Measurement of orientational order and mobility of a nematic liquid crystal in random nanometer confinement

Cramer, Ch.; Cramer, Th.; Kremer, Friedrich; Stannarius, Ralf

doi:10.1063/1.473425

Cited by 86 publications

(33 citation statements)

References 49 publications

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“…A sizeable number of studies on LCs in porous media evidently document that the rate of dipolar relaxations (and thus orientational and translational mobility) usually differ significantly between the molecules in the pore wall proximity and the ones in the channel center [58][59][60][61][62][63][64][65][66]. In seminal dielectric studies (complemented by dynamic light scattering and calorimetric experiments) Aliev et al [67][68][69] could document a slow surface mobility in comparison to the dynamics in the pore centre for liquid crystals confined in tortuous and tubular mesopores.…”

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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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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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“…Many experiments have been reported using the nCB series, with n ranging from 5 to 8. Among experimental techniques used have been various types of NMR studies [13][14][15], magnetically-induced birefringence [16], electro-optics [17], static and dynamic light scattering [18][19][20][21][22], various types of calorimetry [10,19,20,[23][24][25][26][27][28], dielectric spectroscopy [13,29] and cross-polarized microscopy [25]. Porous systems of a number of different related types have been employed, e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Porous systems of a number of different related types have been employed, e.g. anopore-membrane gels [20,23], silica aerosil dispersions [15,25,26,[30][31][32], membrane filters [22], porous glass [13,16,27,28], solid polymer matrix [17], silicaparticle-based random gel [14,17,18], silica aerogel [19,21] and jammed aqueous laponite suspensions [33]. In general, transitions are rounded, order parameters reduced (with the degree of reduction depending on pore size), and long-range order in the nematic phase is lost.…”

Section: Introductionmentioning

confidence: 99%

Computational studies of history dependence in nematic liquid crystals in random environments

et al. 2014

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Glassy liquid crystalline systems are expected to show significant history-dependent effects. Two model glassy systems are the RAN and SSS lattice models. The RAN model is a Lebwohl-Lasher lattice model with locally coupled nematic spins, together with uncorrelated random anisotropy fields at each site, while the SSS model has a finite concentration of impurity spins frozen in random directions. Here Brownian simulation is used to study the effect of different sample histories in the low temperature regime in a three dimensional (d = 3) model intermediate between SSS and RAN, in which a finite concentration p < pc (pc the percolation threshold) of frozen spins interacts with neighboring nematic spins with coupling W . Simulations were performed at temperature T ∼ TNI /2 (TNI the bulk nematic-isotropic transition temperature) for temperature-quenched and field-quenched histories (TQH and FQH respectively), as well as for temperature-annealed histories (AH). The first two of these limits represent extreme histories encountered in typical experimental studies. Using long-time averages for equilibrated systems, we calculate orientational order parameters and two-point correlation functions. Finite size-scaling was used to determine the range of the orientational ordering, as a function of coupling strength W, p and sample history. Sample history plays a significant role; for given concentration p, as disorder strength W is increased, TQH systems sustain quasi-long-range (QLRO) and short-range-order (SRO). The data are also consistent with a long-range order (LRO) phase at very low disorder strength. By contrast, for FQH, only LRO and QLRO occur within the range of parameters investigated. The crossover between regimes depends on history, but in general, the FQH phase is more ordered than than the AH phase, which is more ordered than the TQH phase. We detect also in the QLRO phase a domain-type structural pattern, consistent with ideas introduced by Giamarchi and Doussal [Phys. Rev. B 52, 1242Rev. B 52, (1995] on superconducting flux lattices. In phases in which short-range exponential order occurs, the orientational correlation length in the weak-disorder limit obeys Larkin-Imry-Ma scaling ξ ∼ D −2/(4−d) .

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“…3 gives the relaxation map for AU12. In the isotropic phase one broadened relaxation process (a = 0.86, b = 0.99) is observed in our range of frequency, which is also known for simple liquid crystals such as cyanobiphenyls [28][29][30]. At the isotropic-nematic transition a rapid shift of this process towards lower frequencies is observed.…”

Section: Resultsmentioning

confidence: 77%

“…In the nematic state the activation energy is higher than in the smectic one. This is due to the nematic potential and is also known for cyanobiphenyls [28][29][30].…”

Section: Resultsmentioning

confidence: 99%

Molecular mobility of diepoxy nematics studied by dielectric spectroscopy

Włodarska

Schönhals

Bąk

et al. 2010

Journal of Non-Crystalline Solids

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Measurement of orientational order and mobility of a nematic liquid crystal in random nanometer confinement

Cited by 86 publications

References 49 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

Computational studies of history dependence in nematic liquid crystals in random environments

Molecular mobility of diepoxy nematics studied by dielectric spectroscopy

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