Nanophase Segregation of Nonpolar Solvents in Smectic Liquid Crystals of Bent-Shape Molecules

Instituto de Fi´sica, Universidade de Sa ˜o Paulo, Caixa Postal 66318, 05315-970, Sao Paulo, SP, Brazil~Received 21 February 2002; published 24 September 2002!Electro-optical, calorimetric, x-ray, and dielectric measurements are reported on a mixture containing abent-core liquid crystal 4-chloro-1,3-phenylinebis@4-~4-n-tetradecyloxyphenyliminomethyl! benzoate# mixedwith the nonpolar solvent n-hexadecane~HEX!. It is observed that the addition of HEX depresses the isotropic-to-smectic phase transition temperature, but the crystallization temperature does not change considerably.Instead, the texture of the crystalline phase changes and, at sufficiently high concentrations of HEX(.20 wt %), an optically isotropic phase appears. Above 40 wt % HEX concentrations, the mesophase com-pletely disappears and a direct isotropic solid-to-isotropic liquid transition takes place. At increasing HEXconcentration, the transition enthalpies, the layer ordering, and the magnitude of the electric polarizationdecrease. X-ray studies reveal that HEX molecules pack in between the smectic layers, resulting in an increaseof the layer spacing by about 3 A. The increase of the layer spacing saturates at 5 wt % of HEX. The phasesegregation observed seems to be due to steric interactions between the flexible HEX molecules and the rigidbent cores of the liquid crystal molecules.DOI: 10.1103/PhysRevE.66.031708 PACS number~s!: 61.30.Eb, 61.30.Cz, 61.30.GdI. INTRODUCTION