NMR measurement of smectic ordering and nematic-smectic-A coupling in a liquid crystal

The nuclear magnetic resonance (NMR) spectra of three substituted benzenes as solutes in the liquid crystal 8CB were investigated. The orientational order of all solutes was obtained in the nematic and smectic-A phases. A change in temperature dependence of orientational ordering was observed at the nematic to smectic-A phase transition. We analyzed these results via Kobayashi-McMillan theory applied to solutes, i.e. by incorporating smectic-A layering and nematic smectic-A coupling into a mean-field orientational Hamiltonian. By fitting to experiment, we fully determined Hamiltonian prefactors. The nematic smectic coupling, determined for the first time by NMR, appears solute independent. Solute smectic-A order parameters were self-consistently determined. (C) 2004 Published by Elsevier B.V.