A proton and deuteron spin–lattice relaxation study of the partially deuterated nematogens PAA and MBBA

Abstract

Proton spin–lattice relaxation times (T1) have been measured in methyl deuterated para-azoxyanisole (PAA-d6) and in ring deuterated para-azoxyanisole (PAA-d8) samples as functions of frequency and temperature. When compared with recent order fluctuation theory, the agreement between theory and experiment is not as satisfactory for the intermolecular contribution to the spin–lattice relaxation as for the intramolecular contribution. Deuteron spin–lattice relaxation times (T1Q) have also been measured in a ring deuterated p-methoxybenzylidene p-n-butylaniline (MBBA-d8) sample. The above order fluctuation theory fails to predict the observed temperature dependence and the observed frequency independence of T1Q if the correlation time τc for local motions is taken to be one-third the dielectric relaxation time τD. However, a fair agreement is obtained if one uses τc= (1/100) τD, a value consistent with Ref. 6.

Deuteron spin-lattice relaxation mechanisms in partially deuterated nematic MBBA

“…In the nematic phase the activation energy E is 39 + 4 kJ/mole for the (b) and 42 _+ 4 kJ/mole for the (a) lines. These values can be compared with the earlier reported value [7] of E--39 kJ/mole for the average T1 from the unresolved spectrum.…”