Roto-translational diffusion of biaxial probes in uniaxial liquid crystal phases

Brognara, Andrea; Pasini, Paolo; Zannoni, Claudio

doi:10.1063/1.481087

Cited by 14 publications

(8 citation statements)

References 32 publications

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“…4,5 In this case the mean-field potential, which depends on both the molecular orientation and the displacement within the smectic layers, is the main source of coupling between these degrees of freedom and for this reason the roto-translational coupling in the diffusion tensor was neglected. 4,5 In this case the mean-field potential, which depends on both the molecular orientation and the displacement within the smectic layers, is the main source of coupling between these degrees of freedom and for this reason the roto-translational coupling in the diffusion tensor was neglected.…”

Section: Introductionmentioning

confidence: 99%

Molecular diffusion in liquid crystals and chiral discrimination. I. Theory

Frezzato

Moro

Zannoni

2005

The Journal of Chemical Physics

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The possibility of using cholesteric phases for discriminating enantiomers of a chiral solute on the basis of their different transport properties, motivates the investigation of the translational diffusion by taking fully into account the roto-translational coupling. In this article a detailed theoretical analysis is presented for the transport properties evaluated according to the asymptotic limit of the mean-squared displacement. A general relation is derived for the transport coefficients, having as main ingredients the mean-field potential due to the mesophase, and the diffusion tensor with its purely translational and rotational components, and with the blocks describing the roto-translational coupling. The application of the theory to nematic phases shows that the roto-translational coupling generates a dynamical contribution reducing the transport coefficients evaluated by taking into account only the translational diffusion components in the center of diffusion. The theory is also specialized to a cholesteric phase with a given helical pitch for the director arrangement, in a form which is suitable for calculations of model systems of chiral solutes to be presented in a forthcoming paper.

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Section: Introductionmentioning

confidence: 99%

Molecular diffusion in liquid crystals and chiral discrimination. I. Theory

Frezzato

Moro

Zannoni

2005

The Journal of Chemical Physics

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“…The main point we would like to emphasise is that the analysis of the molecular roto-translational dynamics in layered structures, which in the past has been developed for uniaxial Sm-A phases [8,9], can be extended to biaxial Sm-C phases. This, however, requires appropriate models of the mean-field potential taking into account the molecular features and the peculiarities of the layer organization.…”

Section: Discussionmentioning

confidence: 99%

“…It should be emphasized that complete averages have been employed in Eq. (9). On the other hand, if conditional averages Eq.…”

Section: Equilibrium Distributionsmentioning

confidence: 94%

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Roto-Translational Diffusion in Smectic-C Liquid Crystals

Frezzato

Moro

2003

Molecular Crystals and Liquid Crystals

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Roto-translational diffusion of uniaxial molecules has been investigated in smectic-C (Sm-C) phases. A modified version of the McMillan mean-field potential has been adopted to describe the tilted monoclinic symmetry of the Sm-C domains with respect to the Sm-A. The roto-translational dynamics have been modeled as a diffusive stochastic process, and the relevant first-and second-rank rotational correlation functions used to describe spectroscopic experiments (dielectric relaxation and magnetic resonance respectively) have been calculated. The model calculations show that some peculiar features of the relaxation processes in Sm-C phases emerge in the comparison of the same observables evaluated for phases with different symmetry, and this could suggest new and specific methods of analysis for the experiments on biaxial smectics.

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“…on the determination of the order parameters and orientational dynamics of solutes (molecular probes) dissolved/dispersed into an anisotropic medium. Just to give a few examples, we mention here the maximum entropy techniques for extracting conformational information on flexible molecules [2][3][4], the analysis of fluorescence depolarisation data in liquid crystals [5,6], and more in general the theoretical treatment of rotational-translational diffusion for biaxial molecules in uniaxial and biaxial phases [7][8][9][10][11][12]. Claudio was so keen on putting at test those theories that he also developed an experimental research line within his group, together with Riccardo Tarroni and Alberto Arcioni, to study order and dynamics in various complex anisotropic systems using fluorescence depolarisation measurements [13,14] and ESR based on spin probes [15][16][17].…”

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confidence: 99%