Suppression of Phase Transitions in a Confined Rodlike Liquid Crystal

Grigoriadis, Christos; Duran, Hatïce; Steinhart, Martin; Kappl, Michael; Butt, Hans‐Jürgen; Floudas, George

doi:10.1021/nn203448c

Cited by 91 publications

(107 citation statements)

References 37 publications

(61 reference statements)

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“…Both the collective orientational (isotropic-to-nematic) and the translational (smectic-toliquid or smectic-to-nematic) transitions have turned out to be significantly affected by finite size and interfacial (solid-liquid or liquid-liquid) interactions introduced by confining walls [1][2][3][4][5][6] or the geometrical constraints in nanoporous media [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

“…Thus confinement plays here a similar role as an external magnetic field for a spin system [18,29]: The strong first order I-N transition is replaced by a weak first order or continuous paranematic-to-nematic (P-N ) transition at a temperature T P N and may also be accompanied by pre transitional phenomena in the molecular orientational distribution [30]. An understanding of these phenomonenologies is of high fundament interest, for it allows to explore the validity (and break-down) of basic concepts of condensed matter science at the nanoscale [3,8,13,15,22].…”

Section: Introductionmentioning

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: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

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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“…We see that the T NI is found to reduce linearly with the inverse pore diameter as seen in the experiment [15]. Also, experimentally [15] We have also calculated molar specific heat at constant volume using Eq. (10).…”

Section: Calculations and Resultsmentioning

confidence: 57%

“…Experiments show that the confinement imposed by the rigid AAO pore walls can suppress phase transitions [13,14]. The nematic-to-isotropic, crystal-to-nematic, and supercooled liquid-to-glass temperatures are studied in the * corresponding author; e-mail: govindas63@gmail.com liquid crystal 4-pentyl-4 -cyanobiphenyl (5CB) confined in self-ordered nanoporous alumina and the nematic-toisotropic and the crystal-to-nematic transition temperatures are found to reduce linearly with the inverse pore diameter [15].…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of Nematic to Isotropic Transition in Porous Media

Govind¹,

Banerjee

2016

Acta Phys. Pol. A

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Experimental observations show that the N-I transition temperature (TNI) for liquid crystals embedded in solid porous materials is lower compared to that of the bulk liquid crystals and TNI is reduced linearly with the inverse pore diameter. To explain this, various theoretical studies have been proposed. We propose to use the mean field approach. We modify the Maier-Saupe mean field theory to include the disordering effects of porosity as a disordering surface potential. A molecule near the surface is assumed to feel the mean field potential (the Maier-Saupe type) and also the surface induced potential. We calculate the values of the nematic order parameter and hence find the TNI for different pore diameters. The weighted average of the order parameter is calculated considering the cylindrical symmetry of the pores. Our calculations on the variation of TNI with pore diameter agree with experimental data. Also, the calculated values of specific heat peak decrease with decrease in pore radius, in agreement with experimental trends.

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Suppression of Phase Transitions in a Confined Rodlike Liquid Crystal

Cited by 91 publications

References 37 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

Theoretical Study of Nematic to Isotropic Transition in Porous Media

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