IFEG   20353
INSTITUTO DE FISICA ENRIQUE GAVIOLA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
NMR quasi-equilibria in small spin-clusters in liquid crystals
Autor/es:
BONIN C. J.; SEGNORILE H. H.; GONZÁLEZ C. E. ; ZAMAR R. C.
Lugar:
Villa Carlos Paz, Córdoba
Reunión:
Congreso; 97ª Reunión Nacional de de Física de la AFA; 2012
Institución organizadora:
A.F.A.-Filial Córdoba
Resumen:
Up to now, only two Nuclear Magnetic Resonance (NMR) spin-correlated Quasi-Equilibrium (QE) states were observed in nematic Liquid Crystals (LCs), called S and W Quasi-Invariants (QIs)—besides common uncorrelated proton Zeeman order. The former is a two-spin-correlated quantum state, while W is a multi-spin-correlated quantum state (with at least eight correlated spins). In systems with few degrees of freedom like LC systems, it is difficult to predict if those are the only QIs that can be prepared and observed, after the Jeener-Broekaert radio-frequency pulse sequence, or if it is possible to observe another QE states, either on the short or the large time scale. Consequently, we have explored in this work the possibility of extract from the experiments, and in a simple way, another QE states different from those already known in some protonated samples, dealing with powder adamantane—as a model of regularly distributed large spin network; gypsum—representing an arrangement of weakly interacting equivalent strongly-coupled spin-pairs; and 5CB and PAAd6 LCs as smaller dipole-dipole coupled spin clusters. With a simple procedure, we were able to disentangle from the experiments up to three QIs in 5CB (19 proton spins cluster) LC, besides Zeeman order. The new QIs were observed for times larger than the S and W QE states, suggesting that these ones are multi-spin-correlated QIs. These QIs do not fulfil the total QI-space of each system, since we were not able to reproduce the all time behavior of our experiments; indicating that another QIs might be extracted in further experiments. In addition, we also found that the observed echolike behavior of the time-domain signals is consequence of the capacity of the spin network to create muli-spin correlations among nuclei.