Abdollah Hajalilou

Field Responsive Fluids as Smart Materials

Introduction -- Magnetism -- Magnetorheological (MR) Fluids -- Models between Shear Rate and Stress in MR fluids -- Magnetic particles sedimentation in MR fluids -- MR Fluid Applications -- Temperature Dependence of MR Fluids and their Components -- Electrorheological(ER)fluids -- Ferrofluids -- Properties of Field Responsive Fluids -- Conclusion.

A comparison of field-dependent rheological properties between spherical and plate-like carbonyl iron particles-based magneto-rheological fluids

This work proposes different sizes of the plate-like particles from conventional spherical carbonyl iron (CI) particles by adjusting milling time in the ball mill process. The ball mill process to make the plate-like particles is called a solid-state powder processing technique which involves repeated welding, fracturing and re-welding of powder particles in a high-energy ball mill. The effect of ball milling process on the magnetic behavior of CI particles is firstly investigated by vibrating sample magnetometer. It is found form this investigation that the plate-like particles have higher saturation magnetization (about 8%) than that of the spherical particles. Subsequently, for the investigation on the sedimentation behavior the cylindrical measurement technique is used. It is observed from this measurement that the plate-like particles show slower sedimentation rate compared to the spherical particles indicating higher stability of the MR fluid. The field-dependent rheological properties of MR fluids based on the plate-like particles are then investigated with respect to the milling time which is directly connected to the size of the plate-like particles. In addition, the field-dependent rheological properties such as the yield stress are evaluated and compared between the plate-like particles based MR fluids and the spherical particles based MR fluid. It is found that the yield shear stress of the plate-like particles based MR fluid is increased up to 270% compared to the spherical particles based MR fluid.

Fabrication of spherical CoFe2O4 nanoparticles via sol–gel and hydrothermal methods and investigation of their magnetorheological characteristics

CoFe2O4 nanoparticles are synthesized through sol–gel and facile hydrothermal methods, and their magnetorheological (MR) characteristics are evaluated. X-ray diffraction results indicate the formation of single phase CoFe2O4 after the prepared samples were sintered at 550 °C for 2 h, which was further confirmed by DSC, TG and FT-IR analysis. TEM results exhibit a narrow particle size distribution in the range of 5–40 nm with an average size of 21 nm for the samples prepared via the hydrothermal method. On the other hand, the particle size distribution was in the range of 15–120 nm and an average size of 42 nm was obtained via the sol–gel method. To prepare an MR fluid, CoFe2O4 nanoparticles were added to a micron-sized soft magnetic carbonyl iron (CI)-based suspension and MR effects were measured via rotational tests under different magnetic field strengths. The results reveal that the CoFe2O4–CI-based MR fluids present a higher yield stress with an enhanced MR effect compared to the CI-based MR fluid due to increased magnetic properties. This suggests that the CoFe2O4 nanoparticles fill the cavities of micron-sized CI particles and form chain-like structures, which orient in the direction of the applied magnetic field. On the other hand, depending on the employed synthetic route, the obtained results display slightly higher stress behaviors in the samples prepared via the hydrothermal method. The sedimentation ratio was also evaluated to further confirm the effects of the nanoparticle additive.

A Green Approach for the Synthesis of Silver Nanoparticles Using Ultrasonic Radiation’s Times in Sodium Alginate Media

The synthesis of silver nanoparticles (Ag-NPs) was achieved by a simple green chemistry procedure using sodium alginate (Na-Alg) under ultrasonic radiation as a stabilizer and physical reducing agent. The effect of radiation time on the synthesis of Ag-NPs was carried out at room temperature until 720u2009min. The successful formation of Ag-NPs has been confirmed by UV-Vis, XRD, TEM, FESEM-EDX, zeta potential, and FT-IR analyses. The surface plasmon resonance band appeared at the range of 452ź465u2009nm that is an evidence of formation of Ag-NPs. The XRD study showed that the particles are crystalline structure in nature, with a face-centered cubic (fcc) structure. The TEM study showed the Ag-NPs have average diameters of around 20.16ź22.38u2009nm with spherical shape. The FESEM-EDX analysis confirmed the spherical shape of Ag-NPs on the surface of Alg and the element of Ag with the high purity. The zeta potential showed high stability of Alg/Ag-NPs especially after 720u2009min irradiation with value of ź67.56u2009mV. The FT-IR spectrum confirmed that the Ag-NPs have been capped by the Alg with van der Waals interaction. The Alg/Ag-NPs showed the antibacterial activity against Gram-positive and Gram-negative bacteria. These suggest that Ag-NPs can be employed as an effective bacteria inhibitor and can be applied in medical field.

Models and Modes in MR Fluids

To design magnetorheological devices and to understand how they work, one should first know the relationship between the sheer stress and sheer rate in the magnetorheological fluid [1].

Magnetorheological Fluid Applications

Potential applications of MR fluids are summarized in those devices that need quick, continuous, and reversible transformation in rheological characteristics [1].

Preparation of Magnetic Nanoparticle

Soft magnetic nanoparticles are an important material and used widely for a variety of technological applications. Magnetite(Fe3O4) in the format of soft magnetic nanoparticles have been of major interests to many researchers because of being effectively used in ferrofluids, having magnetoresistance, exhibiting strong magnet property and generating low toxicity in biological and medical applications (Can et al. in Mater Sci Eng 172(1):72–75, 2010).

Temperature Dependence of Magnetorheological Fluids and Their Components

Materials behavior of the magnetorheological (MR) fluids components are important to their control accuracy and service life. Thus, the aim of this section is to focus on the effects of temperature on the material properties of MR fluid components and then its effect on the rheological properties of Magnetorheological fluids.

Insight into the Field Responsive Fluids

Field responsive fluids are those materials that undergo noticeable responses leading to consequent rheological behavior variations upon the influence of an external field. In fact, these fluids are divided into three groups in terms of their response in the presence of externally applied fields, which are briefly described as follows.

Electrorheological (ER) Fluids

Electrorheological (ER) fluids, similar to the MR fluids, belong to the general class of smart materials whose rheological characteristics are identified by applying an electric field instead of magnetic field in MR fluids. In other words, the ER fluids consist of electrical polarizable particles dispersed in carrier fluid with surfactant complimentary, which have an ability to modify their flow under the influence of an applied electric field [1, 2].