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Domenici V. 2H NMR studies of liquid crystal elastomers: macroscopic vs. molecular properties. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 63:1-32. [PMID: 22546343 DOI: 10.1016/j.pnmrs.2011.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 07/27/2011] [Indexed: 05/31/2023]
Affiliation(s)
- Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy.
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Domenici V. Quantitative analysis of 2H NMR T1Q, T1Z and T2 relaxation times in the SmA phase of a liquid crystal dendrimer. Phys Chem Chem Phys 2009; 11:8496-506. [DOI: 10.1039/b902168j] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Dong RY, Chiezzi L, Veracini CA. Deuterium NMR relaxation in the smectic-A phase of a chiral smectogen. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:041716. [PMID: 12005855 DOI: 10.1103/physreve.65.041716] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2001] [Indexed: 05/23/2023]
Abstract
Correlated internal rotations are studied for a deuterated decyloxy chain in the chiral liquid crystal, 1-methylheptyl 4(')-(4-n-decyloxy-benzoyloxy)biphenyl-4-carboxyate (10B1M7) using deuteron spin-lattice relaxation and quadrupolar splitting measurements. The present study is limited to the uniaxial smectic-A phase of 10B1M7, in which the observed deuterium nuclear magnetic resonance spectra show well-resolved peaks. The deuteron Zeeman (T(1Z)) and quadrupolar (T(1Q)) spin-lattice relaxation times are simultaneously determined for the methylene deuterons using the Wimperis broadband pulse sequence at two different Larmor frequencies. The quadrupolar splittings at each temperature are modeled by the additive potential method to obtain the orienting potential of mean torque. A decoupled model using 683 conformations for the decyloxy chain is used to explain the observed relaxation rates. In this model, the overall reorientation is described by a small step rotational diffusion model, while both gauche migration and gauche pair production as well as the so called one- and two-bond motions are allowed to occur in the chain. Transition rates for the chain dynamics and the overall rotational diffusion constants are obtained using a global target analysis of the relaxation data of 10B1M7.
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Affiliation(s)
- Ronald Y Dong
- Department of Physics and Astronomy, Brandon University, Brandon, Manitoba, Canada R7A 6A9.
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Dong RY. An improved decoupled model for spin relaxation in 4-n-alkyloxy-4′-cyanobiphenyls. J Chem Phys 2001. [DOI: 10.1063/1.1355291] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Zakharov AV, Dong RY. Rotational viscosity, dynamic phenomena, and dielectric properties in a long-chain liquid crystal: NMR study and theoretical treatment. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:011704. [PMID: 11304275 DOI: 10.1103/physreve.63.011704] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2000] [Indexed: 05/23/2023]
Abstract
The rotational diffusion constants D(perpendicular) and D(parallel), rotational viscosity coefficients gamma(i) (i=1,2), the orientational correlation times tau(L)mn, and the dielectric permittivities for nematic liquid crystals (NLCs) are investigated. gamma(i) are calculated by a combination of existing statistical-mechanical approach (SMA) and NMR relaxation theory, both based on a rotational diffusion model. In the rotational diffusion model, it is assumed that the reorientation of an individual molecule is a stochastic Brownian motion in a certain potential of mean torque. According to the SMA, gamma(i) are found to be a function of temperature, density, rotational diffusion constant for tumbling motions, and the orientational order parameters. The order parameters and rotational diffusion constant are obtained from an analysis of NMR measurements. Reasonable agreement between the calculated and experimental values of gamma(i) for 4-n-octyloxy-4'-cyanobiphenyl (8OCB) is obtained. The orientational correlation times, and the longitudinal and transverse components of the real chi'(j)(omega) and imaginary chi"(j)(omega) (j= parallel, perpendicular) parts of the complex susceptibility tensor for 8OCB molecules in the nematic phase are also obtained.
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Affiliation(s)
- A V Zakharov
- Department of Physics and Astronomy, Brandon University, Brandon, Manitoba R7A 6A9, Canada
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Dong RY, Carvalho A, Sebastiao PJ, Nguyen HT. Deuteron NMR study of molecular dynamics in a compound exhibiting a reentrant nematic phase. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:3679-86. [PMID: 11088883 DOI: 10.1103/physreve.62.3679] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2000] [Indexed: 11/07/2022]
Abstract
A deuteron NMR study of molecular dynamics in the partial bilayer smectic A(d) and reentrant nematic phases of a pure chain-deuterated compound is presented. The deuteron spin-lattice relaxation times T(1Z) and T(1Q) were measured as a function of temperature for two different frequencies (15 and 46 MHz). The experimental results were interpreted in terms of the internal conformational motions of a chain decoupled from the molecular small-step rotational diffusion and the order director fluctuations. The latter motion was found to be essential to the fit of experimental results in the reentrant nematic phase. The fitting parameters obtained by using a global target fitting method are acceptable when compared with those obtained from other deuteron and proton NMR studies of the same mesophases.
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Affiliation(s)
- RY Dong
- Department of Physics and Astronomy, Brandon University, Brandon, Manitoba, Canada R7A 6A9
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Dong RY, Cheng M. Molecular dynamics in a mixture of 8OCB-d17 and 6OCB showing nematic and reentrant nematic phases: A deuterium nuclear magnetic resonance study. J Chem Phys 2000. [DOI: 10.1063/1.1286962] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Dong RY, Morcombe CR, Calucci L, Geppi M, Veracini CA. Conformational dynamics of a metallomesogen studied by 2H-NMR spectroscopy. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:1559-1566. [PMID: 11046437 DOI: 10.1103/physreve.61.1559] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/1999] [Indexed: 05/23/2023]
Abstract
In this work we present a quantitative analysis of both quadrupolar splittings and deuterium Zeeman and quadrupolar spin-lattice relaxation times reported in the literature for two isotopomers of Azpac, an acetylacetonate derivative of the cyclopalladated 4, 4'-bis(hexyloxy) azoxybenzene. Azpac-d(4) is deuterated at the aromatic rings and Azpac-d(26) is deuterated on the alkoxy chains. The additive potential method is used to model the splittings, while the derived spectral densities are interpreted using the decoupled model in conjunction with the Nordio model. The two side chains are assumed to be noninteracting and identical in their conformations in order to limit the size of the transition rate matrix needed to describe correlated internal bond rotations in the chains. Rotational diffusion constants and internal jump rate constants are derived for this metallomesogen.
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Affiliation(s)
- RY Dong
- Department of Physics and Astronomy, Brandon University, Brandon, Manitoba, Canada R7A 6A9
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Dong RY. Deuteron NMR study of a long-chain smectic liquid crystal: molecular order and dynamics. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:5631-8. [PMID: 11970440 DOI: 10.1103/physreve.60.5631] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/1999] [Indexed: 04/18/2023]
Abstract
Deuteron Zeeman (T(1Z)) and quadrupolar (T(1Q)) spin-lattice relaxation times and quadrupolar splittings were measured in the nematic and smectic A phases of a chain-deuterated 4-n-octyloxy-4'-cyanobiphenyl (8OCB-d17) at 15.1 and 46 MHz. To model the NMR observables, the so-called pentane effect is used to limit the number of possible conformations in the chain, and is found to be a good approximation. The additive potential method is employed to construct the potential of mean torque using the quadrupolar splittings. A decoupled model is used to describe correlated internal motions in the chain, which are independent of the molecular reorientation. The latter motion is treated using the small-step rotational diffusion model of Nordio (Tarroni and Zannoni), while the former motion is described using a master rate equation. In the nematic phase, order director fluctuations are found to be necessary. The relaxation data in both mesophases were treated using a global target method, and the derived motional parameters are acceptable in comparison with those found for 6OCB.
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Affiliation(s)
- R Y Dong
- Department of Physics and Astronomy, Brandon University, Brandon, Manitoba, Canada R7A 6A9
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Zakharov AV, Komolkin AV, Maliniak A. Rotational viscosity in a nematic liquid crystal: a theoretical treatment and molecular dynamics simulation. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 59:6802-7. [PMID: 11969667 DOI: 10.1103/physreve.59.6802] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/1998] [Indexed: 04/18/2023]
Abstract
The rotational viscosity coefficient gamma(1) of 4-n-pentyl-4(')-cyanobiphenyl in the nematic phase is investigated by combination of existing statistical-mechanical approaches (SMAs), based on a rotational diffusion model and computer simulation technique. The SMAs rest on a model in which it is assumed that the reorientation of an individual molecule is a stochastic Brownian motion in a certain potential of mean torque. According to the SMAs, gamma(1) is found to be a function of temperature, density, rotational diffusion coefficient, and a number of order parameters (OPs). The diffusion coefficient and the OPs were obtained from an analysis of a trajectory generated in a molecular dynamics simulation using realistic atom-atom interactions. In addition, a set of experimentally determined diffusion coefficients and OPs was used for evaluation of gamma(1). Reasonable agreement between calculated and experimental values of gamma(1) is obtained. It is shown that near the clearing point gamma(1) is proportional to (-)P22, where (-)P2 is the second-rank OP. This limiting value of gamma(1) is in agreement with mean-field theory.
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Affiliation(s)
- A V Zakharov
- Division of Physical Chemistry, Arrhenius Laboratory, University of Stockholm, S-10691 Stockholm, Sweden.
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Shen X, Dong RY. A comparative study of dynamics in the nematic and reentrant-nematic phases of 60CB and 60CB/80CB mixture by deuteron nuclear magnetic resonance relaxation. J Chem Phys 1998. [DOI: 10.1063/1.476364] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Dong RY, Shen X, Richards GM. Modeling molecular order and dynamics of a liquid crystal by deuteron NMR. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1995; 52:1753-1761. [PMID: 9963595 DOI: 10.1103/physreve.52.1753] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Komolkin AV, Laaksonen A, Maliniak A. Molecular dynamics simulation of a nematic liquid crystal. J Chem Phys 1994. [DOI: 10.1063/1.467460] [Citation(s) in RCA: 104] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Imbardelli D, Wazynska B, Golemme A, Chidichimo G, Dabrowski R. 2H-NMR study of molecular order and dynamics in mixtures of 8OBCAB andnTPCHB. Mol Phys 1993. [DOI: 10.1080/00268979300101971] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Vrbančič N, Vilfan M, Blinc R, Dolinšek J, Crawford GP, Doane JW. Deuteron spin relaxation and molecular dynamics of a nematic liquid crystal (5CB) in cylindrical microcavities. J Chem Phys 1993. [DOI: 10.1063/1.464074] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Conformations and dynamics of surfactants in micelles and liquid crystals by nuclear magnetic relaxation. ACTA ACUST UNITED AC 1992. [DOI: 10.1007/bf00999523] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Dolinšek J, Jarh O, Vilfan M, Žumer S, Blinc R, Doane JW, Crawford G. Two‐dimensional deuteron nuclear magnetic resonance of a polymer dispersed nematic liquid crystal. J Chem Phys 1991. [DOI: 10.1063/1.461014] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Dong RY. Model for spin relaxation by correlated internal motions in liquid crystals. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1991; 43:4310-4319. [PMID: 9905533 DOI: 10.1103/physreva.43.4310] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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