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We investigated the properties of p-type semiconducting columnar phases in self-assembled umbrella-shaped mesogens that have subphthalocyanine cores and oligo-thienyl arms. These compounds have nonswitchable phases that exhibit remanent electric polarization and nonlinear optical activity. Additionally, these compounds can generate photocurrents in the visible spectral range due to their wide absorption band. The photocurrent can be significantly increased by doping materials with fullerene. The charge mobility shows an anomalous field dependence, which decreases with the temperature.

We demonstrate an exceptional ability of a high-polarization 3D ferroelectric liquid to form freely suspended fluid fibers at room temperature. Unlike fluid threads in modulated smectics and columnar phases, where translational order is a prerequisite for forming liquid fibers, recently discovered ferroelectric nematic forms fibers with solely orientational molecular order. Additional stabilization mechanisms based on the polar nature of the mesophase are required for this. We propose a model for such a mechanism and show that these fibers demonstrate an exceptional nonlinear optical response and exhibit electric field-driven instabilities., Competing Interests: Competing interests statement:The authors declare no competing interest.

Recently, there has been an active search for new modifiers to create hybrid polymeric materials for various applications, in particular, membrane technology. One of the topical modifiers is metal-organic frameworks (MOFs), which can significantly alter the characteristics of obtained mixed matrix membranes (MMMs). In this work, new holmium-based MOFs (Ho-MOFs) were synthesized for polyether block amide (PEBA) modification to develop novel MMMs with improved properties. The study of Ho-MOFs, polymers and membranes was carried out by methods of X-ray phase analysis, scanning electron and atomic force microscopies, Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, dynamic and kinematic viscosity, static and dynamic light scattering, gel permeation chromatography, thermogravimetric analysis and contact angle measurements. Synthesized Ho-MOFs had different X-ray structures, particle forms and sizes depending on the ligand used. To study the effect of Ho-MOF modifier on membrane transport properties, PEBA/Ho-MOFs membrane retention capacity was evaluated in vacuum fourth-stage filtration for dye removal (Congo Red, Fuchsin, Glycine thymol blue, Methylene blue, Eriochrome Black T). Modified membranes demonstrated improved flux and rejection coefficients for dyes containing amino groups: Congo Red, Fuchsin (PEBA/Ho-1,3,5-H 3 btc membrane possessed optimal properties: 81% and 68% rejection coefficients for Congo Red and Fuchsin filtration, respectively, and 0.7 L/(m 2 s) flux).

Intercellular communication and transport is the essential prerequisite for the function of multicellular organisms. Simple diffusion as a transport mechanism is often inefficient in sustaining the effective exchange of metabolites, and other active transport mechanisms become involved. In this paper, we use the giant cells of characean algae as a model system to explore the role of advection and diffusion in intercellular transport. Using fluorescent dye as a tracer, we study the kinetics of the permeation of the fluorophore through the plasmodesmata complex in the node of tandem cells and its further distribution across the cell. To explore the role of cytoplasmic streaming and the nodal cell complex in the transport mechanism, we modulate the cytoplasmic streaming using action potential to separate the diffusive permeation from the advective contribution. The results imply that the plasmodesmal transport of fluorescent probe through the central and peripheral cells of the nodal complex is differentially regulated by a physiological signal, the action potential. The passage of the probe through the central cells of the nodal complex ceases transiently after elicitation of the action potential in the internodal cell, whereas the passage through the peripheral cells of the node was retained. A diffusion-advection model is developed to describe the transport kinetics and extract the permeability of the node-internode cell wall from experimental data., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

Impact of membrane excitability on fluidic transport of photometabolites and their cell-to-cell passage via plasmodesmata was examined by pulse-modulated chlorophyll (Chl) microfluorometry in Chara australis internodes exposed to dim background light. The cells were subjected to a series of local light (LL) pulses with a 3-min period and a 30-s pulse width, which induced Chl fluorescence transients propagating in the direction of cytoplasmic streaming along the photostimulated and the neighboring internodes. By comparing Chl fluorescence changes induced in the LL-irradiated and the adjoining internodes, the permeability of the nodal complex for the photometabolites was assessed in the resting state and after the action potential (AP) generation. The electrically induced AP had no influence on Chl fluorescence in noncalcified cell regions but disturbed temporarily the metabolite transport along the internode and caused a disproportionally strong inhibition of intercellular metabolite transmission. In chloroplasts located close to calcified zones, Chl fluorescence increased transiently after cell excitation, which indicated the deceleration of photosynthetic electron flow on the acceptor side of photosystem I. Functional distinctions of chloroplasts located in noncalcified and calcified cell areas were also manifested in different modes of LL-induced changes of Chl fluorescence, which were accompanied by dissimilar changes in efficiency of PSII-driven electron flow. We conclude that chloroplasts located near the encrusted areas and in the incrustation-free cell regions are functionally distinct even in the absence of large-scale variations of cell surface pH. The inhibition of transnodal transport after AP generation is probably due to Ca 2+ -regulated changes in plasmodesmal aperture., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Nematics with a broken polar symmetry are one of the fascinating recent discoveries in the field of soft matter. High spontaneous polarisation and the fluidity of the ferroelectric nematic N phase make such materials attractive for future applications and interesting for fundamental research. Here, we explore the polar and mechanical properties of a room-temperature ferroelectric nematic and its behaviour in a magnetic field. We show that F phase make such materials attractive for future applications and interesting for fundamental research. Here, we explore the polar and mechanical properties of a room-temperature ferroelectric nematic and its behaviour in a magnetic field. We show that N F is much less susceptible to the splay deformation than to the twist. The strong splay rigidity can be attributed to the electrostatic self-interaction of polarisation avoiding the polarisation splay.

We report an unusually strong flow-induced birefringence in an optically isotropic cubic phase occurring below the isotropic chiral conglomerate phase formed by a low-molecular-weight polycatenar mesogen. The transition into the birefringent state occurs thresholdless and the induced birefringence is comparable with that observed in polymeric systems. We suggest that the flow-induced deformation of the cubic structure is responsible for the strong rheo-optical response.

Liquid crystal (LC) based magnetic materials consisting of LC hosts doped with functional magnetic nanoparticles enable optical switching of the mesogens at moderate magnetic field strengths and thereby open the pathway for the design of novel smart devices. A promising route for the fabrication of stable ferronematic phases is the attachment of a covalently bound LC polymer shell onto the surface of nanoparticles. With this approach, ferronematic phases based on magnetically blocked particles and the commercial LC 4-cyano-4'-pentylbiphenyl (5CB) liquid crystal were shown to have a sufficient magnetic sensitivity, but the mechanism of the magneto-nematic coupling is unidentified. To get deeper insight into the coupling modes present in these systems, we prepared ferronematic materials based on superparamagnetic particles, which respond to external fields with internal magnetic realignment instead of mechanical rotation. This aims at clarifying whether the hard coupling of the magnetization to the particle's orientation (magnetic blocking) is a necessary component of the magnetization-nematic director coupling mechanism. We herein report the fabrication of a ferronematic phase consisting of surface-functionalized superparamagnetic Fe 3 O 4 particles and 5CB. We characterize the phase behavior and investigate the magneto-optical properties of the new ferronematic phase and compare it to the ferronematic system containing magnetically blocked CoFe 2 O 4 particles to get information about the origin of the magneto-nematic coupling.

Cellulose nanocrystals (CNCs) are interesting for the construction of biomaterials for energy delivery and packaging purposes. The corresponding processing of CNCs can be optimized through the variation of intercellulose interactions by employing different types of solvents, and thereby varying the degree of cellulose hydrogen bonding. The aim of this work is (i) to show how different types of solvents affect the self-assembled morphology of CNCs, (ii) to study the microscopic dynamics and averaged orientations on the CNCs in aqueous suspensions, including the effect of externally imposed electric fields, and (iii) to explore the nonlinear optical response of CNCs. The homogeneity of self-assembled chiral-nematic phase depends on both the polarity of the solvent and the CNC concentration. The variation of the chiral-nematic pitch length with concentration, as determined from real-space and Fourier images, is found to be strongly solvent dependent. The anisotropic microdynamics of CNCs suspension exhibits two modes, related to diffusion parallel and perpendicular to the (chiral-) nematic director. We have found also the coupling between translational and orientational motion, due to existing correlation length of twisted nematic elasticity. Preliminary second-harmonic generation experiments are performed, which reveal that relatively high field strengths are required to reorient chiral-nematic domains of CNCs.

Coalescence of droplets plays a crucial role in nature and modern technology. Various experimental and theoretical studies explored droplet dynamics in three-dimensional (3D) and on 2D solid or liquid substrates. In this paper, we demonstrate the complete coalescence of isotropic droplets in thin quasi-2D liquids-overheated smectic films. We observe the merging of micrometer-sized flat droplets using high-speed imaging and analyze the shape transformations of the droplets on the timescale of milliseconds. Our studies reveal the scaling laws of the coalescence time, which exhibits a different dependence on the droplet geometry from that in the case of droplets on a solid substrate. A theoretical model is proposed to explain the difference in behavior.

Organ-on-a-chip devices are gaining popularity in medical research due to the possibility of performing extremely complex living-body-resembling research in vitro. For this reason, there is a substantial drive in developing technologies capable of producing such structures in a simple and, at the same time, flexible manner. One of the primary challenges in producing organ-on-chip devices from a manufacturing standpoint is the prevalence of layer-by-layer bonding techniques, which result in limitations relating to the applicable materials and geometries and limited repeatability. In this work, we present an improved approach, using three dimensional (3D) laser lithography for the direct integration of a functional part-the membrane-into a closed-channel system. We show that it allows the freely choice of the geometry of the membrane and its integration into a complete organ-on-a-chip system. Considerations relating to sample preparation, the writing process, and the final preparation for operation are given. Overall, we consider that the broader application of 3D laser lithography in organ-on-a-chip fabrication is the next logical step in this field's evolution.

Switching of liquid crystal phases is of enormous technological importance and enables digital displays, thermometers and sensors. As an alternative to electric fields or temperature, magnetic fields are an interesting trigger, as they are on the one hand versatile to design, and on the other hand, they are compatible with a bouquet of applications. An interesting option to enable the magnetic switchability of nematic phases is by doping them with functional magnetic nanoparticles, but it remains a challenge to achieve well-compatibilized and stable ferronematic phases. Here, we report a new approach for the experimental realization of finely dispersed MNPs and nematic LC by creation of a surface-coupled mesogen-functionalized polymer brush, and the determination of their corresponding magneto-optical response. For this purpose, CoFe 2 O 4 particles are equipped with a covalently attached polymeric shell carrying mesogenic groups and successfully dispersed in 4-pentyl-4'-cyanobiphenyl (5CB) to form a stable ferronematic phase at ambient concentration up to ∼1 vol%, as shown by DSC and Abbé refractometry. The magneto-optic response is detected in planar aligned LC cells. As compared to undoped 5CB, the hybrid system shows a significantly increased magnetic sensitivity, and the magneto-nematic surface anchoring is quantified by analysis of the magneto-nematic cross-correlation.

The dynamics of magnetic nanoparticles in rotating magnetic fields is studied both experimentally and theoretically. The experimental investigation is focused on the conversion of the magnetic forces to a mechanical torque acting on a ferrofluid confined in a spherical cavity in a rotating magnetic field. Polydispersity usually present in diluted ferrofluids is shown to play a crucial role in the torque conversion. Important features observed experimentally are reproduced theoretically in studies on the dynamics of particles with uniaxial magnetic anisotropy in the presence of thermal noise. The phase lag between the rotating magnetic field and the induced rotating magnetization, as well as the corresponding torque which is transferred to the carrier fluid because of the mutual coupling between both, is analyzed as a function of the particle size. It is shown that for large particles the magnetic moment is locked to the anisotropy axis. On lowering the particle radius, Néel relaxation becomes increasingly important. Illustrative numerical calculations demonstrating this behavior are performed for magnetic parameters typical for iron oxide.

Characean internodal cells develop alternating patterns of acid and alkaline zones along their surface in order to facilitate uptake of carbon required for photosynthesis. In this study, we used a pH-indicating membrane dye, 4-heptadecylumbiliferone, to study the kinetics of alkaline band formation and decomposition. The differences in growth/decay kinetics suggested that growth occurred as an active, autocatalytic process, whereas decomposition was due to diffusion. We further investigated mutual interactions between internodal cells and found that their alignment parallel to each other induced matching of the pH banding patterns, which was mirrored by chloroplast activity. In non-aligned cells, the lowered photosynthetic activity was noted upon a rise of the external pH, suggesting that the matching of pH bands was due to a local elevation of membrane conductance by the high pH of the alkaline zones of neighboured cells. Finally, we show that the altered pH banding pattern caused the reorganization of the cortical cytoplasm. Complex plasma membrane elaborations (charasomes) were degraded via endocytosis, and mitochondria were moved away from the cortex when a previously acid region became alkaline and vice versa. Our data show that characean internodal cells react flexibly to environmental cues, including those originating from neighboured cells.

Droplet arrays in thin, freely suspended liquid-crystalline smectic A films can form two-dimensional (2D) colloids. The droplets interact repulsively, arranging locally in a more or less hexagonal arrangement with only short-range spatial and orientational correlations and local lattice cell parameters that depend on droplet size. In contrast to quasi-2D colloids described earlier, there is no 3D bulk liquid subphase that affects the hydrodynamics. Although the films are surrounded by air, the droplet dynamics are genuinely 2D, the mobility of each droplet in its six-neighbor cage being determined by the ratio of cage and droplet sizes, rather than by the droplet size as in quasi-2D colloids. These experimental observations are described well by Saffman's model of a diffusing particle in a finite 2D membrane. The experiments were performed in microgravity, on the International Space Station.

We investigate the structure and the magnetooptical response of isotropic and anisotropic fibrillous organoferrogels with mobile magnetic nanoparticles (MNPs). We demonstrate that the presence of the gel network restricts the magnetooptical response of the ferrogel. Even though the ferrogel exhibits no magnetic hysteresis, an optical hysteresis has been found. This suggests that the magnetooptical response is primarily determined by the dynamics of self-assembly of the MNPs into shape-anisotropic agglomerates. Furthermore, we show that the optical anisotropy of the system can be fine-tuned by varying the concentration of the gelator and the MNPs, respectively. The optical response in structurally anisotropic gels becomes orientation-dependent, revealing an intricate interplay between the gel mesh and the MNPs.

In recent years, liquid crystals (LCs) responding to light or electrical fields have gained significant importance as multifunctional materials. Herein, two new series of photoswitchable bent-core liquid crystals (BCLCs) derived from 4-cyanoresorcinol as the central core connected to an azobenzene based wing and a phenyl benzoate wing are reported. The self-assembly of these molecules was characterized by differential scanning calorimetry (DSC), polarizing light microscopy (POM), electro-optical, dielectric, second harmonic generation (SHG) studies, and XRD. Depending on the direction of the COO group in the phenyl benzoate wing, core-fluorination, temperature, and the terminal alkyl chain length, cybotactic nematic and lamellar (smectic) LC phases were observed. The coherence length of the ferroelectric fluctuations increases continuously with decreasing temperature and adopts antipolar correlation upon the condensation into superparaelectric states of the paraelectric smectic phases. Finally, long-range polar order develops at distinct phase transitions; first leading to polarization modulated and then to nonmodulated antiferroelectric smectic phases. Conglomerates of chiral domains were observed in the high permittivity ranges of the synclinic tilted paraelectric smectic phases of these achiral molecules, indicating mirror symmetry breaking. Fine-tuning of the molecular structure leads to photoresponsive bent-core (BC)LCs exhibiting a fast and reversible photoinduced change of the mode of the switching between ferroelectric- and antiferroelectric-like as well as a light-induced switching between an achiral and a spontaneous mirror-symmetry-broken LC phase., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report on the structure and optical manipulation of the director configurations in emulsions of liquid-crystalline droplets of a compound exhibiting the nematic (N) and the twist-bend nematic (N TB ) phases. We demonstrate a decrease in the ratio of the bent elastic constant K 33 to the splay constant K 11 by nearly 2 orders of magnitude with decreasing temperature in the N phase. The director structures in liquid-crystal droplets doped with a photoswitchable surfactant without and under ultraviolet (UV) light are discussed in light of the strong elastic anisotropy of the investigated compound. We also compare our findings with the results obtained in doped nematic droplets of a conventional 4-cyano-4'-pentylbiphenyl (5CB) liquid crystal. The dynamics of droplets in the N TB phase by UV light irradiation are also studied using polarizing and confocal microscopies.

Magnetic nanoparticles (MNPs) functionalized with (pro-)mesogenic ligands are implemented into a nematic liquid crystal (LC) and studied regarding both colloidal stability and magneto-optical behavior. In this study, the particle surface is specifically engineered to tune the MNP interactions with the LC host. For this purpose, four types of (pro-)mesogenic ligands (ML) are synthesized, which are composed of three structural parts, i.e., a rigid, LC motif (i.e., cyanobiphenyl) and a functional group for nanoparticle binding, both linked via a flexible spacer of different alkyl chain lengths. Electrostatically stabilized CoFe 2 O 4 and γ-Fe 2 O 3 nanoparticles with narrow size distribution and sizes below 3 nm are obtained via co-precipitation and subsequently functionalized to yield MNP@ML nanoparticles. Studies on the behaviour of the MNP@ML nanoparticles in the commercial LC host (i.e., 4-pentyl-4'-cyanobiphenyl (5CB)) in the bulk and in thin films in LC test cells, reveal the initial formation of some heterogeneities after transition from the isotropic to the nematic phase. Homogenous MNP@ML-5CB hybrids with long-term, colloidal stability, however, are obtained after magnetic separation of initially formed particle aggregates. In particular, MLs with carboxy groups and high structural flexibility (i.e., long linker lengths) are shown to be well suited to form stable MNP colloids, allowing for high MNP doping levels. As compared to undoped 5CB, the CoFe 2 O 4 @MLx-5CB hybrids show an increased sensitivity to the magnetic field, affecting the Fréedericksz transition. The strongest effect, however, is observed in magnetic and electric fields. The coupling of the ultrasmall, spherical MNPs with the LC director in the magnetic field suggests the formation of LC-induced, anisometric MNP clusters.

We systematically studied the photoinduced anchoring transition in a nematic liquid crystal containing azo dendrimers. Because the azo dendrimers in the trans-isomer state were spontaneously adsorbed at substrate surfaces, which was confirmed by optical second-harmonic generation (SHG), a homeotropic orientation was established at the first stage. Ultraviolet (UV) light irradiation triggered a transition into a planar state which was accompanied by a suppression of the SH generation. The monotonic decrease of the effective scalar order parameter with increasing UV light intensity was determined by polarized attenuated total reflection infrared (ATR-IR) spectroscopy. The variation of anchoring strength and extrapolation length was evaluated by observing the Fréedericksz transition as a function of UV light intensity at a certain visible (VIS) light intensity. Such a photoinduced variation can be interpreted as a variation of the anchoring strength depending on the trans/cis ratio at the surfaces based on a modified Rapini-Papoular model. Thus, this system provides the opportunity for a controlled change in the anchoring strength.

A new bent-core liquid crystalline material consisting of a 4-cyanoresorcinol unit with two terephthalate based rod-like wings and terminated by two short alkyl chains was synthesized. Its liquid crystalline (LC) self-assembly and the development of polar order in the LC phases were investigated. The polar order is characterised using second harmonic generation and dielectric spectroscopy techniques in addition to XRD and DSC characterisations of the mesophase structure and investigation of freely suspended films. We demonstrate the growth of ferroelectric domains in the paraelectric SmA phase (SmAP R ), which adopt antipolar correlations (SmAP AR ) and eventually condense into a weakly tilted antiferroelectric smectic phase (SmC a P A ).

Two isomeric achiral bent-core liquid crystals involving a 4-cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid-crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result. For the compound with larger dipole moment (CN1) segregation of the carbosilane units is suppressed, and this compound forms paraelectric SmA and SmC phases; polar order is only achieved after transition to a new LC phase, namely, the ferroelectric leaning phase (SmCLs PS ) with the unique feature that tilt direction and polar direction coincide. The isomeric compound CN2 with a smaller dipole moment forms separate layers of the carbosilane groups and shows a randomized polar SmA phase (SmAPAR ) and ferroelectric polydomain SmCs PS phases with orthogonal combination of tilt and polar direction and much higher polarizations. Thus, surprisingly, the compound with the smaller molecular dipole moment shows increased polar order in the LC phases. Besides ferroelectricity, mirror-symmetry breaking with formation of a conglomerate of macroscopic chiral domains was observed in one of the SmC phases of CN1. These investigations contribute to the general understanding of the development of polar order and chirality in soft matter., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Using experiments and molecular dynamics simulations, we explore magnetic field-induced phase transformations in suspensions of nonmagnetic rodlike and magnetic sphere-shaped particles. We experimentally demonstrate that an external uniform magnetic field causes the formation of small, stable clusters of magnetic particles that, in turn, induce and control the orientational order of the nonmagnetic subphase. Optical birefringence was studied as a function of the magnetic field and the volume fractions of each particle type. Steric transfer of the orientational order was investigated by molecular dynamics (MD) simulations; the results are in qualitative agreement with the experimental observations. By reproducing the general experimental trends, the MD simulation offers a cohesive bottom-up interpretation of the physical behavior of such systems, and it can also be regarded as a guide for further experimental research.

A bent-core mesogen consisting of a 4-cyanoresorcinol unit as the central core and laterally fluorinated azobenzene wings forms four different smectic LC phase structures in the sequence SmA-SmCs -SmCs PAR -M, all involving polar SmCs PS domains with growing coherence length of tilt and polar order on decreasing temperature. The SmA phase is a cluster-type de Vries phase with randomized tilt and polar direction; in the paraelectric SmCs phase the tilt becomes uniform, although polar order is still short-range. Increasing polar correlation leads to a new tilted and randomized polar smectic phase with antipolar correlation between the domains (SmCs PAR ) which then transforms into a viscous polar mesophase M. As another interesting feature, spontaneous symmetry breaking by formation of a conglomerate of chiral domains is observed in the non-polar paraelectric SmCs phase., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A rich variety of responsive behavior occurs in complex structured fluids due to their lower symmetries. On the other hand, fluid disorder tends to increase the symmetry of liquid crystal mesophases. Here, we report direct evidence for the existence of a mesophase with CS symmetry. The observations are based on optical studies of director inversion walls in freely suspended films in electric fields under obliquely incident light. This phase is distinguished by the polarization lying in the molecular tilt plane in freely suspended films. Such a low-symmetry polar fluid phase has been long predicted to occur in bent-core liquid crystals. The stability of this phase is attributed to the bent shape of the mesogens and dominating dispersion interactions.

A small amount of azo-dendrimer molecules dissolved in a liquid crystal enables translational and rotational motions of microrods in a liquid crystal matrix under unpolarized UV light irradiation. This motion is initiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the rod surface and the associated director reorientation. The bending direction of the cis conformers is not random but is selectively chosen due to the curved local director field in the vicinity of the dendrimer-coated surface. Different types of director distortions occur around the rods, depending on their orientations with respect to the nematic director field. This leads to different types of motions driven by the torques exerted on the particles by the director reorientations.

We report here the optical manipulation of the director and topological defect structures of nematic liquid crystals around a silica microparticle with azobenzene-containing dendrimers (azo-dendrimers) on its surface. We successfully demonstrate the successive switching processes from hedgehog, to boojum, and further to Saturn ring configurations by ultraviolet (UV) light irradiation and termination. The switching time between these defect structures depends on the UV light intensity and attains about 50 ms. Since the pretreatment of microparticles is not necessary and the surface modification is spontaneously performed just by dissolving the azo-dendrimers in liquid crystals, this dendrimer supplies us with a variety of possible applications.

We report a reversible phase separation phenomenon in nonpolar colloidal suspensions of rod-shaped dichroic pigment particles in an electric field. The voltage-frequency phase diagram features a variety of phases with different morphologies. Single static particle-rich islands, chains of islands, and dynamic patterns were found in this system. We demonstrate that those patterns exhibit complex relaxation dynamics toward the homogeneous field-free state once the external field is removed.

Several series of bent-core mesogens derived from 3,5-diphenyl-1,2,4-oxadiazole with or without lateral groups and with different length terminal chains at both ends, and polycatenar molecules with three to six alkoxy chains are synthesized and their mesomorphic behaviour is investigated by polarizing microscopy, differential scanning calorimetry, X-ray diffraction (XRD), dielectric, electro-optical and second-harmonic generation (SHG) experiments. Most compounds exhibit broad regions of skewed cybotactic nematic (NcybC ) and tilted smectic (SmC) phases with a strong tilt of the aromatic cores (up to 63°), but non-tilted SmA and NcybA phases are also observed for a compound that has only one terminal chain. The XRD patterns of the nematic phases of most of the compounds investigated indicate a 2D periodicity with short correlation length in the magnetically aligned samples. This is of importance for the general interpretation of the small-angle XRD splitting patterns typically observed for aligned samples of bent-core nematic phases. In most nematic phases one current peak is observed in the half period of an applied electric field, though no coherent signal is found in the SHG experiments. Based on additional electro-optical and dielectric results, the nematic phases are considered to be cybotactic nematic phases with local polar order, and show a dielectric reorientation of the polar domains. Only chiral nematic phases (NcybC *), but not blue phases, are obtained for compounds with one or two chiral (3S)-3,7-dimethyloctyloxy tail(s)., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cytoplasmic streaming occurs in most plant cells and is vitally important for large cells as a means of long-distance intracellular transport of metabolites and messengers. In internodal cells of characean algae, cyclosis participates in formation of light-dependent patterns of surface pH and photosynthetic activity, but lateral transport of regulatory metabolites has not been visualized yet. Hydrogen peroxide, being a signaling molecule and a stress factor, is known to accumulate under excessive irradiance. This study was aimed to examine whether H2O2 produced in chloroplasts under high light conditions is released into streaming fluid and transported downstream by cytoplasmic flow. To this end, internodes of Chara corallina were loaded with the fluorogenic probe dihydrodichlorofluorescein diacetate and illuminated locally by a narrow light beam through a thin optic fiber. Fluorescence of dihydrodichlorofluorescein (DCF), produced upon oxidation of the probe by H2O2, was measured within and around the illuminated cell region. In cells exhibiting active streaming, H2O2 first accumulated in the illuminated region and then entered into the streaming cytoplasm, giving rise to the expansion of DCF fluorescence downstream of the illuminated area. Inhibition of cyclosis by cytochalasin B prevented the spreading of DCF fluorescence along the internode. The results suggest that H2O2 released from chloroplasts under high light is transported along the cell with the cytoplasmic flow. It is proposed that the shift of cytoplasmic redox poise and light-induced elevation of cytoplasmic pH facilitate the opening of H(+)/OH(-)-permeable channels in the plasma membrane.

We report on fingering and labyrinthine instabilities of the layer dislocation lines in freely suspended polar liquid-crystalline films. These polar fingerlike and labyrinth structures reversibly form upon a transition into a modulated phase. External electric fields of several kV/m applied in the film plane can reversibly influence the formation of the finger textures. We show that the labyrinthine pattern is intrinsically related to regular splay deformations of the polarization.

We report on the contrasting phase behavior of a bent-core liquid crystal with a large opening angle between the mesogenic units in the bulk and in freely suspended films. Second-harmonic generation experiments and direct observation of director inversion walls in films in an applied electric field reveal that the nonpolar smectic C phase observed in bulk samples becomes a ferroelectric "banana" phase in films, showing that a mesogen with a small steric moment can give a phase with polar order in freely suspended films even when the corresponding bulk phase is paraelectric.

Geometric frustration gives rise to new fundamental phenomena and is known to yield the formation of exotic states of matter, such as incommensurate crystals, modulated liquid-crystalline phases, and phases stabilized by defects. In this Letter, we present a detailed study of polar structure of freely suspended fluid filaments in a polarization modulated liquid-crystal phase. We show that a periodic pattern of polarization-splay stripes separated by defect boundaries and decorating smectic layers can stabilize the structure of fluid fibers against the Rayleigh-Plateau instability. The instability is suppressed by the resistance of the defect structure to a radial compression of the cylindrical fibers. Our results provide direct experimental observation of a link between the stability of the liquid fibers, internal polar order, and geometrical constraints. They open a new perspective on a wide range of fluid polar fiber materials.

We report an electric-field-induced SmA-SmC transition in a liquid crystal formed by achiral bent molecules. The steric moment of such molecules is too small to spontaneously induce the phases characteristic to the bent-core mesogens. On the other hand, its contribution to the thermodynamical properties of the mesophases make it possible to induce tilt and polar order by the action of the external electric field. This effect is unique for bent mesogens and its physical nature differs from an electroclinic effect observed in the SmA* phase of chiral liquid crystals.

We report an unusual behavior of a ferroelectric smectic-CP{F} film formed by bent-shaped molecules. The ground state of the c -director in such film is not uniform but forms a striped pattern with alternating bend deformation. We found that the sense of the alternating bend is not related to an alternating handedness defined by the mutual orientation of the tilt ( c director) and the bow ( p director) of the molecules. Despite its similarity to a previously described twist-bend instability [J. Pang and N. A. Clark, Phys. Rev. Lett. 73, 2332 (1994)], this pattern cannot be explained in terms of spontaneous chiral symmetry breaking with continuous variation of the chirality order parameter, since the synclinic order of the polar molecules predefines the chirality of the film. We discuss possible models describing the spontaneous formation of an ambidextrous bend pattern of the c director.

The influence of cell excitation and external calcium level on the dynamics of light-induced pH bands along the length of Chara corallina cells is studied in the present paper. Generation of an action potential (AP) transiently quenched these pH patterns, which was more pronounced at 0.05-0.1 mM Ca2+ than at higher concentrations of Ca2+ (0.6-2 mM) in the medium. After transient smoothing of the pH bands, some alkaline peaks reemerged at slightly shifted positions in media with low Ca2+ concentrations, while at high Ca2+ concentrations, the alkaline spots reappeared exactly at their initial positions. This Ca2+ dependency has been revealed by both digital imaging and pH microelectrodes. The stabilizing effect of external Ca2+ on the locations of recovering alkaline peaks is supposedly due to formation of a physically heterogeneous environment around the cell owing to precipitation of CaCO3 in the alkaline zones at high Ca2+ during illumination. The elevation of local pH by dissolving CaCO3 facilitates the reappearance of alkaline spots at their initial locations after temporal suppression caused by cell excitation. At low Ca2+ concentrations, when the solubility product of CaCO3 is not attained, the alkaline peaks are not stabilized by CaCO3 dissolution and may appear at random locations.

We study the orientational relaxation of a spiral pattern around a central defect with topological strength S=+1 in free-standing smectic films. Instead of a continuous unwinding, a characteristic stick-slip relaxation is observed, where the elastic anisotropy plays the dominant role for the director anchoring in the vicinity of the defect. A model derived from nematic continuum theory is used to interpret the experimental observations.

We report a simple experiment in freestanding smectic films in which elastic distortions of the c director drive macroscopic flow. The flow field is visualized with tracer particles. Measurements are compared to predictions of a model that employs the coupled dynamic equations for director and velocity fields. Relaxation dynamics depends on the topology of the film center: for defect-free target patterns, shear flow provides the dominating contribution to the c director dynamics. In presence of a central topological defect of strength S = + 1, the influence of flow on the relaxation dynamics is practically negligible, while for a central S = - 1 defect, the influence of vortex flow on the c-director relaxation is roughly twice as large as for the defect-free state.

This paper studies the potential of 3 newly synthesized low molecular weight gelling agents (2 of them with azo groups) with the semicarbazide group as a H-bonding motif to gel the smectic phase of a commercial chiral smectic C material. To detect gelation two methods were used: the stabilization of the director pattern, which measures the interaction of the physical gel network with the LC-director, and the suppression of the onset of electrohydrodynamic instabilities, which measures the increase of viscosity. Special emphasis was put on the influence of the photochemical - isomerization of the gelling agents on gelation.From the stabilization of the director pattern an elastic component can be seen by the memory effect (two different switching times). Photochemical - isomerization destroys this memory effect. The increase of the threshold field for the onset of electrohydrodynamic instabilities in free-standing films measures the increase of viscosity and the supression of flow. Both methods detect the same melting temperature of the gel and the same reduction of the gelling ability upon - isomerization. This proves that the gelling abilities of the new azo-containing gelling agents can be reversibly switched on and off by photoisomerization.

Stable free-standing liquid filaments formed by some layered mesophases of bent-core mesogens are unique structures. Some of their physical properties have been analyzed in recent studies, but their microscopic structure and conditions for stability have still been unclear. We explore details of filament shapes and surface profiles of filaments drawn in liquid crystal phases of bent-core mesogens by AFM and SEM measurements, and we present a microscopic structure model. Conclusions on the stabilizing mechanisms are drawn. Qualitative differences in mechanical properties are found for different mesophases, even though the macroscopic appearance of the filaments is very similar.

This paper describes an investigation of mechanical properties of freely suspended liquid filaments. These unique fluid microstructures may be formed by layered liquid crystalline mesophases. The filaments are electrically deflected and stimulated to mechanical oscillations. Resonance frequencies and damping rates are recorded. We present a model for a basic description of the dynamics, which is used to evaluate and to discuss the forces involved. The dependence of the oscillation parameters upon geometrical parameters and temperature is analyzed.

The formation of stable freely suspended filaments is an interesting peculiarity of some liquid crystal phases. So far, little is known about their structure and stability. Similarly to free-standing smectic films, an internal molecular structure of the mesophase stabilizes these macroscopically well-ordered objects with length to diameter ratios of 10(3) and above. In this paper, we report observations of smectic liquid crystal fibers formed by bent-shaped molecules in different mesophases. Our study, employing several experimental techniques, focuses on mechanical and structural aspects of fiber formation such as internal structure, stability, and mechanical and optical properties.