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Surface-active polymers derived from styrene monomers containing siloxane (S), fluoroalkyl (F) and/or ethoxylated (E) side chains were blended with an elastomer matrix, either poly(dimethyl siloxane) (PDMS) or poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), and spray-coated on top of PDMS or SEBS preformed films. By contact angle and X-ray photoelectron spectroscopy measurements, it was found that the surface-active polymer preferentially populated the outermost layers of the coating, despite its low content in the blend. However, the self-segregation process and the response to the external environment strongly depended on both the chemistry of the polymer and the type of matrix used for the blend. Additionally, mechanical testing showed that the elastic modulus of SEBS-based coatings was one order of magnitude higher than that of the corresponding PDMS-based coatings. The coatings were subjected to laboratory bioassays with the marine algaUlva linza. PDMS-based coatings had superior fouling-release properties compared to the SEBS-based coatings. [ABSTRACT FROM AUTHOR]

The hydrodynamic performance of two, recently developed, nanostructured and fluorinated polymer coatings was explored in a systematic experimental study using the Newcastle University Cavitation Tunnel. The experiments consisted of testing the two coatings on an axisymmetric body apparatus to measure their boundary layer flow and frictional drag simultaneously. The tests also included a smooth reference surface as well as a state-of-the-art commercial fouling-release coating (Intersleek® 900). The boundary layer measurements were performed using a two-dimensional Laser Doppler Velocimetry (LDV) system whilst the direct frictional force measurements were taken using a special load cell installed in the testing body. Careful surface roughness measurements of the test surfaces were also performed including the use of a non-contact high precision laser profilometer. The tests and subsequent analysis of the data highlighted the exceptionally good frictional properties of all the coatings tested as well as some of the drag benefits of the new polymer coatings in the investigated Reynolds number range. [ABSTRACT FROM PUBLISHER]

A new bell-shaped compound, (dec-9-en-1-yl) 3,5-bis{[4'-(n-nonyloxy)biphenyl-4-carbonyl]oxy}benzoate (I), with symmetrical substitution in positions 3 and 5 of the central ring, was prepared. Although this material was not mesogenic, it exhibited low melting and freezing points and was therefore suitable as a component for mixing studies. These were carried out on a binary system composed of I and the rod-like 4-(n-octyloxy)phenyl 4´-(n-hexyloxy)benzoate (II), which exhibits enantiotropic nematic, as well as monotropic SmC and SmX phases. Selected mixtures were studied by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction on non-oriented samples. It was found that the binary mixtures exhibit mesomorphic properties close to room temperature. [ABSTRACT FROM AUTHOR]

New antiferroelectric liquid crystal (AFLC) cells having a uniquely asymmetric hysteresis response were obtained by using dissimilar surface anchoring on the cell glass plates. In particular, a low surface energy fluorinated block copolymer was deposited by spin-coating on one side and Nylon6 was cured and rubbed on the opposite side. These asymmetric AFLC displays featured an unusually large shift of the hysteresis curve and a fairly stable greyscale when driven with previously designed waveforms. The contrast ratio in both quasi static and dynamic conditions was especially high (ca. 100) for AFLCs. The new findings can shine new light on the current proposed models of asymmetric hysteresis, based on ion currents and charge trapping onto the alignment surfaces. [ABSTRACT FROM AUTHOR]

Two classes of thermotropic polymers were synthesized containing the trans-azobenzene unit as both a mesogenic and a photochromic group. In the former class (I) the azobenzene unit is incorporated into the main chain of substituted polymalonates, while in the latter class (II) it is appended as a side chain substituent to a polyacrylate backbone. The liquid-crystalline properties of the polymers were studied as a function of the chemical structure. All of the prepared polymers I have smectic phases. Polymers II are nematic and/or smectic, or cholesteric when including a chiral residue R9. Polymers I and II when radiated at 348 nm in chloroform solution undergo trans-to-cis isomerization of the azobenzene moiety. The calculated rate constants are comparable with those of low molar mass model compounds, and indicate that the macromolecular structure does not significantly affect the photoisomerization rate. [ABSTRACT FROM AUTHOR]

We studied by electron spin resonance (ESR) spectroscopy the reorientational dynamics of the cholestane spin probe dissolved in the matrix of the PMA4 40/60 copolymer containing methyl methacrylate (MMA, 40 mol%) and azobenzene methacrylate (MA4, 60 mol%) counits. Heterogeneities in the probe dynamics at the nanometer length scale were evidenced and attributed to the existence of molecular sites with slow and fast spinning correlation times. Different dynamic regimes were also observed with a crossover temperature T C that was correlated with the glass transition temperature T g of the copolymer, T C = 1.17 T g . Even though the nematic-to-isotropic transition temperature could not be detected, the probe dynamics experienced the onset of nematic order at the molecular level. The results are compared with those of the closely related nematic PMA4 30/70 copolymer. [ABSTRACT FROM AUTHOR]

Two copolymers containing nonmesogenic methyl methacrylate (MMA) and nematogenic azobenzene methacrylate (MA4) side groups (30/70 and 40/60 copolymers) azobenzene were studied in the linear viscoelastic regime. The time-temperature superposition principle was found to hold over the whole investigated temperature range, even across the nematic-isotropic transition in the 30/70 copolymer. Rheological steady state and oscillatory measurements were used to obtain the temperature dependence of the zero shear viscosity. The strength and dynamic fragility of these two copolymers were compared with those of the corresponding PMA4 and PMMA homopolymers, which pointed out the role of the structure of the main chain in dictating the relaxational dynamics. [ABSTRACT FROM AUTHOR]

We prepared new copolymers of a 2-vinyl cyclopropane monomer carrying – (CF 2 ) 8 F fluorocarbon side chains (VCPF8) and vinyl acetate (VAc). The copolymers formed a partly interdigitated S Ad mesophase. Static contact angles ? were measured using various wetting liquids, which proved that thin films of the copolymers were both hydrophobic (? > 110° with water) and lipophobic (? > 65° with n-hexadecane). The surface tensions ? sv of the polymer films were evaluated by two different approaches and resulted to have quite low values (? sv 2 ), even at relatively low contents of fluorocarbon side chains. [ABSTRACT FROM AUTHOR]

In this paper we report recent results on the optoelectronic properties of silicon-rich nitride (SRN), a novel material for microphotonics applications compatible with silicon technology. We have investigated optical emission, energy transfer phenomena to erbium ions and PbS colloidal quantum dots in SRN films and grown active photonic SRN structures. The optical properties of the films were studied by micro-Raman and photoluminescence spectroscopy and, as confirmed by transmission electron microscopy analysis, indicate the presence of small (1–2?nm) Si clusters characterized by efficient (7% quantum efficiency at room temperature), broad-band and near-infrared emission with very large absorption/emission Stokes shift. Time and temperature resolved photoluminescence measurements demonstrate nanosecond-fast, wavelength-dependent recombination dynamics with negligible light emission thermal quenching from 4 to 330?K. First-principles simulations of 1?nm size crystalline and amorphous silicon dots show that nitrogen atoms bonded to the surface of nanometre silicon clusters play a crucial role in the emission mechanism of SRN films. In addition, we show that SRN is a suitable material for the fabrication of light-emitting complex photonic crystals and novel waveguide structures based on resonant transmission of localized light states in aperiodic dielectrics. The versatility of light-emitting SRN systems can provide alternative routes towards the fabrication of optically active CMOS devices. [ABSTRACT FROM AUTHOR]

We prepared several triblock copolymers of the A&sbnd;B&sbnd;C and A–C–B types composed of hydrophobic polystyrene (A), hydrophobic/lipophobic fluorinated polystyrene (B), and hydrophilic PEG-modified polystyrene (C) blocks with greatly varied degrees of polymerization. The resulting surface structure and organization of the polymer films were investigated by measurements of the static contact angle with several interrogating liquids and by X-ray photoelectron spectroscopy at different take-off angles. The contact angle values were also used to evaluate the film surface tensions, following two fundamentally different approaches. The low surface energies found for any of the triblock copolymers were attributed to the pronounced hydrophobicity and lipophobicity of the outermost surface caused by the preferential segregation of the fluorinated block regardless of the distinctly different macromolecular architectures of the triblock copolymers. [ABSTRACT FROM AUTHOR]

We prepared novel macromolecular architectures of main-chain polymers poly(1)–poly(6) by a ruthenium-catalyzed acyclic diene metathesis (ADMET) polymerization of banana diene monomers 1–6. Copolymerization with a calamitic diacrylate monomer 7 yielded a copolymer poly(1-alt-7) in which the banana and the calamitic units regularly alternated along the polymer main chain. We also started the structural characterization of the polymers and found a varied mesophase behavior depending on the nature of the banana mesogen incorporated. [ABSTRACT FROM AUTHOR]

We designed and synthesized new SmA* liquid crystals with different molecular architectures based on the chiral mesogen MR11, which was unsubstituted, or attached at one end and at both ends of a trisiloxane segment in the monosubstituted MSi3-MR11 and disubstituted DSi3-MR11 siloxanes, respectively. We studied the critical divergence of the magnetic susceptibility by measurements of the induced tilt angle Θ ind at the SmA*–SmC* transition. While all three SmA* liquid crystals presented a de Vries character, this was quite distinctive for DSi3-MR11 for which the critical exponent γ = 1.87 was maximal. X-ray diffraction experiments confirmed that the SmA*–SmC* transition occurred with essentially no layer shrinkage. [ABSTRACT FROM AUTHOR]

The enthalpy relaxation mechanism of an azobenzene side chain liquid crystal polymethacrylate is investigated by means of DSC experiments after proper annealing procedures at temperatures below the glass transition. The data are analyzed according to a recently developed trap model. The model is found to be able to describe the experimental enthalpy relaxation data fairly well, providing a means to estimate the cooperativity length of the system. [ABSTRACT FROM AUTHOR]

The properties and structure of de Vries materials in new series of organosiloxane liquid crystalline materials has been studied using electrooptical measurements and UV/V is spectroscopy. The compounds from this series show different strength of the de Vries phase. Two independent parameters to characterize de Vries properties were introduced. The structure-properties relations of these materials were studied. [ABSTRACT FROM AUTHOR]

We synthesized a sample of poly (1H, 1H, 2H, 2H-perfluorododecyl acrylate) (P11) and used it as an alignment layer in different liquid crystalline cells. A good quality of alignment was obtained for both nematic and chiral smectic C phases. Electro-optic response measurement were performed for ZLI 3774 mixture aligned on the semifluorinated polyacrilate to confirm high quality of the alignment. [ABSTRACT FROM AUTHOR]

Due to its liver toxicity, the medicinal use of germander (Teucrium chamaedrys L.) was banned in some countries. Nevertheless, alcoholic extracts are still permitted as flavour ingredients since they are fundamental in providing a bitter aromatic taste. Teucrin A represents the substance of major concern regarding the potential toxicity of germander. Hence, teucrin A represents the best analytical and toxicological marker of alcoholic extracts of T. chamaedrys. A sensitive high-performance liquid chromatography method to detect teucrin A in beverages is reported. Teucrin A was prepared by isolation from the plant extract using column chromatography and crystallization. The identity and purity (99%) were established by melting point, nuclear magnetic resonance and liquid chromatography-mass spectrometry. The high-performance liquid chromatography procedure was validated and its intra- and interday performance was established (relative standard deviation ⩽ 13% and error 10%). In-house validation was carried out by analysing samples of beverages not containing T. chamaedrys spiked with a range of concentrations of teucrin A. The limit of detection was 0.1 ppm and the limit of quantification was 0.3 ppm. Teucrin A accounted for about 70% of the neo-clerodane diterpenoids found in the total extract of a specimen of T. chamaedrys. The content (± standard deviation) in 18 batches of different geographical origin was 2338 ± 740 ppm, per cent coefficient of variation = 32, mini- mum-maximum = 999-3445 ppm. The mean level of teucrin A in 10 bottles of the same brand was 6.1 ± 0.8 ppm, per cent coefficient of variation = 12. In 10 different brands found on the Italian market, the content of teucrin A ranged from not detectable to 10 ppm. [ABSTRACT FROM AUTHOR]

New liquid crystal polymers with unusual macromolecular structure were prepared by copolymerization of a fluorinated vinylcyclopropane (1) with methyl methacrylate (2). The copolymers pol(1-co-2) formed a mesophase despite the high dilution of the perfluorinated side chains along the polymer main chain. The onset of mesomorphism is attributed to the microphase separation of the incompatible fluorocarbon-hydrocarbon components. [ABSTRACT FROM AUTHOR]

ESR studies were carried out on the rotational dynamics of cholestane molecular tracer dissolved in liquid crystal homopolymer and copolymer from well above TNI down to below Tg. Rheological measurements also provided the flow relaxation properties of the polymer matrices. The distribution functions of molecular sites were determined, and their stability was monitored as a function of thermal history. The different molecular site distributions and cooperativity degrees were compared and discussed. [ABSTRACT FROM AUTHOR]

Studies the preparation of a novel mesogenic N-substituted maleimide monomer containing a ((hexadecyloxy)benzoyloxy)phenyl mesogenic unit directly attached to the maleimide ring and its copolymerization with styrene under stable free radical polymerization conditions and conventional free radical polymerization. Materials used in the study; Preparation of intermediate and maleimide monomer; General procedure for the synthesis of polymers; Results of the study.

The mass contents in five samples of a nematic azobenzene polymethacrylate having different molar masses and molar mass distributions were evaluated starting from either Logarithmic Normal (LN) or Zimm-Schulz (ZS) distribution functions. Reliability of these two approaches was verified by comparing the experimental T g with those predicted (Fox-Flory) on the basis of the LN and ZS mass contents. A birefringent bit was induced in the various samples, and its stability on time was monitored at constant temperature. The optical bit was found to be quite stable at temperatures below that at which conformational disorder was frozen in the nematic phase. [ABSTRACT FROM AUTHOR]

The dynamics of the cholestane spin probe dissolved in a nematic azobenzene copolymer was studied by ESR following a suitable thermal procedure. Heterogeneities in the dynamics of the guest molecule resulted to occur only in the high temperature region, slightly above the nematic-isotropic transition temperature. A temperature region above the glass transition was signalled, in which stable optical writing could be obtained. Optical birefringence and topological writing experiments were carried out on polymer films at the macroscopic and nanometer length-scales, respectively. SNOM analysis showed a very homogenous substrate that could be suitable for optical nanowriting. [ABSTRACT FROM AUTHOR]

We synthesized a new chiral liquid crystalline monomer and the corresponding polysiloxane and investigated their electro-optic responses. The monomer exhibited a rich phase sequence, whereas the tendency to polymorphism was strongly reduced in the polymer. The apparent molecular tilt θ pp in the chiral smectic C phase of the monomer differed substantially from that of the polymer. Whereas θ pp of the monomer reached the maximum value of 28°, the one of the polymer was nearly 45° independent of temperature over a wide range of about 30 °C. [ABSTRACT FROM AUTHOR]

In this paper we describe our recent work on optical effects due to photoinduced molecular reorientation in a side chain liquid crystalline polymer, namely azo-polymethacrylate (PMA4). We have studied several kinds of optical effects on space scales ranging from the nanoscopic to macroscopic. In particular, we have built a computer controlled microscope-based apparatus to study photoinduced effects down to the micron scale in thin and ultrathin (Langmuir Blodgett) films of our material. Furthermore we measured the morphology and the photoinduced surface deformation by Atomic Force Microscopy in the submicron scale. [ABSTRACT FROM AUTHOR]

A chiral copolysiloxane was synthesized that exhibited an N * phase in the 9-41 ° C temperature range. A linear electro-optical response with the applied electric field was detected in the N * phase due to the electroclinic effect. At high electric fields, the linearity of the response was strongly affected by dielectric coupling. It was found, however, that the influence of dielectric coupling on the electro-optical response became zero at a particular temperature ( T =37 ° C), which was attributed to a sign reversal of the dielectric anisotropy. [ABSTRACT FROM AUTHOR]