Magnetorheology of dimorphic magnetorheological fluids based on iron nanorods

The aim of this paper is to document suitability of partial substitution of magnetic carbonyl iron (CI) microspheres with iron nanorods to obtain dimorphic magnetorheological (MR) suspensions with comparable MR performance to conventional MR suspensions exclusively based on (CI) microspheres while the sedimentation stability is considerably improved. The morphology of CI and iron nanorods was analyzed via scanning electron microscopy and transmission electron microscopy, respectively, and magnetic properties via vibrating sample magnetometry. The steady shear flow and small-amplitude dynamic oscillatory shear measurements were carried out to confirm effective MR performance. The sedimentation test showed positive role of dimorphic composition of dispersed phase on the sedimentation stability. © Published under licence by IOP Publishing Ltd.Grant Agency of the Czech Republic [14-32114P]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504

Rheology of uncured magnetorheological elastomers

The aim of this paper is to study rheological properties of uncured magnetorheological elastomers comprising iron particles dispersed in silicon elastomer in relation to particle rearrangement by external magnetic field into oriented structures as this process is strongly affected by viscosity. Studied systems vary in used filler volume concentration (0 to 30 vol. %). From measured flow curves flow consistency index is extracted first by fitting experimental data to Herschel-Bulkley model followed by applying two concentration dependency models (Maron-Pierce and Krieger-Dougherty) to normed consistency. Results and model predictions are discussed. © Published under licence by IOP Publishing Ltd.Czech Science FoundationGrant Agency of the Czech Republic [17-24730S]; Ministry of Education, Youth and Sports of the Czech Republic -Program NPU I [LO1504

The surface modification of magnetic particles with polyamidoamine dendron

Magnetorheological elastomers are important kind of intelligent systems that can alter their properties upon an application of an external magnetic field. Crucial for their performance is interaction between polymer matrix and magnetic filler, thus, it is necessary to control the compatibility between the matrix and magnetic particles. In this study, polyamidoamine dendron was successfully introduced onto surface of carbonyl iron particles using divergent approach in order to provide novel magnetic particles for magnetorheological elastomers. The presence of a thin layer of polyamidoamine dendron on the carbonyl iron particles was confirmed by energy dispersive X-ray, infrared spectroscopy and transmission electron microscopy, which confirmed a thin layer in nanometers formed on the surface of the particles. The coated carbonyl iron particles exhibited superior chemical stability when compared to non-coated ones, while the saturation magnetization decreased only negligibly from 207.0 emu g-1 to 203.5 emu g-1 for pure carbonyl iron particles and polyamidoamine dendron-coated carbonyl iron particles, respectively. © 2018 Author(s).Czech Science Foundation [17-24730S]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504

A tensiometric study of magnetorheological suspensions' stability

A thin (3-aminopropyl)triethoxysilane (3APTS) layer with a grafting density around 50 groups per nm2 was coated onto soft magnetic carbonyl iron (CI) particles. Their physical characteristics were examined using various methods, and the results revealed that the coating layer did not affect the particles' morphology and magnetic properties while their resistance against thermal oxidation and chemical degradation was considerably improved. This study further evaluates the surface free energy of the particles under investigation using tensiometry, namely capillary rise experimental methods based on the Washburn theory. The dispersive and polar components of surface free energy were subsequently computed through the application of the Owens-Wendt-Rabel-Kaeble theory. It was observed that the coating of CI particles with 3APTS increased the dispersive component of surface free energy, resulting in the improved compatibility of such particles with non-polar silicone oil which is used as a carrier liquid for magnetorheological (MR) suspensions. Furthermore, the 3APTS coating has a negligible influence on MR properties in comparison with an uncoated CI particle-based MR suspension, as was proved by steady shear and small-strain oscillatory shear tests under various external magnetic fields. The improved compatibility of 3APTS-coated CI particles with silicone oil was reflected in the better sedimentation stability of the MR suspension, observed via tensiometry for the first time for MR suspensions, in comparison with the uncoated CI particle-based suspension. This journal isGrant Agency of the Czech Republic [14-32114P]; Operational Program Research and Development for Innovations; European Regional Development Fund (ERDF); national budget of the Czech Republic, within the framework of the project Centre of Polymer Systems [CZ.1.05/2.1.00/03.0111

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

Ethylene-octene-copolymer with embedded carbon and organic conductive nanostructures for thermoelectric applications

Hybrid thermoelectric composites consisting of organic ethylene-octene-copolymer matrices (EOC) and embedded inorganic pristine and functionalized multiwalled carbon nanotubes, carbon nanofibers or organic polyaniline and polypyrrole particles were used to form conductive nanostructures with thermoelectric properties, which at the same time had sufficient strength, elasticity, and stability. Oxygen doping of carbon nanotubes increased the concentration of carboxyl and C-O functional groups on the nanotube surfaces and enhanced the thermoelectric power of the respective composites by up to 150%. A thermocouple assembled from EOC composites generated electric current by heat supplied with a mere short touch of the finger. A practical application of this thermocouple was provided by a self-powered vapor sensor, for operation of which an electric current in the range of microvolts sufficed, and was readily induced by (waste) heat. The heat-induced energy ensured the functioning of this novel sensor device, which converted chemical signals elicited by the presence of heptane vapors to the electrical domain through the resistance changes of the comprising EOC composites. © 2020 by the authors.Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF)European Union (EU); Operational Program Education for Competitiveness - European Social Fund (ESF); National Budget of the Czech Republic [CZ.1.05/2.1.00/03.0111, CZ.1.07/2.3.00/20.0104]; Fund of Institute of Hydrodynamics [AV0Z20600510

Acoustic investigation of the structure of magneto-rheological fluid

The acoustic spectroscopy is used to study properties and changes in structural arrangement in silicone oil based magneto-rheological fluids with carbonyl iron particles upon the effect of an external magnetic field. Attenuation spectra at three temperatures for various concentrations of magnetic particles are presented. The attenuation of acoustic waves was measured for a jump change of the magnetic field to 200 mT as a function of the temperature. The relaxation effects for the acoustic attenuation after switching off the magnetic field and its decrease to the similar value as for clean silicone oil were observed. The change of acoustic attenuation in magneto-rheological fluid versus angle between the wave vector of acoustic waves and direction of the applied magnetic field was measured, too. For the anisotropy measurement are characteristic two local maxima from which results chain orientation in direction of the magnetic field

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

Fractional viscoelastic models of porcine skin and its gelatin-based surrogates

Viscoelasticity of porcine skin and its material substitute, modelled by variously concentrated bovine gelatin, was determined in static (creep test) and dynamic (oscillatory test) mode by the means of rotational rheometry to obtain creep compliance and complex shear modulus. Mechanical properties characterization was also supplemented with large deformation compression test in order to determine and correlate shear and compression moduli of gelatin with its concentration dependence. Obtained data was fitted with fractional viscoelastic models (Poynting-Thomson, Maxwell) in order to quantify in detail gelatin's transition from viscous-like behavior towards solid-like state with increasing gelatin concentration and hence crosslinking density. Potential of gelatin as biomaterial for skin surrogate was identified as well as a concentration region in which gelatin exhibits closest viscoelastic behavior to native porcine skin used. © 2023 The AuthorsMinisterstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 23-07244