Deuteron spin-lattice relaxation mechanisms in partially deuterated nematic MBBA

Abstract

The frequency and temperature dependence of the spin-lattice relaxation time, T1, of the various benzene ring deuterons in partially deuterated pmethoxybenzylidene-p-n-butylaniline have been measured. It was found that in the nematic phase the deuteron 7'1 is independent of frequency between 4 and 41 MHz and thermally activated. The results seem to demonstrate that benzene ring rotation is the dominant deuteron relaxation mechanism in the MHz region and that the aniline and benzylidene rings reorient at different rates around the para axes.

Rotational diffusion of asymmetric molecules in liquid crystals: A global analysis of deuteron relaxation data

“…2 and by listing the prefactor a DF ͑␣ϭ0.09 is assumed͒ for director fluctuations in Table I. The present analysis seems to indicate that the relaxation data of 5O.7 could better be reproduced by the rotational diffusion of an asymmetric rotor, 25 in the magnitude of D Ќ value seems to exist. It is for this reason that we have not used the pre-exponentials as our target parameters.…”

Deuteron NMR relaxometry applied to confined liquid crystals

“…In addition, deuteron NMR relaxometry gives an insight into the mobility of liquid-crystal molecules in a broad frequency range from about 105 to 10" Hz. With this method, correlation times associated with fast molecular reorientations and conformational changes were determined [8][9][10][11][12] as well as collective orientational order fluctuations, specific for the liquid-crystalline state [13].…”