Electrical Conduction Mechanisms in Ethyl Cellulose Films under DC and AC Electric Fields

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

Fractional rheology of colloidal hydrogels with cellulose nanofibers

Abstract: Colloidal gels are soft solids composed of particles dispersed in a fluid phase. Their rheological behavior highly depends on the particle concentration, but establishing a relationship can be challenging. This article showcases the potential of fractional rheology to model and predict linear viscoelastic responses of colloidal hydrogels containing TEMPO-oxidized cellulose nanofibers. Cellulose nanofiber hydrogels are soft solids whose rheology is directly related to the particle concentration. Therefore, this work defined the rheological behavior of the hydrogels using a fractional order derivative analytically solved to determine rheological responses in frequency, stress relaxation, and creep. Using two parameters, it evaluated the rheology of cellulose nanofiber hydrogels and established tests that predict rheological behaviors for given particle concentrations. The findings suggested that the fractional approach could become a standard method for characterizing cellulose nanofiber hydrogels in the reported concentration regime. The two parameters of the fractional model build a comparison framework to assess the rheology of different viscoelastic materials. Graphic abstract: [Figure not available: see fulltext.]</p

Fabrication and Characterization of Isotropic and Anisotropic Magnetorheological Elastomers, Based on Silicone Rubber and Carbonyl Iron Microparticles

This article focuses on studying the rheological behavior of isotropic and anisotropic magnetorheological elastomers (MREs), made of carbonyl iron microparticles dispersed into a silicone&#8315;rubber matrix by considering 20 and 30 wt % of microparticles. Sample sets were prepared for each composition, with and without the application of an external magnetic field. Experimental measurements of the material rheology behavior were carried out by a shear oscillatory rheometer at constant temperature, to determine both the shear storage modulus (G&#8242;) and shear loss modulus (G&#8242;&#8242;) for all characterized samples. Then, experimental data collected from the isotropic and the anisotropic material samples were used to plot the Cole-Cole diagrams to quantify the interfacial adhesion between carbonyl iron microparticles and the silicone-rubber matrix. Furthermore, the Fractional Zener Model (FZM) with two spring-pots in series is used for quantitative analysis of collected experimental data

Viscoelastic phenomena in methylcellulose aqueous systems:Application of fractional calculus

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.</p

Viscoelastic phenomena in methylcellulose aqueous systems:Application of fractional calculus

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.</p