Frequency Dependent Selective Relaxation Studies of Deuterons in Liquid Crystals

Abstract

Using a novel field-cycling spectrometer with a fast switchable 1.2 T detection field and fast Fourier transform data processing capabilities, frequency dependent selective deuteron T1 relaxation measurements were performed for several deuterated nematic liquid crystals (e.g. PAA, MBBA), and also for some deuterated solutes in a nematic solvent (e.g. p-xylene in MBBA), over the broad Larmor frequency range from v ≈ 400 Hz to 7.5 MHz ¹). Compared with previous proton relaxation dispersion work of the same non-deuterated systems, the longitudinal deuteron relaxation time shows a remarkably small dependence on the frequency, particularly above v ≈ 20 kHz, and it does not clearly reveal in any case the square-root law contribution T₁ ~ v ^1/2 to be expected from collective molecular reorientations, and well-established by proton studies. The strongest variations, namely by factor of up to 10, occur typically below 20 kHz, where the Zeeman and quadrupolar energies of deutoron spins become comparable.