Molecular motions in thermotropic liquid crystals studied by NMR spin-lattice relaxation

Zamar, R. C.; González, C. E.; Mensio, O.

doi:10.1590/s0103-97331998000400007

Cited by 3 publications

(1 citation statement)

References 17 publications

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“…Consequently, the T LC 1 is driven by these motions [247]. NMR studies of the bulk LC materials show that the T LC 1 relaxation is a function of the Larmor frequency (γ L ) [246].…”

Section: Comparison With Bulk Nmr Of 8cb Lcmentioning

confidence: 99%

Quantum Sensing with NV Centers in Diamond

Kumar¹

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This thesis is concerned with studies involving quantum sensing based on Nitrogen-Vacancy (NV) center in diamond. Essentially, it attempts to address two important problems. First, enhancing the sensitivity of a single NV center to external static magnetic fields, and second, probing the phase transitions in a soft condensed matter system using a near surface NV center. NV center's sensitivity to time-varying or AC external magnetic fields is in the range of a few nT and is limited by coherence time of NV. For various applications, including the bio-magnetic measurements, it is necessary to sense nearly static or DC fields rather than the AC fields. However, in diamond samples with natural abundance 13 C concentration (1.1%), the best reported sensitivity to DC fields is in µT range and is limited by short lived spin dephasing time of NV. In the present work, a novel hybrid magnetometer consisting of a ferromagnetic material and a single NV center is utilized to achieve DC field sensitivity down to tens of nT. The ferromagnetic material exhibits a property known Giant magneto-impedance (GMI) and is sensitive to DC fields under certain conditions. The achievable sensitivity of GMI sensors is in the range of pT. By positioning a GMI microwire in close vicinity of a NV center, magnetic interaction between the microwire and NV center can be realized. In the presence of minute changes in the DC fields in the surroundings, the GMI wire responds and encodes information to the NV center. By employing a standard magnetometry sequence on NV this information can be readout. As the sequence relies on long lived NV coherence time, its overall sensitivity could be enhanced by over two orders of magnitude. Second study deals with detecting the temperature driven phase transitions in a soft matter system, namely a liquid crystal (LC) material. The chosen LC material shows distinct ordered phases close to room temperature. By varying the temperature, transitions from solid-like phases to liquid-like phases in a thin layer of LC can be induced. The NV sensors located at a few nm depths detect these transitions in terms of changes in the spin noise signal emanating from nanoscopic volumes containing LC molecules above the diamond surface. Temperature plays a key role in determining the soft matter properties. Since NV centers are also known as nanoscale temperature sensors, it is possible to tune the temperature precisely to the transition points. This way, NV based method is demonstrated as a dual mode sensing for studying soft matter systems at nanoscale, with a control over temperature. The work aims at extending NV centers as novel probes for exploring soft matter systems and address some important questions in that area.

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“…Consequently, the T LC 1 is driven by these motions [247]. NMR studies of the bulk LC materials show that the T LC 1 relaxation is a function of the Larmor frequency (γ L ) [246].…”

Section: Comparison With Bulk Nmr Of 8cb Lcmentioning

confidence: 99%

Quantum Sensing with NV Centers in Diamond

Kumar¹

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Optical detection of heterogeneous single molecule diffusion in thin liquid crystal films

Schulz

Täuber

Friedriszik

et al. 2010

Phys. Chem. Chem. Phys.

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Lateral diffusion of three different dye molecules (terrylene and two perylene diimides) in 4 to 225 nm thin films of 8CB liquid crystals in the smectic-A phase has been investigated on a single molecule level. The influence of film thickness on tracer diffusion can be qualitatively modeled by a hydrodynamic approach. Molecular tracking experiments as well as fluorescence correlation (FCS) studies reveal the presence of diffusion dynamics which span a range of at least more than one order of magnitude in time, which is much larger than the reported anisotropic self-diffusion observed for 8CB bulk samples. We tentatively assign the heterogeneity to the formation of diffusion limiting domains on a micrometer scale within the 8CB films or at the interfaces.

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Nuclear magnetic resonance proton dipolar order relaxation in the selectively deuterated nematic para-azoxyanizole

Mensio

Zamar

Pusiol

et al. 1999

The Journal of Chemical Physics

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Larmor frequency dependent measurements of Zeeman (T1Z) and dipolar order (T1D) relaxation times provide experimental information on the molecular dynamics in liquid crystals. However, at present, a comprehensive theoretical expression relating T1D with the spectral densities of the molecular motions is not available for liquid crystals. In fact, recent relaxation studies in nematic thermotropic liquid crystals have shown that the traditional model of isolated phenyl proton pairs predicts a relaxation of the dipolar order noticeably slower than the observed one. In this work we show that the failure cannot be assigned exclusively to the assumption of isolated spin-pairs. With this aim, we study the dipolar order relaxation in the nematic PAAd6 (methyl deuterated para-azoxyanizole). After calculating a generalized expression for T1D valid for an arbitrary number of spins, we found that the contributions from multispin interactions and correlations are negligible. This means that, from the point of view of the traditional weak collision theory of relaxation, PAAd6 provides an example of an ensemble of isolated spin-pairs. Nevertheless, after measuring T1D over a broad frequency range (103–3×107 Hz), we found a faster relaxation than predicted by the two-spin model, even in this compound. We conclude, therefore, that the failure of the model should be ascribed to basic assumptions of the traditional semiclassical model of spin-lattice relaxation in liquid crystals

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Molecular motions in thermotropic liquid crystals studied by NMR spin-lattice relaxation

Cited by 3 publications

References 17 publications

Quantum Sensing with NV Centers in Diamond

Quantum Sensing with NV Centers in Diamond

Optical detection of heterogeneous single molecule diffusion in thin liquid crystal films

Nuclear magnetic resonance proton dipolar order relaxation in the selectively deuterated nematic para-azoxyanizole

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