Structures and orientational transitions in thin smectic films of tilted hexatic
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RDER, DISORDER, AND PHASE TRANSITIONS IN CONDENSED SYSTEMS
Structures and Orientational Transitions in Thin Smectic Films of Tilted Hexatic¶ P. V. Dolganova, K. I. Belova, V. K. Dolganova, E. I. Demikhova, B. M. Bolotinb, and E. I. Katsc, d a
Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia b Institute of Chemical Reactants and Especially Pure Substances (IREA), Moscow, 107076 Russia c Laue-Langevin Institute F-38042, Grenoble, France d Landau Institute for Theoretical Physics, Russian Academy of Sciences, GSP-1, Moscow, 117940 Russia e-mail: [email protected] Received September 20, 2005
Abstract—We present detailed systematic studies of structural transformations in thin liquid crystal films with the transition from the smectic-C (SmC) to hexatic (HSmB) phase. For the first time, all possible structures reported in the literature are observed for one material (5O.6) with varying temperature and thickness. In unusual modulated structures, the equilibrium period of stripes is twice the domain size. We interpret these patterns in the framework of a phenomenological Landau-type theory, as equilibrium phenomena produced by a natural geometric frustration in a system having spontaneous splay distortion. PACS numbers: 61.30.Eb, 64.70.Md, 68.15.+e DOI: 10.1134/S1063776106040108
1. INTRODUCTION Spontaneous formations of spatial patterns arise in a wide variety of dynamical processes. Even more spectacularly they are observed in equilibrium situations involving fluids, solids, and liquid crystals. Especially remarkable are free standing smectic films, in which the influence of underlying substrates (often dominant in other systems) can be avoided. These systems provide a realization of many models describing diverse apparently disparate physical phenomena (phase transitions, frustrations, ferroelectricity, and magnetism), and an opportunity to study the crossover from twodimensional to bulk behavior by drawing films of increasing thickness. For liquid crystal materials with phase sequences in bulk samples, the HSmB (or crystalline CrB)–SmA phase transformations in thin free-standing films are well studied at present [1, 2]. At a temperature TS1 about 10°C above the bulk transition point TC , the phase transition occurs only in surface smectic layers. The interior layers remain in the SmA phase. Below TS1, there are no phase transitions up to a temperature slightly above TC . The next transition in the nearest-to-surface layer occurs at a temperature TS2 about 1°C above TC . A sequence of discrete layer-by-layer transitions on cooling may constitute from two to five transitions. In thick films, the transition of the whole film into the lowtemperature phase occurs at T ~ TC . ¶
The text was submitted by the authors in English.
A few words on the nomenclature of tilted hexatic smectics (usually labeled SmF, SmI) may be helpful here. The tilt direction is along the local bonds in the SmI phase, halfway between two local bonds in the SmF phase, and lies at an intermediate a
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