Molecular dynamics of a short-range ordered smectic phase nanoconfined in porous silicon

Guégan, Régis; Morineau, Denis; Lefort, Ronan; Moréac, Alain; Béziel, Wilfried; Guendouz, Mohammed; Zanotti, Jean-Marc; Frick, B.

doi:10.1063/1.2435366

Cited by 41 publications

(40 citation statements)

References 43 publications

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“…[24,44,71,72] Albeit the simulation studies indicate a rather smooth transition in the molecular mobility [44,71,72] between the interface region and the core, whereas according to our experiments this transition is quite sharp, resulting in a very distinct monolayer and core behaviour. Moreover, our filling-fraction dependent experiments provide information on the thermotropic orientational order as a function of mesoscopic arrangement of the nematic liquid in the channels (capillary-and film-condensed states).…”

Section: Discussionmentioning

confidence: 50%

“…However, the detailed partitioning, the evolution of the relaxation behaviour and the superposition of the distinct relaxation contributions of LCs as a function of the filling of nanoporous media has been elusive so far and also controversially discussed [44,71,72]. Here we employ dielectric relaxation spectroscopy on an archetypical rod-like liquid crystal (7 CB) confined in an array of isolated channels of approximately 7 nm radius in a monolithic silica membrane.…”

Section: Fig 1: (Color Online)mentioning

confidence: 99%

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Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

et al. 2015

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We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica nanochannels. In the film-condensed regime, a slow interface relaxation dominates the dielectric spectra, whereas from the capillarycondensed state up to complete filling an additional, fast relaxation in the core of the channels is found. The temperature-dependence of the static capacitance, representative of the averaged, collective molecular orientational ordering, indicates a continuous, paranematic-to-nematic (P-N) transition, in contrast to the discontinuous bulk behaviour. It is well described by a Landau-deGennes free energy model for a phase transition in cylindrical confinement. The large tensile pressure of 10 MPa in the capillary-condensed state, resulting from the Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts for a downward-shift of the P-N transition and an increased molecular mobility in comparison to the unstretched liquid state of the complete filling. The strengths of the slow and fast relaxations provide local information on the orientational order: The thermotropic behaviour in the core region is bulk-like, i.e. it is characterized by an abrupt onset of the nematic order at the P-N transition. By contrast, the interface ordering exhibits a continuous evolution at the P-N transition. Thus, the phase behaviour of the entirely filled liquid crystal-silica nanocomposite can be quantitatively described by a linear superposition of these distinct nematic order contributions.

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Section: Discussionmentioning

confidence: 50%

Section: Fig 1: (Color Online)mentioning

confidence: 99%

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

et al. 2015

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“…Both the collective orientational (isotropic-to-nematic) and translational (smectic) transitions have turned out to be significantly by finite size, quenched disorder and interfacial (solid-liquid) interactions introduced by the confining solid walls or the pore topology [1][2][3][4][5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Thermotropic nematic order upon nanocapillary filling

et al. 2013

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Optical birefringence and light absorption measurements reveal four regimes for the thermotropic behavior of a nematogen liquid (7CB) upon sequential filling of parallel-aligned capillaries of 12 nm diameter in a monolithic, mesoporous silica membrane. No molecular reorientation is observed for the first adsorbed monolayer. In the film-condensed state (up to 1 nm thickness) a weak, continuous paranematic-to-nematic (P-N) transition is found, which is shifted by 10 K below the discontinuous bulk transition at TIN =305 K. The capillary-condensed state exhibits a more pronounced, albeit still continuous P-N reordering, located 4 K below TIN. This shift vanishes abruptly on complete filling of the capillaries. It could originate in competing anchoring conditions at the free inner surfaces and at the pore walls or result from the 10 MPa tensile pressure release associated with the disappearance of concave menisci in the confined liquid upon complete filling. The study documents that the thermo-optical properties of nanoporous systems (or single nano-capillaries) can be tailored over a surprisingly wide range simply by variation of the the filling fraction with liquid crystals.

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“…Concerning dynamics, some striking similarities between confined LCs and glass-forming systems are reported in many studies, such as a non-Debye character of the relaxation decay and a non-Arrhenius temperature dependence of the relaxation time [33][34][35]. Elastic fixed window neutron backscattering experiments on 8CB confined in silicon nanochannels are shown in Fig.…”

Section: Dynamics Of Nanoconfined Liquid-crystalsmentioning

confidence: 99%

Physics of fluids confined in nanochannels: A shared space for neutrons and simulation

Morineau¹

2011

Journées de la Neutronique

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Abstract. Manipulating fluids at the nanoscale by geometrical confinement is a major issue of contemporary condensed matter science. It is also an area of research where the complementarity of neutron scattering and molecular simulation is particularly apparent. In the present contribution, we consider different cases from the recent literature, where structural (diffraction) and dynamical (quasielastic scattering) investigations by neutron methods can benefit from realistic (atomistic) and coarse-grained molecular simulations, and viceversa. We will emphasize the special benefits and the limitations of each type of approach with the ultimate hope to inspire more scientists to bridge the gap between experiments and simulation.

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Molecular dynamics of a short-range ordered smectic phase nanoconfined in porous silicon

Cited by 41 publications

References 43 publications

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

Thermotropic nematic order upon nanocapillary filling

Physics of fluids confined in nanochannels: A shared space for neutrons and simulation

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