Separation of nitrogen and oxygen gases by polymeric membrane embedded with magnetic nano‐particle

Asymmetric polyethersulfone (PES) micro‐porous flat sheet membranes were prepared by the phase inversion method (PIM) and used as the support. PES‐PDMS composite membranes were fabricated with coating polydimethylsiloxane on the surface of PES membrane. The FluidMAG‐PAD was coated on PES and PES‐PDMS membrane to prepare super‐paramagnetic membranes for separation of oxygen from nitrogen. Permeance and O₂/N₂ selectivity were evaluated in the absence or presence of external magnetic field. In the absence of external magnetic field, the super‐paramagnetic polymer provides larger surface area leading to extended sites for oxygen adsorption. In the presence of magnetic field, the super‐paramagnetic particles obtained magnetic property leading to a pronounced interaction with oxygen resulting in elevated selectivity and permeability. Copyright © 2011 John Wiley & Sons, Ltd.     

Control of chemical reaction involving dissolved oxygen using magnetic field gradient

This study investigated the control of dissolved oxygen concentration using magnetic forces from gradient magnetic fields near a Nd–Fe–B permanent magnet. Maximum values of magnetic flux density and the product of the magnetic flux density and its gradient were 0.63 T and 44 T²/m, respectively. The magnet was placed under a Petri dish filled with 15 ml of 10% ammonia water. The Petri dish had a copper sheet in the center. Absorbance of tetraamminecopper(II) complex produced by the reaction in oxygen was measured using a spectrophotometer to observe oxygen concentration. Results showed that the magnetic field quantitatively enhanced tetraamminecopper(II) complex production. Moreover, remarkable enhancement of the copper complex production occurred in the magnetic field at less than 2 mm depth. The calculated magnetic force increase near the magnet surface supports this result. These results show that greater enhancement of the reaction rate occurs when the stronger magnetic force acts on oxygen molecules.     

NMR shielding in helium-3 atoms modified by gaseous nitrogen and oxygen

Helium-3 nuclear magnetic resonance (³He NMR) measurements were carried out for the gaseous mixtures of helium-3 with pure nitrogen and synthetic air as the solvents. It was found that ³He shielding is linearly dependent on solvent density up to approx. 6 mol/L. At higher density of the gaseous solvent, the change of ³He shielding is nonlinear and especially distinct when helium-3 atoms can interact with two O₂ molecules. The interaction with paramagnetic oxygen molecules can induce two kinds of ³He shielding changes: (1) due to the isotropic Fermi contact interaction and (2) from the dipolar magnetic interaction between unpaired O₂ electrons and ³He nuclear magnetic dipole moment. The two paramagnetic effects in helium-3 shielding cannot be experimentally separated, although for such small molecular objects, they could be presumably modeled by advanced theoretical calculations.     

Cationic Mn4 single-molecule magnet with a sterically isolated core

The synthesis, structure, and magnetic properties of a ligand-modified Mn(4) dicubane single-molecule magnet (SMM), [Mn(4)(Bet)(4)(mdea)(2)(mdeaH)(2)](BPh(4))(4), are presented, where the cationic SMM units are significantly separated from neighboring molecules in the crystal lattice. There are no cocrystallized solvate molecules, making it an ideal candidate for single-crystal magnetization hysteresis and high-frequency electron paramagnetic resonance studies. Increased control over intermolecular interactions in such materials is a crucial factor in the future application of SMMs.     

Experimental Study of Nitrogen Oxides and Ozone Generation by Corona-Like Dielectric Barrier Discharge with Airflow in a Magnetic Field

We investigated nitrogen monoxide, nitrogen dioxide and ozone generation for corona-like dielectric barrier discharge in a stationary magnetic field with airflow. The magnetic field was produced by the permanent magnet. We showed that nitrogen monoxide could be easily generated at relatively low voltages, by application of a magnetic field on the hollow needle to mesh with a dielectric barrier discharge. For higher voltages generation of nitrogen monoxide falls to zero, and generation of nitrogen dioxide and ozone with increasing voltage increases. We also demonstrated that simultaneous application of the magnetic field with airflow through the needle electrode affects the transition of the discharge from the high to the low voltage regime. This transition is accompanied by important changes in the production of nitrogen oxides and ozone. Changes in the discharge regime are reflected by changes in the voltage–current waveforms. The obtained results could be interesting for various biomedical applications or bacterial decontamination of surfaces.     

快淬NdFeB磁粉颗粒度对聚合物粘结NdFeB磁体永磁性能的影响

研究了快淬ＮｄＦｅＢ永磁粉颗粒及其分布对聚合物粘结ＮｄＦｅＢ永磁材料性能的影响。快淬Ｎｄ－ＦｅＢ永磁粉颗凿大小及其分布显著地影响聚合物结ＮｄＦｅＢ永磁材料的磁性能。适当尺寸的快淬ＮｄＦｅＢ磁粉组合可获得高的结ＮｄＦｅＢ永磁帝主要是由于快淬ＮｄＦｅＢ磁粉硬度高,呈鳞片状,其尺雨越大越难获得高密度,但尺寸太小又将破坏磁粉的结构,导致磁性能恶化。     

Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate

The magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water and oil, unless magnetosensitive particles are added. Herein, we describe a new and additive‐free way to magnetically control the motion of discrete liquid entities. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. A broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones, can be efficiently transported using the moderate magnetic field (ca. 50 mT) produced by a small permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on‐demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment or electric power, in phase with the necessary development of robust and low‐cost analytical and diagnostic fluidic devices.     

Nanodrop of an Ising magnetic fluid on a solid surface

The density functional theory of inhomogeneous simple fluids is extended to an Ising magnetic fluid in contact with a solid surface, which is subjected to an external uniform or nonuniform magnetic field. The system is described by two coupled integral equations regarding the magnetic moment and fluid density distributions. The dependence of the contact angle that a nanodrop makes with the solid surface on the parameters involved in the magnetic interactions between the molecules of fluid and between the molecules of fluid and an external magnetic field is calculated. For the uniform magnetic field, the contact angle increases with increasing magnetic field, approaching an asymptotic value that depends on the strength of the fluid-fluid magnetic interactions. In the nonuniform field generated by a permanent magnet, the contact angle first increases with increasing magnetic field B(M) and then decreases, with the decrease being almost linear for large values of B(M). The obtained results are in qualitative agreement with the experimental data on the contact angle of magnetic drops on a solid surface available in the literature.     

Flow focussing of particles and cells based on their intrinsic properties using a simple diamagnetic repulsion setup

The continuous flow focussing and manipulation of particles and cells are important factors in microfluidic applications for performing accurate and reproducible procedures downstream. Many particle focussing methods require complex setups or channel designs that can limit the process and its applications. Here, we present diamagnetic repulsion as a simple means of focussing objects in continuous flow, based only on their intrinsic properties without the requirement of any label. Diamagnetic polystyrene particles were suspended in a paramagnetic medium and pumped through a capillary between a pair of permanent magnets, whereupon the particles were repelled by each magnet into the central axis of the capillary, thus achieving focussing. By investigating this effect, we found that the focussing was greatly enhanced with (i) increased magnetic susceptibility of the medium, (ii) reduced flow rate of the suspension, (iii) increased particle size, and (iv) increased residence time in the magnetic field. Furthermore, we applied diamagnetic repulsion to the flow focussing of living, label-free HaCaT cells.     

Molecular cube of Re(II) and Mn(II) that exhibits single-molecule magnetism

A pseudocubic, paramagnetic cluster of ReII and MnII, [{MnCl}4{Re(triphos)(CN)3}4], has been prepared, and its magnetic properties have been investigated. Antiferromagnetic coupling is observed between the "S = 1/2" ReII and S = 5/2 MnII centers resulting in an effective S = 8 ground state. AC susceptibility studies reveal that the molecule is a single-molecule magnet with an effective barrier for magnetization reversal of Ueff = 8.8 cm-1.     

Field-induced ferrimagnetic state in a molecule-based magnet consisting of a Co(II) ion and a chiral triplet Bis(nitroxide) radical

We present the synthesis, crystal structure, and temperature and field dependence of the magnetic properties of a new molecule-based magnet, [Co(hfac)2].BNO* (1), where hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato and BNO* is the chiral triplet bis(nitroxide), 1,3-bis(N-tert-butyl-N-oxylamino)-5-{1'-methyl-1'-[2' '-(S)-methylbutoxy]ethyl}benzene. The presence of enantiomer-pure BNO induces the formation of chiral one-dimensional chains that are packed parallel to each other in the noncentrosymmetric P1 space group. 1 exhibits four magnetic ground states: paramagnetic; antiferromagnetic; forced ferrimagnetic; field-induced metastable ferrimagnetic. In the paramagnetic state (T > 20 K), it presents short-range antiferromagnetic interaction between Co ion and nitroxide radical and has a minimum of chimT value at 220 K. The Weiss temperature estimated in the temperature range 220-300 K is found to be -89.9 K. At 20 K (TN), an antiferromagnetic long-range ordering is established. In the temperature range 4 K < T < 20 K, the isothermal magnetization curve show a spin-flip transition to the forced ferrimagnetic state at around 850 Oe. Below 4 K, this compound enters into a field-induced ferrimagnetic state, which is metastable and stabilized by the Ising character of the Co ion. In the low-temperature phase, the material becomes a very hard magnet with wide hysteresis loop whose coercive field reaches 25 kOe at 2 K. The magnetic phase diagram based on these magnetic data is presented.     

The self-diffusion of water and saturated aliphatic alcohols in cation-exchange membranes

The self-diffusion of water, methanol, ethanol, isopropanol, and butanol in membranes based on polyethylene and sulfonated copolymer of styrene and divinylbenzene (MK-100) and membranes based on sulfo-containing aromatic polyamides (PA) and a copolymer of 1,2,4,5-benzenetetracarboxylic acid with 4,4′-diaminodiphenyl oxide (PAK) was investigated by the pulsed magnetic field gradient NMR technique. In MK-100 sulfo cation-exchange membranes and PAK carboxylic membranes, two types of sorbate molecules with translational mobilities differing by an order of magnitude were observed. It was established that, in these membranes, the major diffusant portion was transferred trough transport channels formed by functional groups of membranes, counterions, and diffusant molecules (ionogenic channels). The conclusion was drawn that, in PA membranes, water and alcohol molecules were distributed uniformly and carbonyl croups of the polymeric matrix participated in the formation of transport channels. Relations between the structure of membranes, the character of diffusant-polymeric matrix interaction, and the translational mobility of sorbate molecules were found.     

Magnetic effects in hydroperoxide decomposition in mixed micelles with cationic surfactants

The retardation effect of oxygen and external magnetic field on the yield of radicals in hydroperoxide decomposition in catalytic nanoreactors was discovered. Mixed reverse micelles formed by the cationic surfactants (Surf) and hydroperoxide {mLOOH...nSurf} play the role of nanoreactors. Similar effects of oxygen and external magnetic field (60–150 mT) on the yield of radicals are observed in the catalytic decomposition of hydroperoxide in the presence of acetylcholine. It is noteworthy that the retardation effect of the magnetic field decreases in the presence of paramagnetic particles such as oxygen and relatively stable radicals.     

CRYSTALLOGRAPHIC STRUCTURE AND MAGNETIC PROPERTIES OF R_(2)Fe_(17)N_(2.4)

By a proper thermal treatment, the nitrogen atoms can enter the R2Fe17 structure. The crystallographic and intrinsic magnetic properties as well as their relationship have been studied by magnetic measurements, X-ray and neutron diffraction techniques. The neutron data indicate that the nitrogen atoms occupy the interstitial sites in the Th2Zn17-type rhom-bohedral structure. The inserting nitrogen atoms are found to dilate the cell volume, increase the Curie temperature and enhance the saturation moment by raising the difference in the electron number between the spin-up and spin-down 3d subbands of the Fe atoms. Furthermore, the nitrogen atoms have an important effect on the magnetocrystallic anisotropy, which results in an easy axis with Sm2Fe17N2.4. All these make Sm2Fe17N2.4 favorable for permanent magnet applications.     

Effect of molecular oxygen on the variable-temperature 29Si MAS NMR spectra of zeolite-sorbate complexes

Structure determinations of siliceous zeolite-sorbate host-guest complexes by solid-state NMR require highly resolved 29Si MAS NMR spectra. As the temperature is lowered, the 29Si MAS NMR spectra of many zeolite-sorbate complexes become broadened such that the resolution of the individual 29Si peaks is lost, limiting the application of solid-state NMR for structure determination. It is shown that the 29Si peak widths are related to the 29Si T2 relaxation times and that the source of the 29Si relaxation and the line broadening is paramagnetic molecular oxygen in the channels of the zeolite. Removal of the oxygen by purging the sample with nitrogen gas leads to a dramatic increase in the resolution of the 29Si MAS NMR spectrum of the p-dibromobenzene/ZSM-5 complex. An analysis of the individual 29Si T1 relaxation times reveals that the oxygen molecules are localized mainly in the zigzag channels of ZSM-5, suggesting that the p-dibromobenzene molecules are located in the channel intersections.     

A Paramagnetic Compass Based on Lanthanide Metal-Organic Framework

Macroscopic compass-like magnetic alignment at low magnetic fields is natural for ferromagnetic materials but is seldomly observed in paramagnetic materials. Herein, we report a “paramagnetic compass” that magnetically aligns under ∼mT fields based on the single-crystalline framework constructed by lanthanide ions and organic ligands (Ln-MOF). The magnetic alignment is attributed to the Ln-MOF's strong macroscopic anisotropy, where the highly-ordered structure allows the Ln-ions’ molecular anisotropy to be summed according to the crystal symmetry. In tetragonal Ln-MOFs, the alignment is either parallel or perpendicular to the field depending on the easiest axis of the molecular anisotropy. Reversible switching between the two alignments is realized upon the removal and re-adsorption of solvent molecules filled in the framework. When the crystal symmetry is lowered in monoclinic Ln-MOFs, the alignments become even inclined (47°-66°) to the field. These fascinating properties of Ln-MOFs would encourage further explorations of framework materials containing paramagnetic centers.     

Interaction of pyridinium bis-retinoid (A2E) with bilayer lipid membranes

The accumulation of lipofuscin granules within the retinal pigment epithelium (RPE) cells is correlated with the progression of age-related macular degeneration. One of the fluorophores contained in lipofiscin granules is pyridinium bis-retinoid (A2E). To test its membrane-toxic effect, the interaction of A2E with bilayer lipid membranes (BLM) was studied. The incorporation of charged A2E molecules into the membranes has been detected as a change of either zeta-potential of multilayer liposomes or boundary potential of BLM. It was shown that the presence of up to 25mol% of A2E did not destabilize the bilayers made of saturated phosphatidylcholine (PC). However, the destabilizing effect became very significant when BLM contained negatively charged lipids such as cardiolipin or phosphatidylserine. The electrical breakdown measurements revealed that the A2E-induced decrease of BLM stability was primarily associated with the growing probability of lipid pore formation. It was found from the measurements of boundary potential of BLM that exposure of A2E to light initiates its transformation into at least two products. One of them is epoxy-A2E, which, being hydrophilic, moves from the membrane into water solution. The other product is a non-identified hydrophobic substance. Illumination of A2E-containing BLM made from unsaturated PC by visible light caused the membrane damage presumably due to oxidation of these lipids by singlet oxygen generated by excited A2E molecules. However, this effect was very weak compared to the effect of known photosensitizers. The illumination of BLM with A2E also leads to the damage of gramicidin incorporated into the membrane, as was detected by measuring the conductance of channels formed by this peptide.     

Novel highly elastic magnetic materials for dampers and seals: part II. Material behavior in a magnetic field

The combination of polymers with magnetic particles displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic field sensitive elastomers represent a new type of composites consisting of small particles, usually from nanometer range to micron range, dispersed in a highly elastic polymeric matrix. In this paper, we show that in the presence of built‐in magnetic particles it is possible to tune the elastic modulus by an external magnetic field. We propose a phenomenological equation to describe the effect of the external magnetic field on the elastic modulus. We demonstrate the engineering potential of new materials on the examples of two devices. The first one is a new type of seals fundamentally different from those used before. In the simplest case, the sealing assembly includes a magnetoelastic strip and a permanent magnet. They attract due to the magnetic forces. This ensures that due to high elasticity of the proposed composites and good adhesion properties, the strip of magnetoelastic will adopt the shape of the surface to be sealed, this fact leading to an excellent sealing. Another straightforward application of the magnetic composites is based on their magnetic field dependent elastic modulus. Namely, we demonstrate in this paper the possible application of these materials as adjustable vibration dampers. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of ferrite nanocrystals stabilized by ionic-liquid molecules through a thermal decomposition route

A series of M(x) Fe(3-x) O(4) (M=Fe, Co, Ni, Zn; 0≤x≤1) ferrite nanocrystals stabilized by ionic-liquid molecules have been successfully synthesized through a thermal decomposition route. Instead of the widely used long-chain lipid surfactants and high-boiling solvents, the ionic-liquid molecules not only played the role of surfactants, but also served as reaction and dispersion media simultaneously in the preparation of ferrite nanocrystals. Due to their good fluidity under magnetic fields and high ionic conductivity, the ionic-liquid molecules and M(x) Fe(3-x) O(4) ferrite nanocrystal-based conducting ferrofluids were successfully used as electrolytes in an AC circuit. The open or closed state of the circuit was directly controlled by moving a permanent magnet so as to tune the position of the ferrofluids, and consequently, resulted in the "off" or "on" state of the four indicative yellow-light-emitting diodes. These results demonstrate that the conducting ferrofluids successfully play the role of "magnetic switch".     

Ferromagnetism, paramagnetism, and thermally induced magnetism in photomagnetic CrIII/MnII and CrIII oxalates with the 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f]quinolinium cation

Single crystals of the new cationic chromene, 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f-quinolinium iodide (C₂₅H₂₀NO)I (1), were synthesized. The crystal structure of the new compound was studied, and quantum chemical calculation for the open and closed forms were carried out. The bifunctional compounds containing mono- and bimetallic 3d metal (tris)oxalates with the chromenium cation, (C₂₅H₂₀NO)₃[Cr(C₂O₄)₃] · 4H₂O (2) and (C₂₅H₂₀NO)[CrMn(C₂O₄)₃] · H₂O (3), were prepared. Compound 1 is paramagnetic due to low-lying thermally excited states of the chromene molecules. At low temperatures (∼2 K), the paramagnetic states are frozen, and the compound becomes diamagnetic. Compound 2 is paramagnetic and its magnetic properties are determined mainly by the Cr³⁺ ions and the thermally induced paramagnetic states of the chromene molecules. At high temperatures, the magnetic moment of compound 3 consists of the contributions of the paramagnetic Cr³⁺ and Mn²⁺ ions and the thermally induced paramagnetic states of chromenes. At low temperatures (2–3 K), the thermally induced magnetism of organic molecules is frozen, and the magnetically ordered (and, probably, spin-glass) state is observed in the two-dimensional network of metal oxalates (T _c = 3 K in the zero magnetic field). The UV irradiation leads to an increase in the magnetic moment of the compound in the paramagnetic region due to the generation of radiation defects.