Polysilazane as the source of silica: the formation of dense silica coatings at room temperature and the new route to organic–inorganic hybrids

Xylene solutions of perhydropolysilazane (PHPS) were used as the coating solutions for preparing silica coatings at room temperature. The PHPS-to-silica conversion was achieved by exposing the spin-on coatings to the vapor from aqueous ammonia. In order to examine the significance of the mechanical properties of the PHPS-derived silica coatings, the pencil hardness was measured, which was compared with that of tetraethoxysilane (TEOS)-derived silica coatings. The pencil hardness was over 9H at a load of 1 kg, which was much higher than that of the TEOS-derived silica gel films, and was comparable to that of the TEOS-derived films heat treated at 300 °C. Second, poly(methyl methacrylate) (PMMA)–silica hybrid coatings were prepared from xylene solutions of PMMA and PHPS via exposure to the vapor from aqueous ammonia. Crack-free, optically transparent PMMA–silica hybrid coatings could be prepared, where PHPS-to-silica conversion was confirmed by infrared absorption spectroscopy. The refractive index was around 1.42–1.50, and the contact angle with water increased from 35 to 70° with increasing PMMA content. The pencil hardness greatly increased during the PHPS-to-silica conversion, and was much higher than that of the non-heat treated TEOS-derived hybrid coatings. The durability in tetrahydrofuran (THF) was also evaluated by measuring the reduction in thickness occurring during soaking in THF. The durability decreased with increasing PMMA content, but was much higher than that of the non-heat treated TEOS-derived hybrid coatings. Both the hardness and the durability were comparable to those of the TEOS-derived coatings heated at 300 °C. The hybrid coatings could also be deposited on poly(ethylene terephthalate) substrates, where no cracks were observed at high PMMA contents even when the substrate was bent.     

Fabrication of poly(p-phenylene vinylene) (PPV) nanoheterocomposite films via layer-by-layer adsorption

The fabrication of polyelectrolyte multilayer film architectures composed of a polycation precursor (Pre-PPV) of the electroluminescent poly(p-phenylene vinylene) (PPV) and two different counter-polyanions, cellulosesulfate and poly(vinylsulfate), are reported. All multilayers were characterized by UV/VIS-spectroscopy and X-ray reflectometry. Due to the differences in spatial arrangement of charged groups, rigidity, and conformation of the polyanions, the corresponding multilayer films differ in properties such as average thickness increments and surface roughness. The adsorbed amounts per layer can be adjusted by addition of inorganic salts. Thermal conversion of Pre-PPV to PPV is achieved already slightly above 100 °C, yielding identical absorption spectra for after either 3 h at 160 °C or 20 h at 120 °C. The heat treatment causes the film thickness to be reduced by 24–40% due to elimination of dimethylsulfide and HCl and also the loss of water, but the films stay optically transparent.     

Evolution of crystalline structure in SnS thin films prepared by chemical deposition

Crystal structure and morphology undergo significant evolution in thin films of tin(II) sulfide prepared by chemical deposition, over a narrow interval of bath temperature of 20–40 °C, but has not been recognized in previous studies. The chemical bath is constituted using tin(II) chloride, triethanolamine, ammonia(aq.) and thioacetamide. At bath temperature of 20 °C, the deposition rate of the film is 10 nm/h; and at 24 h, a film of thickness 260 nm is obtained. This film is compact and with a predominantly cubic (Cub-) crystalline structure. At 40 °C, the deposition rate is 25 nm/h, and a film of 600 nm in thickness is deposited in 24 h. However, this film has evolved into vertically stacked platelets of orthorhombic (OR-) crystalline structure. The transition from compact-to-platelet morphology as well as from Cub-to-OR-crystalline structure is observed near a deposition temperature, 35 °C. The Cub-SnS has a characteristic high optical band gap, 1.67 eV (direct gap; forbidden transitions) with an electrical conductivity, 10⁻⁷(Ω cm)⁻¹; both properties being un-affected when films are heated at 300 °C in a nitrogen ambient. In OR-SnS, the band gap is 1.1 eV (indirect gap; allowed transitions). The electrical conductivity of such films is notably higher, 10⁻⁴ (Ω cm)⁻¹, which increases further by an order of magnitude when the films have been heated at 300 °C in nitrogen.     

Effects of humidity,imidization history,and thickness on water sorption behavior of poly(p-phenylene biphenyltetracarboximide) films

Poly(p-phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10^?10 ? 7.50 × 10^?10 cm²/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in-plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.     

Polymethylmethacrylate-silica hybrid thin films heavily doped with spiropyran and exhibiting visual photochromism and high mechanical and chemical durability

Perhydropolysilazane (PHPS)—polymethylmethacrylate (PMMA)—spiropyran (SP) films were prepared by spin-coating using a solution of a mass ratio, PHPS:PMMA:SP:xylene = 0.8:0.2:0.25:3.6. The SP-doped PHPS-PMMA films were then exposed to the vapor from aqueous ammonia at room temperature, resulting in the formation of 1.7 μm thick, deep-red colored SP-doped PMMA-silica hybrid films. Due to the high concentration of SP, which could be achieved by the hydrophobic nature of PHPS and xylene, the photochromic color changes were visualized in spite of the small film thickness. The films had pencil hardness higher than 9H, and no SP leaching was observed even when the films were soaked in xylene for 24 h. Thus, thin films that exhibit visual photochromism with high mechanical and chemical durability could be prepared, which can never been achieved by conventional sol–gel methods.     

Photoinitiated polymerization of styrene from self‐assembled monolayers on gold. II. Grafting rates and extraction

Ultrathin films of polystyrene (PS) were grown from self‐assembled monolayers by the “grafting‐from” technique. The initiating system consisted of a dithiol azobisisobutyronitrile‐type free‐radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform‐reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water‐jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284–3291, 2002     

SYNTHESIS OF POLY(METHYL METHACRYLATE)-SILICA NANO-COMPOSITE

ABSTRACT

Transparent organic/pre-ceramic composite films of poly(methyl methacrylate) [PMMA] and perhydropolysilazane [PHPS] were synthesized by blending poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) [P(MMA-co-HEMA)] random copolymers and PHPS. In the blend films, P(MMA-graft-PHPS) graft copolymers were formed, PMMA and PHPS were microscopically phase-separated in the solid state. Morphology of the microphase separation was investigated by transmission electron microscopy by changing HEMA content of the random copolymers and blend ratio of PHPS to HEMA. To convert PHPS to silica glass, the blend films were calcinated at 100°C. The morphology of the microphase separation of the films was not changed by the calcinations; the calcinated films were transparent. When the molar content of HEMA of P(MMA-co-HEMA) and the molar content of PHPS to HEMA in feed were 14.5% and 150%, respectively, the morphology was well ordered lamellae of PMMA and silica.     

Hafnia sol-gel films synthesized from HfCl4: Changes of structure and properties with the firing temperature

Thin sol-gel hafnia films have been synthesised from HfCl₄, the synthesis has revealed to be a simple route to fabrication of hafnia films with high transparency in the UV-visible range. The films have been fired at different temperatures in air up to 1000°C and have been characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Infrared absorption spectra of hafnia films have allowed to follow the formation of monoclinic crystalline phases together with XRD. Formation of monoclinic hafnia crystallites has been observed upon calcination at temperatures higher than 600°C, as shown by infrared spectroscopy and XRD. The optical transmission and the refractive index as a function of the temperature of firing have been characterized by UV-Visible spectroscopy and spectroscopic ellipsometry. The hafnia films, after firing at 600°C, had a refractive index of 1.92 with a thickness of around 70 nm.     

NLO‐active maleimide copolymers with ­high glass transition temperatures

We synthesized some novel rigid NLO‐active maleimide copolymers bearing DR‐1 moieties ( PMPD , PHSD and PHND ). All copolymers exhibited high T_g's (190～197 °C), good solubilities for common solvents and excellent film‐forming properties. Dependence of film thickness on the d₃₃ value for the poled copolymer films induced by corona poling was investigated and it was demonstrated that in less than thickness of 0.3 µm decrease of the thickness gives rise to remarkable increase in the d₃₃ value. The poled copolymer films exhibited large d₃₃ values (270 × 10^?9 esu (film thickness 0.13 µm) for PMPD , 290 × 10^?9 esu (0.12 µm) for PHSD and 350 × 10^?9 esu (0.08 µm) for PHND ) as well as large r₃₃ values (51.0 pmV^?1 for PMPD and 60.4 pmV^?1 for PHND ) which are significantly large compared to the value of LiNbO₃ (31 pmV^?1) as a typical EO material. The d₃₃ values of the poled copolymers were kept constant even after standing 1000h at 80 °C, although a small decrease was observed at an initial stage. Further, the d₃₃ values did not change up to ca. 123 °C upon heating at the rate of 10 °C/min in all cases. Copyright © 2002 John Wiley & Sons, Ltd.     

Sorption and transport properties of MY720/DDS epoxy reacted with blocking reagents

Thin films of the epoxy formed by the reaction of tetraglycidyl 4,4'-diamino-diphenylmethane and 4,4'-diaminodiphenyl sulfone (73:27 w/w) were reacted with acrylonitrile (ACN) and isocyanates as blocking reagents for hydroxyl, amine, and epoxy groups. The water uptake at 30, 45, 55, and 70°C of the epoxy resin was monitored gravimetrically. At each temperature the epoxy exhibited case I or Fickian behavior. The diffusion coefficient D increased from 30 to 55°C, but decreased at 70°C because of the reaction of water with residual oxirane groups. Diffusion of ACN is accompanied by both reaction and polymerization, so equilibrium could not be reached. Sorption of the isocyanates essentially follows case I or Fickian behavior. Equilibrium moisture absorptions showed a correspondence between the reduction of moisture absorption and the number of blocked functional groups, irrespective of the nature of the blocking groups. Moisture absorption reductions as high as 68% were obtained. Moisture diffusion of the films after blocking with the various reactants exhibits case I or Fickian behavior. At 30°C, D values are significantly higher for reacted films. At 70°C, the value of D is unchanged as compared with the 30°C value for films reacted with ACN, but D values are significantly lower for films reacted with isocyanate blocking reagents as compared with the epoxy resin.     

Microstructure,dielectric properties and optical band gap control on the photoluminescence behavior of Ba[Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>]O<Subscript>3</Subscript> thin films

Ba[Zr_0.25Ti_0.75]O₃ (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400 °C for different times and at 700 °C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultraviolet–visible (UV–vis) absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT thin films heat treated at 700 °C were approximately 148 and 0.08 at 1 MHz, respectively. UV–vis absorption spectra suggested the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was explained through the optical band gap values associated to the visible light emission components.     

Photograft Copolymerization of Methyl Methacrylate on Wool Using Ce4+ -Oxalic Acid Redox Initiator in a Limited Aqueous System

Abstract

Photograft copolymerization of methyl methacrylate on reduced wool (reduction done by treatment with thioglycollic acid, TGA) was studied at nearly 30°C using a Ce⁴⁺ -oxalic acid redox initiator system in a limited aqueous system (2.7 mL water for 0.15 g wool). Reduction of wool for 16 h with 15% TGA solution produced optimum grafting effects. Percent grafting and grafting efficiency under different sets of conditions were studied and compared, and the mechanism of grafting discussed. Generation of grafting sites (radical centers) on reduced wool was more effective in the presence of light than in the dark. Percent grafting of 250–350% and grafting efficiency of 65-80% over a conversion range of 60–90% in 3–5 h were easily obtained.     

Durable Multiblock Poly(biphenyl alkylene) Anion Exchange Membranes with Microphase Separation for Hydrogen Energy Conversion

Anion exchange membrane fuel cells (AEMFCs) and water electrolysis (AEMWE) show great application potential in the field of hydrogen energy conversion technology. However, scalable anion exchange membranes (AEMs) with desirable properties are still lacking, which greatly hampers the commercialization of this technology. Herein, we propose a series of novel multiblock AEMs based on ether-free poly(biphenyl ammonium-b-biphenyl phenyl)s (PBPA-b-BPPs) that are suitable for use in high performance AEMFC and AEMWE systems because of their well-formed microphase separation structures. The developed AEMs achieved outstanding OH⁻ conductivity (162.2 mS cm⁻¹ at 80 °C) with a low swelling ratio, good alkaline stability, and excellent mechanical durability (tensile strength >31 MPa and elongation at break >147 % after treatment in 2 M NaOH at 80 °C for 3750 h). A PBPA-b-BPP-based AEMFC demonstrated a remarkable peak power density of 2.41 W cm⁻² and in situ durability for 330 h under 0.6 A cm⁻² at 70 °C. An AEMWE device showed a promising performance (6.25 A cm⁻² at 2 V, 80 °C) and outstanding in situ durability for 3250 h with a low voltage decay rate (<28 μV h⁻¹). The newly developed PBPA-b-BPP AEMs thus show great application prospects for energy conversion devices.     

Optically transparent superhydrophobic TEOS-derived silica films by surface silylation method

Optically transparent silica films were prepared at room temperature (~27°C) by keeping the molar ratio of TEOS:MeOH:H₂O (0.001 M NH₄F) constant at 1:19.29:6.20, respectively. A surface chemical modification of the films was done with alkylchlorosilanes at different concentrations from 0 to 1 vol. % and aging times varied from half to 2 h. The DMCS and TMCS surface modified silica films showed the static water contact angle of 146° and 162°, respectively. When the DMCS and TMCS modified films were cured at temperatures higher than 240 and 275°C, respectively, the films became superhydrophilic. Further, the humidity study was carried out at a relative humidity of 90% at 30°C temperature over 60 days. We characterized the water repellent silica films by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, % of optical transmission, humidity tests and contact angle measurements.     

Thermal Characterization of Polybutadiyne

Butadiyne was thermally polymerized from the vapor phase onto substrate polyethylene, poly(vinylidene fluoride), polytetrafluoro-ethylene, and fluorinated ethylene propylene films at 20°C. The reaction is characterized as an initial absorption of monomer into the film followed by polymerization in the condensed state. A postpolymerization thermal reaction of the polybutadiyne pendant ethynyl groups was conducted over a 120 to 470°C temperature range with a subsequent surface electrical resistivity decrease to 7 × 10¹¹ ohm/square. The reaction of the pendant acetylenic groups was monitored by DSC and IR spectroscopy and found to be more complex than an intramolecular conversion of an acetylenic polyene to a polyacene structure.     

Reduction in the moisture absorption of cured MY720/DDS epoxy resins

Thin films of cured MY720/DDS epoxy resins were treated with blocking reagents for hydroxyl, amine, and epoxide functional groups. Infrared spectroscopy (IR) and differential scanning calorimetry (DSC) were used to monitor the progress of the reaction. Treated films were soaked in distilled water at 30°C for 720 h, and the corresponding moisture absorption determined gravimetrically. Samples treated with N-methyl-N-t-butyldimethylsilyl trifluroacetamide (MTBSTFA) containing 1% t-butyldimethylchlorosilane (TBDMCS) in dimethylsulfoxide (DMSO) at 30°C showed a maximum reduction in the IR peak at 3400 cm^?1 (OH and NH) of 39% and a 100% reduction in the epoxide peak at 904 cm, ^?1. The moisture absorption was 1.9%, a reduction of 58% compared to the untreated films (ca. 4.5%). The reactions show dependencies on time and temperature and are diffusion controlled. Samples treated with trimethylsilyl isocyanate (TMSI) in DMSO a 70°C showed 72% reduction in the 3400 cm^?1 IR peak; DSC thermograms do not show an exothermic energy, suggesting that all epoxide groups reacted. These reactions are primarily dependent on time and temperature. The moisture absorption of TMSI treated samples was 1.0% (75% reduction). Samples were also treated with m-trifluoromethyl phenyliscyanate (MTFPI). The reduction in the IR peak at 3400 cm^?1 was 9%, but the moisture absorption was 2.4%—a reduction of 47%.     

Study on the crystal transformation of ammonium polyphosphate crystalline form V

The crystal transformation of ammonium polyphosphate crystalline form V (APPv) was studied. The effects of heating time and water content in the reactor were explored. The results showed that APPv underwent complete conversion to crystalline form II (APPii) when heated at 200°C. The pure and water-insoluble APPii was obtained under the alternate wet ammonia and dry ammonia atmosphere. Then, the thermal behavior of APPv and APPii was investigated. The TG analysis showed APPv had high thermal stability over the range of 300°C to 580°C, which was possibly due to its highly cross-linked structures.     

Effect of increasing pH value on the structural,optical and magnetic properties of yttrium iron garnet films prepared by a sol–gel method

Yttrium iron garnets (Y₃Fe₅O₁₂, YIG) nanoparticles thin films with different pH values (pH 1, 2, 3, 4 and 5) were prepared by a sol–gel method. The films were deposited on quartz substrates using a spin coating technique. Annealing of the films was performed at 900 °C in air for 2 h. The structural analysis using an X-ray diffractometer (XRD) exhibited that all films were single phases regardless the differences in pH value. The lattice parameters calculated from the XRD patterns revealed that the distortion of lattice occurred at a high pH value. The crystallites sizes of films also increased from 27.6 to 33.3 nm when the pH value increases from 1 to 5. The films were high agglomeration due to increasing of pH value which caused difficulty to measure the grain size. The films with different pH values showed transmission >80 % in visible range. Additionally, the absorption coefficient (α) of films was found to be of the order of 10⁷ cm^?1. A strong absorption of the films caused by charge transfer transition centered in UV and optical transitions between crystal field levels within the 3d levels of Fe³⁺ ions. The YIG films exhibit highest saturation magnetization value of 76 emu/cm³ at pH 1. The increment of pH value up to 5 caused a decreasing of coercive field due to multidomain formation and the easy movement of the domain walls.     

Effect of thickness and monolayer location on thermostability of metal stearate LB films studied by FT-IR reflection—absorption spectroscopy

LB films of Cd and Ca stearates with 1, 3, 9, and 21 monolayers were fabricated on silver-coated glass slides. 9-Monolayer LB films of Cd and Ca salts of deuterated stearic acid, in which the 1st, 5th, or 9th layer was replaced by 1 monolayer of undeuterated analogues, were also prepared on the above substrates. Temperature dependences of Fourier transform infrared (FT-IR) reflection—absorption (RA) spectra were examined for these LB films in the range 31–140°C. At room temperature, the hydrocarbon chains in these LB films were in a well-ordered state with a high degree of perpendicular orientation to the substrate. However, they became disordered at elevated temperatures. These order-disorder phase transition temperatures were dependent on the film thickness, to a small degree in the Cd stearate LB film (102–108°C), but to a large degree in the Ca stearate LB film (103–129°C). In the latter LB film, the effect of dehydration was inferred. The degree of disorder at high temperatures was dependent on the film thickness and the location of monolayer in the 9-monolayer LB films. This result is discussed in terms of the internal pressure within the LB film.     

Preparation and characterization of electrostrictive polyurethane films with conductive polymer electrodes

All-polymer electrostrictive soft films were developed for the first time by depositing conductive polymer (polypyrrole) directly on both sides of solution-cast electrostrictive polyurethane elastomer films. The final composite films are flexible with strong adhesion between the polyurethane film and the conductive polymer electrode. The conductivity (sheet resistivity ∼1000 Ω/□), of the polymer electrode is appropriate for its intended use. The compatible interface between the polypyrrole electrode polymer and the electrostrictive polyurethane significantly improves the acoustic and optical transparency of these composite films, compared with using a metal electrode film. The all-polymer films also exhibit comparable dielectric properties to gold-electroded polyurethane films in the temperature range from −40^°C to +80^°C. The temperature range covers the soft segment glass transition temperature of the polyurethane elastomers, which is about −20^°C. The films also show large electric field induced strain responses which are dependent on film thickness and measurement frequency. The electrostrictive characteristics in the all-polymer films show similarities to those of the films with gold electrodes under identical measurement conditions. © 1998 John Wiley & Sons, Ltd.