Substrate dependent structure and in-plane dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

The structure, microstructure and in-plane dielectric properties of Barium tin titanate Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single crystal substrates through sol–gel process were investigated. The films deposited on (100) LAO substrate exhibited a strong (100) preferred orientation while the film deposited on (100) MgO substrate showed polycrystalline structure. The in-plane ɛ–T measurements reveal that the films grown on (100) LAO substrate exhibited an obvious room-temperature ferroelectric state, while the film grown on MgO substrate showed paraelectric state in the temperature range of 10–130 °C. A high tunability of 52.11% was observed for the BTS films deposited on (100) LAO substrate at the frequency of 1 MHz with an applied electric field of 80 kV/cm, which is about two times larger than that of the BTS films deposited on (100) MgO substrate. The obvious differences in the dielectric properties could be attributed to the stress in the films, which come from lattice mismatch and difference in the thermal expansion coefficients between the film and substrates. This work clearly reveals the highly promising potential of BTS films for application in tunable devices.     

Effect of the temperature on the physical properties of pure 1-propyl 3-methylimidazolium bis(trifluoromethylsulfonyl)imide and characterization of its binary mixtures with alcohols

In this paper, physical properties of a high purity sample of the ionic liquid 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [PMim][NTf₂], and its binary mixtures with methanol, ethanol, 1-propanol, and 2-propanol were measured at atmospheric pressure. The temperature dependence of density, refractive index and speed of sound (293.15 to 343.15) K and dynamic viscosity (298.15 to 343.15) K were studied at atmospheric pressure by conventional techniques for the pure ionic liquid. For its mixtures with alcohols, density, speed of sound, and refractive index were measured at T = 298.15 K over the whole composition range. The thermal expansion coefficient of the [PMim][NTf₂] was calculated from the experimental results using an empirical equation, and values of the excess molar volume, excess refractive index, and excess molar isentropic compressibility for the binary systems at the above mentioned temperature, were calculated and fitted to the Redlich–Kister equation. The heat capacity of the pure ionic liquid at T = 298.15 K was determined using DSC.     

A study of the overall heat transfer coefficient of greenhouse cladding materials with thermal screens using the hot box method

A laboratory guarded hot box was designed and constructed to investigate the overall heat transfer coefficient, U (W m^?2 K^?1), of different greenhouse polyethylene plastic films with or without thermal screens. Tests were made on plastic films, in both dry and wet (in the presence of condensation) states, with or without thermal screens, as functions of wind velocity and temperature difference. It was found that the overall heat transfer coefficient U increases with increase in temperature difference. For a given temperature difference, the U value increases as the wind velocity increases. The condensation phenomena favored the plastic film, since its U value was always less than that of the corresponding dry film. It was found that using a thermal screen would reduce the U value by about 30%, an energy saving of about 30%.     

New Insights into the Thermal Expansion of Neptunium Dioxide up to 2000 K

We report for the first time the thermal expansion of NpO2 up to 2000 K and compare it to the one of UO2 and PuO2. Lattice parameters were measured as a function of temperature by in situ X-ray diffraction with neutral, reducing and oxidizing atmospheres. Data for NpO2 under neutral and reducing conditions perfectly superpose. Up to 1550 K, thermal expansion varies linearly with increasing temperature. Above, thermal expansion presents a curvature towards higher lattice parameters. No bibliographic data were available for this temperature range for comparison. As for the thermal expansion of UO2, we propose this curvature is certainly inferred by the formation of lattice defects in the oxygen sub-lattice. Expression of thermal expansion and coefficients of thermal expansion at given temperatures for NpO2, are presented.     

Anti-biofouling properties of amphiphilic phosphorylcholine polymer films

Surfaces of amphiphilic phosphorylcholine polymer (PC1036) prepared by spin-coating were characterized by spectroscopic ellipsometry, water contact angle and atomic force microscopy. The antifouling properties of the PC1036 films to marine benthic diatom Nitzschia closterium MMDL533 were also investigated. The results showed that the dry PC1036 film promoted the adhesion of N. closterium MMDL533 because the hydrophobic lauryl groups were present in the film surface. The 2 h-swelled PC1036 films had excellent anti-fouling properties with extremely low attachment densities and retention densities no matter what the annealing temperature was. The thickness of the coated films lower than 147 Å had a profound effect on the film anti-fouling properties. Otherwise, when the film thickness was higher than that value, there was no more improvement of diatom cell reduction observed. The annealing temperature had only a little effect on the film resistant to diatom adhesion, which might be attributed to two factors including the PC group packing densities in the outer PC layer and the equilibrated water volume fraction in the 2 h-swelled PC1036 films.     

Raman spectroscopic study on boron-doped silicon nanoparticles

Raman analyses were performed on thin films prepared from B-doped Si nanoparticles with an average diameter of 15 nm using the spin-coating method. The resulting spectrum exhibited a broad band with a peak near 520 cm⁻¹. The band was decomposed into three bands corresponding to the crystalline, grain boundary (GB), and amorphous regions by the least-squares band-fitting method based on the three Voigt bands. The fractions of the crystalline, GB, and amorphous regions were 37%, 35%, and 28%, respectively. A spherical particle exhibited an ordered crystalline core surrounded by a disordered shell in a transmission electron microscope (TEM) image. The crystalline fraction of the 15-nm B-doped Si nanoparticle film was much lower than that of the 19-nm P-doped Si nanoparticle film. This result suggested that the B-doping mechanism was different from that of P-doping. The temperature of the sample was estimated from the ratio of the peak intensities of anti-Stokes to Stokes Raman bands (I^AS/I^S) observed near 520 cm⁻¹. The temperature of the B-doped Si nanoparticle film upon irradiation at a power density of 4.6 kW/cm² was 298 °C, whereas the temperature of the P-doped Si nanoparticle film was 92 °C. The B-doped Si nanoparticle films were capable of producing light-induced heat.     

Properties of pure 1-methylimidazolium acetate ionic liquid and its binary mixtures with alcohols

Densities and viscosities of the pure ionic liquid 1-methylimidazolium acetate ([Mim]Ac) and its binary mixtures with methanol, ethanol, 1-propanol, and 1-butanol were measured at temperature ranging from T = (293.15 to 313.15) K. The thermal expansion coefficient, molecular volume, standard entropy, and lattice energy of [Mim]Ac were deduced from the experimental density results. A simple linear equation was used to correlate the variation of viscosity of [Mim]Ac with temperature. Excess molar volumes V^E and viscosity deviations Δη for the binary mixtures at above mentioned temperature were calculated and fitted to the Redlich–Kister equation with satisfactory results. Excess molar volumes for {[Mim]Ac + 1-butanol} mixture have an S shape, while those for other mixtures have a negative deviation from ideal behaviour over the entire mole fraction range. Viscosity deviations are all negative deviation for {[Mim]Ac + alcohol} mixtures. The results were interpreted in terms of interactions and structural factors of binary mixtures.     

Structures,thermal expansion properties and phase transitions of ErxFe2−x(MoO4)3 (0.0 ≤ x ≤ 2.0)

Structures, thermal expansion properties and phase transitions of Er_xFe_2−x(MoO₄)₃ (0.0 ≤ x ≤ 2.0) have been investigated by X-ray diffraction and differential thermal analysis. The partial substitution of Er³⁺ for Fe³⁺ induces pronounced decreases in the phase transition temperature from monoclinic to orthorhombic structure. Rietveld analysis of the XRD data shows that both the monoclinic and orthorhombic Fe₂(MoO₄)₃, as well as the orthorhombic Er_xFe_2−x(MoO₄)₃ (x ≤ 0.8) have positive thermal expansion coefficients. However, the linear thermal expansion coefficients of Er_xFe_2−x(MoO₄)₃ (x = 0.6–2.0) decrease with increasing content of Er³⁺ and for x ≥ 1.0, compounds Er_xFe_2−x(MoO₄)₃ show negative thermal expansion properties. Attempts for making zero thermal expansion coefficient materials result in that very low negative thermal expansion coefficient of −0.60 × 10⁻⁶/°C in Er_1.0Fe_1.0(MoO₄)₃ is observed in the temperature range of 180–400 °C, and zero thermal expansion is observed in Er_0.8Fe_1.2(MoO₄)₃ in the temperature range of 350–450 °C. In addition, anisotropic thermal expansions are found for all the orthorhombic Er_xFe_2−x(MoO₄)₃ compounds, with negative thermal expansion coefficients along the a axes.     

Thermophysical properties of hydroxyl ammonium ionic liquids

The thermophysical properties of hydroxyl ammonium ionic liquids: density ρ, T = (293.15 to 363.15) K; dynamic viscosity η, T = (298.2 to 348.2) K; and refractive indices n_D, T = (293.15 to 333.15) K have been measured. The coefficients of thermal expansion α, values were calculated from the experimental density results using an empirical correlation for T = (293.15 to 363.15) K. The variation of volume expansion of ionic liquids studied was found to be independent of temperature within the range covered in the present work. The thermal decomposition temperature ‘T_d’ for all the six hydroxyl ammonium ionic liquids is also investigated using thermogravimetric analyzer (TGA).     

Study of the morphology,thermal and mechanical properties of irradiated isotactic polypropylene films

Thin films of isotactic polypropylene (iPP) are of great economical importance and their production is quite challenging due to the need of very fast uniaxial or biaxial expansion. During the expansion, critical problems usually arise, like structure disruption, shear thinning, causing material, energy and time losses. This work aims to study the surface morphology and compare the thermal, mechanical properties of PP films irradiated by gamma ray in an acetylene atmosphere after uniaxial expansion. PP films were made by compression molding at 190 °C with cooling in water at room temperature and irradiated by gamma ray, at (5, 12.5 and 20 kGy) under acetylene atmosphere. After irradiation the samples were submitted to thermal treatment at 90 °C for 1 h and then stretched out at 170 °C using an Instron machine. The surface of PP films, pristine and modified, (i.e., irradiated), was studied using optical microscopy (OM) and scanning electron microscopy (SEM). The changes in morphology, crystallinity and tensile parameters, like yield stress, rupture stress and elongation strain of the PP with irradiation dose were investigated. The results showed some evidences of gel formation due to crosslinking and/or long chain branching induced by radiation.     

Structural and electrical characterization of boron-containing diamond-like carbon films deposited by femtosecond pulsed laser ablation

The present study investigates the influence of the incorporation of boron in Diamond-Like Carbon (DLC) films deposited by femtosecond laser ablation, on the structure and electrical properties of the coatings within the temperature range 70–300 K. Doping with boron has been performed by ablating alternatively graphite and boron targets. The film structure and composition have been highlighted by coupling Atomic Force Microscopy (AFM), Scanning Electron Microscopy equipped with a field emission gun (SEM-FEG) and High Resolution Transmission Electron Microscopy (HRTEM). Boron dilution ranges between 2 and 8% and appears as nanometer size clusters embedded in the DLC matrix. Typical resistivity values are 100 W cm for pure a-C films, down to few W cm for a-C:B films at room temperature. The resistance decreases exponentially when the temperature increases in the range 70–300 K. The results are discussed considering the classical model of hopping conduction in thin films. Some coatings show temperature coefficients of resistance (TCR) as high as 3.85%. TCRs decrease when the doping increases. Such high values of TCR may have interests in the use of these films as thermometer elements in micro and nanodevices.     

Photoelectrocatalytic activity of immobilized Yb doped WO_3 photocatalyst for degradation of methyl orange dye

Pure WO_3 and Yb:WO_3 thin films have been synthesized by spray pyrolysis technique. Effect of Yb doping concentration on photoelectrochemical, structural, morphological and optical properties of thin films are studied. X-ray diffraction analysis shows that all thin films are polycrystalline nature and exhibit monoclinic crystal structure. The 3 at% Yb:WO_3 film shows superior photoelectrochemical(PEC) performance than that of pure WO_3 film and it shows maximum photocurrent density(Iph= 1090 μA/cm~2) having onset potentials around +0.3 V/SCE in 0.01 M HClO_4. The photoelectrocatalytic process is more effective than that of the photocatalytic process for degradation of methyl orange(MO) dye. Yb doping in WO_3 photocatalyst is greatly effective to degrade MO dye. The enhancement in photoelectrocatalytic activity is mainly due to the suppressing the recombination rate of photogenerated electron-hole pairs. The mineralization of MO dye in aqueous solution is studied by measuring chemical oxygen demand(COD) values.     

Density and surface tension of pure ionic liquid 1-butyl-3-methyl-imidazolium l-lactate and its binary mixture with alcohol and water

The density and surface tension of the pure ionic liquid 1-butyl-3-methyl-imidazolium l-lactate were measured from T (293.15 to 343.15) K. The coefficient of thermal expansion, molecular volume, standard entropy, lattice energy, surface entropy, surface enthalpy, and enthalpy of vaporization were calculated from the experimental values. Density and surface tension were also determined for binary mixtures of {1-butyl-3-methyl-imidazolium l-lactate + water/alcohol (methanol, ethanol, and 1-butanol)} systems over the whole composition range from T (298.15 to 318.15) K at atmospheric pressure. The partial molar volume, excess partial molar volume and apparent molar volume of the component IL and alcohol/water in the binary mixtures were discussed as well as limiting properties at infinite dilution and the thermal expansion coefficients of the four binary mixtures. The surface properties of the four binary mixtures were also discussed.     

Study of natural rubber crosslinked in the state of uniaxial deformation

A natural rubber (NR) film with the thickness of about 1 mm was prepared by removing the liquid phase from NR latex. Two types of NR films crosslinked by γ-irradiation were investigated: (i) samples irradiated in the relaxed state and (ii) samples irradiated in the state of uniaxial deformation. The total irradiation dose varied from 0 kGy (for nonirradiated NR) to 400 kGy and the degree of deformation, defined as λ=l/l₀ (l₀ and l being the lengths of relaxed and uniaxially deformed sample, respectively), was chosen to be λ=1.0 (relaxed state), λ=1.5 and λ=2.0. The amount of sol and gel phase of NR was determined by extracting the sol component in toluene. A significant decrease in the amount of the sol component (from 14.2% to 33.5%, depending on irradiation dose) was observed by increasing the irradiation dose. It has been shown that the application of deformation during the crosslinking leads to the lower crosslink density. Such an effect can be attributed to the loss of the gel component induced mechanically. The electron spin resonance (ESR) spectra of spin probe diffusing in the NR matrix crosslinked under deformation are influenced by both, the local dynamics of the chain segments and their spacious orientation.     

On the existence of temperature induced changes in the magnetic topology of crystals that show no first-order crystallographic phase transitions

The First-Principles Bottom–Up study of the 88 K and 273 K X-ray diffraction structures of the bis-2,3-dimethylpyridinium tetrabromocuprate molecular magnet shows that the analysis of the magnetic properties of a molecule-based magnet, that does not present any first order polymorphic transition in the range of temperature studied, depends on the X-ray structure employed. The reason is the thermal expansion anisotropy when the crystal goes from the low temperature phase to 273 K, which induces changes in the radical–radical J_AB interactions. As a consequence, the magnetic topology of the low temperature and 273 K structures change, a fact that induces a change in the macroscopic magnetic susceptibility curve (only the 88 K structure of bis-2,3-dimethylpyridinium tetrabromocuprate reproduces well the two-leg spin ladder experimental properties of this magnet). When anisotropic thermal effects are suspected one should use low temperature structures to study the magnetic properties at low temperature, and high temperature structures for the study of the magnetic properties in that range of temperatures.     

Volumetric properties under pressure for the binary system ethanol + toluene

The density of the asymmetrical binary system composed of ethanol and toluene has been measured under pressure using a vibrating tube densimeter. The measurements have been performed for nine different compositions including the pure compounds at eight temperatures in the range 283.15–353.15 K and ten isobars up to 45 MPa. The uncertainty in the measured densities is estimated to be 0.1 kg m⁻³. The measured data has been used to study the behavior and influence of temperature, pressure and composition on the isothermal compressibility, the isobaric thermal expansion, and the excess molar volume. At several temperatures the isobaric thermal expansion shows an non-monotonical behavior versus composition, whereas the excess molar volumes reveal a complex sigmoid behavior. These results have been interpreted as changes in the free-volume and as the formation and weakening of the molecular interactions. The VLE behavior of this binary system within the considered temperature range is represented satisfactory by the perturbed-chain statistical association fluid theory (PC-SAFT) equation of state with a single interaction parameter, although no cross association between ethanol and toluene is taken into account. The densities of this binary system (pure compounds and mixtures) are satisfactory predicted by PC-SAFT with an overall AAD of 0.8%, but the behavior of the excess molar volume is not described correctly.     

Thermogravimetric and FTIR studies of chitosan blends

Results of spectrophotometric and thermogravimetric studies of chitosan (CH) blends with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained by casting from solutions in the form of transparent films containing 0–1.0 weight fraction of CH were discussed. Blends containing S are homogeneous only in the case of low-weight fraction of S (to 0.3).On the basis of results of thermodegradation in dynamic and isothermal conditions, thermal stability of the tested systems was estimated. Thermogravimetric measurements in dynamic conditions were carried out in the temperature range of 100–450 °C at constant heating rate 15 °C/min. From thermogravimetry (TG) and DTG curves the activation energy and characteristic parameters of degradation of the tested blends were determined. The observed growth of activation energy and T_p—temperature of initial weight loss, T_max—temperature of maximal rate and C_e—degree of conversion at the end of the measurement (at temperature 450 °C) along with the increase of polymer fraction (HPC and S) in the CH blend provides an evidence of improved thermal stability of the systems tested.Investigations in isothermal conditions in air at temperature from 100 to 200 °C confirmed appreciable improvement of CH thermal stability in the blends being tested.Infrared spectroscopic analysis of the blends showed a distinct stabilization of the process of chain scission. In the band at 1080 cm⁻¹ associated with absorption in –C–O–C– group during degradation of the blends at temperature 200 °C much smaller decrease due to molecular scission were observed than in the case of pure CH.     

Paper-like free-standing polypyrrole and polypyrrole–LiFePO4 composite films for flexible and bendable rechargeable battery

Highly flexible, paper-like, free-standing polypyrrole and polypyrrole–LiFePO₄ composite films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust and highly electrically conductivity. The electrochemical behavior of the free-standing films was examined against lithium counter electrode. The electrochemical performance of the free-standing pure PPy electrode was improved by incorporating the most promising cathode material, LiFePO₄, into the PPy films. The cell with PPy–LiFePO₄ composite film had a higher discharge capacity beyond 50 cycles (80 mA h/g) than that of the cell with pure PPy (60 mA h/g). The free-standing films can be used as electrode materials to satisfy the new market demand for flexible and bendable batteries that are suitable for the various types of design and power needs of soft portable electronic equipment.     

In situ measurement of the thermal expansion behavior of benzocyclobutene films

In situ measurement techniques suitable for determination of the coefficient of thermal expansion (CTE) in thin, spin‐cast polymer films in both the in‐plane and through‐plane directions are presented. An examination of the thermal expansion behavior of cyclotene thin films has been performed. In particular, the effect of film thickness on the in‐plane and through‐plane CTE and in‐plane Young's modulus of spin‐coated cyclotene films was examined. It is shown that the mechanical response of in situ cyclotene films can be adequately described by isotropic film properties. It was also demonstrated that there is no thickness dependence on the free‐standing mechanical properties or on the resulting through‐plane thermal strain in an in situ film. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 311–321, 1999     

Development and characterization of a titanosilicate ETS-10-coated optical fiber reactor towards the photodegradation of methylene blue

An optical fiber reactor (OFR) system containing uniformly distributed quartz fibers coated with titanosilicate ETS-10 crystals was investigated. Optimum ETS-10 film thickness (～1.5 μm) and coating length (15 cm) were determined from the light propagation analysis in a single ETS-10-coated fiber. The nearly constant value of the attenuation coefficient (α ≈ 0.10 cm^?1) for films with different thickness indicated uniform fiber surface coverage with these films. The extinction coefficient, ?, decreased from ～1.6 to ～1.0 μm^?1 with ETS-10 film thickness increasing from ～0.5 to ～1.5 μm, which suggested less contact per unit film thickness between light and ETS-10 crystals inside thicker films, likely due to their lower crystal packing density. Photodegradation of methylene blue (MB) conducted in the OFR showed higher photocatalytic activity for thicker ETS-10 films. Although higher MB photodegradation rates were obtained at higher light intensity, the apparent quantum efficiency, Φ, decreased with increasing light intensity. This is consistent with the charge separation mechanism for MB photodegradation in the UV light range investigated. All ETS-10 samples investigated showed ～4–5 times higher Φ values in the OFR than in the slurry reactor, likely due to the unique light/photocatalyst/reactant contact and high fiber packing density in the OFR.