Room-Temperature Bicontinuous Cubic Phase Formed by Eutectic Mixtures Showing a Strong Adhesive Property

While mixing of several liquid crystalline (LC) components is a good method to extract excellent properties, there have been no successful applications to bicontinuous cubic (Cub_bi) LC materials of isotropically extended three-dimensional networks. We realized a Cub_bi-phase eutectic mixture at around room temperature. Two kinds of binary mixtures of aryloylhydrazine-based compounds were examined, where one component was a nonazo Cub_bi phase-forming compound and the other was two kinds of azo compounds with and without a methyl group at the 2-position of the outer ring in the azobenzene moiety. Both binary mixtures form a Cub_bi phase in their middle composition ranges, but the temperature ranges are markedly different. In the case of the mixture with the azo compound without a methyl group, the Cub_bi-phase temperature range is narrow and limited between 380 and 430 K. In contrast, the mixture with the 2-methyl azo compound is a eutectic mixture of the Cub_bi phase around a molar ratio of 1:1, which expands from 435 K to below room temperature when cooled from the melt. The dynamic viscoelastic measurements revealed a high storage modulus of 2 MPa in the range 300-390 K. This finding encouraged us to examine the adhesion test for the mixture, which uncovered unprecedentedly strong adhesion to glass plates (showing a shear stress at a break of 7 MPa at 298 K). The obtained results indicate that both fluidic and elastic natures of the <i>Ia</i>3̅<i>d</i> Cub_bi LC phase of isotropically extended 3D networks are important for the adhesion property.