J. Phys. II France
Volume 2, Numéro 2, February 1992
Page(s) 219 - 225
DOI: 10.1051/jp2:1992125
J. Phys. II France 2 (1992) 219-225

Proton NMR studies in some cyano-biphenyls, oxy-cyano-biphenyls and PAA at atmospheric pressure

S. K. Roy

Department of Physics, Jadavpur University, Calcutta 700032, India

(Received 30 May 1991, accepted 28 October 1991)

Depolar splitting $\Delta H$ from proton-NMR experiments in 5-8CB, 5-8 OCB and PAA are presented and compared with the quantity $\Sigma$, calculated from refractive index data, in the same set of compounds obtained by Bunning et al. [3]. According to these authors the quantity $\Sigma$ is rather insensitive to the biaxial terms in the ordering matrix and gives the best indication currently available of the temperature dependence of Szz in these materials. Szz can be reliably determined from NMR measurements on suitably deuterated specimens but among the compounds discussed in this paper only 5CB and PAA has so far been studied in this way. The values of Szz for these compounds are compared with $\Sigma$ and the variation is found to be slight (within 3 %). Because of the involvement of the chain protons, in the proton NMR of the undeuterated specimens it is not obvious that $\Delta H$ should be closely proportional to Szz, but for 5CB and PAA it seems to be so (again within 3 %). For 6CB too $\Delta H/\Sigma$ is almost constant but for other compounds a systematic rise on cooling is apparent.

64.00 - 61.30

© Les Editions de Physique 1992