Two-Stage surface freezing of a single top layer in a smectic-<i>A</i>membrane

Jeu, Wim H. de; Fera, Andrea; Konovalov, Oleg; Ostrovskiǐ, B. I.

doi:10.1103/physreve.67.020701

Cited by 6 publications

(4 citation statements)

References 22 publications

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“…Close to the crystallization temperature the in-plane positional correlation length increases by about an order of magnitude (see Table II). The same trend was observed for other LC compounds, such as 46OBC [41] or surface hexatic layers in 4O.8 films [49], where ξ reaches the value of about 16 nm and 40 nm, respectively.…”

Section: A the In-plane Positional Ordersupporting

confidence: 80%

Structural studies of the bond-orientational order and hexatic–smectic transition in liquid crystals of various compositions

et al. 2017

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We report on the X-ray studies of freely suspended hexatic films of three different liquid crystal compounds. By applying angular X-ray cross-correlation analysis (XCCA) to the measured diffraction patterns the parameters of the bond-orientational (BO) order in the hexatic phase were directly determined. The temperature evolution of the BO order parameters was analyzed on the basis of the multicritical scaling theory (MCST). Our results confirmed the validity of the MCST in the whole temperature range of the existence of the hexatic phase for all three compounds. The temperature dependence of the BO order parameters in the vicinity of the hexatic-smectic transition was fitted by a conventional power law with a critical exponent β ≈ 0.1 of extremely small value. We found that the temperature dependence of higher order harmonics of the BO order scales as the powers of the first harmonic, with an exponent equal to the harmonic number. This indicates a nonlinear coupling of the BO order parameters of different order. We demonstrate that compounds of various compositions, possessing different phase sequences at low temperatures, display the same thermodynamic behavior in the hexatic phase and in the vicinity of the smectic-hexatic phase transition.

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Section: A the In-plane Positional Ordersupporting

confidence: 80%

Structural studies of the bond-orientational order and hexatic–smectic transition in liquid crystals of various compositions

et al. 2017

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“…The temperature dependence of ξ 0 (T ) obtained for the single-domain case [see Fig. 3(b)] is in agreement with the previous results [8,11,12,25,26]. The correlation lengths ξ n (T ) associated with the higher harmonics of BO order [see Fig.…”

supporting

confidence: 80%

X-ray cross-correlation analysis of liquid crystal membranes in the vicinity of the hexatic-smectic phase transition

et al. 2013

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We present an x-ray study of liquid crystal membranes in the vicinity of the hexatic-smectic phase transition by means of angular x-ray cross-correlation analysis. By applying two-point angular-intensity cross-correlation functions to the measured series of diffraction patterns the parameters of bond-orientational (BO) order in hexatic phase were directly determined. The temperature dependence of the positional correlation lengths was analyzed as well. The obtained correlation lengths show larger values for the higher-order Fourier components of BO order. These findings indicate a strong coupling between BO and positional order. About 30 years ago it was realized that the phase transition between a two-dimensional (2D) crystal and the liquid phase can proceed through an intermediate hexatic phase [1]. The corresponding mechanism involves dissociation of dislocation pairs. The 2D hexatic phase is characterized by a sixfold quasilong-range bond-orientational (BO) order, while the positional order is short range and the shear modulus is zero. Phases with hexatic order have been found in several systems, such as electrons at the surface of helium [2], charged polymer colloids [3,4], and smectic liquid crystals (LCs) [5][6][7]. In the last case a hexatic phase was experimentally observed quite unexpectedly in three-dimensional (3D) stacked molecular systems [8]. In the 3D hexatic phase the positional order is short range, while the BO order persists over a long range. However, the mere existence of a hexatic phase does not imply a specific melting mechanism, and the origin of hexatic order and its relation to the defect-mediated melting transition is still controversial. Smectic liquid crystals are particularly suitable to investigate these problems, as they can be suspended over an opening in a solid frame. Such smectic membranes are substrate-free and have a controlled thickness ranging from two to more than thousands of layers [9].Smectic-A membranes can be described as stacks of liquid layers. The in-plane structure is liquidlike with positional correlations between the molecules decaying exponentially with a correlation length ξ 0 . While cooling a hexatic phase may occur, which shows a long-range BO order. This leads to a sixfold rotational symmetry and the BO correlations are characterized by the local ordering field ψ(r) ∝ exp[i6θ (r)], where θ (r) is the angle between the "bonds" and some reference axis. Upon decreasing the temperature, the width of the radial-intensity peak decreases simultaneously with a further development of the BO order. This indicates a coupling * Present address: The University of California, San Diego, La Jolla, CA 92093, USA.† Corresponding author: ivan.vartaniants@desy.de between the positional correlations and the BO order [10]. Additionally, at even lower temperatures a 3D crystalline phase appears with a hexagonal in-plane lattice or a rectangular lattice with a so-called herringbone order [6,7]. The common way to study the BO order is to perform x-ray or electron diffraction me...

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“…The resulting temperature dependence of ξ 0 obtained for the single domain case [see Fig. 3(b)] is in agreement with the previous results [8,11,12,24,25]. The correlation lengths ξ n associated with the higher harmonics of BO order [see Fig.…”

Section: Resultssupporting

confidence: 90%

X-ray cross-correlation analysis of liquid crystal membranes in the vicinity of hexatic-smectic phase transition

Kurta,

Ostrovskii,

Singer

et al. 2013

Preprint

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We present an x-ray study of liquid crystal membranes in the vicinity of hexatic-smectic phase transition by means of angular x-ray cross-correlation analysis (XCCA). By applying two-point angular intensity cross-correlation functions to the measured series of diffraction patterns the parameters of bond-orientational (BO) order in hexatic phase were directly determined. The temperature dependence of the positional correlation lengths was analyzed as well. The obtained correlation lengths show larger values for the higher-order Fourier components of BO order. These findings indicate a strong coupling between BO and positional order that has not been studied in detail up to now.

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Two-Stage surface freezing of a single top layer in a smectic-Amembrane

Cited by 6 publications

References 22 publications

Structural studies of the bond-orientational order and hexatic–smectic transition in liquid crystals of various compositions

Structural studies of the bond-orientational order and hexatic–smectic transition in liquid crystals of various compositions

X-ray cross-correlation analysis of liquid crystal membranes in the vicinity of the hexatic-smectic phase transition

X-ray cross-correlation analysis of liquid crystal membranes in the vicinity of hexatic-smectic phase transition

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