Tailoring performance, damping, and surface properties of magnetorheological elastomers via particle-grafting technology

A novel concept based on advanced particle-grafting technology to tailor performance, damping, and surface properties of the magnetorheological elastomers (MREs) is introduced. In this work, the carbonyl iron (CI) particles grafted with poly(trimethylsilyloxyethyl methacrylate) (PHEMATMS) of two different molecular weights were prepared via surface-initiated atom transfer radical polymerization and the relations between the PHEMATMS chain lengths and the MREs properties were investigated. The results show that the magnetorheological performance and damping capability were remarkably influenced by different interaction between polydimethylsiloxane chains as a matrix and PHEMATMS grafts due to their different length. The MRE containing CI grafted with PHEMATMS of higher molecular weight exhibited a greater plasticizing effect and hence both a higher relative magnetorheological effect and enhanced damping capability were observed. Besides bulk MRE properties, the PHEMATMS modifications influenced also field-induced surface activity of the MRE sheets, which manifested as notable changes in surface roughness. © 2018 by the authors.Czech Science Foundation [17-24730S]; Internal Grant Agency of Tomas Bata University in Zlin [IGA/CPS/2017/004]; Ministry of Education, Youth and Sports of the Czech Republic-Program NPU I [LO1504]; Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF); national budget of the Czech Republic [CZ.1.05/2.1.00/19.0409

Monitoring of CRT-D devices during radiation therapy in vitro

Background: Using of active cardiac medical devices increases steadily. In Europe, there were 183 implants of ICD and 944 implants of PM, 119 of biventricular ICD and 41 of biventricular PM, all per million inhabitants in 2014. Healthcare environments, including radiotherapy treatment rooms, are considered challenging for these implantable devices. Exposure to radiation may cause the device to experience premature elective replacement indicator, decreased pacing amplitude or pacing inhibition, inappropriate shocks or inhibition of tachyarrhythmia therapy and loss of device function. These impacts may be temporary or permanent. The aim of this study was to evaluate the influence of linear accelerator ionizing radiation dose of 10 Gy on the activity of the biventricular cardioverter-defibrillator in different position in radiation beam. Methods: Two identical wireless communication devices with all three leads were used for the measurement. Both systems were soused into solution saline and exposed in different position in the beam of linear accelerator per 10 Gy fractions. In comparison of usually used maximum recommended dose of 2 Gy, the radiation doses used in test were five times higher. Using the simultaneous monitoring wireless communication between device and its programmer allowed watching of the devices activities, noise occurrence or drop of biventricular pacing on the programmer screen, observed by local television loop camera. Results: At any device position in radiation beam, there were no influences of the device activity at dose of 10 Gy neither a significant increase of a solution saline temperature in any of the measured positions of CRT-D systems in linear accelerator. Conclusions: The results of the study indicated, that the recommendation dose for treating the patients with implantable devices are too conservative and the risk of device failure is not so high. The systems can easily withstand the dose fractions of tens Gy, which would allow current single-dose-procedure treatment in radiation therapy. Even though the process of the random alteration of device memory and electrical components by scatter particles not allowed to specify a safe dose during ionizing radiation, this study showed that the safe limit are above the today used dose fractions.Web of Science15art. no. 2

A rheological evaluation of steady shear magnetorheological flow behavior using three-parameter viscoplastic models

Knowledge of the complicated flow characteristics of magnetorheological (MR) suspensions is necessary for simulations, calculations in engineering processes, or designing new devices utilizing these systems. In this study, we employed three constitutive equations (three-parameter models) for an evaluation of steady shear behavior of MR suspensions. The predictive/fitting capabilities of the Robertson-Stiff (R-S) model were compared with the commonly used Herschel-Bulkley (as a reference) and the Mizrahi-Berk models. The appropriateness of the models was examined using rheological data for diluted as well as concentrated MR systems. The effect of magnetic field strength on model fitting capabilities was also investigated. The suitability of the individual models was evaluated by observing correlation coefficient, sum of square errors, and root mean square errors. A statistical analysis demonstrated that the best fitting capabilities were exhibited by the R-S model, while others provided less accurate fits with the experimental data. Therefore, shear stresses and the yield stress predicted according to the R-S equation can be considered as the most accurate under defined conditions in comparison with the Herschel-Bulkley and the Mizrahi-Berk model predictions. We also showed that the consistency index obtained from the R-S model increased with increasing magnetic field and particle concentration, which physically reflected more rigid internal structures generated in MR suspensions upon an external magnetic field. This behavior was indistinguishable when other models were applied. © 2016 Author(s).Ministry of Education, Youth and Sports of the Czech Republic-Program NPU I [LO1504

Magnetic properties of electrospun polyvinyl butyral/Fe2O3 nanofibrous membranes

In this contribution, magnetic Fe2O3 nanoparticles (MNPs) were successfully incorporated into the polyvinyl butyral (PVB) nanofibrous membranes using the electrospinning process. The effects of the MNP concentration on the morphology of the nanofibres and their magnetic properties were investigated. Scanning electron microscopy and transmission electron microscopy confirmed their concentration-dependent, yet uniform diameter, and the presence of well-embedded MNPs inside the PVB nanofibres. The magnetic properties of the PVB/MNP membranes were studied using the vibrating-sample magnetometry. The saturation magnetization increased from 6.4 to 45.5 emu/g as the MNP concentration in the feedstock solution increased from 1 to 15 wt%. The fabricated PVB/MNP nanofibrous membranes possessed the ability to respond to the external magnetic fields, which determines their potential in the development of the advanced smart textiles. © NANOCON 2019.All right reserved.Ministry of Education, Youth and Sports of the Czech RepublicMinistry of Education, Youth & Sports - Czech Republic [LTC 19034]; COST ActionsEuropean Cooperation in Science and Technology (COST) [CA17107]; Czech Science FoundationGrant Agency of the Czech Republic [17-24730S

Preparation of electrospun magnetic polyvinyl butyral/Fe(2)O(3)nanofibrous membranes for effective removal of iron ions from groundwater

Removing iron ions from groundwater to purify, it is a challenge faced by countries across the globe, which is why developing polymeric microfiltration membranes has garnered much attention. The authors of this study set out to develop nanofibrous membranes by embedding magnetic Fe2O3 nanoparticles (MNPs) into polyvinylbutyral (PVB) nanofibers via the electrospinning process. Investigation was made into the effects of the concentration of the PVB and MNPs on the morphology of the nanofibers, their magnetic properties, and capacity for filtration to remove iron ions. The fabrication and presence of well-incorporated MNPs in the PVB nanofibers were confirmed by scanning electron microscopy and transmission electron microscopy. Depending on the concentration of the MNPs, the membranes exhibited magnetization to the extent of 45.5 emu g−1; hence, they exceeded the performance of related nanofibrous membranes in the literature. The magnetic membranes possessed significantly higher efficiency for filtration compared to their nonmagnetic analogues, revealing their potential for groundwater treatment applications. © 2020 Wiley Periodicals LLC.d Ceske Republiky [67985874]; Grantova Agentura Ceske RepublikyGrant Agency of the Czech Republic [17-24730S]; Ministerstvo Skolstvi, Mladeze a Te [LTC 19034

The effect of zinc oxide filler on mechano-physical and electromechanical properties of PVDF

This study deals with the effect of star-like zinc oxide (ZnO) filler addition into poly(vinylidene fluoride) (PVDF) matrix on its structural and physical properties with the consequences to mechanical energy harvesting performance. In this case, the microwave-assisted synthesis was optimized for the preparation of unique star-like shape of ZnO particles. Their crystallinity and star-like morphology/elemental composition were analyzed using XRD and SEM/EDX spectroscopy, respectively. The investigation of α-crystalline phase transformation into β-crystalline phase of neat PVDF matrix, and upon introducing various ZnO concentrations was performed using FTIR spectroscopy. Finally, the mechanical energy harvesting capability measurements showed that the addition of star-like ZnO filler enhanced the d33 electro-mechanical coupling coefficient more than two times when compared to neat PVDF matrix. © NANOCON 2019.All right reserved.Czech Science FoundationGrant Agency of the Czech Republic [19-17457S]; Ministry of Education, Youth and Sports of the Czech Republic - program NPU I [LO1504

The chemical stability and cytotoxicity of carbonyl iron particles grafted with poly(glycidyl methacrylate) and the magnetorheological activity of their suspensions

Carbonyl iron (CI) particles were grafted with poly(glycidyl methacrylate) (PGMA) using atom transfer radical polymerization. Compact coating of PGMA largely improved the chemical stability of the particles in an acid environment and thus reduced the common drawback of bare CI particles. Furthermore, due to possible medical applications of CI-polymer systems for magnetic drug targeting, an in vitro cytotoxicity test was performed using an NIH/3T3 cell line. The cell viability was evaluated by spectrometric assay (MTT). The results show that the prepared particles are not cytotoxic. Moreover, bare CI particles as well as synthesized core-shell particles were suspended in silicone oil, and the rheological behavior of MR suspensions was investigated in controlled shear rate mode under various magnetic field strengths. Dynamic yield stress as a measure of the rigidity of the created internal structures of the suspensions was determined using the Herschel-Bulkley model, which provided a reasonably good fit for rheological data. MR suspensions of PGMA-coated particles exhibited only slightly decreased yield stresses due to their negligibly-affected magnetic performance. This journal is © The Royal Society of Chemistry.Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF); National Budget of the Czech Republic [CZ.1.05/2.1.00/03.0111]; TBU in Zlin [IGA/CPS/2015/007]; Centre of Excellence FUN-MAT; Czech Science Foundation [13-08944S

Effect of extrusion process and various elongation ratios on the structural and dielectric properties of pvdf-based copolymer containing micro and nano-sized crystallites

In this contribution, the effect of the extrusion process of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) with the subsequent elongation/poling on its structural and dielectric properties is presented. The extrusion can be understood as continuous processing of polymer melts in the large scale (in comparison to solvent casting), when the thickness of the final product can be varied depending on the final operation conditions. Herein, the PVDF-co-HFP sheets of 5 cm in width were extruded using a single screw extruder. The fabricated sheets were cooled down and then, they were cut to the stripes and subsequently stretched to various elongations (100, 200 and 500 %) using a universal tensile testing machine. Such samples were investigated using FTIR in order to determine the effect of the elongation process on the transformation of the a-phase to the β-crystalline phase. The extend of the electro-active β-phase was quantified and its impact on the dielectric properties was investigated. The results clearly demonstrated that the elongation has a crucial effect on the final dielectric properties of the PVDF-co-HFP. © 2021 TANGER Ltd., Ostrava.Czech Science FoundationGrant Agency of the Czech Republic [19-17457S]; Ministry of Education, Youth and Sports of the Czech Republic DKRVO [RP/CPS/2020/003, RP/CPS/2020/006]RP/CPS/2020/003, RP/CPS/2020/006; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 19-17457

PVDF/PVDF-TRFE blends loaded with BaTiO3: from processing to performance testing

Concerns surrounding the limited supply of fossil fuels have been the subject of much debate. As of promising solutions, polymers like poly(vinylidene fluoride) (PVDF) have gained attention due to their ability to generate electrical energy from the waste mechanical vibrations. The energy harvesting and vibration sensing potential of PVDF is however limited due to its low content of electroactive β-phase, which has to be increased by indirect post-processing. Recently, a synergistic effect was found in PVDF directly blended with its trifluoroethylene copolymer (PVDF-TrFE) due to strong interfacial polarization. In this study, we aim to further increment the piezoelectric performance of PVDF/PVDF-TrFE blends by incorporating a small amount of BaTiO3 nanocrystals via a facile and scalable processing route. The β-phase content was monitored using FTIR and XRD. Melt rheology experiments showed that co-blending of PVDF-TrFE as well as the addition of BaTiO3 slightly increased melt viscosity and complex modulus. Despite that, rheological data suggested that developed formulations can be processed by conventional techniques intended for a large-scale production. More importantly, PVDF/PVDF-TrFE binary blends supplemented with BaTiO3 are expected to exhibit superior d33 compared to conventional neat blends, which could make them highly promising for modern energy harvesting and sensor-related applications. © 2021 NANOCON Conference Proceedings - International Conference on Nanomaterials. All rights reserved.RP/CPS/2020/003, RP/CPS/2020/006; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 19-17457

Reprocessing of injection-molded magnetorheological elastomers based on TPE matrix

Nowadays, the magnetorheological elastomers (MREs) represent an important composite group with a wide range of applications. They are however predominantly typified by chemically cross-linked polymer matrices which makes them difficult to be reprocessed or recycled. Here, we demonstrate the concept of the MREs’ reprocessing for the first time. The thermoplastic elastomer (TPE) was adopted as a suitable matrix allowing the MRE production via injection-molding, while making them also reusable. Each processing iteration was accompanied by thermo-mechanical degradation causing the gradual TPE oxidation, decrease in the TPE molecular weight and a viscosity reduction of their melts. In the MREs, the unexpected processing-induced particle/matrix bonding was revealed, which promoted their stiffening. As a result, the magnetic field-induced particle mobility was limited decreasing the magnetorheological activity of the MREs by tens of percent per the processing cycle. We expect that the injection-molded TPE-based MREs could offer a new pathway for producing the smart engineering composites owing to the ability to be easily reprocessed. © 2019 Elsevier LtdEU Funds - OP Research, Development and Education [CZ.02.2.69/0.0/0.0/16_027/0008464]; Ministry of Education, Youth and Sports, Czech Republic; Czech Science Foundation [17-24730S]; Ministry of Education, Youth and Sports of the Czech Republic Program NPU I [LO1504