Effect of prestrain on the actuation characteristics of dielectric elastomers

Dielectric elastomers (DEs) represent a class of electroactive polymers that deform due to electrostatic attraction between oppositely charged electrodes under a varying electric field. Over the last couple of decades, DEs have garnered considerable attention due to their much-coveted actuation properties. As far as the precise measurement systems are concerned, however, there is no standard instrument or interface to quantify various related parameters, e.g., actuation stress, strain, voltage and creeping etc. In this communication, we present an in-depth study of dielectric actuation behavior of dielectric rubbers by the state-of-the-art “Dresden Smart Rubber Analyzer” (DSRA), designed and developed in-house. The instrument allowed us to elucidate various factors that could influence the output efficiency of the DEs. Herein, several non-conventional DEs such as hydrogenated nitrile rubber, nitrile rubber with different acrylonitrile contents, were employed as an electro-active matrix. The effect of viscoelastic creeping on the prestrain, molecular architecture of the matrices, e.g., nitrile content of nitrile-butadiene rubber (NBR) etc., are also discussed in detail

Effect of Prestrain on the Actuation Characteristics of Dielectric Elastomers

Dielectric elastomers (DEs) represent a class of electroactive polymers that deform due to electrostatic attraction between oppositely charged electrodes under a varying electric field. Over the last couple of decades, DEs have garnered considerable attention due to their much-coveted actuation properties. As far as the precise measurement systems are concerned, however, there is no standard instrument or interface to quantify various related parameters, e.g., actuation stress, strain, voltage and creeping etc. In this communication, we present an in-depth study of dielectric actuation behavior of dielectric rubbers by the state-of-the-art "Dresden Smart Rubber Analyzer" (DSRA), designed and developed in-house. The instrument allowed us to elucidate various factors that could influence the output efficiency of the DEs. Herein, several non-conventional DEs such as hydrogenated nitrile rubber, nitrile rubber with different acrylonitrile contents, were employed as an electro-active matrix. The effect of viscoelastic creeping on the prestrain, molecular architecture of the matrices, e.g., nitrile content of nitrile-butadiene rubber (NBR) etc., are also discussed in detail

Magnetorheological Payne effect in bidisperse MR fluids containing Fe nanorods and Fe3O4 nanospheres: A dynamic rheological study

The spherical Fe3O4 with 300 nm in diameter was synthesized by typical thermal decomposition of Fe (III) organometallic precursor in polyol and polyacrylic acid. Fe-nanorods were prepared by reducing Fe (III) nitrate in presence of polyol-hydrazine-CTAB. Morphology and magnetic characterization of the nanoparticles were performed by FESEM, XRD and VSM studies. We performed detailed non-linear magnetorheological properties of three MR fluids (10 vol-%) containing isotropic Fe3O4 and anisotropic Fe-nanorods under both small and large amplitude oscillatory flow. The MR samples demonstrated strong magnetorheological Payne effect i.e. rapid stress relaxation under increasing deformation and uniform magnetic field beyond linear viscoelastic region (LVR), which was not studied in detail before in case of bidisperse MR fluids. We have also shown that stress softening was more pronounced for MR fluids with higher anisotropic contents, in contrast to isotropic MR fluid. The onset strains for LVR to non-linear region transition for anisotropic fluids were much lower than that of isotropic spherical nanoparticle containing fluid. The stronger MR response for nanorod-containing MR fluids can be explained in terms of enhanced field-induced structuration. (C) 2016 Elsevier B.V. All rights reserved

Recent trends in multi-layered architectures towards screening electromagnetic radiation: challenges and perspectives

The quick advancement in wireless information technology, especially in the high-frequency range, has led to a new kind of pollution; electromagnetic interference (EMI). This issue has been of increasing criticality and importance in worldwide consideration. One key answer is to fabricate materials that can constrict the undesirable electromagnetic waves. The coveted properties of these materials include low reflection loss, wide attenuation band, lightweight and economic viability. In this critical review, we endeavoured to condense a logical guide to different methodologies derived in the last few years to improve EM retention utilizing multi-layered sandwich designs. The prime focus of this review is to highlight the crucial and fundamental scientific necessities and preferred standpoint of using such designs. We likewise attempt to provide the necessary outlook and direction in which the future research will continue to thrive

Wool-Ball-Type Core-Dual-Shell FeCo@SiO₂@MWCNTs Microcubes for Screening Electromagnetic Interference

Engineered nanostructure-reinforced lightweight polymer composites with superior electromagnetic (EM) shielding effectiveness (SE_T) are widely employed in high-end applications such as aerospace and microelectronic devices. Recently, carbon nanotube-based three-dimensional nanostructures have shown enormous potential due to unmatched processability, mechanical, and electronic properties. In this study, we present for the first time, highly permeable FeCo-based core-double shell <i>wool-ball</i>-type microcubes chemically enclosed by dielectric silica and conducting multiwalled carbon nanotubes (MWCNTs) sequentially; the resulting reinforced nanocomposites with low filler loading produced superior SE_T of −35 dB at 18 GHz for a specimen of 3 mm thickness. The excellent dispersion of microstructures in the soft matrix owing to the encapsulation of hard FeCo magnets by MWCNTs ensures low density and excellent flexibility for high-precision applications. The nanoengineered core-dual shell strategy for fabricating magnetic-dielectric-conducting microcubes ensures strong magnetic loss, coupled with dielectric and conduction loss, respectively, from SiO₂ and MWCNT shells. This approach, being unique in terms of nanofabrication and subsequent formulation of lightweight flexible composites, demonstrates a highly efficient way toward designing advanced nanocomposites for cutting-edge shielding application

FeCo-Anchored Reduced Graphene Oxide Framework-Based Soft Composites Containing Carbon Nanotubes as Highly Efficient Microwave Absorbers with Excellent Heat Dissipation Ability

Conducting polymer composites containing ferromagnetic grafted-graphene derivatives are already appreciated for their lightweight, flexibility, and cost effectiveness in terms of microwave absorption. To further leverage the said properties of this wonder material, we propose a highly efficient replacement by blending conducting multiwall carbon nanotube (MWCNT) and FeCo anchored covalent cross-linked reduced graphene oxide (rGO) with poly­(vinylidene fluoride) (PVDF). Interconnected conducting network of MWCNTs introduces higher electrical conductivity in the blend which is essential for microwave absorption. FeCo-anchored porous interconnected rGO framework was designed via solvent-mediated <i>in situ</i> coreduction in the presence of Fe­(II) and Co­(II) precursors. Resulting cross-linked-rGO/FeCo displays fascinating coexistence of ferromagnetism and conducting-dielectric behavior, while largely preserving the robust 3D porous interconnected structure. Coupled with conducting MWCNTs, diamine cross-linked rGO/FeCo in a soft polymer matrix yields remarkably high total shielding effectiveness (SE_T) of −41.2 dB at 12 GHz, for a meager 10 wt % filler content. In addition, the composite materials display efficient heat dissipation abilities in conjunction with the trend in their thermal conductivities. This new-age microwave-absorbing material, powered by multifunctionality and tunable magnetodielectric properties, henceforth offers an amendable, cost-effective replacement to the existing solutions

Tuning the Shape Anisotropy and Electromagnetic Screening Ability of Ultrahigh Magnetic Polymer and Surfactant-Capped FeCo Nanorods and Nanocubes in Soft Conducting Composites

Herein, we demonstrate that very high electromagnetic (EM) shielding efficiency can be achieved by dispersing nanoengineered FeCo anisometric nanostructures in a poly­(vinylidene difluoride) matrix in the presence of conductive nanofillers (multiwall carbon nanotubes, MWCNTs). The FeCo nanorods (∼800 nm) and nanocubes (∼100 nm) were fabricated by a facile surfactant and polymer-assisted one-pot borohydride reduction method. The growth mechanism depicted a two-directional growth for cubes, whereas for nanorods, a unidirectional growth pattern across the (110) plane was evident. A total shielding effectiveness (SE_T) of −44 dB at 18 GHz was achieved for a particular combination of FeCo nanorods and MWCNT, and for nanocube-based composites, it was found to be −39 dB at 18 GHz. It was observed from zero field cooled-field cooled curves that the samples displayed room temperature ferromagnetism. An excellent correlation between high aspect ratio FeCo nanorod and superior EM absorption (89%) was explored, pertaining to the fact that nanorods possessed higher magnetic saturation (177.1 emu/g) and coercivity (550 Oe) in contrast to the nanocubes with similar composition. Furthermore, theoretical insight into the mechanism revealed a high degree of interface scattering between conductive MWCNT and magnetic loss components, giving rise to an excellent synergy between magnetic and dielectric parts