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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.

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.

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.

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 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.

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.

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.

Cells are ion conductive gels surrounded by a ∼5-nm-thick insulating membrane, and molecular ionic pumps in the membrane establish an internal potential of approximately −90 mV. This electrical energy store is used for high-speed communication in nerve and muscle and other cells. Nature also has used this electric field for high-speed motor activity, most notably in the ear, where transduction and detection can function as high as 120 kHz. In the ear, there are two sets of sensory cells: the “inner hair cells” that generate an electrical output to the nervous system and the more numerous “outer hair cells” that use electromotility to counteract viscosity and thus sharpen resonance to improve frequency resolution. Nature, in a remarkable exhibition of nanomechanics, has made out of soft, aqueous materials a microphone and high-speed decoder capable of functioning at 120 kHz, limited only by thermal noise. Both physics and biology are only now becoming aware of the material properties of biomembranes and their ability to perform work and sense the environment. We anticipate new examples of this biopiezoelectricity will be forthcoming.

We report on the converse flexoelectric effect in two bent-core nematic liquid crystals with opposite dielectric anisotropies. The results are based on electro-optic investigations of inplane field-driven distortions in homeotropic samples (the Helfrich method). They are interpreted by an extension of the Helfrich theory that takes into account the higher order distortions. The bend flexocoefficient for both the compounds is of the usual order of magnitude as in calamitics, unlike in a previously investigated bent-core nematic for which giant values of the bend flexocoefficient are reported. In order to resolve this discrepancy, we propose a molecular model with nonpolar clusters showing quadrupolar flexoelectricity. The study also includes measurements on surface polarization instabilities in the dielectrically positive material; the splay flexocoefficient thereby deduced is also of the conventional order.

Electric field-induced second harmonic generation (EFISH) was studied for the liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) (a nematic phase material at room temperature). The intensity of coherent SHG from 5CB cells upon DC electric field was measured for various initial orientations of the liquid crystal. The dependence of the SHG intensity on the pump beam incidence angle was obtained in transmission geometry using sample rotation method. The experimental results (the registered light intensity in the output SHG interference patterns) were theoretically modelled and analyzed.

We are delighted to present the Proceedings of the 18th International School on Condensed Matter Physics: Challenges of Nanoscale Science: Theory, Materials, Applications, organized by the Institute of Solid State Physics of the Bulgarian Academy of Sciences and chaired by Professor Alexander G Petrov. On this occasion the School was held in memory of Professor Nikolay Kirov (1943-2013), former Director of the Institute and Chairman between 1991 and 1998. The 18ISCMP was one of several events dedicated to the 145th anniversary of the Bulgarian Academy of Sciences in 2014, and was held in the welcoming Black Sea resort of St. Constantine and Helena near Varna, at the Hotel and Congress Centre Frederic Joliot-Curie. Participants from 16 countries delivered 32 invited lectures, and 71 contributed posters were presented over three lively and well-attended evening sessions. Manuscripts submitted to the Proceedings were refereed in accordance with the guidelines of the Journal of Physics: Conference Series, and we believe the papers published herein testify to the high technical quality and diversity of contributions. A satellite meeting, Transition Metal Oxide Thin Films - Functional Layers in Smart Windows and Water Splitting Devices: Technology and Optoelectronic Properties was held in parallel with the School (http://www.inera.org, 3-6 Sept 2014). This activity, which took place under the FP7-funded project INERA, offered opportunities for crossdisciplinary discussions and exchange of ideas between both sets of participants. As always, a major factor in the success of the 18ISCMP was the social programme, headed by the organized events (Welcome and Farewell Parties) and enhanced in no small measure by a variety of pleasant local restaurants, bars and beaches. We are most grateful to staff of the Journal of Physics: Conference Series for their continued support for the School, this being the third occasion on which the Proceedings have been published under its auspices.

Homeotropic nematic layers of MBBA have been studied by a phase-sensitive flexoelectric spectroscopy method. They have been oriented by films of dilauroyl phosphatidyl choline (DLPC) and cetyl trimethyl-ammonium bromide (CTAB) self-assembled onto the cell glass plates. Using continuum theory, the transmitted light versus excitation frequency spectral shapes have been derived in terms of space variation of the nematic parameters (elastic constant, flexoelectric coefficient, rotational viscosity, and birefringence). These viscoelastic spectra contain information about the surface dissipation of the orientational energy for different aligning films that partially desorb from the surface and dissolve in the nematic, producing a gradient of the surfactant. A new type of flexoelectric effect dependent on the space derivative of flexo-coefficients has been identified. This effect consists of a bulk flexo-torque source that substantially influences the apparent liquid crystal anchoring. Static and dynamic cases h...

We are pleased to introduce the Proceedings of the 17th International School on Condensed Matter Physics: Open Problems in Condensed Matter Physics, Biomedical Physics and their Applications, organized by the Institute of Solid State Physics of the Bulgarian Academy of Sciences. The Chairman of the School was Professor Alexander G Petrov. Like prior events, the School took place in the beautiful Black Sea resort of Saints Constantine and Helena near Varna, going back to the refurbished facilities of the Panorama hotel. Participants from 17 different countries delivered 31 invited lecturers and 78 posters, contributing through three sessions of poster presentations. Papers submitted to the Proceedings were refereed according to the high standards of the Journal of Physics: Conference Series and the accepted papers illustrate the diversity and the high level of the contributions. Not least significant factor for the success of the 17 ISCMP was the social program, both the organized events (Welcome and Farewell Parties) and the variety of pleasant local restaurants and beaches. Visits to the Archaeological Museum (rich in valuable gold treasures of the ancient Thracian culture) and to the famous rock monastery Aladja were organized for the participants from the Varna Municipality. These Proceedings are published for the second time by the Journal of Physics: Conference Series. We are grateful to the Journal's staff for supporting this idea. The Committee decided that the next event will take place again in Saints Constantine and Helena, 1–5 September 2014. It will be entitled: Challenges of the Nanoscale Science: Theory, Materials and Applications. Doriana Dimova-Malinovska, Diana Nesheva, Emilia Pecheva, Alexander G Petrov and Marina T Primatarowa Editors

We report on UV light-induced tilted anchoring in a mixture of the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA) with a photoactive liquid crystalline azo dye (4-hexyloxybenzoloxy-4'-cyanoazobenzene) at 1 wt.% concentration. The surface anchoring found in this guest-host liquid-crystal system confined in homeotropic thin films is due to trans-cis photoizomerization of the guest azo molecules upon UV light.

The linear electro-optic response of polymer-dispersed liquid crystal films has been studied. Micrometer-sized droplets of a cyanobiphenyl mixture (E7) were formed in a Norland Optical Adhesive 65 photopolymer by photopolymerization-induced phase separation. Samples with various average nematic droplet sizes were systematically investigated. The temperature dependence of the first-harmonic electro-optic spectra was obtained. Peculiar peaks and double peaks in the phase spectra were found at temperatures close to the clearing point. Samples with narrow distributions of droplet sizes were characterized by a double peak of the amplitude spectra in the low-frequency range. A flexoelectric origin of the first-harmonic spectra in confined nematic systems is discussed.

The effect of cadmium and mercury ions on channels formed by alamethicin in lipid bilayers has been investigated. Mercury increases the opening probability of alamethicin ion channels, but cadmium reduces it. Thus, a heavy-metal sensor concept could be suggested.

We generalize a previous model that was proposed to interpret the thickness dependence of the anchoring energy relevant to the nematic-liquid-crystal-solid substrate interaction. We show that beside the dielectric coupling between the surface electric field and the nematic liquid crystal, the quadrupolar flexoelectric coupling plays an important role. Possible nonmonotonic trends of the anchoring energy strength versus the thickness of the sample are predicted to be due to this new coupling mechanism

We are pleased to introduce the Proceedings of the 16 ISCMP, organized by the Institute of Solid State Physics of the Bulgarian Academy of Sciences. The Chairman of the School was Professor Alexander G Petrov. The School was dedicated to the late Professor Joe Marshall, who served for a long time as Chairman and Honorary Chairman and left us just after having completed the proceedings of the previous School. Like previous events, the School took place in the beautiful Black Sea resort of Saint Constantine and Elena near Varna, going back to the renewed facilities of the Panorama hotel. Participants from 19 different countries delivered 34 invited lecturers and 75 posters, contributing to three sessions of poster presentations. Papers submitted to the Proceedings were refereed according to the high standards of the Journal of Physics: Conference Series and the articles published in this volume illustrate the diversity and the high level of the contributions. Not the least significant factor in the success of the 16 ISCMP was the social program, both the organized events (Welcome and Farewell Parties) and the variety of pleasant local restaurants and beaches. These Proceedings are published for the first time in Journal of Physics: Conference Series. We are grateful to the Journal's staff for encouraging this idea. The Scientific Committee of the ISCMP dedicates this volume of the Proceedings to the living memory of Professor Joe Marshall, Honorary Chairman of the ISCMP. The Committee decided that the next event will take place again in Saint Constantine and Elena, in September 2012. It will be entitled: Open Problems in Condensed Matter Physics, Biomedical Physics and their Applications. Doriana Dimova-Malinovska, Diana Nesheva, Alexander G Petrov and Marina T Primatarowa

The influence has been studied of single-walled carbon nanotubes with a concentration between 0.0001 and 0.001 wt % and a dried zwitter-ionic phospholipid (SOPC: l-stearoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine) layer of thickness, smaller than 0.5 μm, deposited only on a half of one of the two glass plates, on the behaviour of the gradient flexoelectric and surface polarization induced domains arising in a homeotropic nematic E7 (a mixture of 5CB, 7CB, 8OCB and 5CT) layer. We have observed for the first time different polar on/off formation of the surface polarization induced domains in the region of the liquid crystal cell without surface deposited lipid SOPC layer. On the other hand, the SOPC layer strongly decreases the gradient of the electric field thus leading to less-pronounced flexoelectric domains. However, the SOPC layer does not influence the creation of surface polarization induced domains and of injection induced domains arising at voltages above 4V. Appropriate dynamic light transmitted curves have been recorded and typical microphotographs have been taken.

A digitalized version of the standard method of conoscopy was employed to register the bend deformation of molecular orientation in homeotropic nematic layers caused by an in-plane applied DC electric field, and influenced by UV light illumination. Two guest-host systems prepared by mixing of a nematic liquid crystal and an azobenzene-containing photochromic liquid crystalline material featuring a longitudinal molecular asymmetry, were studied. Upon continuous UV irradiation, a photo-isomerization of the photochromic molecules occurs resulting in an enhanced flexoelectric response of the guest-host mixtures. The dependence of the photoflexoeffect on the field strength and UV light intensity was also examined.