Deuteron NMR relaxometry applied to confined liquid crystals

We discuss the capability of deuteron nuclear magnetic resonance (NMR) spec troscopy and relaxometry to reveal molecular ordering and dynamics in confi ned liquid crystals. The attention is focused on the high-temperature phase above the nematic-isotropic transition, which is - in the absence of the l ong-range orientational order - very suitable for the study of surface inte ractions. Deuteron NMR spectra and relaxation rates are presented for two r epresentatives of confined liquid-crystal systems: 8CB in cylindrical cavit ies of Anopore membranes and 5CB with an embedded polymer network. A substa ntial increase in the transverse spin relaxation rate, stimulated by the su rface-induced order in enclosures, has been observed. In cylindrical caviti es, it exhibits a strong temperature dependence on approaching the phase tr ansition, whereas in the polymer network dispersion it is temperature-indep endent. The increase of T-2(-1) provides information on the effect of spati al constraints on molecular mobility and on the surface orientational order parameter. Using deuteron relaxometry. one can measure the degree of orien tational order in the isotropic phase not only in cylindrical but also in s pherical cavities and enclosures of irregular shape, where the standard app roach based on quadrupolar splitting of the NMR spectrum fails.