Articles you may be interested inPhase and orientational ordering of low molecular weight rod molecules in a quenched liquid crystalline polymer matrix with mobile side chains A system of linear polymer liquid crystal ͑PLC͒ macromolecules is considered. Each macromolecule constitutes an alternating copolymer of flexible and LC sequences. The macromolecules can be either unconnected or else connected into a PLC network. The system is characterized with respect to local orientation. Competition between energetic effects of anisotropic orienting interactions between LC sequences and entropic effects determined mainly by flexible parts is considered. The Maier and Saupe mean-field approach is assumed for the representation of LC interactions. Types and orders of phase transitions that the system can undergo with respect to local order are discussed in terms of the Landau classification. All transitions are found to be of the first order. Thermodynamical and structural parameters of the system at phase transition points are represented by phase diagrams.

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The influence of mechanical stress on low frequency AC magnetic permeability was studied. The cold-drawn bars with C45 steel were subjected to investigation. The tensile stress (within elastic regime) was applied by means of material testing machine. Simple measuring system was assembled, which consisted of: function generator with magnetizing coil, detection coil and precise AC voltmeter. The registered changes of induced voltage were proportional to the change of magnetic permeability of the stretched rods. The obtained results were almost frequency-independent due to low frequency limit (250-500 Hz, weak eddy currents, no spin-origin energy dissipation). A significant magneto-mechanical hysteresis was observed slightly evolving from cycle to cycle with tendency of stabilization. The extension of basic Stoner-Wohlfarth model of magnetic permeability allowed to fit the data reproducing hysteretic behavior and considering the relaxation of the internal stress. The proposed, low-cost method is suitable in the industrial applications for stress control in large-sized steel elements.

The starting point is our previous study of influence of the internal molecular mean field of dipole‐dipole interactions on local orientation and phase transitions in polymer liquid crystal (PLC) systems of longitudinal chains.[1, 2] Electric dipoles are created by LC mesogen moieties. The longitudinal PLC is a macromolecule of consecutively copolymerized LC and flexible polymer sequences. We now amplify the model by inclusion of dipole‐external electric field interactions. We find that the external fields can seriously modify the local orientational order of the system and affect phase transition parameters dependent on that order. In particular, the external fields induce the formation of disoriented nematic phases with negative values of the second order orientation parameter 〈P2〉 for LC sequences in the longitudinal PLCs while the first order parameter 〈P1〉 is positive. However, some rapid decreases in 〈P1〉 are observed at points of positive‐to‐negative transitions of 〈P2〉; thus the LC disorientation manifests itself. The limiting case of the monomer liquid crystal (MLC) systems is included also.

Temperature studies of lattice dynamics and ionic conductivity, within the temperature range of 100 to 700 K, are performed for PbF2 and PbF2:6% LiF superionic crystals. The doped crystals exhibit a decreased activation energy of the conductivity. A decrease, by about 70 degrees, in the temperature at which the ionic conductivity changes and Raman spectra anomalies occur is observed. It is found that at temperatures significantly lower than that of the superionic state transition, the Raman line form is determined by processes of phonon scattering at thermally excited defects.

Conversion electron Mössbauer spectroscopy and magneto-optical Kerr effect were applied to investigate hyperfine interactions and macroscopic magnetic properties of Finemet-type thin films. Phase analysis as well as compositional evolution of hyperfine parameters and coercivity was performed in the range of chromium percentage 0 ≤ x ≤ 14. Essential differences in structure and hyperfine parameters were found for films of different chromium concentration. Coercivity shows non-monotonic dependence with minimal value at x = 5.