Polyhedral oligomeric silsesquioxane polyimide nanocomposites for color filters and flexible conductive films

Color filters and conductive films are widely used in spacecraft, while the lack of lightweight, flexibility, and atomic oxygen (AO) durability confine their potential applications in low earth orbit. In this study, a clear poly(amic acid) with an empirical 20 wt% polyhedral oligomeric silsesquioxane (POSS) solid content is designed for transparency and AO durability. Red, green, blue, and yellow dyes are reinforced with small amounts of 1–5 wt% in POSS polyimides for color filters. A silver nanowire network film is infiltrated onto the POSS polyimide for conductive film. Erosion depth upon hyperthermal AO exposure, surface morphology, surface chemistry, optical transparency, and conductivity have been systematically investigated. The erosion yields of all 20 wt% POSS polyimides decrease by an order of magnitude when subjected to 2.32 ± 0.05 and 2.39 ± 0.06 × 10²⁰ atoms cm⁻² AO fluences, as passivating SiO_x networks are formed on film surface. The small-amount dye additives into polyimides do not introduce obvious changes in AO durability and surface chemistry. The silver nanowire infiltrated POSS polyimide film shows a 65.7% transmittance at 550 nm and a sheet resistance of 8.50 ± 0.36 Ohm square⁻¹. This study reveals promising attempts of POSS-polyimide-based color filters and flexible conductive films for potential space applications.     

Photocatalytic degradation of oxalic acid on a semiconductive layer of n-TiO2 particles in a batch plate reactor. Part III: Rate determining steps and nonsteady diffusion model for oxygen transport

The effect of oxygen concentration on the photocatalytic degradation rate of oxalic acid on a fixed layer of TiO₂ particles in a batch mode plate photoreactor was investigated at various light intensities. The regions where the photocatalytical decomposition rate is controlled by the flux of oxygen, photons, or both, were identified. For low oxygen concentration (0–0.15 mol m^–3) and photon flux intensity in the range from 10 to 24 × 10^–5 einstein m^–2 s^–1 the experimentally determined photocatalytical decomposition rate was in agreement with that theoretically calculated assuming the process to be controlled by the limiting flux of oxygen to the TiO₂ surface. At higher concentrations of oxygen (0.15–0.94 mol m^–3) the rate of photocatalysis was controlled simultaneously by both the flux of oxygen and photons. The influence of the oxygen concentration decreased with decreasing photon flux. For low photon flux intensities (3.5 × 10^–5 einstein m^–2 s^–1), the reaction rate was controlled by the photon flux. The concentration profile of oxygen in the diffusion layer along the reactor plate was calculated and showed a significant decrease in oxygen concentration on the TiO₂ surface.     

Surface-initiated atom transfer radical polymerization of polyhedral oligomeric silsesquioxane (POSS) methacrylate from flat silicon wafer

A polyhedral oligomeric silsesquioxane (POSS) methacrylate monomer, i.e. 3-(3,5,7,9,11,13,15-heptacyclopentyl-pentacyclo [9.5.1.1.^3,91.^5,151^7,13]-octasiloxane-1-yl) propyl methacrylate (POSS-MA), was directly grafted from flat silicon wafers using surface-initiated atom transfer radical polymerization (ATRP). Two methods were used to improve the system livingness and control of polymer molecular weights. By ‘adding free initiator’ method, a linear relationship between the grafted poly(POSS-MA) layer thickness and monomer conversion was observed. By ‘adding deactivator’ method, the poly(POSS-MA) thickness increased linearly with reaction time. Poly(POSS-MA) layers up to 40 nm were obtained. The chemical compositions measured by X-ray photoelectron spectroscopy (XPS) agreed well with their theoretical values. Water contact angle measurements revealed that the grafted poly(POSS-MA) was extremely hydrophobic. The surface morphologies of the grafted polymer layers were studied by an atom force microscopy (AFM).     

Tin(IV) Polymers: Part 1. Synthesis of Diorganotin Esters of Thiosalicylic Acid: X-ray Crystal Structure of Polymeric Thiosalicylatodiorganotin

Thiosalicylatodiorganotin, [R₂Sn(O₂CC₆H₄S)]_n, (R=Me (1), n-Bu (2), Ph (3), 3-Cl–PhCH₂ (4)), are prepared from thiosalicylic acid and diorganotin chlorides. All the compounds, 1–4, are characterized by elemental analysis as well as IR and ¹H-NMR spectroscopy. X-ray crystallographic analysis of the 2 and 4 shows that the structures are polymeric with neighboring diorganotin centers being linked by one O-atom of the carboxylate ligands. The carboxylate moiety is involved in coordination to one Sn atom via one O-atom while the other O-atom coordinates to the neighboring Sn atom. The mercaptotropone sulfur atom is bonded to the central Sn atom thereby establishing that Sn is five-coordinate and exists in a trigonal bipyramidal geometry.     

Superhydrophilicity on nano-rough carbon surfaces achieved by hyperthermal oxygen-atom beam exposure

In order to investigate a method to increase hydrophilicity on nano-rough carbon surfaces, a nano-rough surface of C₆₀ film and an atomically flat surface of highly oriented pyrolytic graphite (HOPG) were oxidized by hyperthermal oxygen-atom beam exposure and the hydrophilicities of the surfaces were investigated. Superhydrophilicity were achieved on these exposed carbon surfaces, which had low O/C ratio of approximately 28% and surface roughness (Ra) of approximately 3 nm. The direct oxidations on sp² bonded carbon atoms (basal plane) of these two carbon materials by the exposure of hyperthermal O-atom beam would contribute the superhydrophilicity.     

Oxygen at the interface of CVD diamond films on silicon

The oxygen incorporation at the interface between the silicon substrate and chemical vapour deposited (CVD) diamond films nucleated by the bias-enhanced nucleation (BEN) procedure has been studied by heavy-ion elastic recoil detection (ERD). Using standard process conditions for the realisation of heteroepitaxial films, oxygen with a concentration equivalent to about 1 nm SiO₂ has been found, which was mainly incorporated during textured growth with a certain CO₂ admixture to the process gas. By completely omitting CO₂ during nucleation and growth, the oxygen at the interface can be reduced by nearly one order of magnitude to 6.3×10¹⁵ at cm⁻², corresponding to 0.14 nm SiO₂. Intentional addition of highly enriched C¹⁸O₂ to the gas phase shows that the oxygen incorporation is strongly enhanced during BEN with hydrocarbon in the gas phase. The results indicate that roughening of the surface, the deposition of Si_xO_yC_z phases and strong lateral inhomogeneities at the silicon interface may explain the coexistence of epitaxial crystallites and amorphous phases. It is suggested that a further reduction of the oxygen concentration at the interface may have consequences for an improved heteroepitaxy of diamond on silicon.     

Mechanism of RF plasma induced fragmentation of SiCl4 and surface functionalization of polymeric substrates from SiClx species

The generation of extremely reactive species of silylium (silicenium) ions under plasma conditions opens up new ways for surface modification, even of the most inert polymeric surfaces. To control the plasma-induced chemistry and to tailor new molecular surface architecture, the mechanism of formation of the active species of the discharge must be understood. In this work the plasma-induced molecular fragmentation of SiCl₄ was studied and the surface functionalization of cellulose paper (CP), polyester (PET), polypropylene (PP), and polytetrafluoroethylene (PTFE) substrates with silicon atom based active species was evaluated. Gas chromatograph mass spectroscopy (GC-MS) and low Energy Electron MS (LEEMS) measurements carried out both on SiCl₄ and on the molecular mixture resulting from the recombination of plasma generated species indicate that the most predominant fragments are SiCl₃⁺ cations accompanied by SiCl₂⁺ and SiCl⁺ species. Survey and high-resolution electron spectroscopy for chemical analysis (ESCA) data collected from plasma functionalized surfaces show significant silicon and oxygen atom content regardless of the nature of the substrates. © 1996 John Wiley & Sons, Inc.     

Influence of Octasilane POSS on Non-Isothermal Crystallization,Thermal Stability and Conductivity of Poly(vinyl alcohol) Nanocomposite

Nonisothermal crystallization kinetics and properties of poly(vinyl alcohol)/octasilane polyhedral oligomeric silsesquioxanes nanocomposite were investigated by differential scanning calorimetry and compared with pure poly(vinyl alcohol). The effects of octasilane polyhedral oligomeric silsesquioxanes content and cooling rate on the degree of crystallinity (X_c), crystallization half time (t_1/2), Ozawa exponent (m), and Mo kinetics parameters were studied. The role of thermal treatment on the morphology and structure of the samples was studied by X-ray diffraction and scanning electron microscopy analyses. UV–visible analysis was used to show the polyhedral oligomeric silsesquioxanes effect on the nanocomposite structure. Electrochemical impedance spectroscopy analysis demonstrated that the best conductivity was for the nanocomposite with 1 wt% of octasilane polyhedral oligomeric silsesquioxanes.     

Unique polyhedron CeO2 nanostructures for superior formaldehyde gas-sensing performances

Highly exposed surface area CeO₂ polyhedral nanostructures were successfully prepared via a two-step hydrothermal route for gas-sensing applications. The surface chemistry and formation of polyhedral nanostructures was attributed to the interaction between polyvinylpyrrolidone and ammonium bicarbonate surfactants with parent ceria. The synthesized polyhedron CeO₂ structures were characterized using XRD, XPS, BET, SEM, EDS and TEM, respectively. The polyhedrons exhibited a high specific surface area 98.76?m²/g. For gas-sensing applications, the CeO₂ polyhedrons were exposed to different gases at various temperatures, from a low to high concentration range (1–150?ppm). At an optimal temperature 220?°C, superior gas-sensing response towards formaldehyde was observed than other target gases. The enhanced sensor response was attributed to multifaceted polyhedral nanostructures. The polyhedral structure based sensors have great potential in industrial sensing applications.     

Oxygen vacancy,permeability and stability of Si doping Pr0.6Sr0.4FeO3-δ ceramic membrane for water splitting

The high-valence inorganic metalloid element of silicon was used for doping perovskite type oxides Pr_0.6Sr_0.4Fe_1-xSi_xO_3-δ (PSFSi_x, x = 0?0.1), as the oxygen transport membranes (OTM) for thermochemical water splitting to hydrogen production, which were fabricated by sol-gel method successfully. The effects of Si doped on microstructure, thermal expansion, permeability, and stability were investigated systematically. Although the crystal structure does not change, the metal-oxygen average binging energy (ABE) and oxygen vacancy concentration at room temperature increase after Si⁴⁺ doped. Furthermore, the phase transition process is reduced below the operating temperature by silicon doped. Due to the increase of ABE, the oxygen vacancy concentration of PSF exceeds that of the Si-doping samples with the temperature elevated. This is why the oxygen permeation flux of Si-doping samples is gradually exceeded by PSF. The long-term stability of water splitting to hydrogen is enhanced because the Si-doping increases the chemical stability of samples in reducing atmosphere.     

Synthesis,characterization, and properties of a polyhedral oligomeric octadiphenylsulfonylsilsesquioxane

A novel polyhedral oligomeric octadiphenylsulfonylsilsesquioxane (ODPSS) was synthesized from octaphenylsilsesquioxane and benzenesulfonyl chloride via a Friedel–Crafts reaction with a high yield. ODPSS was identified by Fourier transform infrared spectroscopy, ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI–TOF MS), wide‐angle X‐ray diffraction, and elemental analysis to be a kind of polyhedral oligomeric silsesquioxane of a T₈R₈ structure. ODPSS exhibited superior thermal stability according to thermogravimetric analysis. Its initial thermal decomposition temperature (T_onset) was at 491°C in air and 515°C in nitrogen. Thermal and mechanical properties of epoxy resin (EP) composites with ODPSS added were studied by differential scanning calorimetry and tensile testing. The results show that the incorporation of ODPSS at a low loading content not only improved the glass‐transition temperature of the EP composites but also enhanced their tensile strength. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40892.     

Erosion resistance of polycrystalline diamond films to atomic oxygen

Polycrystalline diamond films deposited using hot filament chemical vapor deposition (CVD) technique have been investigated in atomic oxygen simulated as low earth orbit environment to examine their erosion resistance properties. After exposure to the atomic oxygen beam with a flux of 2.6×10¹⁶ atoms/cm² s, the diamond films only show a small mass loss. The reaction efficiency is estimated to be between 6.35×10⁻²⁶ and 8.28×10⁻²⁶ cm³/atom. Oxidation mechanism is investigated through the reaction temperature influence on the reaction rate. We suggest that atomic oxygen reacts with diamond surface and forms ether (C-O-C) and carbonyl (>CO) configurations besides eroding the surface.     

Oxygen transport in crosslinked,silicon-containing copolymers of methyl methacrylate

Copolymers of methyl methacrylate and 1,3-bis(methacryloxy methyl)-1,1,3,3-tetramethyl disiloxane were prepared by chemically induced copolymerization/crosslinking at 60°C and 49 mm Hg. Crosslinked, glassy copolymers were obtained with copolymer mole fraction of the silicon-containing monomer varying from 0.09 to 0.55. Oxygen transport studies were performed with thin films as prepared and after sub-T_g annealing. The results of this study indicated that an enhancement of both the steady state oxygen permeation rate and the oxygen diffusion coefficient was achieved through copolymerization. The oxygen diffusion coefficients through the copolymers were found, within experimental error, to be independent of silicon content and ranged from 0.80 × 10^?7 to 1.90 × 10^?7 cm²/s vs. oxygen diffusion coefficient for pure poly(methyl methacrylate) of 1.5 × 10^?8 cm²/s. Sub-T_g annealing effected a reduction of approximately equal magnitude in both the oxygen diffusion coefficient and the steady state oxygen flux for the copolymers. In addition, the normalized oxygen flux data were predicted with Fick's law, assuming constant boundry conditions and diffusion coefficient. These results were explained in terms of the free volume theory and the combined effects of increased crosslinking density, chain mobility, and oxygen solubility with increased copolymer silicon content.     

EFFECT OF COMPOSITION AND THERMAL HISTORY ON DIELECTRIC CONSTANTS OF SODA-BOROSILICATE GLASSES*

The dielectric constants, densities, and refractive indices of two series of soda-boro-silicate glasses were measured at 25° C. on some quenched specimens and on other specimens that were stabilized at different temperatures. The compositions of the two series were Na₂O-4.69 SiO₂-B₂O, (0 to 45%) and Na₂O B₂O₃-SiO₂ (30 to 100%), respectively. The structure of the glasses was found to depend on the ratio of oxygen atoms to the sum of the boron and silicon atoms and also on the concentration of the sodium ions. If the ratio of O to B + Si is greater than 2.0 or if the ratio of oxygen to sodium ions is less than 6.0, some of the oxygens are bonded only to one boron or to one silicon atom. The presence of “single-bonded” oxygen atoms in the glass structure leads to a lower density and a higher dielectric constant and refractive index. The dielectric constant decreases and the density increases continuously as the temperature of heat treatment is lowered. The effect of heat treatment is greater for the glasses which contain the larger number of “single-bonded” oxygen atoms and the higher concentration of sodium ions.     

Symmetric and asymmetric membranes based on La0.5Sr0.5Fe0.7Ga0.3O3-δ perovskite with high oxygen semipermeation flux performances and identification of the rate-determining step of oxygen transport

This work focuses on identifying the rate-determining step of oxygen transport through La_0.5Sr_0.5Fe_0.7Ga_0.3O_3-δ membranes with symmetric and asymmetric architectures. The best oxygen semipermeation fluxes are 3.4 10⁻³ mol. m^-2.s^-1 and 6.3 10⁻³ mol. m^-2.s^-1 at 900 °C for the symmetric membrane and asymmetric membrane with a modified surface. The asymmetric membrane with a modified surface leads to an increase of approximately 7 times the oxygen flux compared to that obtained with the La_0.5Sr_0.5Fe_0.7Ga_0.3O_3-δ dense membrane without surface modification. This work also shows that the oxygen flux is mainly governed by gaseous oxygen diffusion through the porous support of asymmetric La_0.5Sr_0.5Fe_0.7Ga_0.3O_3-δ membranes.     

Evaluation of mixed‐conducting lanthanum‐strontium‐cobaltite ceramic membrane for oxygen separation

In this study, La_0.4Sr_0.6CoO_3‐δ (LSC) oxide was synthesized via an EDTA‐citrate complexing process and its application as a mixed‐conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four‐probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatography method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (D_v) and surface exchange coefficient (K_ex) for LSC membrane were derived by model regression. The importance of surface exchange kinetics at each side of the membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6‐mm‐thick La_0.4Sr_0.6CoO_3‐δ membrane was ～4.0 × 10^?7 mol cm^?2 s^?1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10^?5 mol cm^?2 s^?1 through a 5‐μm‐thick LSC membrane with ideal surface modification when operating at 950°C for air separation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Performance of an oxygen-permeable membrane reactor for partial oxidation of methane in coke oven gas to syngas

Perovskite-type oxygen-permeable membrane reactors of BaCo_0.7Fe_0.2Nb_0.1O_3−δ packed with Ni-based catalyst had high oxygen permeability and could be used for syngas production by partial oxidation of methane in coke oven gas (COG). The BCFNO membrane itself had a poor catalytic activity to partial oxidation of CH₄ in COG. After the catalyst was packed on the membrane surface, 92% of methane conversion, 90% of H₂ selectivity, 104% of CO selectivity and as high as 15 ml/cm²/min of oxygen permeation flux were obtained at 1148 K. During continuously operating for 550 h at 1148 K, no degradation of performance of the BCFNO membrane reactor was observed under the condition of hydrogen-rich COG. The possible reaction pathways were proposed to be an oxidation-reforming process. The oxidation of H₂ in COG with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and H₂O reacts with CH₄ by reforming reactions to form H₂ and CO.     

Synthesis and Characterization of Some Triphenyltin(IV) Complexes from Sterically Crowded [((E)-1-{2-Hydroxy-5-[(E)-2-(aryl)-1-diazenyl]phenyl}methylidene)amino]acetate Ligands and Crystal Structure Analysis of a Tetrameric Triphenyltin(IV) Compound

Four new triphenyltin(IV) complexes containing [((E)-1-{2-hydroxy-5-[(E)-2-(aryl)-1-diazenyl]phenyl}methylidene)amino]acetate ligands (L) have been synthesized with formulations of Ph₃SnLH. They have been studied by multinuclear (¹H, ¹³C, ¹¹⁹Sn) NMR, ¹¹⁹Sn M?ssbauer and IR spectroscopy. A full characterization of one complex, Ph₃SnL¹H (1), was accomplished by single crystal X-ray crystallography, which revealed the compound to be a macrocyclic tetramer. In the tetramer, the five coordinate tin atoms have distorted trigonal bipyramidal geometries with the three phenyl groups occupying equatorial positions, while an oxygen atom of the carboxylate group of one L ligand and the oxide O-atom (formerly the hydroxy group) of a second L ligand in an apical positions. The carboxylate ligands bridge adjacent tin atoms and coordinate in the zwitterionic form with the phenolic proton moved to the nearby nitrogen atom. ¹¹⁹Sn NMR results indicate that the tetrameric structures of the complexes in the solid state, in which the tin atoms are five-coordinated, dissociate in solution to yield four coordinate monomeric species.     

Ab initio study of the binding strength of POSS-cation complexes

Polyhedral oligomeric silsesquioxane (POSS) is a cage-shaped molecule comprised of alternating silicon and oxygen atoms that have found increasing use as filler in polymer nanocomposites. The presence of four oxygen atoms on each face of the POSS cage suggests that the molecule forms a stable complex with a cationic atom or molecule. Although experimental evidence exists for gas-phase binding, the lack of an estimate of this binding strength makes it difficult to predict if complex formation is feasible in condensed systems. This paper presents an ab initio DFT study of the binding strength of POSS-cation complexes based on cation type, POSS cage functionalization, and the presence of a counterion. The binding strength of an unfunctionalized (i.e. with H-terminated corners) POSS molecule with a Li⁺ ion is found to be ∼80 kT at room temperature in vacuo. In a poly(styrene) solvent, the polarity of the medium is estimated to affect little this binding energy. Cyclohexyl ligand substitution is found to increase the binding strength by an additional 30 kT. In the presence of a tightly bound counterion (Cl⁻), the binding energy drops to the still substantial value of ∼20 kT. POSS is found also to bind cationic surfactants (through study of the model ⁺NH₃CH₃) at ∼25 kT, suggesting a possible new route to POSS modification to hinder agglomeration. This study supports the conclusion that POSS-cation complex formation is feasible in the presence of polymer.     

Synthesis and characterization of AB block copolymers based on polyhedral oligomeric silsesquioxane

Well-defined diblock copolymer based on polyhedral oligomeric silsesquioxane (POSS) was synthesized by atom transfer radical polymerization (ATRP) using POSS/PMMA-Cl as a macroinitiatior. POSS/PMMA-Cl was prepared by POSS-Cl initiating the polymerization of MMA in the presence of CuCl, 2, 2, - bipyridine at 110 °C. The structure of the block copolymer had been characterized by FTIR, ¹H NMR and GPC, which all agreed well with the theoretical values. XRD measurements revealed that POSS molecules were successfully monodispered in the hybrid composite.