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The influence of the geometry of a cell with side electrodes and the parameters of applied pulsed-periodic voltage on the director orientation in nematic liquid crystal 5CB is analyzed. It is shown that the two-dimensional model of director motion taking into account the electric field inhomogeneity in the cell provides satisfactory agreement with experimental results.

The effect of static electric field on a nematic cell with side electrodes in the transition state (which occurs in the initial stage of field effect on the cell) has been investigated within the two-dimensional dynamic model. The dynamic model is compared with the previously used static one. The two-dimensional dynamic model is found to yield better agreement with the experiment.

A series of flexible and free standing composite membranes based on polyethylene oxide (PEO) and the nematic liquid crystal (LC) E8 were prepared using solution casting technique. The effect of the LC concentration on the structural modifications of PEO/E8 LC composites was investigated by Fourier transform IR spectroscopy, X-ray photoelectron spectroscopy (XPS), micro-Raman and differential scanning calorimetry (DSC). The electrochemical impedance measurements were performed in the applied frequency range of 0.1 Hz – 2 MHz. The dielectric properties of the PEO/E8 LC membranes were studied upon variation of the LC concentration and results were analyzed by Kohlrausch – Williams – Watts and Havriliak – Negami formalisms. These investigations pointed out that LC doped polymeric membranes display remarkable features that could be interested for their use as novel composite electrolytes for rechargeable metal ions batteries.

Photoactive nanofilled nematic is proposed. Stable three-component photoresponsive nanocomposite was prepared from photo-insensitive nanofilled nematic by inclusion of 3 wt.% azobenzene-containing photoactive mesogen 4-(4′-ethoxyphenylazo)phenyl hexanoate (EPH). The host nanofilled nematic was produced from the room-temperature nematic liquid crystal 4-n-heptyl cyanobiphenyl (7CB) and 3 wt.% filler of Aerosil 300 hydrophilic silica nanospheres of size 7 nm. Apparent effect of stimulation with a relatively weak continuous illumination by UV light (375 nm wavelength) takes place for both the alternating-current electric field-dependent optical transmittance and the electro-optic amplitude-frequency modulation by thin films (25 µm thick) of the EPH/aerosil/7CB nanocomposite. The light-stimulated electro-optics of EPH-doped aerosil/7CB films and the corresponding reversible light control are achieved through trans-cis-trans photoisomerization of the photoactive agent EPH. As such, the initial electro-optical response of the studied photoactive nanocomposites is recovered with continuous blue-light illumination. The examined EPH/aerosil/7CB nanocomposites exhibit photo-controllable electro-optical response that is of practical interest.

Poly (ethylene oxide) (PEO)/polyvinylpyrrolidone (PVP) blended nanocomposite polymers, incorporating graphene oxide (GO) nano-sheets and embedded with NaIO4 salt, were prepared using solution casting technique. The as-prepared nanocomposite electrolyte membranes were characterized by SEM, TEM, XRD, and Raman vibrational spectroscopic techniques to confirm the dispersion of GO nano-sheets and to understand the synergistic properties of GO/polymer interactions as a function of GO nano-sheets concentration. GO fillers incorporated electrolyte membranes demonstrated distinctive surface morphology composed of circular-shaped protuberances of different dimensions. The decrease of Raman intensity ratio (ID/IG) and in-plane crystallite size (La) values of the nanocomposites suggested the good dispersion and confinement of the GO nano-sheets. The optical properties of blend electrolyte films were studied as a function of GO filler concentration using optical absorption and diffuse reflectance spectra. In reference to PEO/PVP/NaIO4, the resultant PEO/PVP/NaIO4/GO (0.4% in weight) electrolyte membrane demonstrated both an increase in tensile strength of ca. 42% and in Young’s modulus of ca. 40%, improvements coupled with a maximum fractured elongation of 3%. Through impedance spectroscopy analysis, the role of the GO nano-sheets onto the room temperature conductivity properties of the prepared electrolyte membranes has been probed.

Poly (ethylene oxide) (PEO)/Polyvinyl pyrrolidone (PVP) blended solid polymer electrolytes complexed with NaIO4 salt at different weight percentage ratios were prepared using solution casting technique. Effect of salt complexation on structural properties of pure blend (PEO/PVP) electrolyte was investigated by X-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopic (SEM) studies. Modifications in glass transition temperature and thermal stability of the blend electrolytes were measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) studies. The determined refractive index values from optical absorption spectra were found to increase with the increase of salt concentration. Impedance measurements were made in the frequency range of 0.1 Hz–1 MHz to explore dielectric response and ion dynamics of the blend electrolytes as a function of NaIO4 salt concentration. The PEO/PVP blend complexed with 10 wt% of NaIO4 salt was demonstrated higher room temperature conductivity of 1.56 × 10−7 S/cm. The temperature dependence of DC conductivity of blend electrolytes was followed the Arrhenius behaviour. Determined diffusion coefficients (DNa+) using Trukhan model and estimated mobility (μ) values of sodium ions were increased with increase of salt concentration. To get the further insights into the ion dynamics, the complex dielectric permittivity has been modeled with Havriliak–Negami function.

We studied the change in optical, electro-optical and electrical response of liquid crystal (LC) E7 when this room-temperature nematic is mixed with a very small amount of graphene nanoparticles at concentration of 10−3 wt.%. Being nematic nanocomposite material, such graphene-doped LC material is of interest for electro-optics and organic electronics, and the examined properties are of importance for both electro-optical and electrical performance of practical LC devices. Thin planar-oriented films with a thickness of 7 µm of graphene-doped E7 were inspected and their responses were compared to those of films of pure LC E7 measured under identical experimental conditions. Even at this very low level of doping with graphene nanoparticles, one can achieve a considerable positive effect on electrical transport in graphene/E7 nanocomposites, useful for their electro-optic applications.

We report an experimental study on structural, electrical and dielectric properties of electrolytic system composed of polymer poly(ethylene oxide) (PEO) and nematic-type liquid crystals E8 (at composition ratio PEO:E8 = 70:30 wt.%), being of interest for practical applications in rechargeable mini-batteries and organic electronics. Flexible thin films of this organic electrolyte with a thickness of ∼ 0.1 mm were characterized by frequency spectra of complex electrical impedance and dielectric function. As compared to the host polymer PEO, a significant improvement of both electrical transport and dielectric properties of PEO-E8 composite electrolyte was achieved. The obtained results were compared with the corresponding values and characteristics measured for advanced metal-organic solid-state polymer electrolytes based on PEO or blends of PEO with polyvinylpyrrolidone (PVP) - ionic polymer electrolyte complexes from PEO/PVP doped with inorganic ionic compound and currently trending nanoparticles.

Based on experimental results, we consider an important feature of the electro-optical (EO) response of nematic liquid crystal (NLC) nanocomposite doped with a photoactive NLC. The basic nanocomposite was NLC with nanosilica fillers. The host compound of the investigated nanocomposite was the nematogen 4-n-heptyl cyanobiphenyl (7CB). This NLC was filled (3 wt.%) with hydrophilic silica nanoparticles (Aerosil 300) of size ∼ 7 nm. To obtain a photoresponsive nanofilled NLC, the photo-insensitive aerosil/7CB nanogel was doped (3 wt.%) with azobenzene NLC 4-(4′-ethoxyphenylazo)phenyl hexanoate (EPH). By illumination with UV light at the wavelength of 375 nm, a large reduction of the threshold voltage takes place for the voltage-dependent optical transmittance of thin (25 µm) optical films of the produced EPH-doped aerosil/7CB NLC. The photo-induced depression of the threshold of the LC reorientation upon AC electric field occurs due to trans-cis photoisomerization of EPH molecules that decorate the network of the aerosil/7CB nanogel. The origin and nature of this effect are discussed. Our explanation involves a model consisting of uniform distributed capacitances related to LC domains confined in the gel structure that are connected in series. Based on this model the term Confined Freedericksz Transition (CFT) is coined.

The method of flexo-dielectro-optical spectroscopy was initially developed to study the spectra of the linear and quadratic electro-optic response of continuous nematic liquid crystal layers as a function of the frequency of the applied electric field at low frequencies (0.1–10000 Hz) [1]. Subsequently, it was applied to the microconfined PDLC system [2].In the present study a nanoconfined nematic system of 4-n-heptyl cyanobiphenyl liquid crystal (7CB) containing hydrophilic silica nanoparticles (Aerosil 300) was investigated. The method was implemented by a lock-in detection of the 1st and 2nd harmonic of transmitted laser light through a nanonematic layer subjected to a.c. electric field, the results of which are compared with those for pure 7CB. The optical spectra recorded at various temperatures in the nematic phase of pure and nanostructured samples are presented along with data from static and dynamic measurements of the Freedericksz transition.The data so obtained contain information about liquid ...

We studied the change of electro-optic properties of room-temperature nematic pentylcyanobiphenyl (5CB) when this liquid crystal is mixed with a small amount (∼ 0.5 wt.%) of polymer-capped gold nanoparticles (AuNPs). The AuNPs were spherical-shaped, with a diameter of about 12 nm, the size of the polymer-capped AuNPs was ca. 25 nm. Instead of well pronounced stationary longitudinal domains observed in planar 5CB nematic layers upon static electric field, hybrid longitudinal texture pattern oriented along the rubbing of the cells takes place in this case in identical cells of 5CB doped with AuNPs. The micro-periodic-modulated morphology is reflected on the electro-optic response of AuNPs/5CB nanocomposites. The effect from the nano-dopants is elucidated by detailed investigation (optical, thermo-optical, electrical and electro-optical macroscopic measurements).

The effect from the inclusion of nematic liquid crystal (LC) E8 into the polymer poly(ethylene oxide) (PEO) was inspected by studying of structural and electrical properties of PEO-E8 composites at weight percentage of E8 ranging from 10 % to 50 %. Flexible PEO-E8 films with a thickness of 0.1 mm were structurally characterized by X-ray diffraction and X-ray photo-electron spectroscopy. The results obtained by our analyses indicate that a polymer-LC intermolecular complex is formed by inclusion of E8 LC molecules in the PEO host at a certain their concentration level. The structural properties of PEO-E8 composites were correlated with their electro-conducting properties as depending on the E8 LC concentration. By the amount of the LC fraction one can achieve a controlled modification of the structural and electro-conducting properties of the PEO-E8 material. As compared to PEO, the inclusion of E8 LC in the PEO polymer matrix can lead to a considerably enhanced electrical conductivity of PEO-E8 composites.

We present a study on electrically- and spatially-controllable laser beam diffraction, electrooptic (EO) phase modulation, as well as amplitude-frequency EO modulation by single-layer microscale polymer-dispersed liquid crystal (PDLC) phase gratings (PDLC SLPGs) of interest for device applications. PDLC SLPGs were produced from nematic liquid crystal (LC) E7 in photo-curable NOA65 polymer. The wedge-formed PDLC SLPGs have a continuously variable thickness (2–25 µm). They contain LC droplets of diameters twice as the layer thickness, with a linear-gradient size distribution along the wedge. By applying alternating-current (AC) electric field, the PDLC SLPGs produce efficient: (i) diffraction splitting of transmitted laser beams; (ii) spatial redistribution of diffracted light intensity; (iii) optical phase modulation; (iv) amplitude-frequency modulation, all controllable by the driven AC field and the droplet size gradient.

Electrically controllable two-beam reflection of coherent light double-passed through the microscale polymer-dispersed liquid crystal (PDLC) single layer is reported. By PDLC medium, the intensities of two reflected beams can be reciprocally changed by applying a suitable voltage in the range 0–100 V. The optical phase shift electrically induced for coherent light propagating in two passes through the single-layered PDLC film, as well as the additional phase shift externally introduced by the substrate of the PDLC cell, are responsible for the electrically controllable reflection in a pair of two beams with complementary voltage-dependent intensity behaviors.

The electrically and spatially controllable coherent light diffraction by single-layered polymer-dispersed liquid crystal (PDLC) films is studied. Particularly, a wedge-formed thin film of E7/NOA65 microscale PDLC is examined. The PDLC single layer of thickness varying from a few micrometers to 25 μm contains liquid crystal (LC) droplets with double-truncated spherical shapes and a linear-gradient size distribution along the film length. The single-layer arrangement and compact packing of the micrometer-sized PDLC structure render the ellectrically-commanded coherent light diffraction controlled by LC/polymer interface.

A two-dimensional model of Fredericks effect was used for the investigation of the static electric field influence on nematic liquid crystal director orientation in the side-electrode cell. The solutions of the equations describing the model were obtained by finite-difference methods. Fredericks transition threshold for the central part of the cell, as well as dependencies of the distribution of the director orientation patterns on the electric field and location, were obtained. The numerical results are found to agree qualitatively with the experiment. Further investigations are needed to elucidate completely the Fredericks effect.

An experimental study of coherent light diffraction by wedge-formed single layers composed of liquid crystal (LC) micro-sized droplets dispersed in a transparent solid polymer matrix is reported. The micrometer-sized polymer-dispersed liquid crystal (PDLC) material contains prolate-ellipsoid-like LC droplets with a linear-gradient size distribution along the wedge slope. The droplet diameter in the films reaches several tens of micrometers, defined by the wedge. Such a droplet organization in a two-dimensional layer provides both spatial and electrical control of the coherent light diffraction by the LC/polymer interface.

We report on single-layered optical material of linear-gradient microscale polymer-dispersed liquid crystal (PDLC). E7/NOA65 composite films formed by pulsed UV laser photopolymerization-induced phase separation exhibit two morphology types, namely a bipolar and a hybrid alignment of liquid crystal droplets. The specific structural properties of the produced PDLC layers, such as the droplet shape uniformity and alignment, as well as the droplet size control through the film thickness, facilitate the efficient control on the electro-optical (EO) response, thus being of practical interest for EO device applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Planar nematic layers of 5CB oriented by “sliding on” nanolayers of PTFE were studied by electrooptic methods. Deposited layers have been characterized by AFM and polarizing videomicroscopy. By using a drop method it was established that the preferred director alignment is tilted opposite to the sliding direction. In some of these samples an unusual modulated domain pattern after switching off a prolonged a.c. excitation was observed for the first time. A possible relation between the domain origin and loosely deposited PTFE layers was suggested.

Lipid-mediated anesthetic effect is theoretically modeled, in which the open probability of ion channels in nerve membranes is influenced by the change of the pressure distribution in the perpendicular direction of lipid membrane by adsorbing anesthetics.

Second harmonic generation, optical microscopy, and atomic force microscopy (AFM) are used for the investigation of the thin films of azobenzene and trans-stilbene derivatives. Film morphology is studied at micron and submicron scale. The approach allows one to estimate the size and internal ordering of the crystalline molecular aggregates. The effect of the dilution with stearic acid is discussed.

The theory and experiments on model and biomembrane flexoelectricity are reviewed. Biological implications of flexoelectricity are underlined. Molecular machinery and molecular electronics applications are pointed out.

Composite material prepared from polyethylene oxide (PEO) and polyvinylpyrrolidone (PVP) doped with Sodium (meta)periodate (NaIO4) salt was studied by complex impedance spectroscopy at room temperature. The polymers PEO and PVP were mixed in a weight ratio 70:30 %, and the concentration of the embedded NaIO4 compound was 7.5 wt.%. The effect from NaIO4 filler on the dielectric permittivity of the three-component mixed system was analyzed in the frequency range 0.1 Hz – 1 MHz. As compared with the two-component polymer host PEO/PVP, a distinctly enhanced electrical and dielectrical response and an increase of the value of dielectric constant of the polymeric (PEO/PVP):NaIO4 composite were present. This suggests the potential of this material for soft electronics and applications such as solid electrolytes.

We studied nanomaterials composed from 3 wt.% aerosil nanospheres and the room-temperature nematic liquid crystal 4-n-heptyl cyanobiphenyl (7CB), as doped with the photoactive liquid crystal 4-(4'-ethoxyphenylazo)phenyl hexanoate (EPH). The molecules of the azobenzene photoactive agent EPH were included at concentration ranging from 1 wt.% to 10 wt.%. The object of our interest is the effect of the EPH amount on the photosensitized electro-optical properties of thin films of aerosil/7CB/EPH nematic nanocomposites.

We report on the observation of flexoelectricity of an asymmetric “swallow-tail” compound by dissolving it in a BMAOB nematic matrix and studying the thickness dependence of the period of longitudinal (2nd order) domains in planar layers under d.c. excitation. From the experimental data and Bobilev-Pikin theory we estimate the value of the flexocoefficient difference |e*| = |e 1z - e 3x| as a function of the evaluation about expected concentration and evaluate an extrapolated value of this difference for the “swallow-tail” compound.

The effect of photoinduced conformational transitions between closed and open form of an alkyl-substituted spiropyrane derivative upon the conductance of bilayer lipid membranes (BLM) was investiga...

Homeotropic nematic layers of MBBA, oriented by self-assembled layers (on glass substrates) of dilauroyl phosphatidyl choline (DLPC), cetyl trimethyl-amonium bromide (CTAB) and silane orienting agent (ODS-E), were studied by phase-sensitive flexoelectric spectroscopy method. DLPC solutions in chloroform provided multilayers with different thickness on dipped glass substrates, depending on bulk DLPC concentration. CTAB solutions in water provided, on the other hand, just monolayers, with surface density depending on pulling speed of substrates. Finally, ODS-E solutions provided orienting layers that can be cross-linked at elevated temperatures. The viscoelastic spectra of these layers contained information about surface dissipation of orientational energy under variable structure of orienting layers that may, or may not, dissolve partially in the nematic.

The tip-dip patch clamp method was used to study the effect of three polyamines, putrescine, spermidine and spermine, on bilayer lipid membrane (BLM) stability. Two kinds of mixed lipid-polyamine membranes were investigated. The poration voltage (V(p)), and the closed (sigma(cl)) and open (sigma(op)) state conductances for pure and polyamine-treated lipid membranes were determined by the method of current-voltage surfaces. It was demonstrated that putrescine and spermidine destabilized lipid membranes under all circumstances. BLM stabilization by spermine was observed when it was added to preformed membranes.

A complete theory of surface nematic anchoring was developed earlier, including steric, dielectric, flexoelectric, and notably, surface polarization coupling mechanisms. In the last three cases surface electric field due to the adsorption of surface charges on the substrates is of ultimate importance. The extent of penetration of surface electric field inside a nematic is shorter than believed, due to the important surface screening. This leads to a substantial dehancement of dielectric coupling. Surface polarization, due to the biphilic character of the short-range interaction of asymmetric nematic mesogens with the substrates, can be parallel or antiparallel to the surface electric field. This amounts to a stabilization or a destabilization of the anchoring. Based on the general theory the nonmonotonic behavior of anchoring energy of 5CB on LB films of DPPC with variable surface density is rationalized.

Homeotropic nematic layers of MBBA oriented by self-assembled monolayers of CTAB were studied by phase-sensitive flexoelectric spectroscopy method. Higher frequency part of the viscoelastic spectra provided information about surface dissipation of orientational energy. Temperature dependence of surface viscosity was revealed for the first time. Influence of area density of CTAB monolayer was also investigated.

ALEXANDER G. PETROV Biomolecular Layers Department, Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko chaussee, 1784 Sofia, Bulgaria Nowadays, a modern physical heory becomes of a principle importance int understanding the complexities of the living world: the physics of lyotropic states of matter. We demonstrate here what kind of specification is necessary in the molecular description of lyomesogens, in the theory of elastic and flexoelectric phenomena, in order to make this part of liquid crystal physics suitable for describing and understanding the complex behaviour and structure-function relationship of biomembranes. We underline the role of a mechanical degree of freedom, the curvature, of liquid crystal systems, both model and living ones. Moreover, we stress the interrelation of the mechanical degree of freedom to the electrical, optical and chemical degrees of freedom of membranes, resulting in the sophisticated living cellular mechanisms. Keywords: lyotropics, biomembranes, elasticity, flexoelectricity

Patch clamp recordings have been made from adult locust (Schistocerca gregaria) muscle membrane to study the mechanosensitivity of potassium channels (BK and IK) in cell-attached patches by transiently applying measured pressures to the contents of the patch pipettes. The aim of the investigations was to demonstrate a novel gating behaviour by pressure of the BK channel in contrast to the familiar behaviour of the IK channel. The open probability (p 0) of the IK channel increased rapidly in response to a pressure step and monotonically during a pressure ramp. This gating was readily repeatable and rapidly reversible. The relationship between ln[p 0/(1–p 0)] and transmembrane pressure was linear. In comparison, p 0 for the BK channel was also increased by pressure, but its gating was delayed, cumulative, and hysteretic.

The Langmuir-Blodgett technique was used for deposition of monolayer lipid films of dipalmitoyl phosphatidylcholine (DPPC) on glass with a variable surface density of lipid molecules. In a certain range of surface density these surfaces oriented homeotropically the highly polar nematic liquid crystal of 4-cyano-${4}^{\ensuremath{'}}$-$n$-pentylbiphenyl (5CB). Optical transmission curves of liquid crystal layers sandwiched between orienting lipid monolayers were recorded versus magnetic field with high accuracy. They were further converted into optical retardation and fitted by a complete theory of the transition containing anchoring strength as a parameter. Independent measurements of refractive indices of 5CB were also performed by the prism method. Anchoring energies thus obtained showed a nonmonotonic behavior with increasing packing density of DPPC monolayers and a pronounced minimum around $0.82 {\mathrm{nm}}^{2}$ per molecule. This is explained by a complete theory of surface anchoring including steric, electric, flexoelectric, and notably surface polarization coupling mechanisms. The last one stands for surface polarized layers at the liquid-crystal interfaces interacting with surface electric field due to lipid molecules. The competition of these mechanisms leads to an initial dehancement followed by an enhancement of the anchoring strength at monotonically increasing DPPC packing density. Surface polarization evaluated from the experimental data is in good correspondence with molecular parameters.

The photoflexoelectric effect in homeotropic MBBA/D1 azo-dye nematic layers in a horizontal electric field subjected to UV illumination was investigated. About 10 per cent, reversible increase of the flexoresponse (i.e. the increment of transmitted light intensity between crossed polarisers due to an in-plane electric field) was found under epi-UV-illumination, with relaxation times of the order of 15 s. The d.c. voltage dependences of both dark and light flexoresponses followed the predictions of the theory. An UV-dependent amplification of the amplitude of flexo-oscillations (excited by an a.c. voltage) was also registered. The relative importance of bulk and surface contributions to the photoflexoresponse was discussed.

Mechano-electricity is a fundamental property of membranes, related to their mechanical and electrical degrees of freedom. Special importance in this respect is paid to the following pairs of variables: membrane tension and conducting defects' state; membrane curvature and polarization. Charge transfer processes are profoundly influenced by the interrelation between the tilted membrane characteristics. The effect of membrane tension on the probability of opening of ion channels in locust muscle membrane has been studied using patch clamp techniques. The data emanating from these studies are consistent with a linear model of stress activation of these channels. Mechanosensitive defects (ion pores) in model dip-tip lecithin membrances containing peptide cyanobacterial toxins (microcystin and nodularin) have also been studied. In this case application of tension caused a progressive opening of defect states of higher conductance, according to a model for pore gating by lateral tension. Membrane curv...

Aim of this work is to model cadmium and mercury ions' effects on the two components of a native membrane: the lipid matrix and the ion channels. The effects of heavy metal ions on soybean lecithin bilayer lipid membranes (BLMs) and BLM containing alamethicin ion channels have been studied. We have found that cadmium ions increase the membrane stability against electroporation (electroformation of nanosized conducting pores) and decrease the open probability of alamethicin channels. It was also found that the membrane stability was influenced by mercury ions in a nonmonotonic concentration-dependent manner and that open probability of alamethicin channels was increased.

We report the amplitude-frequency electro-optical (EO) modulation by a specific type of polymer-dispersed liquid crystal (PDLC) composites – planar single layers of large nematic microdroplets aligned by teflon nanolayers. Such a surface modifying PDLC system exhibits a selective modulated 2nd harmonic EO response by the dielectric oscillations of the nematic director. The bandlike behavioural characteristic of the amplitude-frequency modulation of light, achieved by the single-layered PDLC films, can be tuned by AC voltage applied on the PDLC cell. This property can be applied to tunable EO modulators operating in the infrasound frequency range.

In this chapter, the experimental data about the mechanical and the electromechanical properties of lipid bilayers and native membranes are collected and reviewed together with the existing methodology for their measurements. The emphasis is on the important mechanical property, membrane bending rigidity. The discussion is accompanied by illustrative experimental examples for the curvature elasticity of lipid bilayers with different compositions and in various environments. Particular attention is given to the alteration of the bending stiffness of lipid membranes as a consequence of the presence of biologically significant molecules such as cholesterol, carbohydrates, or amphiphilic peptides.

Flexoelectricity provides an exact relationship between electric and mechanical degree of freedom of a bilayer membrane, i.e. between transmembrane voltage and membrane curvature. Detailed studies by means of laser stroboscopic interferometry technique of direct flexoelectric effect in dipolar, zwitterionic and charged black lipid membranes (BLMs) and first observation of converse flexoelectric effect in an uranyl acetate-stabilized BLM are reviewed and theoretically interpreted. A new effect also involving another, optical degree of freedom of BLM, i.e. photo-flexoelectricity, was discovered very recently. It is observed in a composite BLM containing in-situ generated photo-semiconductor CdS nanosized particles (mimicking integral proteins of biomembranes) upon bandgap illumination. Light-dependent flexoelectric response is rationalized in terms of curvature-modulated BLM photo-potential. Possible applications of these new effects in membrane sensors (for sound, light, chemical species), in membrane actuators and their biological relevance are discussed.

The family of nematic liquid crystals has been recently enlarged with the class of metallorganic molecules. Among them, AZPAC [4,4′‐bis(hexiloxy)‐azoxybenzene–palladium complex] presents some unusual behavior as a transitory ‘‘ferroelectric’’ state, which we explain by considering bound multimers of AZPAC of peculiar steric conformation.

Flexoelectricity of pure Azpac (an HOAB-palladium complex) was studied using planar nematic layers under an in-plane electric field. Longitudinal domains were observed with a period inversely proportional to the applied d.c. electric field. These domains were considered as a first experiment manifestation of the theoretical prediction of R. B. Meyer (1969) and their study has permitted the evaluation of the difference in flexo-coefficientse 1z - e 3x. Their appearance can also be followed for the non-complexed HOAB, using instant video-microscopy frames. Mixtures of Azpac, up to 10wt%, and MBBA were oriented homeotropically and band flexoelectric deformations were observed, both in d.c. and in a.c. (1 to 1000 Hz) electric fields normal to the director. The dynamics of director reorientation were studied by the method of flexoelectric light modulation. A system comprising a He-Ne laser and a lock-in amplifier interfaced by a PC was developed. By operating this in a frequency sweep regime, viscoela...

Thin films (25 μm) of nanocomposites formed from nematic liquid crystal (LC) pentylcyano-biphenyl (5CB) doped with 0.5% wt. silver (Ag) nanospheres with a mean diameter ~ 10 nm were characterized by electrical measurements and dielectric spectroscopy in the frequency range from 1 mHz to 100 kHz. By using LC cells in which the electrodes are stripes of 1.2 mm width separated by a distance of 50 μm, it was possible to study the properties of Ag-5CB nematic nanocomposites by applying the external electric field either in the plane or perpendicular to the plane of the films. The results were compared with those obtained for undoped nematic 5CB in identical configurations of the experiments.

Planar lipid bilayers formed from monolayers of diphytanoyl lecithin (DPhL) were found to interact with plasmid DNA (5.6 kbp; M r = 3.7 × 10 6 ) leading to an increase in the conductance of the membrane. The association of DNA with a lipid bilayer greatly facilitates the transport of the small ions of the main salt KCl. The appearance of long-lived current levels, for instance, of 27.6 pA at V m = + 60 mV membrane voltage, where the actual contact (adsorption) is electrophoretically enhanced, suggests a locally conductive DNA/lipid interaction zone where parts of the DNA strand may be transiently inserted in the bilayer, leaving other parts of the DNA probably protruding out from the outer surface of the bilayer. At V m = − 60 mV, where DNA can be electrophoretically moved away from the membrane, the membrane current is practically zero. This current asymmetry is initially also observed at higher voltages, for instance at 200 mV. However, if the voltage sign ( V m = + 200 mV) is changed after a transient positive current (≈ 15 pA) was observed, there is also now (at V m = −200 mV) a finite negative current at the negative membrane voltage. Thus, it appears that at V m = + 200 mV the adsorbed parts of the polyelectrolyte DNA are not only transiently inserted in, but actually also electrophoretically pulled through, the porous zones onto the other membrane side leaving the bilayer structure basically intact. These data provide direct electric evidence for the electrophoretic transport of a highly charged and hydrated macromolecule, probably together with the associated gegen-ions, through the thin hydrophobic film of the lipid bilayer.

Anchoring interaction of MBBA and MBBA + 5CB nematic layers with monomolecular films of CTAB on ITO glass supports is studied by videomicroscopy in the presence of an electric field. Planar-planar or homeotropichomeotropic electrode substrates are used to make the nematic cells. The substrate symmetry is broken by coating only one electrode with self-assembled CTAB film. In a DC electric field we observe some new effects; (i) polarity-dependent breaking of anchoring and switching to two oblique states in dielectrically stable planar cells; (ii) a polarity-dependent flow-induced metastable anchoring transition in homeotropic cells to a planar or tilted alignment after the field is switched off. These results are discussed in terms of a surface transition assisted by electric transport of biphilic CTAB ions and by a surface memorization of the flow-induced planar alignment.

A survey of the published data on the type of anchoring (homeotropic, planar or tilted) of nematic liquid crystals on Langmuir-Blodgett (LB) films of charged and dipolar amphiphiles, as a function of surface density of molecules and number of molecular layers in the film, reveals a complex and seemingly controversial picture. A theoretical model of the anchoring, taking into account the non-homogeneous electric field originating from surface charges and dipoles, which dictates the liquid crystal orientation via a competition of dielectric, flexoelectric and ordoelectric torques, predicts a rich variety of anchoring states, depending on the sign of surface charges, the orientation of surface dipoles and the signs of dielectric anisotropy and total flexocoefficient. In specific situations, critical molecular densities and thicknesses for anchoring transitions (either first or second order) from homeotropic to tilted to planar or vice versa are predicted. Reentrance sequences, homeotropic-planar-homeotropic and planar-homeotropic-planar, are also possible, while surface density increases monotonically. Thus, the model resolves the apparent contradictions between various experiments and puts them in a general framework for the first time.