Anticlinic structures at the surface of freely suspended smectic-C films

Ellipsometric studies have been conducted on freely suspended films of chiral smectic liquid crystals. In the temperature range of the smectic-C phase, we observe sharp steplike changes of the ellipsometric quantity Δ indicating sudden inversions of the molecular tilt direction in single smectic layers near the surface. These tilt inversion transitions are strongly hysteretic with temperature differences up to 10 K between heating and cooling runs. Although the films possess two identical free surfaces, metastable states occur in which the tilt is inverted at only one surface

Ellipsometric study of freely suspended smectic films of a partially fluorinated compound

High-resolution ellipsometric studies have been conducted on freely suspended films of a chiral, partially perfluorinated liquid-crystal compound near its smectic-A–smectic-C transition. The surface-enhanced transition is unusually close to the bulk transition temperature. Moreover, in the ferroelectric smectic-C phase an unexpected tilt direction inversion with respect to the direction of an applied electric field is found in films thinner than about 20 layers whereas it does not occur in thick films

Structure of the chiral smectic-C_α^* phase

Ellipsometric measurements of freely suspended films of a chiral liquid-crystal compound possessing the phase sequence smectic-A–smectic-C*α–smectic-C* have been conducted in order to elucidate the structure of the smectic-C*α phase. The measured ellipsometric quantities Δ and Ψ are compared with values, which were calculated for model films using the 4×4 matrix method. Our results confirm, for the compound under investigation, predictions of a phenomenological model [M. Čepič and B. Žekš, Mol. Cryst. Liq. Cryst. 263, 61 (1995)] according to which the smectic-C*α phase is characterized by a short-pitch helical structure

Polarization sign inversion and smectic-A - smectic-C surface transitions in freely suspended films of fluorinated and nonfluorinated compounds

We report ellipsometric measurements on freely suspended films of chiral liquid-crystal compounds near their smectic-A-smectic-C transition. The temperature difference between the surface and the bulk transition is found to vary considerably within a homologous series. In two compounds possessing a fluorinated alkyl chain an unexpected sign inversion of the spontaneous polarization in the ferroelectric smectic-C phase is observed which occurs only in thin but not in thick films

Competition between ferroelectric and flexoelectric polarization in freely suspended smectic films

We report a detailed ellipsometric study of freely suspended films of chiral liquid-crystal compounds possessing smectic-A and smectic-C phases. In the temperature region between the smectic-A - smectic-C bulk and surface transitions, a discontinuous reconstruction of the tilt profile across the film is observed in the presence of a constant d.c. electric field. Comparison of the measured ellipsometric quantities with values calculated from model tilt profiles reveals a competition between a structure possessing a homogeneous tilt direction and large ferroelectric polarization and a structure with opposite tilt direction in the two film halfs and large flexoelectric polarization

Structure of freely suspended chiral smectic films as determined by x-ray reflectivity and optical ellipsometry

We report on a combined x-ray reflectivity and optical ellipsometry study of freely suspended smectic (Sm) films of a chiral liquid crystalline compound with the phase sequence Sm−A–Sm−C*α–Sm−C*–Sm−C*γ–Sm−C*A. Using tilt magnitude profiles from x-ray reflectivity as input to model the average optical properties obtained by ellipsometry, tilt direction profiles are also obtained. In this way realistic models can be elaborated for the various types of chiral Sm-C films. We find that the surface layers are more tilted than the interior layers due to surface interactions and finite size effects. For the ferrielectric Sm−C*γ phase the tilt direction profile corresponds to a three-layer helix, in agreement with the clock model of chiral Sm-C phases. In thin films the surface interactions suppress the bulk helix structure of the Sm−C*α phase and a Sm−C*A-like structure is formed with an anticlinic layer-by-layer alternation of the tilt directions

Structure of freely suspended chiral smectic films as determined by x-ray reflectivity and optical ellipsometry

We report on a combined x-ray reflectivity and optical ellipsometry study of freely suspended smectic (Sm) films of a chiral liquid crystalline compound with the phase sequence Sm−A–Sm−C*α–Sm−C*–Sm−C*γ–Sm−C*A. Using tilt magnitude profiles from x-ray reflectivity as input to model the average optical properties obtained by ellipsometry, tilt direction profiles are also obtained. In this way realistic models can be elaborated for the various types of chiral Sm-C films. We find that the surface layers are more tilted than the interior layers due to surface interactions and finite size effects. For the ferrielectric Sm−C*γ phase the tilt direction profile corresponds to a three-layer helix, in agreement with the clock model of chiral Sm-C phases. In thin films the surface interactions suppress the bulk helix structure of the Sm−C*α phase and a Sm−C*A-like structure is formed with an anticlinic layer-by-layer alternation of the tilt directions