Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

Kralj, Samo; Cordoyiannis, George; Jesenek, Dalija; Zidanšek, Aleksander; Lahajnar, G.; Novak, Nikola; Amenitsch, Heinz; Kutnjak, Zdravko

doi:10.1039/c1sm06884a

Cited by 24 publications

(19 citation statements)

References 32 publications

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“…This analysis gives T I N − T * approximately equal 3.4 K (5CB) and 3.2 K (6CB), respectively, i.e., values close to the magnitude of 3.5 K obtained for 8CB [7]. In fact, the difference T I N − T * , which defines the proximity of the system to the tricritical point, may vary, in general, under confinement conditions, as has been recently emphasized by Kralj et al [23,24]. This effect appears to be dominant if surface wetting interactions are weak, which is observed in samples containing relatively highly flexible LCs molecules, as, e.g., 12CB.…”

Section: Resultssupporting

confidence: 79%

Influence of nanoconfinement on the nematic behavior of liquid crystals

et al. 2012

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We explore the nematic ordering of the rodlike liquid crystals 5CB and 6CB, embedded into parallel-aligned nanochannels in mesoporous silicon and silica membranes as a function of mean channel radius (4.7 ≤ R ≤ .3 nm), and, thus, geometrical confinement strength, by optical birefringence measurements in the infrared region. The orientational order inside the nanochannels results in an excess birefringence, which is proportional to the nematic order parameter. It evolves continuously on cooling with a precursor behavior, typical of a paranematic state at high temperatures. These observations are compared with the bulk behavior and analyzed within a phenomenological model. Such an approach indicates that the strength of the nematic ordering fields σ is beyond a critical threshold σ(c) = 1/2 that separates discontinuous from continuous paranematic-to-nematic behavior. In agreement with the predictions of the phenomenological approach, a linear dependency of σ on the inverse channel radius is found and we can infer therefrom the critical channel radii, R(c) separating continuous from discontinuous paranematic-to-isotropic behavior, for 5CB (12.1 nm) and 6CB (14.0 nm). Our analysis suggests that the tangential anchoring at the channel walls is of similar strength in mesoporous silicon and mesoporous silica membranes. A comparison with the bulk phase behavior reveals that the nematic order in nanoconfinement is significantly affected by channel wall roughness, leading to a reduction of the effective nematic ordering.

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Section: Resultssupporting

confidence: 79%

Influence of nanoconfinement on the nematic behavior of liquid crystals

et al. 2012

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“…(ii) For relatively short molecules, as 6CB or 7CB, the strength of the first-order character of the isotropic-tonematic transition is not expected to be affected by the confinement as has been ascertained in recent theoretical studies [30,31]. This substantially simplifies the theoretical analysis based on the KKLZ approach.…”

Section: Introductionmentioning

confidence: 92%

“…Given the proximity of the system to the tricritical point, ∆T * may, in principle, vary depending on the confinement conditions. Particularly it appears to be sensitive to surface wetting interactions [30,31]. However, for relatively short and rigid nematogen molecules, such as e.g.…”

Section: Fig 6: (Color Online) Nematic Ordering Field σ Vs Mole Framentioning

confidence: 99%

Paranematic-to-nematic ordering of a binary mixture of rodlike liquid crystals confined in cylindrical nanochannels

et al. 2014

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We explore the optical birefringence of the nematic binary mixtures 6CB1−x7CBx (0 ≤ x ≤ 1) imbibed into parallel-aligned nanochannels of mesoporous alumina and silica membranes for channel radii of 3.4 ≤ R ≤ 21.0 nm. The results are compared with the bulk behavior and analyzed with a Landau-de-Gennes model. Depending on the channel radius the nematic ordering in the cylindrical nanochannels evolves either discontinuously (subcritical regime, nematic ordering field σ < 1/2) or continuously (overcritical regime, σ > 1/2), but in both cases with a characteristic paranematic precursor behavior. The strength of the ordering field, imposed by the channel walls, and the magnitude of quenched disorder varies linearly with the mole fraction x and scales inversely proportional with R for channel radii larger than 4 nm. The critical pore radius, Rc, separating a continuous from a discontinuous paranematic-to-nematic evolution, varies linearly with x and differs negligibly between the silica and alumina membranes. We find no hints of preferred adsorption of one species at the channels walls. By contrast, a linear variation of the nematic-to-paranematic transition point TPN and of the nematic ordering field σ vs. x suggest that the binary mixtures of cyanobiphenyls 6CB and 7CB keep their homogeneous bulk stoichiometry also in nanoconfinement, at least for channel diameters larger than ∼7 nm.

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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%

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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Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

Cited by 24 publications

References 32 publications

Influence of nanoconfinement on the nematic behavior of liquid crystals

Influence of nanoconfinement on the nematic behavior of liquid crystals

Paranematic-to-nematic ordering of a binary mixture of rodlike liquid crystals confined in cylindrical nanochannels

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

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