Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR

L. BULJUBASICH; G. A. MONTI; R. H. ACOSTA; C. J. BONÍN; C. E. GONZÁLEZ; R C ZAMAR

AIP

Año: 2009 vol. 130 p. 1 - 1

revious work showed that by means of the Jeener–Broekaert (JB) experiment, twoquasiequilibrium states can be selectively prepared in the proton spin system of thermotropicnematic liquid crystals (LCs) in a strong magnetic field. The similarity of the experimental resultsobtained in a variety of LC in a broad Larmor frequency range, with crystal hydrates, supports theassumption that also in LC the two spin reservoirs, into which the Zeeman order is transferred,originate in the dipolar energy and that they are associated with a separation in energy scales: Aconstant of motion related to the stronger dipolar interactions (S), and a second one (W) corresponding to the secular part of the weaker dipolar interactions with regard to the Zeeman and the strong dipolar part. We study the nature of these quasi-invariants in nematic 5CB4-pentyl-4-biphenyl-carbonitrile and measure their relaxation times by encoding themultiple-quantum coherences of t