Ferro- and Antiferroelectric Properties of Langmuir-Blodgett Films Composed of Mesogenic Bent-Core Molecules

Abstract

A bent-core mesogenic compound was used for preparation of thin solid Langmuir films (25-100 nm) that were transferred onto glass substrates and supplied with Al electrodes evaporated in vacuum. The Langmuir-Blodgett technique allowed us studying the thin polar films of the banana-shaped liquid crystal in sandwich geometry that keep amazing integrity on heating, even up to high-temperature B 2 phase, and show antiferroelectric and ferroelectric properties, which depend on film thickness. The magnitude of the measured switched polarization (400 nC/cm 2 ) is similar to that of the bulk material. The strong confinement of film results in high coercive field which reaches the value of 10 8 V/m for the thinnest film. The investigations of dielectric properties are reported.

Planar-homeotropic transition observed for B2phase of banana-shaped thioester

“…Since the discovery of ferroelectric order in smectic C phases composed of polar achiral banana-shaped molecules, many experimental studies have been done [1][2][3][4][5][6][7][8][9][10][11][12]14,[18][19][20]] that confirm ferro-or antiferroelectric order inside the layers and positive or negative correlations between the layers. Theoretical studies were focused on intermolecular interactions within the layers as well as interlayer correlations [12,13].…”

“…Recent studies of thin Langmuir-Blodgett films reveal an interesting property that polarization of nano-layers is about the same as bulk polarization [6]. Both ferro-and antiferroelectric orders have been observed.…”

“…Calamitic mesogens may also form smectic structures (lamellar) which are important for living systems, whereas discotic molecules form columnar mesophases. Banana-shaped molecules may form lamellar and/or columnar mesophases, which have become a subject of intensive experimental [1][2][3][4][5][6][7][8][9][10][11][12]14,[18][19][20] and theoretical [12][13] studies in the last decades. In the first place, research on electro-optic switching in ferro-and antiferroelectric phases composed of bent-core molecules is being done because of possible practical applications.…”

Electric‐ and Light‐Responsive Bent‐Core Liquid Crystals: From Molecular Architecture and Supramolecular Nanostructures to Applications

“…Photopolymerization using photopolymerizable groups such as acrylate or methacrylate has been used to lock the FE order and improve the mechanical properties of materials [189][190][191]. Moreover, other macromolecular designs such as polymers [192][193][194][195][196], Langmuir-Blodgett films [197][198][199], or sol-gel materials [200], can also be explored for bent-core NLO applications.…”

Ferroelectric Liquid Crystals Composed of Banana-Shaped Thioesters

“…Due to this the secondary order parameter (spontaneous polarization) is almost temperature independent. Thin Langmuir-Bloggett films composed of bent-core molecules studied by reversal current method (Geivandov, 2006) reveal an interesting property that polarization of nano-layers is similar to bulk polarization. Both ferro-and anti-ferroelectric order have been observed.…”