Petra Peer

Improved thermooxidation and sedimentation stability of covalently-coated carbonyl iron particles with cholesteryl groups and their influence on magnetorheology

Sedimentation of particles in magnetorheological suspensions represents a crucial problem that concerns their efficient long-term application in practice. Prepared carbonyl iron (CI) microparticles coated with a low density substance, cholesteryl chloroformate, via a two-step reaction and immersed in silicone oil, exhibit three positive aspects: (1) the CI particle modification increased the compatibility between the particles and the silicone oil resulting in improved long-term stability (reduction in sedimentation); (2) the coating provided the particles with enhanced thermal stability in the oxygen atmosphere; and (3) rheological measurements proved a promising magnetorheological performance at different particle weight fractions.

A dimorphic magnetorheological fluid with improved oxidation and chemical stability under oscillatory shear

The aim of this work was to prepare a dimorphic magnetorheological (MR) fluid for which sedimentation stability, oxidation and chemical stability are enhanced in comparison with common MR fluids, while at the same time preserving the MR effect at its fullest practical level. A dimorphic MR fluid exhibiting these properties was prepared in two steps. The first step involved the partial substitution of carbonyl iron (CI) spherical microparticles with Fe rod-like particles synthesized via a surfactant-controlled solvothermal method. This improved sedimentation stability in comparison with the application of CI particles alone. In the second step both spherical CI and Fe rod-like particles were coated with a polysiloxane layer through the hydrolysis–condensation polymerization of tetraethylorthosilicate. This ensured better oxidation and chemical stability balance with an acceptable decrease in the MR effect. This effect is still markedly better than that based on Fe3O4 particles.

Cholesteryl-coated carbonyl iron particles with improved anti-corrosion stability and their viscoelastic behaviour under magnetic field

In principle, bare particles used in magnetorheological suspensions exhibit apparent corrosion instability. To suppress substantially this adverse phenomenon, the carbonyl iron particles modified with cholesteryl group (CI-chol) were suspended in silicone oil. There was found a deterioration of magnetorheological efficiency in comparison when only bare carbonyl iron (CI) particles are used; nevertheless, from the viewpoint of applicability, this change is fully acceptable. However, an anti-corrosion stability was significantly improved. Furthermore, dynamic oscillatory measurements and other characterizations were carried out and analyzed when both CI and CI-chol particles are applied.

Magnetorheology of carbonyl iron particles coated with polypyrrole ribbons: The steady shear study

The aim of this study is a preparation and application of polymer coating on the surface of carbonyl iron particles. Oxidative polymerization of the pyrrole provides ribbon-like morphology. Compact coating of particles has a slightly negative impact on their magnetic properties (measured for magnetic field strength in the range from 0 to 300 mT); however, there is a significant increase in sedimentation stability. The effect of the particle concentration and temperature on the toughness of the internal structures was also investigated.

Magnetorheological behaviour and electrospinning of poly(ethylene oxide) suspensions with magnetic nanoparticles

The properties of poly(ethylene oxide) aqueous suspensions with magnetic nanoparticles synthesized under microwave-assisted radiation are studied. The magnetic nanoparticles are formed by iron (III) chloride hexahydrate (FeCl3·6H2O) dissolved in ethylene glycol (C2H4(OH)2) and subsequently in aqueous ammonia solution (approx. 25 wt% aq.). The polymer suspension exhibits substantial advantages over a suspension when ‘classical’ carrier fluids (water and silicone oil) are used. First, the presence of poly(ethylene oxide) significantly contributes to a fabrication of nanofibrous webs, the morphology of which is documented by scanning electron microscopy technique. Second, better sedimentation stability of the processed suspension during electrospinning reflects in a uniform distribution of magnetic nanoparticles along the nanofibres, thus ensuring even magnetic performance of the resulting membranes.

Magnetorheological characterization and electrospinnability of ultrasound-treated polymer solutions containing magnetic nanoparticles

In order to fabricate a magnetic nanofibrous membrane by electrospinning, it is necessary to follow a suitable method for incorporating nanoparticles into a polymer solution. Ultrasound treatment represents a very effective technique for distributing magnetic nanoparticles within polymer solutions. Adverse effects caused by sonication over time on the given nanofibrous membrane (polymer degradation and appearance of defects) were evaluated by using rotational (magneto)rheometry, transmission and scanning electron microscopy, and magnetometry. A magnetorheological approach was selected to estimate the optimal duration of sonication, and findings were experimentally verified. It was concluded that the processed nanofibrous membrane showed promise as an advanced magnetoactive device.

Rheology of Poly(vinyl butyral) Solution Containing Fumed Silica in Correlation with Electrospinning

The rheological properties in question are influenced by many factors, ranging from the characteristics of the given polymer or solvent to the flowing conditions. The primary focus of this study is to analyse the rheological behaviour of poly(vinyl butyral)—Mowital B 60H—(PVB) solutions dissolved in methanol and a blend of these with fumed silica nanoparticles. The preparation of the nanofibrous web and the quality of nanofibres were correlated with the rheology of the polymer solution. It was discerned that drastically intensifying shear viscosity and the elasticity of the solution exerted a negligible effect on the formation of fibres, a finding which has rarely been discussed in the literature. The morphologies and structures of the PVB/silica nanofibrous membranes were investigated by scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy.

Quality of nanofibrous mats in relation to rheological characterization of PVB and PVB/silica solutions

Rheological properties are influenced by many factors ranging from the characteristics of the carrier fluid (poly(vinyl butyral)), solvent (methanol) and a filler (fumed silica nanoparticles) to the flowing conditions. There is compared rheological characterization of the neat PVB solution with the PVB/silica suspension. This characterization is confronted with quality of the corresponding nanofibrous mats and a role of elasticity is discussed. It is shown that in this case a role of elasticity is rather limited.

Nanofibrous web quality in dependence on the preparation of poly(ethylene oxide) aqueous solutions

Abstract The method of preparation of polymer solutions significantly influences the quality of the corresponding electrospun nanofibrous webs. However, this factor is often ignored, and in a majority of presentations concerning the electrospinning process, the applied method is not mentioned. This paper compares the influence of magnetic stirring, vibrational shaking and ultrasonication on a solution of poly(ethylene oxide) in distilled water. Along with the methods of preparation, other parameters were altered such as concentration, intensity of mixing and molecular weight. The best results from the viewpoint of electrospinning were achieved with moderate magnetic stirring.

Comparison of electrorheological characteristics obtained in two geometrical arrangements: Parallel plates and concentric cylinders

The electrorheological characteristics of suspensions of PANI powders suspended in silicone oil measured by a rotational rheometer Physica MCR 501 (Anton Paar Co.) are compared for two different geometrical arrangements – parallel plates and concentric cylinders. The individual differences in the results of the measured parameters are discussed.