The B4 phase of bent-core liquid crystals has been shown to be an assembly of twisted layers stacked to form helical nanofilaments. Interestingly, some of them have structural colours that cannot be explained by the nanofilaments alone. Here cryogenic-transmission electron microscopy observations on 40-120 nm films of four bent-core liquid crystal materials show that the filaments are present even in contact with a carbon substrate with only minor deformation, thus representing bulk properties. We find that the subsequent arrays of nanofilaments are not parallel to each other, but rotate by an angle of 35-40°with respect to each other. This doubly twisted structure can explain the structural colour. Being principally different from the packing of molecules in the twist grain boundary and blue phases, the double-twist structure of helical nanofilaments expands the rich word of nanostructured organic materials.

We demonstrate subnanometer resolution cryo-TEM imaging of smectic layers in the smectic and nematic phases of two bent-core liquid crystals. Our results show perfect periodicity over several hundred layers in the smectic phase and also provide the first direct evidence of smectic clusters on length scales of 30-50 nm in a nematic liquid crystal. The results are corroborated with small angle x-ray scattering measurements. The observation of smectic clusters in the nematic phase is of special interest in bent-core liquid crystals, where the smectic clusters are stable over wide temperature ranges, in contrast to the well-known pretransitional "cybotactic" clusters that appear only in the vicinity of a bulk smectic phase. The means to characterize and manipulate this nanoscale molecular order could open up completely new liquid crystal-based technologies.

Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155 ) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138 in the SmA and about 146 in the nematic phase). Dielectric and SHG measurements give evidence that in the SmA phase a polar structure can be induced by application of an electric field which disappears in the isotropic liquid phase. The electric field not only leads to a slight textural change even in the SmA phase but also polar-type electric current response (P S about 200 nC cm À2 ) is observed. This unusual electrooptical behaviour is discussed on the basis of the orientation of polar clusters formed by the bent molecules. In the paper we not only attempt to characterize the mesophases and to describe their physical properties, but we also show that these types of molecules represent the borderline between bent-shaped and calamitic liquid crystals.

Recently soft fiber mats electrospun from solutions of Barium Titanate (BT) ferroelectric ceramics particles and polylactic acid (PLA) were found to have large (d 33 $ 1 nm/V) converse piezoelectric signals offering a myriad of applications ranging from active implants to smart textiles. Here, we report direct piezoelectric measurements (electric signals due to mechanical stress) of the BT/PLA composite fiber mats at several BT concentrations. A homemade testing apparatus provided AC stresses in the 50 Hz-1.5 kHz-frequency range. The piezoelectric constant d 33 $ 0.5 nC/N and the compression modulus Y $ 10 4-10 5 Pa found are in agreement with the prior converse piezoelectric and compressibility measurements. Importantly, the direct piezoelectric signal is large enough to power a small LCD by simple finger tapping of a 0.15 mm thick 2-cm 2 area mat. We propose using these mats in active Braille cells and in liquid crystal writing tablets. V

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The construction and properties of scattering type liquid crystal depolarizers are discussed. The Mueller matrices that describe these devices are measured and compared to ideal depolarizers and ideal linear materials. The present depolarizers do not perform as well as crystal pseudodepolarizers. Nevertheless, when polarized light is incident on one of these devices the polarization of the transmitted light can be uniform to within 5%. These devices have the advantage that they can be made to areas as large as 30-30 cm or larger, are inexpensive, and can be electrically switched off and on.

The role of chirality in membrane-forming lipids is not well appreciated at present. Here we demonstrate that the chirality of phospholipids makes fluid lipid bilayers piezoelectric. Thus, chiral lipids would play a central role in the functioning of cell membranes as active mechanotransducers. By periodically shearing and compressing nonaqueous lamellar phases of left ( L-alpha -phosphatidylcholine), right (D- alpha -phosphatidylcholine), and racemic (DL- alpha -phosphatidylcholine) lipids, we induced a tilt of the molecules with respect to the bilayer's normal and produced electric current perpendicular to the tilt plane, with the chiral lipids only. This effect is due to the Sm-A;{*} phase liquid crystal structure of the bilayers, which under molecular tilt becomes a ferroelectric Sm-C;{*} phase, where the polarization is normal to the tilt plane. This coupling allows for a wide variety of sensory possibilities of cell membranes such as mechanoreception, magnetosensitivity, as well as in-plane proton membrane transport and related phenomena such as adenosine triphosphate (ATP) synthesis, soft molecular machine performance, etc.

Some liquid crystalline phases of bent-core mesogens are known to form stable freely-suspended filaments with length to diameter ratios of 1000 and larger. These structures can behave like thin liquid chords. We study filament oscillations excited with harmonic sound waves. From amplitudes of the filament motion and phase shifts respective to the harmonic excitation signal we develop a model for the filament dynamics. Like in solid chords, the resonance frequency f 0 is inversely proportional to their length. The dependence of f 0 upon the filament radius allows one to draw conclusions on the nature of the filament tension. For thin filaments, this tension can be largely attributed to surface tension, while for thick filaments there must be other, bulk contributions in addition. The decay time of the filament oscillations is proportional to the filament length. This can be explained by the assumption that dissipation is restricted to the two filament ends. An important observation is that thick filaments often deviate significantly from cylindrical shape.