Studies of a mixing process induced by a transverse rotating magnetic field

This study reports on research results in the field of a mixing process under the action of a transverse rotating magnetic field (TRMF). The main objective of this paper is to present the effect of this type of a magnetic field on the mixing time. The proposed dimensional analysis of Navier–Stokes equation including the Lorentz force allows describing the analyzed process by means of the relationships basing on the dimensionless numbers (the mixing time number, the magnetic Taylor number, and the rotational Reynolds number). The possibility of using the magnetic particles (Fe₃O₄) as active micro-stirrers under the influence of a TRMF for active enhancement of a mixing process was considered. Moreover, the effect of a particle content on homogenization efficiency by applying a TRMF was also investigated. The obtained experimental results suggest that the mixing time under the TRMF and MDF conditions may be worked out by using the relation between the mentioned mixing time number and the modified Reynolds number (particle Reynolds number). Important conclusions referring to the discussion of experimental studies of a mixing process are also specified.     

Near field and magnetic field generator for thermal assisted magnetic recording

We fabricated a generator that produces optical near field and magnetic filed in a nanometer area for achievement of thermally assisted magnetic recording. The generator consists of an embedded wire with a bottleneck structure on a SiO₂ substrate. The magnetic field is mainly generated around the bottleneck structure by feeding current through the wire. The near field is produced on an edge of the narrow wire by focusing a laser beam on the bottleneck structure through the backside of the substrate. The generator is anticipated as application to control ordering, chirality, and phase transition of diamagnetic materials in a nano-area. We confirmed the three-dimentional localization of near field in the nanometer size around the bottleneck structure by means of a near field scanning optical microscope.     

Millisecond mixing of liquids using a novel jet nozzle

A millisecond mixing process for liquids was implemented using a new mixer design, i.e., a jet nozzle connected with a trumpet-shaped module. The jet nozzle can facilitate two or three liquid channels, performing an initial impingement mixing of liquid sheets in the thickness at millimeters. Then, the joint liquids sheet out of the jet nozzle was stretched thinner and thinner on the expanded solid surface of the trumpet-shaped module, which significantly intensified the liquid mixing process. Accordingly, dual controls on the liquid mixing can be accomplished flexibly by optimizing the operating conditions and the module configuration. Experiments were carried out to investigate the influencing factors on the mixing performance, where the planar laser induced fluorescence (PLIF) technique was used to measure the mass transport of fluorescent dye between the liquids. The intensity of segregation (IOS) and 95% mixing time (τ₉₅) were employed to characterize the mixing performance. The results showed that the module with a greater curvature surface possessed a better mixing performance owing to the rapid reduction of the liquid sheet thickness, which strengthened the mixing process in the lateral direction along the flow development. The mixing behaviors are greatly influenced by the flow rate ratio between the liquids. An optimum mixing state could be achieved when Q_S1/Q_S2 is 1:1. An increase of Q_T under the same flow rate ratio does not affect the mixing pattern in space, but the corresponding τ₉₅ is almost linearly shortened. By splitting one liquid stream into two surrounding streams, the so called Sandwich operation brought further improved mixing performance compared with the two liquids mixing process. Using the novel jet nozzle design, millisecond(s) mixing of liquids can be easily achieved with flexible control.     

The mixing state of fine powders measured by magnetic resonance imaging

The usefulness of magnetic resonance imaging (MRI) for the spatially resolved, quantitative characterization of mixtures of fine powders in the size range of about 10 μm is investigated. The sources of errors inherent in the signal translation process between raw MRI data and local concentrations are analyzed in detail. Possibilities for their correction are pointed out in deriving a global characteristic such as the standard deviation.The analysis of the mixing state of powders by MRI and the benefits of error correction are then illustrated by simple examples covering a wide range of compositions and mixing states. These experiments were made by mixing spherical, oil-filled (hence “visible” to MRI) melamine microcapsules in the size range of about 1-20 μm with solid melamine spheres of similar size and density. The mixture volume of typically 1 cm³ was imaged with an isotropic resolution of 235 μm, providing over 60,000 contiguous data points per measurement. The benefit of error correction is shown to be significant, provided the mixtures are homogeneous to a large extent.     

Microfluidics for selective concentration of nanofluid streams containing magnetic nanoparticles

Microfluidics is well-known for many Lab-on-a-Chip applications including sensing, cell sorting, separation, chemical reaction, emulsification, de-emulsification, droplet generation, energy generation and similar applications. The current research scenario in the field of interfacial science and colloidal technology has facilitated the advancement of microfluidics as a miniaturized option for many targeted tasks. Here we show how the microfluidics offers a low-cost solution for concentrating the dispersion of magnetic nanoparticles. The synthesized nanofluids were fed to the microchannels subjected to magnetic field. It has been found that the feed flow rate is one of the very crucial factors which affect the control of concentration of the nanofluids.     

Magnetic liposomes for colorectal cancer cells therapy by high-frequency magnetic field treatment

In this study, we developed the cancer treatment through the combination of chemotherapy and thermotherapy using doxorubicin-loaded magnetic liposomes. The citric acid-coated magnetic nanoparticles (CAMNP, ca. 10 nm) and doxorubicin were encapsulated into the liposome (HSPC/DSPE/cholesterol = 12.5:1:8.25) by rotary evaporation and ultrasonication process. The resultant magnetic liposomes (ca. 90 to 130 nm) were subject to characterization including transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), zeta potential, Fourier transform infrared (FTIR) spectrophotometer, and fluorescence microscope. In vitro cytotoxicity of the drug carrier platform was investigated through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using L-929 cells, as the mammalian cell model. In vitro cytotoxicity and hyperthermia (inductive heating) studies were evaluated against colorectal cancer (CT-26 cells) with high-frequency magnetic field (HFMF) exposure. MTT assay revealed that these drug carriers exhibited no cytotoxicity against L-929 cells, suggesting excellent biocompatibility. When the magnetic liposomes with 1 μM doxorubicin was used to treat CT-26 cells in combination with HFMF exposure, approximately 56% cells were killed and found to be more effective than either hyperthermia or chemotherapy treatment individually. Therefore, these results show that the synergistic effects between chemotherapy (drug-controlled release) and hyperthermia increase the capability to kill cancer cells.     

Enhancing liquid micromixing using low‐frequency rotating nanoparticles

Magnetic nanofluid actuation by rotating magnetic fields was proposed as a high‐performance tool for liquid mixing with enhanced micromixing features. A comparative study was conducted to evaluate the mixing index in T‐type mixers of magnetic and nonmagnetic fluids subject to static (SMF), oscillating (OMF), and rotating (RMF) magnetic fields. RMF excitation unveiled superior mixing indices with strong dependences to magnetic field frequency and content of magnetic nanoparticles. The impact of magnetic field types on micromixing was further examined at low and moderate Re numbers using the Villermaux–Dushman reaction and IEM micromixing model. The IEM‐inferred micromixing times were remarkably shorter by nearly four orders of magnitude in comparison with OMF and SMF excitations, and without magnetic field. The proposed mixing strategy is foreseen to complement innovative microfluidic devices with valuable mixing tools and methods for the diagnosis of the coupling between transport and intrinsic kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 337–346, 2017     

Morphological effect of oscillating magnetic nanoparticles in killing tumor cells

Forced oscillation of spherical and rod-shaped iron oxide magnetic nanoparticles (MNPs) via low-power and low-frequency alternating magnetic field (AMF) was firstly used to kill cancer cells in vitro. After being loaded by human cervical cancer cells line (HeLa) and then exposed to a 35-kHz AMF, MNPs mechanically damaged cell membranes and cytoplasm, decreasing the cell viability. It was found that the concentration and morphology of the MNPs significantly influenced the cell-killing efficiency of oscillating MNPs. In this preliminary study, when HeLa cells were pre-incubated with 100 μg/mL rod-shaped MNPs (rMNP, length of 200 ± 50 nm and diameter of 50 to 120 nm) for 20 h, MTT assay proved that the cell viability decreased by 30.9% after being exposed to AMF for 2 h, while the cell viability decreased by 11.7% if spherical MNPs (sMNP, diameter of 200 ± 50 nm) were used for investigation. Furthermore, the morphological effect of MNPs on cell viability was confirmed by trypan blue assay: 39.5% rMNP-loaded cells and 15.1% sMNP-loaded cells were stained after being exposed to AMF for 2 h. It was also interesting to find that killing tumor cells at either higher (500 μg/mL) or lower (20 μg/mL) concentration of MNPs was less efficient than that achieved at 100 μg/mL concentration. In conclusion, the relatively asymmetric morphological rod-shaped MNPs can kill cancer cells more effectively than spherical MNPs when being exposed to AMF by virtue of their mechanical oscillations.     

Improvement of granular mixing of dissimilar materials in rotating cylinders

We have found that periodic flow inversions of free-flowing materials may be used to effectively eliminate both size and density segregation in free-surface flows. In a rotating cylinder, these inversions may be induced by placement of an axially located baffle within the flow. In this work, we report on an experimental study of radial mixing and segregation for binary mixtures of granular materials in a rotating cylinder both with and without an axially-located baffle. Qualitative and quantitative measures of the segregation/mixing are shown via digitized images and the intensity of segregation, respectively. We define a mixing improvement factor (ψ) to quantify the relative impact of the axial baffle for a variety of baffle placements and geometries. We find that the maximum extent of mixing is achieved when the baffle size is equal to the radius of the cylinder and fixed either at the free surface or within the shear layer. In contrast, we show that segmenting the baffle, baffle placement outside the shear layer (in fixed bed), or placement at the periphery of the cylinder resulted in an insignificant increase in mixing. Mixing was found to be independent of the shape of a baffle.     

Effect of the rare-earth substitution on the structural,magnetic and adsorption properties in cobalt ferrite nanoparticles

Rare-earth (RE) substituted cobalt ferrite CoFe_1.9RE_0.1O₄ (RE=Pr³⁺, Sm³⁺, Tb³⁺, Ho³⁺) nanoparticles are synthesized by a facile hydrothermal method without any template and surfactant. The effects of RE³⁺ substitution on structural, magnetic and adsorption properties of cobalt ferrite nanoparticles are investigated. Structure, morphology, particle size, chemical composition and magnetic properties of the ferrite nanoparticles are studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), high solution transmission electron microscopy (HRTEM), energy-dispersive spectrometer (EDS), Fourier transform spectroscopy (FTIR), Raman spectra and vibrating sample magnetometry (VSM). The results indicate that the as-synthesized samples have the pure spinel phase, uniform crystallite size and narrow particle size distribution. Meanwhile, the RE³⁺ substitution leads to the decrease in the particle size, magnetization and coercivity of the CoFe₂O₄ ferrite. Notably, it demonstrates that the RE³⁺ doping can apparently enhance the adsorption capacity for Congo red (CR) onto ferrite nanoparticles. Adsorption equilibrium studies show that adsorption of CR follows the Langmuir model. The monolayer adsorption capacities of CoFe_1.9Sm_0.1O₄ and CoFe_1.9Ho_0.1O₄ are 178.6 and 158.0 mg/g, respectively. The adsorption kinetics can be described by the pseudo-second-order model.     

Facile and high-efficient immobilization of histidine-tagged multimeric protein G on magnetic nanoparticles

This work reports the high-efficient and one-step immobilization of multimeric protein G on magnetic nanoparticles. The histidine-tagged (His-tag) recombinant multimeric protein G was overexpressed in Escherichia coli BL21 by the repeated linking of protein G monomers with a flexible linker. High-efficient immobilization on magnetic nanoparticles was demonstrated by two different preparation methods through the amino-silane and chloro-silane functionalization on silica-coated magnetic nanoparticles. Three kinds of multimeric protein G such as His-tag monomer, dimer, and trimer were tested for immobilization efficiency. For these tests, bicinchoninic acid (BCA) assay was employed to determine the amount of immobilized His-tag multimeric protein G. The result showed that the immobilization efficiency of the His-tag multimeric protein G of the monomer, dimer, and trimer was increased with the use of chloro-silane-functionalized magnetic nanoparticles in the range of 98% to 99%, rather than the use of amino-silane-functionalized magnetic nanoparticles in the range of 55% to 77%, respectively.     

Spinel nanoparticles characterization by inverting scanning magnetic microscope maps

Research in nanotechnology, especially in nanoparticles, has been growing in several fields of study, from nanoelectronics to biotechnology. This wide range of applications requires different techniques for characterizing these nanoparticles in terms of properties such as structure, morphology, magnetic profile and chemical composition. The Scanning Magnetic Microscopy can be used for the magnetic characterization of these materials obtaining the magnetic maps and, with the use of the inversion technique, making it possible to recover the magnetic moment and then obtain the magnetization curve of these measurements. In this work, iron-aluminum spinel nanoparticles were produced by combustion reaction and characterized structurally by Transmission Electron Microscopy, and the magnetic properties by Scanning Magnetic Microscopy. For the inversion process, we model a set of magnetic maps using a cylindrical shape to obtain the magnetic moments, and then construct a magnetization curve. The inversion method is thereby validated by comparing the results with an in-line method already used in previous works.     

Construction of cardiac tissue rings using a magnetic tissue fabrication technique

Here we applied a magnetic force-based tissue engineering technique to cardiac tissue fabrication. A mixture of extracellular matrix precursor and cardiomyocytes labeled with magnetic nanoparticles was added into a well containing a central polycarbonate cylinder. With the use of a magnet, the cells were attracted to the bottom of the well and allowed to form a cell layer. During cultivation, the cell layer shrank towards the cylinder, leading to the formation of a ring-shaped tissue that possessed a multilayered cell structure and contractile properties. These results indicate that magnetic tissue fabrication is a promising approach for cardiac tissue engineering.     

Measurement and characterization of mixing time in shake flasks

As yet, investigations on mixing time have been focused on small and large scale stirred tanks. The aim of this study was to develop a new method for characterizing the mixing process and quantitatively measuring the mixing time in shake flasks by introducing a rotating camera for online observation of the fluid flow in combination with a typical colorimetric method using a pH indicator. In this presented scheme, only one drop of sulfuric acid was injected with a peristaltic pump into a bulk solution consisting of either deionized water or a viscous polyvinylpyrrolidone (PVP) solution. In this study, a novel interpretation of mixing time for the colorimetric method was introduced. The macroscopic mixing time is independent of the concentration of added acid. Interestingly, the recorded mixing time was similar irrespective of the shaking diameters (25, 50 mm). In addition, the dimensionless mixing number stayed constant in the regime of high Reynolds number. Our results showed that mixing number of the fluid in the regime of high Reynolds number is independent of the given geometries of flasks.     

Pb-Sn-Cd三元合金纳米微粒的制备与表征

纳米合金材料由于具有熔点低、硬度小和拉伸强度低等特点。近年来已成为人们研究的热点．这类材料在电、磁、催化和摩擦学等方面表现出的非常独特的性质使得它们在现代化工生产和应用过程中正日益受到重视。     

不同磁场作用下Fe3O4/water纳米流体层流流动对流传热系数的实验研究

对体积分数为3%的Fe₃O₄/water纳米流体在不同温度、不同磁场大小和方向的均匀磁场和梯度磁场作用下的对流换热进行了详细的实验研究。首先,开展了纳米流体能量方程的量纲1分析,讨论了纳米流体强化换热的机理。发现磁性纳米粒子所受到的磁力远远大于布朗运动力。实验测试结果与量纲1分析相吻合,在垂直均匀磁场作用下,纳米流体层流流动的平均对流传热系数提高了5.2%;在垂直梯度磁场作用下,平均对流传热系数提高了9.2%。而在水平均匀磁场作用下,纳米流体平均对流传热系数下降了4.8%。另外,随着温度的升高,对流传热系数均逐渐升高。     

Magnetically stabilized fluidization of a mixture of magnetic and non-magnetic particles in a transverse magnetic field

This paper presents an investigation of the hydrodynamic behavior of a gas-solid magnetically stabilized fluidized bed. It consists of a mixture of spherical steel particles with glass balls subjected to a magnetic field, transverse to the gas flow, which is created by two permanent magnets. Pressure drop, bed stability and expansion are studied. A data correlation in good agreement with experimental results was developed. It takes into account the modification of the bed structure in the presence of two types of particles: steel particles forming chains following the field lines and considered as “pseudo-plate” particles and non-aggregated non-magnetic particles.     

A numerical study of stir mixing of liquids with particle method

The process of stir mixing of two viscous liquids is simulated using the moving particle semi-implicit (MPS) method. A mixing rate is defined within the particle method to characterize the level of mixing, as the number, position, period, and rotating speed of the stirring stick(s) and liquid viscosity are changed. The motions of liquid particles are tracked to reveal the flow field and mixing mechanisms. The variation of the mixing rate shows that the mixing rate is higher when the sticks are rotating monotonically at high speed, and an optimum position of the stick can be identified. The mixing rate does not enhance significantly when three or more sticks are employed, and the liquid viscosity has minor influences on the mixing rate. These results give useful qualitative suggestions on controlling the mixing rate during chemical reactions.     

A study of the mixing of solids in gas-fluidized beds, using ultra-fast MRI

Magnetic resonance imaging has been used to measure the rate of axial mixing in a vertical direction of a small batch of poppy seeds suddenly added to the upper surface of a bed of sugar crystals fluidized by air.