A sequence of seven nematic phases has been observed in chiral mesogenic dimers, having odd number of carbon atoms in the spacer, thus a bent shape. The highest temperature phase is a chiral nematic (cholesteric) phase on heating or blue phases on cooling. The lowest temperature nematic phase expels the chiral twist and exhibits spontaneous bent-splay modulation. Fig. 1 General molecular structure of studied dimers.

Systematic studies on three dimensionally ordered liquid crystalline phases of different cubic and tetragonal symmetries are presented. The structures of the phases are determined by reconstruction of the electron density distribution from the X-ray diffraction patterns. The known models for electron densities in cubic structures were used whereas a new theoretical model for the structure of the tetragonal phase, which shows good agreement with the experimentally obtained electron densities, was proposed. For the first time a continuous phase transition between three dimensional phases with tetragonal and monoclinic symmetries was observed for an optically pure compound.

The magnetic-field-induced birefringence in a ferrofluid composed of spherical cobalt nanoparticles has been studied both experimentally and theoretically. The considerable induced birefringence determined experimentally has been attributed to the formation of chains of nanoparticles. The birefringence has been measured as a function of the external magnetic field and the volume fraction (f) of nanoparticles. It is quadratic in f as opposed to the Faraday effect, which is linear in f. Experimental results agree well with the theoretical model based on a simple density functional approach. For dilute solutions the experimental results can be explained by assuming that only dimers of nanoparticles are formed while the concentration of longer chains is negligible.

Glassy carbon electrodes modified with films composed of a network of single-wall carbon nanotubes (SWCNTs) and liquid-crystalline cubic phase were used for dioxygen reduction catalyzed by laccase. In the presence of pristine SWCNTs, the overpotential of dioxygen reduction was decreased by 0.5 V (E 1/2 ¼ À 0.09 V). Adding laccase to the system shifted the potential of oxygen reduction to þ 0.52 V vs. Ag/AgCl reference electrode. Carbon nanotubes increased the electrode working area and improved the conductivity of the film. The current density of oxygen reduction was further enhanced by using a common mediator, 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS). Two procedures for modifying carbon nanotubes with ABTS were compared: by adsorption and by covalent binding. Covalent binding of ABTS to the nanotubes is advantageous since it completely eliminates leaching of mediator to the solution and leads to a stable biocathode system.

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