Alignment in magnetic fields

Anwer and Windle [109,110] reported the kinetics of the alignment of poly (p-hydroxybenzoic add-co-2,6-hydroxynaphthoic acid) s of different molar masses ranging from 4600 to 36000 g mol in a magnetic field applied at elevated temperatures in the nematic state. The order parameter of a specimen held in a magnetic field increased rapidly with time and finally reached a plateau value. The data obtained fitted the following equation  

Unoriented poly (p-hydroxybenzoic acid-co-2,6-hydroxynaphthoic acid) exhibited smoothly wandering director fields in three dimensions. Alignment with a 1.1 T magnetic field for 30 min at 300 C transformed this structure to domains with an anisotropic shape within which the polymer was highly oriented, and the global order parameter amounted to 0.85 [110]. Boundaries were of the splay-bend type and involved a 180 director rotation. At lower field strengths, the domains were less 

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Regarding the possible applications of metathesis-derived LCPs, it was shown that the mesophases of SCLCPs can be aligned in magnetic fields, leading to optically transparent materials with high birefringence (Sect. 2.1). These materials are certainly interesting materials for optical applications. 

Molecules of nematic Hquid crystals also are aligned in flow fields which results in a viscosity that is lower than that of the isotropic Hquid the rod-shaped molecules easily stream past one another when oriented. Flow may be impeded if an electric or magnetic field is appHed to counter the flow orientation the viscosity then becomes an anisotropic property. 

Figure 9.1 Spin angular momenta, s, depicted as arrows, are randomly aligned in zero field, H = 0 (a), and align with the applied field, H > 0 (b), thereby decreasing the magnetic entropy of the system.

The pairing of electrons in the MOs can manifest itself in certain physical properties of the molecule. Paramagnetism results when there are unpaired electrons in the molecular orbitals. Paramagnetic molecules magnetize in magnetic fields due to the alignment of unpaired electrons. Diamagnetism occurs when there are all paired electrons in the MOs. We will revisit these properties in Chapter 6. 

Polyelectrolyte cylindrical brushes behave in similar ways as the polyelectrolyte stars in many aspects. Due to their anisotropic architecture, their morphologies can be tuned between worms, helices, and spheres. Polyelectrolyte core-shell cylindrical brushes have been used for the fabrication of inorganic NPs or NWs. In particular, superparamagnetic hybrid cylinders with magnetic NPs in the core of the brushes were prepared. They can be aligned on the substrate in magnetic field. This provides another way for the directed assembly of hybrid materials in a controlled manner. 

The third type of interaction which enters into the interpretation of Mossbauer spectra is the interaction of the nucleus with a magnetic field. Although the field may be due to external sources we are primarily interested in magnetic fields due to electronic spin alignments. We shall suppose that the quadrupole interaction is also present so that a coordinate system is defined by the principal axis sj stem of the EFG tensor. For a magnetic field arbitrarily oriented relative to this system of axes, the Hamiltonian for the magnetic interaction is... 

If we expose a system of fixed and similarly oriented molecules, containing a quadrupolar nucleus of spin I, for a static magnetic field we know that the nuclear magnetic moments will tend to align in this field. The resulting nuclear Zeeman energy levels are given by... 

Critical current densities on the order of 10 A cm at 77 K in zero field were measured on BSCCO thin films. In Fig. 4.2-46 the field dependence of 7c of a B12212 film is shown for two temperatures [2.90] and Fig.4.2-47 demonstrates the Jc(B, T) dependence of a B12223 film [2.87]. In magnetic fields aligned parallel to the plane of the film, that is perpendicular to the c axis of the crystal structure, 7c is practically independent on the field strength, even at higher temperatures such as 60 K. The reasons for this behavior are discussed below in connection with the Jc(B, T) correlation of wires and tapes. 

Abstract Smart composites based on carbonyl iron powder, micro and nano size Fe304 in ethylene - propylene and acrylonitrile - butadiene rubber were manufactured and studied. Elastomer samples with various volume fractions of magnetic particles were tested. To improve dispersion of applied fillers in polymer matrix, ionic liquids were added during the process of composites preparation. To align particles in elastomer, cross-linking process took place in magnetic field. 

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