Randomly constrained orientational order in porous glass

Iannacchione, Germano S.; Crawford, G. P.; Žumer, S.; Doane, J. William; Finotello, Daniele

doi:10.1103/physrevlett.71.2595

Cited by 218 publications

(111 citation statements)

References 20 publications

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“…often pre-smectic behaviour is ob- * E-mail: andriy.kityk@univie.ac.at, patrick.huber@tuhh.de servable far above the bulk nematic-to-smectic A transition. [7,25] It has also been shown experimentally [12,26,27], in agreement with expectations from theory [7,28], that there is no "true" isotropic-nematic (I-N) transition for LCs spatially restricted in at least one direction to a few nanometers. The molecular anchoring at the confining walls, quantified by an interfacial field, imposes a partial orientational, that results in a partially nematic ordering of the confined LCs, even at temperatures T far above the bulk I-N transition temperature T b IN .…”

Section: Introductionsupporting

confidence: 73%

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: Introductionsupporting

confidence: 73%

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

et al. 2015

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“…Then the transition is rendered continuous with a paranematic high-temperature phase, where even at highest temperatures the pore walls (anchoring fields) induce a residual collective orientational, paranematic order and no isotropic liquid is observable [4,7,8,12].…”

Section: Introductionmentioning

confidence: 99%

“…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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“…3 This has ramifications for a wide variety of fields, including geology, 4 biology, 5−7 chemical engineering, 8 and supramolecular chemistry. 9 Still, little is known, let alone understood, about the effects of confinement on fluids in tubes that are so thin that only a single file of fluid molecules fit in.…”

Section: ■ Introductionmentioning

confidence: 99%

Probing Weak Intermolecular Interactions in Self-Assembled Nanotubes

Bouteiller

Schoot

2012

J. Am. Chem. Soc.

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Extreme confinement affects the physical properties of fluids, but little quantitative data is available. We report on studies of a bisurea compound that self-assembles into nanotubes to probe solvent confinement on the angstrom scale. By applying a statistical model to calorimetric data obtained on solvent mixtures, we show that the thermodynamic stability of the nanotubes is an extremely sensitive function of the solvent composition because solvent interactions inside and outside of the nanotubes are different. We are able to measure energetic effects as small as 0.01 kT and relate them to the differences in molecular structure of the solvents.

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Randomly constrained orientational order in porous glass

Cited by 218 publications

References 20 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

Probing Weak Intermolecular Interactions in Self-Assembled Nanotubes

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