Tests of the tricritical point in the SmA-to-N phase transition of binary mixtures of butyloxybenzylidene octylaniline and hexyloxybenzylidene octylaniline

Abstract

The present work arises from the significant difference between the experimental Landau tricritical point (LTCP) in the Sm A-to-N phase transition in binary mixtures of butyloxybenzylidene octylaniline (4O.8) and hexyloxybenzylidene octylaniline (6O.8) predicted by Stine and Garland, and that arising from the thermodynamic assessment using the Oonk's Equal Gibbs Curve method. By use of specific heat measurements the 4O.8 + 6O.8, phase diagram has been determined anew. The results of the subsequent application of Oonk's thermodynamic analysis are discussed and their compatibility with the behaviour universally exhibited by other liquid crystal binary mixtures for which a LTCP in the SmA-to-N phase transition has been experimentally determined are analysed.

Keywords:

• binary mixtures
• composition–temperature diagrams
• Landau tricritical point
• SmA-to-N phase transition
• Halperin–Lubensky–Ma theory

Acknowledgements

The authors are grateful for financial support from the MICINN of Spain (project MAT2009–14636–C03–01,02,03) and from the Gobierno Vasco (project GI/IT–449–10). The authors also wish to acknowledge the recognition given by the Govern de la Generalitat de Catalunya of GRPFM as an Emergent Research Group (2009–SGR–1243).