Showing papers by "Grzegorz Czechowski published in 2005"
TL;DR: In this paper, the structural transitions in ferronematic based on 8CB and 6CHBT, exposed to combined electric and magnetic fields, were investigated and the influence of the presence of magnetic admixture on the Fredericksz transition threshold was studied.
32 citations
TL;DR: In this article, the rotational diffusion process in the vicinity of the I-N phase transition in comparison to the N-SA phase transition has been investigated and it is shown that the fractal parameter α is temperature dependent with an extremely sharp variation at the I−N transition point in the form of a lambda-like profile.
Abstract: Dielectric relaxation measurements are performed with very high accuracy on a liquid crystalline compound n-octylcyanobiphenyl (8CB) in the isotropic (I), nematic (N) and smectic A (SA) phases. The data obtained display an essential difference in the rotational diffusion process in the vicinity of the I–N phase transition in comparison to that taking place in the vicinity of the N–SA phase transition. Thus, for the I–N transition, anomalously slow diffusion (subdiffusion), characterized by an anomalous coefficient α<1, is observed, while normal Brownian rotational diffusion with is found for the N–SA transition. It is also shown how the fractal parameter α is temperature dependent with an extremely sharp variation at the I–N transition point in the form of a lambda-like profile.
21 citations
TL;DR: It seems to be important that the fitting-determined temperatures of the virtual second-order transition in the solutions, T*, correspond well to the experimentally observed low-temperature limits of the two-phase isotropic+nematic region.
Abstract: Static dielectric measurements are performed in the temperature range of the isotropic-nematic phase transition of binary mixtures of mesomorphic n-heptylcyanobiphenyl (7CB) and nonmesomorphic: (a) n-heptylcyanophenyl (7CP) and (b) carbon tetrachloride (CCl4) , the solutes of different molecular shape and polarity. In the whole studied range of the solutes mole fraction (x) (x(max) approximately equal to 0.17) , the critical-like temperature behavior of the permittivity in the vicinity of the transition from the isotropic phase to the two-phase (nematic+isotropic) region can be well described with a critical exponent close to 0.5, as in a pure 7CB, indicating the tricritical nature of the transitions. It seems to be important that the fitting-determined temperatures of the virtual second-order transition in the solutions, T*, i.e., the temperature limit of the thermodynamic stability of supercooled isotropic phase, correspond well to the experimentally observed low-temperature limits of the two-phase isotropic+nematic region.
10 citations
TL;DR: Linear dielectric relaxation studies performed on two isotropic liquids showed that, at given temperature, the relaxation times corresponding to the rotation around the short axis of the two kinds of molecules coincide to each other, regardless the polarity of the molecules and their abilities to accomplish dipolar aggregation.
Abstract: Linear dielectric relaxation studies performed on two isotropic liquids composed of the molecules of the same moment of inertia and a quite different polarity: C10H21-O-Ph-COO-Ph-CN (the dipole moment of about 5 D) and C10H21-O-Ph-OOC-Ph-CN (2.5 D) showed that, at given temperature, the relaxation times corresponding to the rotation around the short axis of the two kinds of molecules coincide to each other, regardless the polarity of the molecules and their abilities to accomplish dipolar aggregation. The studies allow one to estimate the lifetime of the intermolecular aggregates due to the dipolar interactions in liquids as no longer than 0.1 ns.
4 citations