Martin Stenicka

The Effect of Compatibility of Suspension Particles With the Oil Medium on Electrorheological Efficiency

The compatibility of solid phase–liquid medium appears to be an important factor for controlling the electrorheological (ER) efficiency of ER fluids. Controlled protonation of polyaniline particles with perfluorooctanesulfonic, tartaric, or sulphamic acid provides particles in a broad range of hydrophobicity as a suitable model to study this phenomenon. The relation between organization of such particles in silicone oil suspensions in on/off electric field at rest and during flow at various volume concentrations was demonstrated.

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.

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.

Solvothermal synthesis of different TiO2 morphology and their electrorheological characteristics

Titanium dioxide (TiO2) with different morphologies was prepared using solvothermal synthesis. The morphology and crystalline structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrorheological (ER) effect and dielectric properties of 5 wt. % suspensions were evaluated.

On the comparison of electrorheological measurements with different generation of an electric field

The rheological measurements of PANI powders mixed (10 wt.%) in silicone oil were compared using two electrorheological (ER) apparatuses different in generation of an electric field: (i) a rotational rheometer Physica MCR 501 (Anton Paar Co.) equipped with the electrorheological cell, (ii) a rotational rheometer Bohlin Gemini CVOR 150 (Malvern Instruments) modified for ER experiments. It was shown that the data obtained for a plate-plate arrangement using the Physica MCR 501 provide the highest values exceeding both the plate-plate data for the Gemini 150 and the, mutually comparable, concentric cylinders data for both rheometers.

A note on secondary electrorheological patterns

The development and character of ring structures created in the suspension of glass beads in an electric field flow were investigated. Two suspension media significantly differing in viscosity were used. The influence of various sequences of electric field strength and shear application, as well as shearing intensity with respect to the development of electrorheological patterns in time, was analyzed.

Electrorheological Properties of Suspensions of Polypyrrole Ribbon Particles in Silicone Oil

A new polypyrrole (PPy) ribbon particles structure has been synthesized by solution chemistry method (oxidative polymerization) in the presence of surfactant cetyltrimethylammonium bromide (CTAB) with oxidizing agent ammonium persulfate (APS). The resulted polymer was treated with ammonium hydroxide (NH4OH) several times to obtain different sample conductivity. PPy morphology was characterized by SEM. The suspensions were prepared by dispersing PPy with different conductivities in silicone oil. The electrorheological effect (ER) for the suspensions was examined under various electric fields using a rotational rheometer. It was found that suspension of only 3 wt. % of PPy ribbon particles showed large ER effect providing yield stress of 256 Pa at 3 kV.mm−1.