Structural characterization of surface hexatic behavior in free-standing 4O.8 liquid-crystal films

Cy, Chao; Tc, Pan; Chou, Chia-Fu; Jt, Ho

doi:10.1103/physreve.62.r1485

Cited by 4 publications

(1 citation statement)

References 16 publications

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“…We conclude that the grazing-incidence x-ray-diffraction results for the isotropic-hexatic transition in a 4O.8 top layer are in qualitative agreement with the BKT theory. Chao et al (2000) performed transmission electrondiffraction studies of 4O.8 membranes between 3 and 12 layers. They report somewhat surprisingly an intermediate ''phase'' between isotropic and hexatic Sm-B, associ- ated with the absence of a modulated ring of scattering between 62 and 59°C.…”

Section: Crystallization Of a Single Top Layermentioning

confidence: 99%

Structure and fluctuations of smectic membranes

2003

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Smectic membranes are perfect model systems for studying low-dimensional phase transitions and the associated fluctuations. During the last two decades we have seen important progress in the understanding of the structure and fluctuation behavior of these systems, driven by both new experimental techniques and theoretical developments. Phase transitions are reviewed involving liquid, hexatic, and crystalline layers, which provide several types of model system for low-dimensional melting. The authors discuss the influence of the surfaces on the physical properties of the membranes as well as the crossover from three-to two-dimensional behavior. The layer-displacement fluctuations in smectic membranes have been investigated by specular and diffuse x-ray reflectivity. Theoretical and experimental aspects of the displacement-displacement correlation function are discussed. Of special interest is the quenching or enhancement of fluctuations at surfaces, which is directly related to the phenomenon of surface ordering. The authors consider the conditions under which fluctuations are conformal throughout a membrane, and then the dynamic aspects of the layer-displacement correlation function, which include the effects of finite size, surface tension, and viscous dissipation. This leads in smectic membranes to a discrete spectrum of elastic and viscous relaxation modes, which have been studied experimentally with coherent x rays at third-generation synchrotron sources. The fluctuating character of crystalline-B membranes is also considered. Finally, the article looks briefly at thinning transitions, smectic membranes of chiral molecules, smectic films on substrates, and applications to biologically relevant systems. Open questions and future trends in the field are discussed. CONTENTS I. Motivation and Scope 182 II. Smectic Membranes 183 A. Smectic liquid-crystal phases 183 B. Main features of x-ray patterns 185

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Section: Crystallization Of a Single Top Layermentioning

confidence: 99%

Structure and fluctuations of smectic membranes

2003

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

et al. 2003

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The crystallization of a single liquid top layer of smectic membranes of the compound 4O.8 has been studied with grazing-incidence x-ray diffraction. As this process takes place in two steps, involving an intermediate hexatic smectic-B layer before the final crystalline-B surface structure is reached, it provides a model for melting in two dimensions. The positional order has been investigated quantitatively by measuring the scattering profiles and the associated correlation lengths. The surface liquid-hexatic phase transition is found to be continuous, while the hexatic-crystal transition is weakly first order with an abrupt change of the in-plane positional correlations. The surface phase transitions do not modify the liquid in-plane structure of the interior layers.

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Smectic membranes in aqueous environment

et al. 2010

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We present a study of thermotropic smectic liquid crystal films in aqueous environment. Macroscopic freely suspended films in water with a size up to 7.4 × 15 mm2 were prepared with the help of a surfactant, which ensures a strong homeotropic anchoring at liquid crystal/water interfaces. The films were studied by optical microscopy and ellipsometry. Attention was paid to the stability and the thinning transitions which occurred at temperatures above the bulk smectic- A -isotropic transition temperature. In addition, we investigated the formation and rupture kinetics of thin smectic membranes separating water droplets in microfluidic devices. Besides possible applications in discrete microfluidics, smectic films in aqueous environment may expand the general range of possible studies of freely suspended smectic films.

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Structural characterization of surface hexatic behavior in free-standing 4O.8 liquid-crystal films

Cited by 4 publications

References 16 publications

Structure and fluctuations of smectic membranes

Structure and fluctuations of smectic membranes

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

Smectic membranes in aqueous environment

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