Rheological properties and particle behaviors of a nondilute colloidal dispersion composed of ferromagnetic spherocylinder particles subjected to a simple shear flow: analysis by means of mean-field approximation for the two typical external magnetic field directions

We have analyzed the orientational distributions and rheological properties of a nondilute colloidal dispersion composed of ferromagnetic spherocylinder particles subjected to a simple shear flow. In order to understand the effects of the magnetic interactions between the particles, we have applied the mean-field theory to a nondilute colloidal dispersion for the two typical external magnetic field directions, that is, the direction parallel to the shear flow and the direction parallel to the angular velocity vector of the shear flow. The main results are summarized as follows. The particle-particle interactions suppress the Brownian motion of the particles and, therefore, make the particles incline toward the same direction. For the magnetic direction parallel to the shear flow, the influence of the particle-particle interactions makes the peak of the orientational distribution sharper and higher. The viscosity generally increases as the interactions between particles become stronger in the case where the effects of the shear flow and magnetic field are relatively small. For the magnetic direction parallel to the angular velocity vector of the shear flow, the influence of the particle-particle interactions on the orientational distribution appears significantly, when the influences of the shear flow and magnetic field are not so strong that the particles can be aligned sufficiently to form stable chainlike clusters in a certain direction.     

Rheology and orientational distributions of rodlike particles with magnetic moment normal to the particle axis for semi-dense dispersions (analysis by means of mean field approximation)

We have considered a semi-dense dispersion composed of ferromagnetic rodlike particles with a magnetic moment normal to the particle axis to investigate the rheological properties and particle orientational distribution in a simple shear flow as well as an external magnetic field. We have adopted the mean field approximation to take into account magnetic particle-particle interactions. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved numerically. The results obtained here are summarized as follows. For a very strong magnetic field, the magnetic moment of the rodlike particle is strongly restricted in the field direction, so that the particle points to directions normal to the flow direction (and also to the magnetic field direction). This characteristic of the particle orientational distribution is also valid for the case of a strong particle-particle interaction, as in the strong magnetic field case. To the contrary, for a weak interaction among particles, the particle orientational distribution is governed by a shear flow as well as an applied magnetic field. When the magnetic particle-particle interaction is strong under circumstances of an applied magnetic field, the magnetic moment has a tendency to incline to the magnetic field direction more strongly. This leads to the characteristic that the viscosity decreases with decreasing the distance between particles, and this tendency becomes more significant for a stronger particle-particle interaction. These characteristics concerning the viscosity are quite different from those for a semi-dense dispersion composed of rodlike particles with a magnetic moment along the particle direction.     

Influence of magnetic interactions between clusters on particle orientational characteristics and viscosity of a colloidal dispersion composed of ferromagnetic spherocylinder particles: analysis by means of mean field approximation for a simple shear flow

We have theoretically investigated the particle orientational distribution and viscosity of a dense colloidal dispersion composed of ferromagnetic spherocylinder particles under an applied magnetic field. The mean field approximation has been applied to take into account the magnetic interactions of the particle of interest with the other ones that belong to the neighboring clusters, besides those that belong to its own cluster. The basic equation of the orientational distribution function, which is an integrodifferential equation, has approximately been solved by Galerkin's method and the method of successive approximation. Some of the main results obtained here are summarized as follows. Even when the magnetic interaction between particles is of the order of the thermal energy, the effect of particle-particle interactions on the orientational distribution comes to appear more significant with increasing volumetric fraction of particles; the orientational distribution function exhibits a sharper peak in the direction nearer to the magnetic field one as the volumetric fraction increases. Such a significant inclination of the particle in the field direction induces the large increase in viscosity in the range of larger values of the volumetric fraction. The above-mentioned characteristics of the orientational distribution and viscosity come to appear more significantly when the influence of the applied magnetic field is not so strong compared with that of magnetic particle-particle interactions.     

Transport coefficients and orientational distributions of spheroidal particles with magnetic moment normal to the particle axis (Analysis for an applied magnetic field normal to the shear plane)

We have investigated the influence of the magnetic field strength, shear rate, and rotational Brownian motion on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of rodlike particles of a dilute colloidal dispersion. The rodlike particle is modeled as a magnetic spheroidal particle which has a magnetic moment normal to the particle axis; such a particle may typically be a hematite particle. In the present study, an external magnetic field is applied in the direction normal to the shear plane of a simple shear flow. The basic equation of the orientational distribution function has been derived from the balance of torques and solved numerically. The results obtained here are summarized as follows. Although the orientational distribution function shows a sharp peak in the shear flow direction for a very strong magnetic field, such a peak is not restricted to the field direction alone, but continues in every direction of the shear plane. This is due to the characteristic particle motion that the particle can rotate around the axis of the magnetic moment in the shear plane, although the magnetic moment nearly points to the magnetic field direction. This particle motion in the shear plane causes negative values of the viscosity due to the magnetic field. The viscosity decreases, attains a minimum value, and then converges to zero as the field strength increases. Additionally, the diffusion coefficient is significantly influenced by such characteristic particle motion in the shear plane for a strong magnetic field.     

Rheological properties and particle behaviors of a non-dilute colloidal dispersion composed of ferromagnetic spherocylinder particles subjected to a simple shear flow (analysis by means of mean-field approximation)

We have investigated the rheological properties and the orientational distributions of particles of a non-dilute colloidal dispersion, which is composed of ferromagnetic spherocylinder particles, subject to a simple shear flow. The mean-field approximation is applied to take into account the interactions between spherocylinder particles. The basic equation of the orientational distribution function has been derived from the balance of the torques (including the term due to the mean field approximation) acting on the particle in an applied magnetic field; this is an integrodifferential equation. Then, the governing equation has been solved by means of the method of successive approximation and Galerkin's method. The results obtained here are summarized as follows. For the case of strong magnetic interactions between particles, the particle exhibits a sharp peak of the orientational distribution even for a weak applied magnetic field. In this case, the mean magnetic moment of the particle becomes large, which leads to strong interactions between the applied magnetic field and the particle. Thus, the particle tends to point to the magnetic filed direction under these situations. Also, in this case, a large increase in viscosity is obtained due to such a restriction concerning the particle orientation.     

Synthesis, structure, and magnetic properties of two new ferromagnetic/antiferromagnetic one-dimensional nickel(II) complexes. Magnetostructural correlations

Two new one-dimensional nickel(II) complexes were synthesized and characterized: [Ni(N,N-dimethylethylenediamine)(N3)2] (1) and [Ni(2-aminoethylpyridine)(N3)2] (2). The crystal structures of 1 and 2 were solved. Complex 1 crystallizes in the monoclinic system, space group P2(1)/n with a = 10.569(2) A, b = 7.331(4) A, c = 12.9072(8) A, beta = 111.324(10) degrees, and Z = 4. Complex 2 crystallizes in the monoclinic system, space group P2(1)/c with a = 12.299(5) A, b = 14.307(2) A, c = 12.604(3), beta = 106.72(2) degrees, and Z = 4. The two complexes are similar and may be described as one-dimensional systems with double-azido-bridged ligands in end-to-end and end-on coordination alternatively. The end-on moiety is almost identical for 1 and 2, but the end-to-end moiety is different in each structure: for 1 this part is almost planar but for 2 is nonplanar. In both cases the Ni atoms are situated in similar distorted octahedral environments. The magnetic properties of the two compounds were studied by susceptibility measurements vs temperature. The chi M vs T plots for 1 and 2 show a global antiferromagnetic behavior with a maximum near room temperature for 1 and at very low temperature for 2. J values for 1 and 2 were deduced from the spin Hamiltonian -sigma(J1SiSi+1 + J2Si+1Si+2). The computational method was based on the numerical solution for finite systems of increasing size. J values for 1 were J1 = -187 cm-1 and J2 = +77 cm-1 and for 2 J1 = -28 cm-1 and J2 = +73 cm-1. The positive values correspond to end-on azido ligands and the negative values to end-to-end azido ligands. Since the geometries of the [Ni(N3)]2 moieties involving the end-on azido ligands are almost the same in the two structures, the ferromagnetic coupling is nearly identical in the two compounds, while the significantly different antiferromagnetic couplings reflect the near planarity of the end-to-end Ni2(N3)2 fragment in 1 and its twisted geometry in 2.     

Low-temperature field dependence of the magnetic moment of ferromagnetic tetranuclear nickel(II) clusters

We examine the characteristics of the low-temperature behavior of the magnetic moment of tetranuclear methoxo complexes of nickel(II) of the type [Ni(OCH₃L· (CH₃OH)]₄ (L is the residue of 2,4-dinitrophenol (I), 2,4,6-trichlorophenol (II) and acetylacetone (III)), having the cubane structure. Within the model taking into account the isotropic Heisenberg interaction (J₁₂=J₂₃=J₃₄=J₄₁=J, J₁₃=J₂₄=J_iso), the local anisotropy (parameters D and g_i), intercluster exchange (parameter J_ic), we could interpret both the field dependence (=0.4-0.8 T) and the temperature dependence of the magnetic moment. We have established that the nature of the ligand L exerts a substantial effect on the magnetic proper ties of the considered compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 339–344, May–June, 1989.     

Transport coefficients and orientational distributions of rodlike particles with magnetic moment normal to the particle axis under circumstances of a simple shear flow

We have investigated the influences of the magnetic field strength, shear rate, and random forces on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of rodlike particles of a dilute colloidal dispersion. This dispersion is composed of ferromagnetic spheroidal particles with a magnetic moment normal to the particle axis. In the present analysis, these spheroidal particles are assumed to conduct the rotational Brownian motion in a simple shear flow as well as an external magnetic field. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved numerically. The results obtained here are summarized as follows. For a very strong magnetic field, the rodlike particle is significantly restricted in the field direction, so that the particle points to a direction normal to the flow direction (and also to the magnetic field direction). However, the present particle does not exhibit a strong directional characteristic, which is one of the typical properties for the previous particle with a magnetic moment parallel to the particle axis. That is, the particle can rotate around the axis of the magnetic moment, although the magnetic moment nearly points to the field direction. The viscosity significantly increases with the field strength, as in the previous particle model. The particle of a larger aspect ratio leads to the larger increase in the viscosity, since such elongated particles induce larger resistance in a flow field. The diffusion coefficient under circumstances of an applied magnetic field is in reasonable agreement between theoretical and experimental results.     

Synthesis, structure and magnetic properties of two new azido-Co(II) coordination architectures: from ferromagnetic coupling to single-chain-magnets

Two new azido-Co(II) complexes with pyrazine carboxylato ligands, [Co(N(3))(L)·H(2)O](n) (L = pyrazine-2-carboxylato) (1) and [CoNa(N(3))(2)(L)](n) (2), have been obtained by carefully tuning the Co(II):N(3)(-) ratio. Here we present the structural and magnetic characterization of these new species. Modulation of the coordination environment of Co(II) leads to a variation of the magnetic properties of the obtained compounds. Complex 1 exhibits ferromagnetically coupled [Co(2)] units that form the rungs of the ladder with a nearly negligible coupling between these units, while complex 2 is a 2D arrangement of 1D Co(II) single-chain magnets.     

The effect of magnetic field on the band structure of polymers Part 1. Static magnetic field

The Hartree-Fock equations for a periodic polymer chain in the presence of a static magnetic field are formulated. The cases of homogeneous and inhomogeneous static field are treated separately. In the case where the magnetic field strength is dependent on the coordinate z (the direction of the main axis of the polymer), the periodic symmetry of the polymer breaks down. For the case of weak z dependence of the magnetic field the chain can be divided into segments, each one characterized by an averge field, and the interface of these segments can be treated with the help of two Dyson equations (one for each segment at the interface).     

Multiblock copolymers of styrene and isoprene. II. Microstructure and dilute solution properties

Dilute solution properties of linear (SI)₃ six-block copolymers of styrene and isoprene are compared to those of random, two-block, and three-block copolymers of the same system. All the copolymers were prepared with sec-butyllithium in benzene. The microstructure of the polyisoprene blocks is close to that of homopolyisoprene prepared under the same conditions. In contrast, the random copolymer shows a larger amount of trans-1,4 isoprene units. The intrinsic viscosities of the copolymers in methylisobutyl ketone, a poor solvent for both polystyrene and polyisoprene, and in toluene, a good solvent for both homopolymers, are examined on the basis of the Fox–Flory relation for homopolymers. All the copolymers behave similarly in each solvent. In methylisobutyl ketone, the viscosity results indicate a random coil conformation with a small expansion owing to the extra repulsive interactions between the dissimilar units. In all cases, the heterocontact repulsive interactions are small and can be characterized by an interaction parameter χ_ab close to 0.025. In toluene, the perturbation caused by the heterocontacts becomes negligible and the expansion factor α_η can be predicted from a weighted average of those of the parent homopolymers of the same molecular weight as the copolymer.     

Rheological properties of sodium montmorillonite in exhaustively deionized dispersions and in the presence of sodium chloride

The rheological properties of sodium montmorillonite particles were studied in exhaustively deionized aqueous dispersions and in the presence of a small amount of sodium chloride. The shear viscosities were several magnitudes higher than those expected from Einstein's coefficient and decreased sharply when the concentration of sodium chloride increased. The storage moduli of deionized dispersions were constant, irrespective of the angular frequency, whereas they decreased sharply when the salt concentration and the angular frequency increased. The phase of the deionized dispersion was "solid" and transformed into "liquid" on the addition of sodium chloride.     

Synthesis,spectroscopic, magnetic properties and MMX force field study of two imidazolate-bridged dinuclear copper(II) complexes

Two new imidazolate-bridged dinuclear Cu^II complexes, Na[Cu₂(L¹)₂(im)] and K[Cu₂(L²)₂(im)] (where H₂L¹=6-amino-1,3-dimethyl-5(2-carboxyphenyl)azouracil and H₂L²=1,3-dimethyl-5(2-carboxyphenyl)azobarbituric acid) have been prepared and characterized by magnetic susceptibility and spectroscopic measurements. Both compounds exhibit the expected antiferromagnetic behaviour with 2J=−54.8 and −30.4 cm⁻¹, respectively. Because of the lack of suitable crystals for single crystal X-ray analysis, we have calculated the lowest energy structures using a program based on the MMX force field. On the basis of the results, the magnitude of the magnetic interaction is discussed. TMC 2623     

Conductance equation of dilute mixed strong electrolytes. II. Hydrodynamic and osmotic terms in relaxation field

The hydrodynamic and osmotic terms in the relaxation field are computed up to order linear in concentration for a dilute solution of mixed strong electrolytes using the primitive model. The computation is based on the relative function μ_ji computed in part earlier for the purely electrostatic interaction and in part in this work for the hydrodynamic interaction assuming the adequacy of the Fuoss velocity field. The results are compared with the earlier computations of Fuoss and Onsager, Murphy and Cohen, and Falkenhagen, Ebeling, and Kraeft. It is found that some terms of the new results are in agreement with the earlier computations and the other terms represent an improved computation.     

Influence of nanoparticle surface chemistry on the thermomechanical and magnetic properties of ferromagnetic nanocomposites

The effect of nanoparticle surface chemistry on the thermal, mechanical, and magnetic properties of poly(methyl methacrylate) (PMMA) nanocomposites with cobalt ferrite nanofillers was studied by comparing nanofillers coated with oleic acid (OA; which does not covalently bond to the PMMA matrix) and 3‐methacryloxypropyltrimethoxysilane (MPS, which covalently bonds to the PMMA matrix). Thermogravimetric analysis revealed an increase in the thermal degradation temperature of the nanocomposites compared with the neat polymer. The effect of cobalt ferrite nanofiller on the glass transition temperature (T_g) of the nanocomposite was evaluated by differential scanning calorimetry. The T_g value of the material increased when the particles were introduced. Dynamic mechanical analysis indicated an increase in the storage modulus of the nanocomposite because of the presence of nanofiller and a shift in the peak of loss tangent toward higher temperature. Magnetic measurements indicated that both nanocomposites had a small hysteresis loop at 300 K and no hysteresis at 400 K. However, estimates of the nanofiller's rotational relaxation times and measurements of the zero field cooled temperature‐dependent magnetization indicate that the observed lack of hysteresis at 400 K is likely because of particle rotation in the polymer matrix. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Quantitative interpretation of TG and DTG curves obtained for some ferromagnetic substances in low intensity A.C. generated magnetic field

Earlier studies on the possibility of magnetochemical analysis, employing a simultaneous TG-DTG-DTA method, have been extended. Several magnetic samples of different chemical compositions, e.g. spinels, garnets and hexagonal ferrites, were examined. Investigations involved both soft (NiFe₂O₄, MnMg ferrite, Y₃Fe₅O₁₂) and hard magnetic materials such as BaFe₁₂O₁₉, SrFe₁₂O₁₉. The capability of the method, referred to in the following as DTMG, for the qualitative and the quantitative analysis of a wide variety of magnetic materials is proposed. The results are discussed in terms of the basic magnetic parameters such as a magnetocrystalline anisotropy, magnetic moment and ferromagnetic Curie point temperature, T_c. The relationship between DTMG line intensities and concentrations of the respective magnetic substances was found. The results are interpreted on the basis of the Curie point measurements by means of DTMG curves in the temperature range between 20 and 1200°C. It is a proposal to call the TG and DTG curves taken simultaneously in the presence of an alternating magnetic field as the TMG and DTMG curves, respectively. The term DTMG stands for Derivative Thermo-Magneto-Gravimetry. The idea of the method has been developed in this laboratory.The DTMG method is capable of good precision within resonable time. The method can be applied to polycrystalline as well as to single crystals of the magnetic materials and the sample can be in the solid or powder state.     

Side chain liquid crystalline elastomers II. Thermal properties and orientational behaviour of the LCE based on unsaturated copolyesters

The effect of crosslinking density on the phase behaviour of smectic liquid crystalline networks was studied; the results showed that crosslinking in their smectic phases can greatly enhance the stability of the liquid crystalline phase. The higher the crosslinking density, the higher the smectic-isotropic transition temperature. The mechanically-induced orientation was studied by polarized FTIR spectroscopy. The smectic liquid crystalline network could be oriented parallel to the mechanical field at higher draw ratio λ, while at lower λ the mesogenic groups are oriented perpendicular to the field for the networks with higher crosslinking density. The observed mechanically-induced orientation is interpreted by a proposed mechanism.     

Crystal structure and magnetic properties of two isomeric three-dimensional pyromellitate-containing cobalt(II) complexes

The hydrothermal preparation, crystal structure determination, and magnetic study of two isomers made up of 1,2,4,5-benzenetetracarboxylate and high-spin Co(II) ions of formula [Co2(bta)(H2O)4]n x 2n H2O (1 and 2; H4bta = 1,2,4,5-benzenetetracarboxylic acid) are reported. 1 and 2 are three-dimensional compounds whose structures can be described as (4,4) rectangular layers of trans-diaquacobalt(II) units with the bta(4-) anion acting as tetrakis-monodentate ligand through the four carboxylate groups, which are further connected through other trans-[Co(H2O)2](2+) (1) and planar [Co(H2O)4](2+) (2) entities, with the bridging units being a carboxylate group in either the anti-syn (1) or syn-syn (2) conformations and a water molecule (2). The study of the magnetic properties of 1 and 2 in the temperature range 1.9-300 K shows the occurrence of weak antiferromagnetic interactions between the high-spin Co(II) ions, with the strong decrease of chi(M)T upon cooling being mainly due to the depopulation of the higher energy Kramers doublets of the six-coordinated Co(II) ions. The computed values of the exchange coupling between the Co(II) ions across anti-syn carboxylate (1) and syn-syn carboxylate/water (2) bridges are J = -0.060 (1) and -1.90 (2) cm(-1) (with the Hamiltonian being defined as H = -Jsigma(i,j)S(i) x S(j)). These values follow the different conformations of the carboxylate bridge in 1 (anti-syn) and 2 (syn-syn) with the occurrence of a double bridge in 2 (water/carboxylate).     

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.     

Automation of Structure Analysis. Part II. Automation of the Evaluation

The extent to which it is possible to automate the determination of a structure from the data collected with automatic measuring equipment is discussed. The development of the automatic evaluation is synchronous with that of digital computer program.—Even the simple calculation of structure factors from the intensities (i.e. the analysis of the geometrical and physical intensity factors) takes several weeks when the many thousand reflections are processed “manually”, i.e. with a desk calculator. A large electronic computer, on the other hand, executes these calculations in a few seconds. Nevertheless, even the largest computers available at present are too small for many of the complex steps in the calculation and for the quantity of data involved. Evaluation methods which, owing to long computing times, can at present only be tested on relatively simple structures will become more attractive with the advent of machines with computing times in the nanosecond range. For corrigendum see DOI: 10.1002/anie.196605112