Relaxation Processes in sheared films of ethyl-cyanoethyl cellulose cholesteric liquid crystalline solutions

The relaxation processes in sheared films of ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) cholesteric liquid crystalline (LC) solutions were studied by polarizing optical microscopy (POM) and UV-Vis spectrophotometry. Under shearing normal to the helix axis and above the critical shear rate, the planar texture arrangement of the (E-CE)C/AA cholesteric LC solution was destroyed and transformed to the nematic phase. Observed by POM, the banded texture formed quickly following the cessation of the shear, but it was unstable and disappeared after several minutes. The reflection spectrum of the sheared (E-CE)C/AA cholesteric LC solution film was recorded as a function of relaxation time. It was found that the selective reflection property was lost under the shear, but the shape of the reflection spectrum recovered quickly with cessation of the shear, and the reflection peak in the spectrum became sharper with time, returning to the original form before shearing. A proposed model of the structural transformation during the relaxation was confirmed by additional optical measurement and transmission electron microscopy.     

Alignment of liquid crystal molecules on oriented (E-CE)C/PAA films

A film of ethyl-cyanoethyl cellulose/polyacrylic acid, (E-CE)C/PAA, using an alignment layer of liquid crystal (5CB), was prepared by shearing and then photo-polymerization of an (E-CE)C/AA solution. The orientation of the (E-CE)C chains in the sheared film and the alignment of the 5CB molecules on the films were investigated by polarizing optical microscopy and FTIR. It was found that the (E-CE)C/PAA oriented film showed perfect alignment ability for the 5CB molecules. The director of the 5CB molecules on the oriented film does not lie along the orientation direction of the (E-CE)C main chains, but inclines to that of the (E-CE)C main chains. The direction of the 5CB molecular orientation on the (E-CE)C/PAA oriented film is influenced by the degree of orientation of the (E-CE)C chains in the oriented film.     

Textures and defects in lyotropic liquid crystals of ethyl-cyanoethyl cellulose

Textures and defects in ethyl-cyanoethyl cellulose [(E-CE)C]/dichloroacetic acid (DCA) cholesteric liquid crystalline solutions and in (E-CE)C/polyacrylic acid (PAA) composites were observed and studied by polarizing microscopy and electron microscopy. The existence of χ, λ and τ disclinations were observed in the mesophase with disk-like and band-like textures. Pairs of disclinations with different signs were also found in the mesophase with the band-like texture. Domain walls were observed in (E-CE)C/PAA composite films with cholesteric order by TEM. The orientation of polymer chains in the vicinity of the core of the disclinations is discussed.     

Polymorphic tin dioxide synthesis via sol–gel mineralization of ethyl–cyanoethyl cellulose lyotropic liquid crystals

The polymorphic tin dioxide (SnO₂) was synthesized by calcinating the sol–gel mineralized hybrid of the tin source solution (SnCl₄/ethanol/H₂O) and the lyotropic liquid crystal of ethyl–cyanoethyl cellulose((E-CE)C)/acrylic acid (AA). The sub-micrometer SnO₂ spheres with bimodal distribution at 370 and 860 nm were obtained after calcinating the hybrid at 400°C for 5 h. When the hybrid was exposed to ultraviolet first and then calcinated the flying-saucer-like SnO₂ was formed. The exposure time was found to influence the morphology of the as-prepared SnO₂. Except for the spherical and the flying-saucer-like SnO₂, a small amount of well-developed polyhedral SnO₂ was also observed in the as-prepared samples. On this basis, the lyotropic liquid crystal of (E-CE)C/AA afforded a novel route to obtain polymorphic SnO₂.     

BANDED TEXTURE FORMATION IN NEMATIC SOLUTION OF POLY (1,4-BENZAMIDE) IN SULFURIC ACID

The banded texture in films prepared from nematic poly (1,4-benzamide) (PBA)/H_2SO_4 solution by shearing and without shearing has been studied by using microscopy techniques. The kinetic parameters of banded texture formation γ_c and τ_b were measured for nematic solution of PBA by using parallel-plate shearing apparatus. The banded texture was also observed in randomly packed domains for nematic solution of PBA on standing without shearing. The properties of banded texture show no difference between the two samples with or without shearing.     

PREPARATION AND PROPERTIES OF ETHYL-CYANOETHYL CELLULOSE/POLYACRYLIC ACID COMPOSITE FILMS WITH REFLECTION COLORS*

Ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) becomes a cholesteric liquid crystalline solution withvivid colors when the (E-CE)C concentration is 42 wt%～52 wt%. (E-CE)C/polyacrylic acid (PAA) composites withcholesteric structure were prepared by polymerzing AA in (E-CE)C/AA liquid crystalline solutions. The layers of orderedpolymer chains in the cholesteric phase were inclined during polymerization and the degree of the inclination depended onthe polymerization temperature and the concentration of the solution before polymerization. The cholesteric structure in thecomposites could not be changed when temperature was lower than 100℃. Cross-linking of the PAA in compositesimproved their water-resistance. The cholesteric order of the composites without cross-linking was destroyed when theywhere immersed in water. The color derived from the selective reflection of the cholesteric phase of the cross-linkedcomposites turned from blue to red after the composites absorbed water. The color of the composites could be returned to theoriginal one when the absorbed water was removed from the swollen composites.     

THE MORPHOLOGY AND STRUCTURE OF ETHYLCYANOETHYL CELLULOSE IN STYRENE AND POLYSTYRENE

Ethyl-cyanoethyl cellulose ((E-CE)C)/styrene solution could form anisotropic system when the concentration was high enough. The (E-CE)C/polystyrene(PS)multiphase polymer could be obtained by radical polymerization of the styrene in the solution. The (E-CE)C/PS multiphase polymer maintained both the crystalline structure of the (E-CE)C and the amorphous structure of the PS. In the multiphase polymer produced from the isotropic solution, however, the (E-CE)C formed spherulites and spread in the PS amorphous phase. While, in the multiphase polymer produced from the anisotropic solution, the (E-CE)formed cylinderic crystalline aggregates. Moreover, the ordered lamellar texture was also observed in the multiphase polymer produced from the anisotropic solution.     

Preparation of nanocrystalline porous titania films on titanium substrates by a sol–gel method with polyethylene glycol as a template

Porous nanocrystalline TiO₂ films have been prepared on cp-Ti substrates for biomedical usage by a sol–gel process from the solutions containing polyethylene glycol (PEG) as a template. Variations of the crystal structure with heat-treatment temperature determined by XRD are different for TiO₂ films and powders, due to the effect of titanium substrate. The surface texture of porous TiO₂ films is analyzed by means of SEM and found to greatly depend on the concentration and molecular weight of PEG. The pore formation mechanism is discussed in relation to the self-assembly of PEG and phase separation between PEG adsorbed on TiO₂ oligomers and ethanol.     

Two-Dimensional Sol-Gel Synthesis of Ultrathin Zirconia and Hetero-Layered Titania/Zirconia Films

Synthesis of ZrO₂ and hetero-layered TiO₂/ZrO₂ ultrathin films was investigated by two-dimensional sol-gel process assisted by n-octadecylacetoacetate (C₁₈AA). When a hexane solution of tetrabutoxyzirconium (TBZ) and C₁₈AA was spread on the water surface, Zr-based gel films stabilized with C₁₈AA were formed at the air/water interface. After deposition on substrates, the gel films were successfully transformed into ZrO₂ ultrathin films by heating at 773 K for 0.5 h, the thickness of which was controllable on the order of sub-nanometer level by the number of gel-layer deposition and the molar ratio of [TBZ]/[C₁₈AA]. Well-organized hetero-multilayers composed of ultrathin TiO₂ and ZrO₂ layers could be fabricated by the alternate deposition of C₁₈AA-stabilized Ti- and Zr-gel films.     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of Vapor Phase Pretreatments of Epoxy Surfaces on the Nucleation of MOCVD Copper Thin Films

Vapor phase pretreatments of epoxy composite material reinforced with carbon fibers were carried out prior to the growth of Cu thin films by metal-organic chemical vapor deposition (MOCVD) using Cu (hfa)(COD) as copper precursor. These dry surface oxidation processes include H₂O/UV, O₂/UV and O₂/Plasma treatments. Oxygen plasma method is the most efficient to oxidize the surface and it has the greatest effect to improve the wettability of epoxy samples. As a consequence, the higher hydrophilicity of the plasma-modified epoxy surface induces a higher nucleation density in the Cu film. Furthermore, this treatment reduces drastically the induction period observed for the growth of the metal. Even though the O₂/UV pretreatment incorporates almost the same amount of oxygen in the epoxy surface than the plasma treatment, the functional groups are different, as revealed by XPS analyses, and the surface is less hydrophilic. Correlations between oxidation, wettability and nucleation density of the Cu films are discussed.     

Synthesis,UV-curing behavior and surface properties of fluorine-containing vinyl ether polymers

Five fluorine-containing vinyl ether monomers were prepared by the reaction between 2-vinyloxy ethanol, a fluorinated alcohol and hexafluorobenzene in the presence of sodium hydride in dimethylformamide. Two representative properties of these monomers, UV-curing behavior initiated by a cationic photo-initiator PAG 201 and surface free energy of coating films, were investigated. Photo-polymerization proceeded both rapidly and completely with a high double-bond conversion （〉 90%） and a fast curing rate （maximum curing time 〈 21 s） for three monomers. The surface energies of the monomers and the resulting polymer films were then investigated. The minimum surface free energy of the UV-cured homopolymer films reaches 7.1 mJ/m2. X-ray photoelectron spectroscopy data show that the low surthce tension is influenced by fluorine content in the soft segments and fluorinated chains＇ migration to the surface. The five monomers exhibit low viscosity, low surface energy, good thermal stability and good photo-polymerization properties, which make them great candidates for UV coating and photoresist applications.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO<Subscript>2</Subscript> composite films

TiO₂ sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO₂ composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO₂ through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO₂ were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO₂ system was carried through electron transfer mechanism.     

ITO films on glass substrate by sol–gel technique: synthesis,characterization and optical properties

The present paper extensively demonstrates synthesis, characterization and optical properties of semiconductor indium tin oxide (ITO) thin films on glass substrate using sol–gel technique for gas sensor applications. Turbidity, pH values, wettability and rheological properties of the prepared solutions were measured to determine solution characteristics by turbidimeter, pH meter, contact angle goniometer and rheometer machines prior to coating process. Thermal, structural, microstructural, mechanical and optical properties of the coatings were characterized by differential thermal analysis–thermogravimetry (DTA/TG), fourier transform infrarared, X-ray diffraction (XRD), scanning electron microscopy, scratch tester, refractometer and spectrophotometer. Four different solutions were prepared by changing solvent concentration. Turbidity, pH, contact angle and viscosity values of the solutions were convenient for coating process. Glass substrates were coated using the solutions of InCl₃, SnCl₂, methanol and glacial acetic acid. The obtained gel films were dried at 300 °C for 10 min and subsequently heat-treated at 500 °C for 10 min in air. The oxide thin films were annealed at 600 °C for 60 min in air. DTA/TG results revealed that endothermic and exothermic reactions are observed at temperature between 70 and 560 °C due to solvent removal, combustion of carbon based materials and oxidation of Sn and In. The spectrum of ITO precursor film annealed at 500–600 °C shows an absence of absorption bands corresponding to organics and hydroxyls. In₂Sn₂O_7−x phase was dominantly found as well as SnO₂ with low intensity from XRD patterns. It was found that surface morphologies of the film change from coating island with homogeneous structures to regular surface and thinner film structures with increasing solvent concentration. The films prepared from the solutions with 8 mL methanol have better adhesion strength to the glass substrate among other coatings. Refractive index, thickness and band gap of ITO thin films were determined to be 1.3171, 0.625 μm and 3.67, respectively.     

Layer—by—layer Multilaryer Films Self—assembled from a Rare—earth—containing Poly—oxometalate,Na9[Eu（W5O18）2] and Poly （allylamine hydrochloride） and Their Photoluminescent Properties

Ultrathin multilayer films of a rare-earth-containing polyoxometalate Na9[Eu(W5O18)2](EW) and poly (allymamine hydrochloride)(PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solution.The fabrication process of the EW/PAH multilaryer films was followed by UV-vis spectroscopy and ellipsometry,which show that the deposition process is linear and highly reproducible from layer to layer.An average EW/PAH bilayer thickness of ca.2.1nm was determined by ellipsometry.In addition,the scanning electron microscopy(SEM) image of the EW/PAH film indicates that the film surface is relatively uniform and smooth.The photoluminescent properties of these films were also investigated by fluorescence spectroscopy.     

BAND-LIKE TEXTURE OF ETHYLCYANOETHYL CELLULOSE MESOPHASE

In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough and merge with each other with increasing concentration. The band-like texture is composed of parallel equidistant bright and dark alternative strips which are about 0.2-2.0 μm in width. In the band-like texture, the layers of ordered polymer chains are perpendicular to the solution film and the axes of helicoids are parallel to it. The width of the strips is different in different zones. Under the effect of an external magnetic field, the strips in the band-like texture first become wider and then narrower gradually.Moreover, the axes of helicoids in the (E-CE) C/DCA mesomorphic solution change from the direction normal to the magnetic field to the agreement with the magnetic field direction.     

UV assisted pyrolysis of solution deposited BiFeO<Subscript>3</Subscript> multiferroic thin films. Effects on microstructure and functional properties

BiFeO₃ thin films were processed on platinized silicon substrate via chemical solution deposition. Short wave UV assisted pyrolysis was conducted in oxygen atmosphere in order to obtain a fine and homogeneous grain structure. Phase pure thin films with a pronounced (100) texture were obtained at a fairly low annealing temperature of 600°C. For comparison specimens processed without UV assisted pyrolysis were also investigated. It is shown that UV assisted pyrolysis leads to a substantial improvement of leakage resistance properties. Polarization switching could also be obtained using capacitance-voltage (C-V) curves. The leakage current was investigated as a function of temperature. Interpretation in terms of Frenkel-Poole mechanism leads to a high trap depth in the range of 2.4 eV which is attributed to the creation of Fe²⁺ centres. For both microstructures investigated well saturated magnetization loops were obtained with a remnant magnetization of 2Mr = 5.4 emu/cm³ and a coercive fields in the range of 2Hc = 200 Oe. Slightly higher saturation magnetization 2Ms of 55.4 emu/cm³ was obtained for UV assisted pyrolysis in comparison to 45.8 emu/cm³ for the thin films processed without UV.     

总气压与Ar/O2流量比对直流对向靶磁控溅射TiO2薄膜光催化性能的影响

采用对向靶磁控溅射法在不同气压和Ar/O₂流量比条件下, 以氟化SnO₂ (FTO)导电玻璃为基底制备了多晶TiO₂薄膜. 台阶仪测量结果显示所制备TiO₂薄膜的平均厚度约为200 nm. 随着溅射气压的升高, TiO₂薄膜由锐钛矿与金红石混晶结构转变为纯锐钛矿结构. 分别采用场发射扫描电镜(FESEM)和原子力显微镜(AFM)分析了不同气压和Ar/O₂流量比对TiO₂薄膜表面形貌的影响, 结果显示TiO₂薄膜的表面粗糙度随溅射总气压和Ar/O₂流量比的增加而增大. 以初始浓度为100×10^-6 (体积分数)的异丙醇(IPA)气体为目标物检测所制备TiO₂薄膜的光催化性能, 并分析该气相光催化反应的机理, 在紫外照射条件下异丙醇先氧化为丙酮再被氧化为CO₂.当总溅射气压为2.0 Pa、Ar/O₂流量比为1:1时, 溅射所得TiO₂薄膜具备最优光催化活性并可在IPA降解反应中保持较高的催化活性和稳定性.     

An electron diffraction study of deposited docosanoic acid monolayers

Docosanoic acid monolayers deposited on thin polymer films under different water surface conditions have been investigated using transmission electron diffraction at normal and tilted incidence. Diffraction patterns obtained from the L₂ and L₂' phase are quite similar, but distinctly different to samples coated from the CS phase. The former were consistent with molecules perpendicular to the substrate, arranged in a texture of grains with unusual orthorhombic packing. There is evidence for a phase transition from a liquid crystalline phase on the water surface.     

Photocatalytic Efficiency Tuning by the Surface Roughness of TiO2 Coatings on Glass Prepared by the Doctor Blade Method

A set of opaque films were prepared with Degussa P25^® or Hombikat UV100^® TiO₂ powders by the doctor blade method on glass slides with different compositions of polyethylene glycol of 20 kDa (PEG20), and they were characterized by spectroscopy, microscopy and photochemical kinetics measurements. After annealing treatment at 450 °C, about 5–7% C atom was incorporated into the films, as a consequence of the degradation of the organic complexing agents, inducing a small reduction of the energy band gap of TiO₂ (i.e. 3.02 ≤ E_g (eV) ≤ 3.08). All films were about 15 ± 2 μm thick but their micro‐morphological characteristics depended on the content of PEG20, showing different patterns of cracks and aggregates that produce intense light scattering and retransmission phenomena with the result of a three‐dimensional excitation of the TiO₂ particles in the thick film. Back‐face excitation with UVA light (365 ± 42 nm) of the opaque films in contact with an aqueous solution produced both surface‐bound and free hydroxyl radicals (HO^?), as detected using a coumarin solution as a radical dosimeter. The photogeneration efficiency of HO^? decreased with the surface roughness of the films, which varied between 135 and 439 nm depending on the film's composition.