This article focuses on studying the rheological behavior of isotropic and anisotropic magnetorheological elastomers (MREs), made of carbonyl iron microparticles dispersed into a silicone–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′) and shear loss modulus (G′′) 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.

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:The aim of this article focuses on identifying how the addition of iron micro-and nanoparticles influences the physical properties of magnetorheological composite materials developed with a polydimethylsiloxane (PDMS) matrix with different contents of silicone oil used as additive. A number of characterization techniques have been performed in order to fully characterize the samples, such as cyclic and uniaxial extension, rheology, swelling, Vibrating sample magnetometer (VSM), X-ray Diffraction (XRD), Scanning electron microscopy (SEM), Fourier-Transform Infrared (FTIR), X-ray photoelectronic spectroscopy (XPS) and Thermogravimetric analysis (TGA). The comparison between two matrices with different shore hardnesses and their mechanical and chemical properties are elucidated by swelling and tensile tests. In fact, swelling tests showed that higher crosslink density leads to increasing elongation at break and tensile strength values for the composite materials. The best mechanical performance in the magnetorheological material was observed for those samples manufactured using a higher silicone oil content in a hard polymeric matrix. Furthermore, it has been found that the magnetic properties are enhanced when nanoparticles are used as fillers instead of microparticles.

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A Polymeric Magnetic Hybrid Material (PMHM), consisting of iron-oxide nanoparticles synthesized in-situ in a Polymer Matrix of Polyvinyl Butyral (PVB), was developed in two stages. First, a precursor film hybrid material (Fe(II)-PVB) was obtained. In the second stage, Fe(II)-PVB was treated with H 2 O 2 under alkaline conditions to obtain the PMHM. Characterization by XRD shows that the crystalline structure of iron oxide into PMHM corresponds to goethite, and to maghemite or magnetite phases. FTIR-spectroscopy reveal that the PVB-matrix preserves its chemical structure into the PMHM. HRTEM-images show that iron oxide nanoparticles (~5 nm) with sphere-like morphology are embedded into PVB-matrix; and diagrams of magnetization versus temperature, show that embedded nanoparticles have a superparamagnetic-like behavior. Finally, magnetorheological results show that mechanical properties of PMHM can be modified under the application of an external magnetic field, showing that it is a good alternative to carry out functions as actuator or sensor in electronic or mechatronic devices.

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En este trabajo se describen algunas aplicaciones de la derivada conformable en la solución de ecuaciones diferenciales de orden fraccionario. Las derivadas de orden no entero son presentadas en función del tiempo para resolver el modelo de Maxwell, el circuito eléctrico RC en serie y la ley de enfriamiento de Newton. Los resultados obtenidos muestran la variación del parámetro α del operador fraccional conformable para modelar el comportamiento de los fenómenos propuestos. Se obtiene que los parámetros esfuerzo, corriente eléctrica y temperatura en función del tiempo, presentan un decaimiento más pronunciado a medida que α disminuye. La derivada conformable es una herramienta matemática que permite resolver ecuaciones diferenciales de orden fraccionario en una forma más simple.