2009
DOI: 10.1063/1.3042235
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Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Abstract: Previous work showed that by means of the Jeener-Broekaert (JB) experiment, two quasiequilibrium states can be selectively prepared in the proton spin system of thermotropic nematic liquid crystals (LC) in a strong magnetic field. The similarity of the experimental results obtained in a variety of LC in a broad Larmor frequency range, with crystal hydrates, supports the assumption that also in LC the two spin reservoirs into which the Zeeman order is transferred, originate in the dipolar energy and that they a… Show more

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Cited by 8 publications
(21 citation statements)
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“…It provided a comprehensive explanation, compatible with previous experimental evidence 13,21 , on the mechanisms which turn the proton spin system density matrix of nematic LC's into a quasi-equilibrium form after an arbitrary initial coherent state . Accordingly, the decoherence process transforms the initial state into a block diagonal matrix in the eigenbasis of the spin-environment interaction Hamiltonian.…”
Section: Introductionsupporting
confidence: 67%
“…It provided a comprehensive explanation, compatible with previous experimental evidence 13,21 , on the mechanisms which turn the proton spin system density matrix of nematic LC's into a quasi-equilibrium form after an arbitrary initial coherent state . Accordingly, the decoherence process transforms the initial state into a block diagonal matrix in the eigenbasis of the spin-environment interaction Hamiltonian.…”
Section: Introductionsupporting
confidence: 67%
“…On the contrary, only two constants of motion were observed in gypsum when the magnetic field B [010] and only one at an orientation that makes the protons at the water molecules equivalent. The fact that compounds having very different numbers of interacting spins (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) in LCs and infinite in gypsum) admit the preparation of more than one dipolar QI, indicates that their occurrence is not exclusively determined by the size of the dipolar network. Instead, both the occurrence of multiple QIs and the many-spin character they show, do depend strongly on the topology of the spin network, since it determines the quantum dynamics of the spin system.…”
Section: Discussionmentioning
confidence: 99%
“…In fact, the "interpair" state observed in hydrated crystals admits multiple quantum coherences up to the fourth order on the X-basis, implying four-spin correlations. 19 Then the question arises about which are the necessary characteristics the dipolar network must have in order to admit the preparation of more-than-one dipolar QI. A coarse criterion could be (i) the occurrence of a doublet in the NMR spectrum, which generally implies the possibility of classifying the dipolar couplings according to their intensity into "strong" and "weak", and (ii) the possibility of truncating the weaker term of the dipolar Hamiltonian with respect to the stronger term.…”
Section: Discussionmentioning
confidence: 99%
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