA), observing a mechanical relaxation related to glass transition of around ~402 K. Furthermore, we propose a mathematical framework that describes the transient current in EC using a fractional differential equation, whose solution involves the Mittag–Leffler function. The fractional order, between 0 and 1, is related to the energy dissipation rate and the molecular mobility of the polymer. Subsequently, the conduction mechanisms are considered, on the one hand, the phenomena that occur through the polymer–electrode interface and, on the other hand, those which manifest themselves in the bulk material. Finally, alternating current (AC) conductivity measurements above the glass transition temperature (~402 K) and in a frequency domain from 20 Hz to 2 MHz were carried out, observing electrical conduction described by the segmental movements of the polymeric chains. Its electrical properties also position EC as a potential candidate for electrical, electronics, and mechatronics applications. [ABSTRACT FROM AUTHOR]

Dielectric and thermal properties of polyvinyl butyral (PVB) were studied in this work, using dynamic electrical analysis (DEA) at frequencies from 100 Hz to 1 MHz and temperatures from 293 K to 473 K. Two electrical relaxation processes were investigated: glass transition and interfacial polarization. Above the glass transition temperature (~343 K), interfacial polarization dominates conductive behavior in polyvinyl butyral. The framework of the complex electric modulus was used to obtain information about interfacial polarization. The viscoelastic behavior was analyzed through dynamic mechanical analysis (DMA), where only the mechanical manifestation of the glass transition is observed. The experimental results from dielectric measurements were analyzed with fractional calculus, using a fractional Debye model with one cap-resistor. We were successful in applying the complex electric modulus because we had a good correlation between data and theoretical predictions. The fractional order derivative is an indicator of the energy dissipated in terms of molecular mobility, and the calculated values close to 1 suggest a conductive behavior at temperatures above the glass transition temperature of PVB. [ABSTRACT FROM AUTHOR]

Today, shape memory alloys (SMAs) have important applications in several fields of science and engineering. This work reports the thermomechanical behavior of NiTi SMA coil springs. The thermomechanical characterization is approached starting from mechanical loading–unloading tests under different electric current intensities, from 0 to 2.5 A. In addition, the material is studied using dynamic mechanical analysis (DMA), which is used to evaluate the complex elastic modulus E* = E′ − iE″, obtaining a viscoelastic response under isochronal conditions. This work further evaluates the damping capacity of NiTi SMA using tan δ, showing a maximum around 70 °C. These results are interpreted under the framework of fractional calculus, using the Fractional Zener Model (FZM). The fractional orders, between 0 and 1, reflect the atomic mobility of the NiTi SMA in the martensite (low-temperature) and austenite (high-temperature) phases. The present work compares the results obtained from using the FZM with a proposed phenomenological model, which requires few parameters for the description of the temperature-dependent storage modulus E′. [ABSTRACT FROM AUTHOR]

This study deals with the fabrication and characterization of a magnetic hybrid film, IONP/EC, comprised of iron oxide nanoparticles and ethyl cellulose. Its manufacture followed two steps: the fabrication of a precursor hybrid film, and its alkaline treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), and thermogravimetric analysis (TGA) demonstrated a successful in-situ synthesis of IONPs in the EC matrix. Furthermore, through vibrating sample magnetometer (VSM) and dynamic mechanical analysis (DMA), the magnetic and viscoelastic properties of the film were characterized, respectively. Using XRD analysis, the crystalline structure of IONPs showed to be an iron oxide hydroxide phase. Although it cannot be dismissed other phases, such as maghemite and magnetite. FTIR results revealed that the EC matrix preserved its chemical structure. Images obtained by HRTEM evidenced quasi-spherical IONPs embedded into the EC matrix with an average particle size of 2.4 nm. The IONP/EC film exhibited a superparamagnetic-like behavior, showing a blocking temperature at 20 K. After TGA analysis, IONPs slightly impacted the thermal stability of the EC matrix. Finally, DMA results revealed a modification on the structural relaxation phenomena of EC, which arose from the presence of IONPs in the matrix. [ABSTRACT FROM AUTHOR]

A fractional calculus approach was used to study the correlation between the complex elastic modulus and the complex relative permittivity for a polystyrene (PS) film with thickness of ~80 μm. Experimental measurements were carried out using dynamic mechanical analysis and dynamic dielectric analysis. Experimental results show the mechanical and dielectric manifestations of the main relaxation (glass transition process), whose molecular mobility was analyzed by two innovative models: a mechanical fractional model and a dielectric fractional model. Parameters of fractional models show that, when temperature increases, the molecular mobility of the main relaxation also increases, but the cooperativity of mobility decreases. Besides, molecular mobility is greater in the mechanical manifestation of the main relaxation than in the electric manifestation. From theoretical results obtained from fractional models for the isochronal mechanic storage modulus, E′(T), and the isochronal relative permittivity, εr′T, a correlation model for mechanical and dielectric properties of PS film was obtained. This correlation model describes εr′T in function of E′(T). These results suggest that this correlation model can be used to study molecular mobility of mechanical and dielectric dynamic properties of the polymer films samples and predict changes in their behavior by modifying ambient conditions. [ABSTRACT FROM AUTHOR]

Fractional calculus models can potentially describe the viscoelastic phenomena in soft solids. Nevertheless, their successful application is limited. This paper explored the potential of using fractional calculus models to describe the viscoelastic properties of soft solids, focusing on methylcellulose aqueous systems. Methylcellulose is an important food additive, and it is known for its complex rheological behaviors, including thermogelation, which still puzzle rheologists. Through dynamic mechanical analysis and fractional rheology, we demonstrated that fractional calculus described the frequency- and temperature-dependent rheology of methylcellulose. This paper also showcased how including one springpot could potentially replace numerous spring-dashpot arrangements. Our findings using fractional calculus suggested that the thermogelation of methylcellulose involves the cooperative mobility of polymer chains and can be described as a process analogous to the glass transition in polymers. This study highlighted the power of combining fractional calculus and rheology to understand complex viscoelastic phenomena in soft solids. [Display omitted] [ABSTRACT FROM AUTHOR]