arXiv subjects

Longin N. Lisetski

Publications and source records attributed to Longin N. Lisetski.

3 recordsLinked to original sources

arXiv2026

Broadening the temperature range of blue phases using $azo$ compounds of various molecular geometries assembled from modular "LEGO" molecular units

The temperature range of the blue phases (BPs) formed in highly chiral mixtures based on cholesteryl oleyl carbonate (COC) and the nematic liquid crystal E7 was studied in the presence of various chemical structures. The $azo$ compounds used were of both chiral and achiral nature, and their molecular geometry was modified by substitution of modular "LEGO" molecular units of varying alkyl chain lengths and types of bridging groups, which could substantially affect the mesomorphic properties of the matrix mixture. It was shown that in many cases these dopants effectively broadened the BP temperature range. This effect depends on both the variation in the molecular geometry of the $azo$ compounds and the increase in the $cis$-isomer concentration under UV irradiation. The presence of the $cis$-isomers formed have a stronger impact on broadening the BP temperature range than the initial $trans$-isomers. These results demonstrate that the temperature range of BPs can be precisely controlled via a combination of molecular engineering and $trans$-$cis$ photo-isomerization.

cond-mat.soft↗

arXiv2024

Induced smectic ordering and blue phase formation in mixtures of cyanobiphenyls and cholesterol esters

It has been found that in mixtures of nematic E7 and smectogenic cholesteryl oleyl carbonate (COC) the S$_A$-N* transition temperature is substantially (by ~20 K) increased, as compared with pure COC, at E7 concentrations around ~40%. Within the same concentration range, the isotropic transition is preceded by formation of blue phase, with its maximum width of ~3.5 K clearly correlated to the increased thermal stability of the S$_A$ phase. With other cholesterol esters or cyanobiphenyls (cholesteryl nonanoate, 5CB), this effect was either much weaker or not observed. No enhancement of smectic phase was noted when E7 was replaced by N$_{tb}$-forming nematic mixture based on CB7CB with two cyanobiphenyl moieties. Selective Bragg reflection of light (BRL) spectra were measured in all three temperature regions, including the unwinding of the cholesteric helix on cooling towards S$_A$ phase and characteristic selective BRL changes in the blue phase. In the latter case, the measured λ$_{max}$ values were dependent both on the helical twisting power in the cholesteric phase and on the lattice size and orientation in the blue phase. Also considered were the effects of ferroelectric BaTiO$_3$ nanoparticles accumulated at disclination lines upon the blue phase thermal stability.

cond-mat.soft↗

arXiv2011

Dispersions of multi-walled carbon nanotubes in liquid crystals: new challenges to molecular theories of anisotropic soft matter

Aggregation of carbon nanotubes dispersed in nematic liquid crystalline medium is discussed. A model is proposed, which assumes that the aggregates consist of a "skeleton" formed by stochastically arranged nanotubes and a "shell" ("coat") of incorporated and adjacent nematic molecules. The aggregates of this type can be considered as large quasi-macroscopic particles in the nematic matrix. The resulting composite system represents a new type of complex molecular liquids involving self-organization of particles in anisotropic medium. Many essential features and implications of the theoretical model (e.g., effects of concentration of the nanotubes, their aspect ratio and orientational order parameter on the size and fractal dimensionality of the aggregates formed, as well as on the rate of aggregation) are in good agreement with experimental data obtained by various physical methods.

cond-mat.mes-hall↗