Smectic A: cholesteric phase transition investigated by small angle X-ray diffraction and viscosity measurements

• Published in: Brazilian journal of physics Vol. 32; no. 2b; pp. 495 - 500
• Main Authors: Duarte, E. L., Itri, R., Sampaio, A. R., Simões, M., Palangana, A. J.
• Format: Journal Article
• Language: English; Spanish; Portuguese
• Published: Sociedade Brasileira de Física 01.06.2002
• Subjects: Física; PHYSICS, MULTIDISCIPLINARY
• ISSN: 0103-9733; 1678-4448; 1678-4448
• DOI: 10.1590/S0103-97332002000300007

We have studied the in influence of the mean molecular length on the nature of the cholesteric (N*) – smectic A (A) liquid crystal phase transition for thermotropic compounds of cholesteryl myristate (C14), cholesteryl nonanoate (C9), and binary mixtures of C14 – C9 and cholesteryl caproate (C6) phase (dA), the mean molecular length ( ) in the N* domain, and the correlation length (epsilon), as well as changes along the N* – A phase transition, were determined from the X-ray diffraction data. The results show a decrease in A phase domain and an expansion of the N* – domain as the mean molecular length is diminished. Such effect induces a second order A – N* phase transition for a particular mixture of 63.1 mol% of C9 and 36.9 mol% of C6, evidenced by viscosity measurements in good agreement with previous density data.