NMR study of alloys exhibiting a reentrant nematic phase

Abstract

Proton T1 was measured at 30 MHz as a function of temperature in three binary mixtures (27.7, 25.2, and 22.9 wt. % 60CB in 80CB) exhibiting a reentrant nematic phase. Proton T1 and T1D were also measured at 7.07 and 30 MHz, respectively, in 27.6 wt. % 60CB. The angular dependence of T1 was studied in the SA phase of 22.9 wt. % 60CB at 30 MHz and in the SA phase of 27.6 wt. % 60CB at 7.07 MHz. It was found that T1 and T1D show different behavior in the high temperature nematic and reentrant nematic phases. Nematic orientational order director fluctuation (ODF) and/or molecular self-diffusion are used to account for the relaxation rates in various mesophases. ODF seems to be an important relaxation mechanism in the reentrant nematic phase, while molecular self-diffusion appears to be responsible for spin relaxation in the high temperature nematic phase. It would appear that molecular dynamics for nematic and reentrant nematic phases are tied closely to the viscosity of the sample.