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We study the thermodynamic properties of pure and hydrated samples of SOPC (stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) membrane via Differential Scanning Calorimetry. We estimate the fundamenta...

Nanocomposites of the hydrogen-bonded dimeric liquid crystal heptyloxybenzoic acid (7OBA) with admixture of graphene flakes (GFs) are investigated with microtexture polarization analysis for new effects in their electro-optical behavior and characterized with Raman spectroscopy. In the nanocomposite with GF concentration of 3 × 10−4 wt% we establish as lowest-temperature LC state the triclinic smectic CG phase featuring chirality and ferroelectricity, previously found only in 7OBA nanocomposites with carbon nanotubes and in large banana-like bent-core molecules even though pure 7OBA is typically achiral. In the present study we find the CG phase manifested as two detached sub-structures with a smooth transition between them. For the appearance of the CG phase with its substructures denoted as CGcl and CGln we propose an explanation based on the π–π interaction of the 7OBA molecules with graphene and different coupling combinations of the clinic and leaning degree of freedom of the doubly tilted molecular geometry in the CG ordering. We examine the response of these structures to electric field, and demonstrate the presence in both of them of ferroelectric polarization with polar vector pointing out of the smectic layer planes. Molecular models are proposed for the 7OBA ordering in the substructures CGcl and CGln which are supported by the Raman spectroscopy results. The dispersion of the GFs in the nanocomposite bulk is confirmed by scanning electron microscopy in the solid state.

One of the primary roles of cholesterol (Chol) in the biological cell is to modulate the physical properties of the bilayer phospholipid membrane. Moreover, the effect of cholesterol on lipid bilayers is strongly dependent on the concentration, hence it can easily adapt to the changes in the cell temperature. Incorporation of cholesterol in membranes induces diverse changes in the bilayer properties, including variation of the bilayer thicknesses and changing the lipid order. Taking into consideration these physical and structural characteristics of the lipid membranes with cholesterol, as well as their optical birefringence, we apply the typical structural methods for studying these complex biological systems. We have used Fourier transform infrared (FTIR) and micro-Raman spectroscopy, aiming on study of the specific physical characteristics of the lipid membrane of the type 1-stearoyl-2-oleoyl-sn-glycerol-3-phosphocoline (SOPC). The analysis of the FTIR and Raman fingerprint spectral range, including band deconvolution, indicated that hydrogen bonds (HBs) exist between the hydroxyl groups of cholesterol and the carbonyl ester groups of the polar–apolar interface of the bilayer membrane. Upon insertion into the bilayer Chol actively participates in H-bonding at the C O sites, facilitates H-bonding of water to the PO2-site and relaxes the “improper H-bonding” of H2O molecules to the choline moiety. We also establish an overall ordering effect of Chol on the lipid bilayer. The interplay of cholesterol and water in realization of HB with the phospholipid moieties, in dependence on the Chol concentration, was analyzed.

The surface photo charge effect (SPCE) was applied for the first time at structure and phase transitions study of hydrogen bonded in dimer liquid crystals (HBDLCs). Due to the high sensitivity of t...

We investigated the seventh homologues of the hydrogen bonded in dimers liquid crystals p,n alkyloxybenzoic acids (7OBA), which in its pristine state displays achiral nematic (N) and smectic C (SC) states. The mixture of this liquid crystal with nanoparticles, expressing various shapes and sizes, where the liquid crystal serves as a matrix, introduces new optical and electrooptical properties of the composite material. We concentrated on the mixture 7OBA with single wall carbon nanotubes (SWCNTs), which exposes a set of chiral and ferroelectric states, including the unique one (smectic CG) state, which do not appear in the pristine achiral 7OBA. On the base of polarization microtextural, thermal and polarization spectroscopic (FT far infra red-FT FIR and microRaman) analyses we present a qualitative model of the smectic CG state in low-molecular dimeric liquid crystals.

Microtextural polarization, phase transitions, and electro-optical effects are studied in a series of nanocomposites, grown by mixing alkyloxybenzoic acids (nOBAs), displaying hydrogen-bonded dimeric liquid crystal (LC) state, with non-mesogens (single-walled carbon nanotubes (SWCNTs), perfluorooctanoic acid) or mesogens (bent-core LC compound D14F3). Each of the studied nanocomposites, in which the nOBA serves as a matrix, forms complexes with bent-shaped dimeric, caused by the interaction between the dopant structural units and the dimer rings. This feature, coordinated with the surface anchoring, bulk and electrical effects, leads to drastic reduction of the LC system symmetry. As a result, transitions from achiral (characteristic for the pristine nOBA) to chiral states (including ferroelectric smectic C with C2 symmetry and ferroelectric smectic CG with the lowest C1 triclinic one) take place. The functionalization of the SWCNTs causes drastic increase of the ferroelectricity.

A smectic C liquid crystal texture consisting of well oriented distinct local single crystals was grown using predefined orientation of single wall carbon nanotubes (SWCNTs) adsorbed on a SiO x layer deposited on a ITO treated glass surface. The orientation features of the SWCNTs were analyzed by microtexture analysis and polarized Raman spectroscopy. It was found that the surface memory effect, induced by the SWCNT/SiO x /ITO/glass surface and manifested in the preservation of the smectic C texture in the nematic phase, was many times stronger than memorization promoted by conventional SiO x /ITO/glass and ITO/glass surfaces, usually used for liquid crystal orientations. We observe surface anchoring and memorization strength reinforcement due to trapping of liquid crystal bulk charges by the SWCNTs (surface charge density increase). The SWCNT/SiO x /ITO/glass surface is found to cause a substantial enlargement of the smectic C distinct local single crystals as compared to SiO x /ITO/glass and ITO/glass surfaces. We also discuss the physical nature of the erasure activation energy components contributing to the surface memorization process.

Flexible supercapacitors are attractive devices for portable applications including those integrated in clothes. Highly conducting flexible electrodes can easily be fabricated by graphene powder and PE polymer foil but reliable fabrication of supercapacitor structure is still a challenge. A promising solution could be the incorporation of conducting polymer as polyaniline (PANI) intended to stabilize the mesoporous carbon and graphene plates, to form a conductive porous composite and to increase the capacitance. Low-cost aqueous electrolyte (1V) supercapacitor devices based on graphene/PANI composite were developed, tested in series configurations and compared in electrical performance. Preliminary applications in portable solar chargers are discussed.

Recent advances in supercapacitor technology reveals new opportunities for energy storage devices for application in electro-transportation and renewable energy sectors. In this paper results on device fabrication are reported. A low-cost screen-printing technology to obtain electrodes of supercapacitor has been applied. The device structure is based on Cu plate/hydrocarbon ink electrodes and gel electrolyte. Carbon ink is prepared from naturally occurring not full carbonized particles in the chimney's soot. The cyclic charge/discharge measurements confirm supercap behaviour and specific capacitance around 5 F/g at discharge current of 0.62 A/g. The flat configuration of the supercaps allows easy connection in series and adjustment to DC loads. A pack of four supercaps driving conventional LED has been thoroughly tested for more than 100 cycles.

The angular dependence of the surface anchoring energies of the smectic C with temperature independent tilt angle (type C1) on two surfaces, SiO x /ITO/glass and holographic diffraction grating, were measured using a twist-cell method. The smectic C monodomains rotation, starting at a critical imposed bulk twist, revealed a surface anchoring breaking. The surface anchoring strengths of the SiO x /ITO/glass and holographic grating were evaluated. A model for the bulk twist influence on the smectic C monodomain growth was suggested.

We study the zenithal anchoring strength of the nematic 5CB on holographic gratings of different amplitudes and a period Λ=0.5 μm. The surface monostable planar anchoring can be broken by short external electric pulses after which the director displays bistable textures: uniform and half-turn twisted. The measured threshold of the surface anchoring breaking is about 6 V/μm and is independent from the grating amplitude.

A new class of mixtures: 4, n -alkyloxybenzoic acids ( n -OBA) and 4-hydroxypyridine (HOPY) are investigated using FT-Far IR spectroscopy and polarisation microscopy. The macroscopic (chirality and structure phase transition induced by the mixture) and the spectroscopic (dynamic of the OH-bond deformation vibrations) characteristics of the complexes built through the bonding of both kinds of molecules are discussed. A weight ratio n -OBA:HOPY about 20 is predicted to be the most effective for realisation of a consistence with suitable chiral and anisotropic properties. The influence of the hydrophilic (polyvinylalcohol) and hydrophobic (polyimide) orienting surface on the spectral and textural properties of the complex is considered. A pronounced liquid crystal (characterized with fluid chains)–gel (rigid chains) transition was observed. An aggregation mechanism of the complex realization is suggested.

The surface-induced memorization of a smectic C liquid crystal texture in the temperature range of the nematic phase of 4-n-heptyloxybenzoic acid oriented by obliquely evaporated SiO on ITO was removed by imposing a bulk twist (Prevention of surface memorization was not observed when we used a simple ITO coating as the orienting surface.) A twist angle value (Ωc ≈ 70°) above which the surface memorization is prevented was found. Using microtextural polarization analysis of the smectic C texture, a qualitative explanation of the phenomenon is suggested. The conditions for preventing the surface memorization were deduced in terms of the balance between the surface and bulk torques. These conditions provide surface anchoring breaking, so removing the surface memory effect.

The aim of this work is to examine the photosensitivity of dye-sensitized materials. Three types of organic dye sensitizers, i.e. perylene diimide (PDI) derivatives with different terminal groups were synthesized. The synthesized PDI derivates were deposited by dipping on a glass/ITO substrate covered with arrays of ZnO nanorods (NR) grown by an electrochemical process. An Ag grid contact was deposited on the PDI films on the stack glass/ITO/ZnONR/PDI; then I-V characteristics of the structures were measured in dark and under illumination with a halogen lamp. The photosensitivity of the different dye-sensitized materials is discussed.

In this paper we report results of a study of the structural and optical properties of ZnO nanostructured (NS) array layers electrochemically deposited on different conductive substrates. The following types of substrates have been used: (i) conductive multilayer stack structures glass/ZnO:Al/Ag/ZnO:Al and glass/Ag/ZnO:Al/Ag/ZnO:Al, (ii) conductive multilayer stack structures glass/ZrO2/Ag/ZrO2, and (iii) ITO on the front side of Si heterojunction solar cells (SHJ). An analysis of the surface morphology of ZnO NS layers was performed by means of scanning electron microscopy (SEM). It was observed that the morphology of the deposited ZnO structures strongly depends on the type of the substrate used. It was also found that ZnO NS array with different shapes such as nanorods (NRs) or nanowhiskers (NWs) are grown. Reflection spectra of ZnO NS have been recorded. It was found that the deposited ZnO NS layers on the conductive multilayer stacks lead to decreasing reflectance but increasing diffuse reflection. In the case of ZnO NS growth on ITO on the front side of SHJ both direct and diffuse reflection decrease. Possible applications of ZnO NR or NW structures for production of advanced Si-based solar cells are discussed.

Structural, optical and electrical properties of ZnO thin films doped with different elements (Al, Al + H, V, Nb), deposited by r.f. magnetron sputtering on glass substrates at different temperature Ts between 50 and 500 °C are studied. XRD spectra demonstrate a preferential (002) crystallographic orientation with the c-axis perpendicular to the substrate surface and grains sizes of about 19–29 nm. The value of band gap energy Eg is in the range of 3.49–3.58 eV for ZnO:Al, 3.51–3.58 eV for ZnO:Al:H, 3.44–3.47 eV for ZnO:V, and 3.28–3.44 eV for ZnO:Nb. The deposited ZnO films doped with Al, H, V and Nb have low resistivities of 1.6–2.2⋅10−3 Ωcm. The transparency of the studied films is about 85–90 % in the visible region. The obtained transparent conductive ZnO thin films can be applied in solar cells and other optoelectronic devices as TCO.

By using polarizing microscopy analysis we have found that several achiral homologues of the 4-n-alkyloxybenzoic acids, displaying only the nematic phase, exhibit the optical properties of a chiral liquid crystal system. These acids possess a mesophase due to the formation of dimers via hydrogen bonding. The microtextural analysis was carried out in the temperature ranges of the isotropic, nematic and crystal phases. The nucleation of a chiral texture in small domains emerging on cooling in the isotropic phase was observed. These small domains are characterized by a conoscopic cross which presents an azimuth of 45° with respect to the polarizer axis, contrary to the usual nematic drops, for which the conoscopic cross is not rotated. On further cooling, these domains coalesce in the nematic phase close to the clearing point, thus building large chiral monodomains. Such coalesced droplets exhibit very thin stripe lines, as in the case of pure cholesterics with a tilted helix axis. Moreover, left- and right-...

A microscopical mechanism of the interaction between dimerized nematics of 4, n -alkyloxybenzoic acids and hydrophilic solid surfaces is developed. The liquid crystal molecules: monomers and closed dimers are considered like dipoles and quadrupoles, respectively. It is demonstrated that in the low-temperature and the high-temperature ranges of the nematic phase, the mechanisms of the microscopical interaction are different thus providing different macroscopical effects. The cell thickness and the temperature trends of the scalar order parameter, the effective surface energy and the concomitant anomalies in these trends are discussed on the basis of the proposed microscopical mechanism.

An optical polarization method for indication of recorded oriented smectic C textures by the process of surface memorization and their accumulation and storage in the nematic temperature range is presented. The recorded accumulated data are identified with the surface conditions-the polar and azimuthal angles. Using strong boundary conditions the assumption is made that the interval for recorded and accumulated textures increases when the anchoring energy is weak.

Electrical control of the surface memorization of an oriented smectic C texture in the temperature range of dimerized nematics with short range smectic C order (4-n-alkyloxybenzoic acids) is presented. It is demonstrated that by suitable choice of the electric field parameters and surface conditions it is possible to separate the thermal and electrical components of the total erasure activation energy. The significant role of the double charge electric layer in the mechanism of the surface memorization is verified. By the electrical control of the memorization, we have confirmed the electrical part of the modified Rapini-Papoular anchoring energy in the effective surface energy.

The temperature and the cell thickness trends of the scalar order parameter for the dimerized nematic with short-range smectic order of 4, n -nonyloxybenzoic acid (NOBA) are indicated by FT-FIR spectroscopy. The temperature dependence of this parameter shows an anomaly, in respect to the dependence typical for the classical nematics, at a definite temperature T ∗ in the nematic range. The scalar order parameter increases nonlinearly at cell thickness ( d ) decreasing between 20 and 6 μm and goes to saturation when d →∞, while below 6 μm down to 2 μm it decreases tending to a finite small value. It is indicated that the order parameter increasing of 0.035 with the thickness decreasing from 20 to 6 μm is comparable to order increasing induced by a stabilizing electric or magnetic fields; the order parameter decreasing at small cell thickness is an analog of a disordering induced by destabilizing fields. The anomalies in the temperature and cell thickness trends of the scalar order parameter are explained by the dynamics of the hydrogen bonding of the monomers in dimers stimulated by temperature and surface action variations. The relation between the surface order parameter square and the anchoring energy is indicated to be a linear dependence near the nematic–isotopic phase transition temperature. The trend of the anchoring energy on the cell thickness is explained by a modification of the Rapini–Papoular surface energy as an effective one, adding one dielectric part stimulated by phenomena as: existence of a double electric layer, thickness dependence of the surface charge density and surface polarization.

The surface memory effect (SME) storage of smectic C textures in the nematic temperature range has been investigated at various conducting and dielectric orienting coatings. The surface memorization for p-n-heptyl-,-octyl- and-nonyl-oxybenzoic acids (HOBA, OOBA, NOBA) consisting of dimer molecules is relatively strong and is observed only on conducting coatings (ITO, SiO/ITO) while dielectric surfaces depress the effect. p-n-Decyloxybenzoic acid (DOBA) exhibits a SME neither for conducting nor for dielectric coatings. The basic role of adsorption in the surface memorization is discussed in combination with the influence of surface polarization and of certain mechanical properties of the liquid crystal molecules. It is demonstrated that the erasure activation energy V hyperbolically decreases with increasing cell thickness d and reaches saturation values at d 250mum. Probably this dependence indicates the role of the dielectric state of the coatings in the surface memorization process. The problem of the p...

Using far-IR spectroscopy, the temperature dependence of the conformational order parameter of the nematics with flexible molecules (sixth, ninth and tenth homologues of p-n-alkyloxybenzoic acids) is found to deviate from that known for the orientational order parameter of the classical nematics. Conformational order ↔ disorder at a critical temperature T ∗ is indicated. Short-range smectic order fluctuations are detected in the sixth homologue and which do not display smectic C phase in its bulk phase diagram.

A surface memory effect (SME) is found in the dimerized nematic with short range smectic C order of 4-n-octyloxybenzoic acid (OOBA) in a cell whose walls have been covered with an obliquely evaporated SiO or ITO layer. The recording and erasure processes are discussed and erasure in the nematic phase is realized. A mechanism for the surface memorization is presented which takes into account the specific character of dimerized nematics preceding cooling into a smectic C phase.

We have studied the mechanism of the spontaneous twist of surface orientation observed when cooling down 4-n heptyloxybenzoic and 4-n octyloxybenzoic acids (HOBA and OOBA) in their dimerized nematic phase, above a SiO evaporated dielectric surface. We apply an electric field parallel to the dielectric substrate. When the field is parallel to the high temperature surface projection of the director, we up or down shift the temperature of the twist surface bifurcation, linearly in field. For perpendicular field, of defined sign, we can induce surface transitions from one twisted state to the other one. These observations can be explained by a simple polar model : the order electric polarization close to SiO is almost parallel to the substrate, since the molecular tilt is around the magic angle. Surface undulations create an anisotropic surface depolarizing field, which forces the polarization to rotate. We estimate a strong flexoelectric coefficient for 4-n octyloxybenzoic acid e ∼ +10 -3 cgs. This could be associated with the large electric quadrupole momentum of the hydrogen bonds in the nematic dimers.

We report on onset of a surface induced phase in droplets of OOBA liquid crystals desplaying optical properties typical for the smectic-A state. The latter state does not exist in the bulk phase diagram of the system. The surface phase appears in a temperature range close to the bulk nematic- smectic-C transition temperature TNC . The results are interpreted through a Landau-de Gennes type model with additional δ function terms.

The 6 - 10th homologues of 4-n-alkoxybenzoic acid, i.e. hexyl-, heptyl-, octyl-, nonyl- and decyloxybenzoic acids (60BA, HOBA, OOBA, NOBA and DOBA) are used for the present investigations. Far IR spectroscopy is used to study the state of hydrogen bonding at temperature variation of the nematic liquid crystal phase. The observed spectral bands are assigned to different OH deformation vibrations. From the analysis of the temperature dependence of the spectral band widths a cyclic ↔ open dimer transformation is indicated at different vibration frequencies and polarizations. The activation energy for the dimer and monomer reorientation is calculated and compared with that per hydrogen bond. The correlation lengths parallel and perpendicular to the nematic director (ξ‖ and ξ⊥) are calculated and an anisotropy is found in the temperature dependence of the critical index of the correlation length. A comparison with nonoriented nematics with hydrogen bonded molecules is presented.

Far-infrared transmittance spectra (200-30 cm−1) of the hydrogen bond in cyclic dimers of 4-n-heptyl-, octyl- and nonyloxybenzoic acids are observed and investigated. The spectral bands at 42, 63, 68 and 82 cm−1 are assigned to the four deformation vibrations: twisting, bending (in and out of the dimer ring plane) and stretching by halfwidth spectral band temperature analysis. The hydrogen band evolution in the isotropic and nematic phases is investigated. A cyclic ↔ open dimer transformation at different vibration frequencies and polarizations is shown. The critical character of the temperature T ∗ , defined as the temperature dividing the nematic phase of the nematics with hydrogen-bonded molecules into high-temperature (classical) and low-temperature (smectic-like) subphases, is demonstrated.

We investigated a series of nanocomposites, built of the hydrogen-bonded liquid crystal (LC) p-n-heptyloxybenzoic acid (7OBA) and single-walled carbon nanotubes (SWCNTs) by optical microtexture analysis and other complementary methods. The surface orientation strength of the LC cell and the bulk interaction of the dimeric LC molecules with the SWCNTs turn out to mainly govern the type (symmetry), thermal stability, and chirality of the LC states induced in these nanocomposites. As a result, a cascade of phase transitions and phases not typical for pristine 7OBA were observed and additionally confirmed by temperature-dependent Raman spectroscopy and differential scanning calorimetry. The most effective SWCNT concentrations in the LC matrix, ensuring both the necessary conformability between these materials and induction of liquid crystal phases with unique optical and electro-optical properties, were found to be in the range of 0.01-0.007 wt%. Reversal of smectic phases into reentrant nematic states as well as induction of chirality in all LC phases were observed in the SWCNT-7OBA nanocomposite, even though pure 7OBA is typically achiral. However, our most intriguing result is the detection below the reentrant nematic of a triclinic smectic-C(G) phase, which is chiral and biaxial, and exhibits bulk ferroelectricity.

The equilibrium constant for the equilibrium 2(monomer) ↔ dimer is calculated and as a result the energy per linear hydrogen bond is estimated. The hydrogen bond force constants (in the harmonic approximation) dependence on the deformation vibration frequencies is found. The activation energy for the dimer and monomer reorientation is calculated and compared with that per hydrogen bond. The critical character of the temperature T * (defined as the temperature dividing the nematics with hydrogen-bonded molecules into high-temperature (classical) and low-temperature (smectic-like) subphases) is demonstrated. The anisotropy of the critical index of the correlation length temperature dependence is found. The correlation lengths parallel and perpendicular to the nematic director (ξ | and ξ ⊥ ) are calculated. A theoretical conclusion concerning T * shifting at a set of bulk elastic deformations is confirmed. A value (1.036) for the critical index μ ⊥ of NOBA is found. This value coincides with that characterizing the susceptibility temperature dependence of He 4 and is interesting since the corresponding critical index cannot be measured in the superfluid.

Far-IR spectroscopy (200−30 cm−1 was used to study the temperature evolution of the hydrogen bonds in the nematic liquid crystal phase of 4, n-heptyl-, octyl- and nonyl-oxybenzoic acids (HOBA, OOBA and NOBA). The observed absorption bands (νOH = 82, 68, 63 and 42 cm−1) are assigned to the four predominant vibrations respectively — stretching, bending (out of and in the dimer ring plane) and twisting. From a spectral band half-width temperature analysis hydrogen-bond evolution in the isotropic and nematic phases is investigated. A cyclic ⇌ open dimer transformation at different vibrational frequencies and polarizations is indicated.

The equilibrium concentration of cyclic dimers, open dimers and monomers in 4,n-heptyloxybenzoic acid (HOBA) has been determined by IR spectroscopic investigations. It was found that the evolution of correlation between these molecular forms upon temperature variation provokes a strong textural transition in the nematic phase at temperature T*. The decisive role of local orientational order in the process of formation and destruction of hydrogen bonds is discussed. In addition, the shift of T* caused by bulk deformation of the nematic phase of HOBA on the basis of temperature variation of dimer-monomer concentration is considered as well. A new peculiar temperature (T f ) was found in the nematic phase where maximal dispersion in the temperature dependence of the cyclic and open dimer concentration is established. Strong textural oscillation is observed at that temperature.

A theoretical description of the electrodynamical instability for the initial and the fundamental domain regimes in smectic C liquid crystals is presented. On the basis of the bi-axial aspects of the problem, a dependence of the threshold field, charge and curvature relaxation times on the director n tilt angle (ω) were found. It is demonstrated that the electrodynamical instability is a priority of the C1 type smectics, where the director tilt angle is temperature independent in the smectic C temperature range. It was found that the dielectric reorientation processes are stimulated mainly in C2 smectics, where the director tilt angle is small and temperature dependent. The role of the sign and the magnitude of the dielectric anisotropy on the character of the electrooptic responses (pure electrohydrodynamic instability, pure dielectric reorientation or a mixture of the two) is discussed.

The liquid crystal HOBA exhibits a nematic phase between the achiral smectic C region and the isotropic one. In the nematic phase two subphases N1 and N2 can be distinguished. A shift of the transition temperature N1 − N2 has been observed, if an elastic deformation is involved, with respect to the unidirectional homogeneous case. In the present paper the experimental data concerning a twist distortion are discussed, and a theoretical model is given.

In this paper, results are reported from the study of the structural and optical properties of ZnO nanostructured arrays with nanorods (NRs) grown electrochemically on ITO seeding layers with two different thicknesses deposited on a glass substrate. The properties are compared of the ZnO NRs grown on ITO seeding layers with resistivity 6.4 × 10-4 Ω cm, sheet resistance 80 Ω/ and 8 Ω/ and different ITO thicknesses - 80 and 800 nm, respectively. The optical spectra of reflectance, transmittance, diffused reflection and diffused transmission and the haze ratio in transmission and reflection of the samples carried out before and after ZnO NRs deposition are compared and discussed. The structures' properties are studied by scanning electron microscopy (SEM). The ZnO NRs arrays with increased values of diffused transmission and reflection compared to the seeding layer substrates can be used in thin-film solar cells for increasing the light trapping.

The liquid crystals (LC), due to their naturally high bulk ordering, strong birefringence and easy electrooptical driving, serve as matrix in the nanocomposites doped with non-mesogenic or mesogenic nanoparticles. The nanocomposite's structural units exhibit very complex molecular form indicating the strength and the intermolecular interaction between the matrix and dopant's molecules. Hydrogen bonds are of particular significance for the formation of the nanocomposite structural units, since the symmetry of the LC nanocomposite could be controlled and controllably decreased due to the acceptor-donor interaction between the dimeric matrix and the dopants. As a result, the LC nanocomposite can reach the lowest symmetry, known as triclinic - C1. Using the LC p,n-alkyloxybensoic acids (nOBA) in form of hydrogen-bonded dimers as matrix and non-mesogenics - single walls carbon nanotubes (SWCNT), perfluorooctanoic acid (PFOA), 4-hydrooxypiridin (HOPY) or mesogen - cholesteryl benzoate (ChB) as dopants and choosing optimal concentrations (where the typical LC state was preserved), we obtained nanocomopsites 7OBA/SWCNT, 7OBA/PFOA, 9OBA/HOPY and 8OBA/ChB. We indicate two forms of ferroelectricity in the studied nanocomposites: developable ferroelectricity, characteristic for the 9OBA/HOPY, 7OBA/PFOA compounds and developed ferroelectricity characteristic for 8OBA/SWCNT, 8OBA/ChB.

A comparative study of some mesogenic azobenzene compounds and their organometallic palladium(II) derivatives is reported. On the basis of the textural properties, calorimetric data and uniaxial order parameters (as deduced approximately from infrared spectroscopy), the main features induced by palladium complexation are (i) the transition temperatures increase, (ii) the number of ordered mesophases increases, (iii) the nematic uniaxial order parameter decreases, (iv) the textures are typical of highly ordered phases, and (v) an optical biaxiality appears in the nematic phase. The calorimetric data as well as the order parameters, if discussed in terms of molecular biaxiality result are interpreted at least qualitatively. Optical investigations show that macroscopical biaxial ordering can be achieved.

Optical and electrooptical properties of chiral dopants induced by cholesteric phase in 7 and 8 homologues (HOBA and OOBA) of the 4-n-alkyloxybenzoic acid are studied. A temperature Tp is found, where some anomalies in the electrooptical characteristics, the helix pitch of the system and a strong textural transformation, are detected. Similar to the nematic with smectic ordering, this temperature divides the induced cholesteric phase in two ranges with different characteristics. An electrooptical memorization of the fingerprint texture is found above Tp but not below Tp. The shift of the temperature Tp is investigated. Es werden die optischen und elektrooptischen Eigenschaften von Chiral-Donatoren untersucht, die durch eine Cholesterin-Phase in 7- und 8-Homologe (HOBA und OOBA) der 4-n-Alkyloxybenzoesaure induziert werden. Eine Temperatur Tp wird gefunden, bei der einige Anomalien in den elektrooptischen Charakteristiken, die Helixsteigung des Systems und eine starke texturelle Transformation entdeckt werden. Ahnlich wie beim nematischen und smektischen Ordnungsprozes, teilt diese Temperatur die induzierte Cholesterinphase in zwei Gebiete mit unterschiedlichen Charakteristiken. Oberhalb Tp, jedoch nicht unterhalb Tp, wird eine elektrooptische Speicherung einer Fingerabdrucktextur gefunden. Die Verschiebung der Temperatur Tp wird untersucht.

A ferroelectric smectic C state was induced in 4-n-octyloxybenzoic acid (OOBA) and 4-n-heptyloxybenzoic acid (HOBA) by the chiral dopants-cholesteryl benzoate (CB) and DOBAMBC—M1 and M2 mixtures respectively. A strong electrooptic effect was found for a DC electric field in the ferroelectric state of the M1 mixture stabilized by the boundaries. This effect is characterised by six increasing electric field thresholds (E (1) th-E (6) th), where drastic textural and colour changes occur. The electrooptic responses in AC electric field for the two mixtures are discussed. A qualitative model to explain the observed phenomenon is presented.

Professor Nikolay Kirov Nikolov graduated in Chemistry from Sofia University 'St. Kliment Ohridski', Bulgaria, in 1968. He received his Ph.D. degree in 1973, D.Sc. in 1988 and was appointed to the position of Professor of Physics in the Institute of Solid State Physics (ISSP), Bulgarian Academy of Sciences (BAS), in 1989. Prof. Kirov rose to become an international authority in the area of molecular spectroscopy, and in particular in the vibrational spectroscopy of thermotropic liquid crystals. Prof. Kirov was a scientist of high reputation both in Bulgaria and globally. His scientific papers, numbering some 150, focus on the physics of liquid crystals. His systematic investigations of the vibrational spectroscopy of a wide class of thermotropic liquid crystals were collected in the monograph Vibrational spectroscopy of liquid crystals (1984), in which the molecular structure and properties of various liquid crystals, vibrational assignments, orientational order parameters and their calculation by molecular dynamics are presented. A range of liquid crystal materials was categorised and reported in his second book Atlas of vibrational spectra of liquid crystals (1988). Both publications remain a valuable source of information for specialists in the field of molecular spectroscopy. The outstanding contributions and growing reputation of Prof. Kirov led to periods as Visiting Scientist in the Universities of Parma, Calabria and Wroclaw. His abilities as a scientific organizer and leader were also notable, and led to a long and distinguished period of service in the Institute of Solid State Physics, being first appointed in 1980 as Scientific Secretary, and subsequently as Head of the Laboratory of Optics and Spectroscopy (1990-1998) and Director of the Institute (1991-1999). He was Chairman of the Scientific Council of ISSP over this period, and a member of the Specialized Scientific Council on Condensed Matter Physics. Prof. Kirov was a member of the High Testimonial Committee of the Republic of Bulgaria during 1996. Nikolay Kirov was a key figure in the organization, promotion and success of the International School on Condensed Matter Physics (ISCMP), where he was able to use his network of international contacts to excellent effect. He served as Scientific Secretary (1988-1990), Chairman and Editor of the ISCMP Proceedings (1992-1998), and as Chairman Emeritus (2002-2012). Prof. Kirov is an Honorary Member of the Institute of Solid State Physics. He received the Honorary Diploma 'Nicola Obreshkov' in 1986 and the "Marin Drinov" Sign of Honour BAS (on a ribbon) in 1998, for achievements in the physical and mathematical sciences. He was also honoured outside his native Bulgaria, receiving a Gold Medal from Wroclaw University, Poland, in recognition of successful scientific collaborations in the area of molecular structure.

Surface plasmon resonance (SPR) is widely used in different types of optical detection schemes and for light manipulation at sub-wavelength scale. Usually Kretschmann configuration is used for effective SPR excitation. There are a lot of experimental and theoretical investigations about the influence of the dielectric, adjacent to the metal, on SPR. However, till now the influence on liquid crystal layer, adjacent to the metal, is not considered to our best knowledge. The purpose of the present paper is to cover this gap. We simulate the influence of thin layer of liquid crystal, adjacent to the metal, on the SPR characteristics. For this purpose Maxwell equations are numerically solved for layer structure: prism/gold/liquid crystal/air. The light reflection spectra are calculated for chiral structure of ferroelectric smectic C (SmC*) liquid crystal layer. The angular and wavelength response are considered. Special attention is paid to SPR excitation for variation of tilt angle and different angle of incident light. The influence of SPR of the pitch length and cell thickness is also considered.

The liquid crystalline (LC) nature of alkyloxybenzoic acids is preserved after adding of any mesogenic or non-mesogenic compound through hydrogen bonding. However, this noncovalent interaction provokes a sizable effect on the physical properties as, e. g. melting point and mesomorphic states. In the present work we investigate nanocomposites, prepared by mixture of the eighth homologue of p-n-alkyloxybenzoic acids (8OBA) with single-walled carbon nanotubes (SWCNT) with the purpose to modify the optical properties of the liquid crystal. We exercise optical control on the LC system by inserting SWCNT specially functionalized by carboxylic groups. Since the liquid crystalline state combines order and mobility at the molecular (nanoscale) level, molecular modification can lead to different macroscopical nanocomposite symmetry. The thermal properties of the functionalized nanocomposite are confirmed by DSC analyses. The mechanism of the interaction between surface-treated nanoparticles (functionalized nanotubes) and the liquid crystal 8OBA bent- dimer molecules is briefly discussed.

ZnO nano structured (NS) arrays are grown by electrochemical method on conductive seeding layers of ZnO doped with V (ZnO:V) deposited by magnetron sputtering on glass substrates. The surface morphology of the ZnO NS is studied by Scanning Electron Microscopy. The spectra of transmittance, diffused and specular reflectance are measured for the ZnO NS arrays deposited for 30 and 60 min. and are compared to the corresponding spectra of the substrate with seeding ZnO:V film. The values of diffused reflection are higher than those of the seeding layers due to the grown of nanostructured ZnO arrays. Increasing of the diffused reflection with the time of electrochemical growth is observed and is explained by increasing size of the grains. The results show the possibility for deposition of nanostructured ZnO arrays on low cost ZnO:V seeding layers with large effective surface area that could be applied in thin film solar cells for increasing light harvesting.