Plasma polymer deposition from mixture of tetramethoxysilane and oxygen on PET films and their oxygen gas barrier properties

Plasma polymerization of silane compounds has been discussed for deposition of SiOx positron emission tomography (PET) films at room temperature. A mixture of tetramethoxysilane (TMOS) and oxygen containing 60 mol % O₂ is a preferable raw material for SiOx formation by plasma polymerization. The deposited plasma polymers consist mainly of Si(SINGLE BOND)O networks with small amount of Si(SINGLE BOND)OH and Si(SINGLE BOND)C groups. A part of Si(SINGLE BOND)O networks in the plasma polymers is distorted by the Si(SINGLE BOND)OH and Si(SINGLE BOND)C groups. The oxygen permeability coefficient for the plasma polymer itself is 2.1 × 10⁻¹⁵ (STP) cm³/cm/cm²/s/cm Hg, which is lower than that for hydrolyzed ethylene-vinylacetate copolymer (Eval) and poly(vinylidene chloride) (Saran). Conclusively, the plasma polymer deposited from the mixture of TMOS and oxygen containing 60 mol % O₂ is a material with good oxygen barrier properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1031–1039, 1997     

New precursors to SiCO ceramics derived from linear poly(vinylsiloxanes) of regular chain composition

Two linear polysiloxanes with vinyl groups regularly distributed in their chains (D₂V polymer with a vinyl group at every third and V₃ polymer with a vinyl group at each Si atom) were cross-linked with different hydrogensiloxanes (linear difunctional ^HMM^H, linear branched tetrafunctional Q(M^H)₄, cyclic tetrafunctional D₄^H) and studied as new precursors to SiCO ceramics. It was found that thermal properties of the cross-linked D₂V and V₃ polymers are governed mainly by functionality of the initial macromolecule as well as functionality and molecular structure of hydrogensiloxane. Transformation of the systems into ceramics was examined by recording FTIR spectra of the samples obtained after heat treatment of the cross-linked polymers under Ar at several temperatures. Analysis of the products formed at 1 000 °C, allowed establishing that they are a mixture of silicon oxycarbides and a free carbon phase. Lack of pores is a characteristic feature of these materials.     

Microporous polypropylene sheets containing polymethylsilsesquioxane filler

Plasma polymerized membranes were prepared from octamethyltrisiloxane for the purpose of separation of O₂ over N₂. The obtained membrane consisted of plasma prepared polymer layer on top of a porous polyproplene substrate. The membrane polymerized under the mild plasma condition (low power input and high monomer flow rate) showed the high permeation rate. Selectivity, however, was hardly affected by the plasma conditions. The selectivity and permeation rate obtained were 2.6 and 2.5 × 10^?10 kmol/(m²·s·Pa) (=7.5×10^?4 cm³/(cm²·s·cmHg)), respectively. This high permeation rate was attributed to the use of the monomer with the long, flexible siloxane chain and the mild plasma condition. Moreover, the membranes were prepared from a series of monomers with different siloxane chain lenghts (methoxytrimethylsilane, hexamethyldisiloxane, and octamethyltrisiloxane), and from those with different alkyl chain lenghts (methoxytrimethylsilane, propoxytrimethylsilane, and hexyloxytrimethylsilane). As the siloxane chain lenghts of the starting monomers increased and the alkyl chain lengths decreased, the permeation rates of the corresponding polymers increased. The selectivities were nearly constant regardless of the difference in the starting monomer structures. The structures of the plasma prepared polymers were analyzed by XPS and IR measurements, and discussed in relation to the membrane efficiencies. © 1994 John Wiley & Sons, Inc.     

29Si nuclear magnetic resonance studies of oligomeric and polymeric siloxanes: 4. Chemical shift effects of end-groups

²⁹Si n.m.r. spectra have been obtained for mixtures of polysiloxane oligomers in four cases, viz. MD_nM, M^HD_nM^H, M^OHD_nM^OH and MD^H_nM. Spectral dispersion is best (under the conditions studied) for the M^OHD_nM^OH series, where signals due to oligomers up to n = 9 have been separately detected. The spectra have been fully assigned, and shift effects due to the end-groups (equivalent to shifts expected in long chain polymers) have been derived. The significance of the data is discussed.     

Porous,Sintered Glass‐Ceramics from Inorganic Polymers Based on Fayalite Slag

The present paper deals with the synthesis of porous, sintered glass‐ceramics obtained at temperatures below 1150°C, originating from inorganic polymers based on fayalite slag. Firing led to the evaporation of water, dehydroxylation, and oxidation of Fe²⁺ above 345°C. For heating >700°C, the Si–O stretching band shifted from the 1160 and 750 cm^?1 to the 1255 and 830 cm^?1 region, due to a structural reorganization of the amorphous phase, whereas Fe–O bands appeared at 550 cm^?1. The final microstructure consisted predominantly of an amorphous phase, hematite, and franklinite. The open porosity and compressive strength decreased and increased, respectively, as the firing temperature increased. The final values suggest properties comparable to that of structural lightweight concrete, still, the materials synthesized herein, are lighter, and made primarily from secondary resources.     

Gas permeation properties of a composite membrane filled with poly(ethylene oxide) into a porous membrane

The permeability coefficients of O₂, N₂, and CO₂ gases at 25°C were examined for composite membranes that were prepared by filling poly(ethylene oxide)(PEO) with different molecular weights into a porous membrane. The permeability coefficients of O₂, N₂, and CO₂ were 2 × 10⁻¹⁰ – 4 × 10⁻¹⁰, 5 × 10⁻¹¹ – 9.5 × 10⁻¹¹, and 6 × 10⁻¹⁰ – 1 × 10⁻⁹ (cm³ STPcm/cm² s cmHg), respectively. The higher permeability coefficients of CO₂ are explained in terms of high solubility of CO₂ in filled PEO. The permeability coefficient of CO₂ was affected by the degree of crystallinity of PEO in the composite. On the other hand, there was little effect of crystallinity on O₂ and N₂ permeability coefficients. Some probable relationships between selectivities of O₂ to N₂ and CO₂ to N₂ and the degree of crystallinity of PEO were observed. The CO₂ gas permeability coefficients of the composite membrane for PEO50000 (M_w = 5 × 10⁴) showed a marked change due to melting or crystallization of PEO. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2733–2738, 1999     

Study on the Si–Si Vibrational States of the Near Surface Region of Porous Silicon

The Si–Si vibrational states near the surface region of porous silicon has been characterized using Fourier Transform Infrared Spectroscopy (FTIR) due to its enlarged surface area. By means of anodic etch and oxidization experiments, two Si–Si vibration modes of porous silicon have been identified as near the surface regions and in the bulk, respectively. The intensity of absorption peak at 620 cm^–1, which originates from the Si–Si bonds vibrations on the surface and near surface regions of porous silicon, is found to vary depending on the length of etch and degree of oxidation of porous silicon, which exists before etching and is recovered again after fully oxidation. The peak of 610 cm^–1 doesn't change throughout the oxidation experiment, and to be assigned for Si–Si bond vibrations in the bulk. With an extra irradiation of Nd:Yag laser on the PS sample the Raman and FTIR spectra reveal a red shift. These results can give an interpretation to explain the different phenomenon of Si–Si vibrations of Raman and FTIR spectroscopy.     

Synthesis, proton conductivity and methanol permeability of a novel sulfonated polyimide from 3-(2′,4′-diaminophenoxy)propane sulfonic acid

A novel sulfonated diamine monomer, 3-(2′,4′-diaminophenoxy)propane sulfonic acid (DAPPS), was successfully synthesized and the sulfonated polyimide (SPI) was prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and DAPPS. The resulting SPI, NTDA-DAPPS, was soluble in common organic solvents. The SPI membrane displayed proton conductivity σ values of 0.12-0.35 S/cm at temperatures ranging from 35 to 90 °C in liquid water, which were similar to or higher than those of Nafion 117 and sulfonated hydrocarbon polymers. The σ of the SPI membrane decreased significantly with decreasing relative humidity (RH) and became much lower than that of Nafion 117 at 30% RH. The SPI membrane displayed good water stability at 80 °C and was thermally stable up to 240 °C. It showed reasonable mechanical strength of a modulus of 1.3 GPa at 90 °C and 90% RH. Its methanol permeability P_M was 0.57×10⁻⁶ cm²/s at 30 °C and 8.6 wt% methanol in feed, which was a fourth of that of Nafion 117. As a result, its ratio of σ/P_M was 21×10⁴ S cm⁻³ s, which was about 4 times larger than that of Nafion 117, suggesting potential application of the SPI membrane for direct methanol fuel cell.     

Glow discharge polymerization of tetramethylsilane by capacitive coupling of 20 kHz frequency and surface hardening of polyethylene sheet

Glow discharge polymerizations of tetramethylsilane (TMS) were performed by the capacitive coupling of a 20 kHz frequency in comparison with those by the inductive coupling of a 13.56 MHz frequency. The polymers prepared by the former coupling were poorer in carbon and hydrogen, but richer in silicon than those prepared by the latter coupling. These two polymers showing similar infrared spectra contained CH₃, CH₂, CH, Si? O? C, Si? O? Si, Si? CH₃, and Si? CH₂? CH₂? Si groups. Some physical properties involving surface energy, thermal stability, and absorption spectra in the regions of the UV and visible light were determined. This coating procedure was applied for surface hardening of a polyethylene sheet. The surface hardness of the polyethylene sheet was enhanced by a coating of plasma films prepared from TMS or the TMS/O₂ mixtures. Surface hardness was determined by the pencil method and hardness was enhanced from 2B to 2H. The adhesion between these plasma films and polyethylene sheet was good even when immersed in 0.9% NaCl solution at 40°C for 10 days.     

Suppression of radiation‐induced oxidation of polymers by sputtered silicon oxide coating

Oxygen barrier coating on polymers was attempted to obtain polymeric composite materials with improved radiation resistance. Silicon oxide (SiO_1.6) films ranging from 120 to 240 nm thick were formed on polypropylene (PP) and polyethylene (PE) by radio frequency (RF) magnetron sputtering. Oxygen permeability after SiO_1.6 deposition was reduced significantly in all samples studied, indicating that silicon oxide is a useful gas barrier. The oxygen permeability coefficient of deposited films for PP was 1.7–2.2 × 10^?14 cm³‐cm/cm²/s/cmHg and that for PE was 2.8–4.8 × 10^?13 cm³‐cm/cm²/s/cmHg. We studied the effect of such films on the radiation resistance of polymers in the presence of oxygen by microscopic infrared (IR) absorption spectroscopy. Silicon oxide films 180 nm thick were deposited on the surfaces of PP and PE, and the formation of carbonyl groups after irradiation in air was measured as a function of depth from the surface. Results compared with those for uncoated PE and PP showed that the radiation‐induced polymer oxidation is dramatically suppressed by silicon oxide coating. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 186–190, 2002     

Synthesis of Pure VSH-2 in Large Quantities and Its Characterization

A method to produce pure VSH-2 in large quantities (~20 g) was developed. The reagents were silica sol, V₂O₅, H₂SO₄, CsOH, and ethanol. Despite the fact that V₂O₅ was used as the vanadium source the oxidation states of most of the vanadium atoms in the produced VSH-2 were 4+, indicating that ethanol acts as a reducing agent. The crystals adopted individual octahedral shapes or aggregated states depending on the gel composition. The total surface area of the pristine VSH-2 with the general formula of Cs₂(VO)(Si₆O₁₄)·3H₂O was only 40 m²/g, indicating that the pores are blocked by the large Cs⁺ ions. The surface area increased to 149 m²/g upon exchanging Cs⁺ with Na⁺. Analyses of the diffuse reflectance UV–Vis spectra of Mⁿ⁺–VSH-2 (Mⁿ⁺ = Cs⁺, Na⁺, Ca²⁺, and Pb²⁺) revealed that the 215, 250, and 313 nm bands arise due to the V⁴⁺ to O^2? metal-to-ligand charge transfer (MLCT) and the 437, 590, and 914 nm bands arise due to the d–d transition of V⁴⁺. This reveals an unprecedented interesting situation that in dehydrated VSH-2 the framework oxide plays the role of both acceptor to V⁴⁺ and donor to Mⁿ⁺. The measured atomic magnetic moment (μ) was 1.64 BM, indicating that most of the V atoms exist in V⁴⁺. The ESR spectrum of VSH-2 showed a strong signal due to V⁴⁺ with the g value of 1.959 with ΔH_pp value of 168 G. The Raman spectra of Mⁿ⁺–VSH-2 revealed the existence of strong V=O stretching at 960 cm^?1, and other weak peaks. The V=O stretching band shifted to a higher energy region upon increasing the Sanderson’s electronegativity of Mⁿ⁺. The thermogravimetric (TGA) analysis showed that VSH-2 is thermally stable up to 550 °C and above which the oxidation of V⁴⁺ occurs.     

High temperature oxidation behavior of porous MoAlB ceramic from 800 °C to 1100 °C in air

MoAlB possesses the characteristics of both metals and ceramic materials, which has attracted extensive attention due to its excellent high-temperature oxidation resistance. For this reason, porous MoAlB is considered applicable to the practice of filtration under harsh environment. In this study, the high-temperature oxidation behavior of porous MoAlB ceramics is systematically studied at the temperatures ranging from 800 to 1100 °C. According to the results, the porous MoAlB exhibits good oxidation resistance at a maximum temperature of 1000 °C. The oxidation kinetics of porous MoAlB can be divided into three stages, and the estimated activation energies of the three stages are 253.83 kJ·mol⁻¹, 367.48 kJ·mol⁻¹ and 317.84 kJ·mol⁻¹, respectively. In the stable stage at 1000 °C, the quadratic mass gain per unit area shows linearity over time, and the oxidation rate of porous MoAlB reaches 37.31 mg²·cm⁻⁴·h⁻¹. As revealed by the analysis of the composition and microstructure of oxide layers, the main components of the oxide layer include MoO₃, MoO₂, Al₂O₃, B₂O₃. With the extension of oxidation time, the content of Al₂O₃ in the oxide films increases. The average pore size, permeability and open pore porosity of porous MoAlB show a trend of first decreasing and then tending to be stable. In addition, a discussion is conducted on the high-temperature oxidation mechanism of porous MoAlB.     

A novel porous‐dense dual‐layer composite membrane reactor with long‐term stability

A porous‐dense dual‐layer composite membrane reactor was proposed. The dual‐layer composite membrane composed of dense 0.5 wt % Nb₂O₅‐doped SrCo_0.8Fe_0.2O_3‐δ (SCFNb) layer and porous Ba_0.3Sr_0.7Fe_0.9Mo_0.1O_3‐δ (BSFM) layer was prepared. The stability of SCFNb membrane reactor was improved significantly by the porous‐dense dual‐layer design philosophy. The porous BSFM surface‐coating layer can effectively reduce the corrosion of the reducing atmosphere to the membrane, whereas the dense SCFNb layer permeated oxygen effectively. Compared with single‐layer dense SCFNb membrane reactor, no degradation of performance was observed in the dual‐layer membrane reactor under partial oxidation of methane during continuously operating for 1500 h at 850°C. At 900°C, oxygen flux of 18.6 mL (STP: Standard Temperature and Pressure) cm^?2 min^?1, hydrogen production of 53.67 mL (STP) cm^?2 min^?1, CH₄ conversion of 99.34% and CO selectivity of about 94% were achieved. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4355–4363, 2013     

1,2‐propanediol–cellulose–acrylamide graft copolymers

1,2‐Propanediol–cellulose–acrylamide graft copolymers (PCACs) were developed for enhanced oil recovery. They were prepared with acrylamide and 1,2‐propanediol (PDO)–cellulose, which was formed through the addition of glycols to cellulose by the Shotten–Baumann reaction between 3‐chloro‐1,2‐propanediol and cellulose. The graft copolymerization was initiated with a redox system between Ce⁴⁺ and glycols in cellulose. The infrared spectrum of PDO–cellulose had some characteristic absorption bands around 2960 (νC? H) and 1050 cm^?1 (νC? O) that also appeared for the PDO group and pyranose ring of cellulose, respectively. The rate of Ce⁴⁺ consumption by PDO–cellulose was investigated through the calculation of the overall kinetic constant from the slopes of ln(D ? D_R) versus time (where D is the absorbance and D_R is the absorbance of the original polysaccharide solution) The results showed that PDO–cellulose had high reactivity and that there were two mechanisms of oxidation by Ce⁴⁺ with PDO–cellulose. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3022–3029, 2004     

Syntheses and gas-transport properties of alkylsilane-modified SBS membranes

Alkylsilane-modified styrene-butadiene-styrene (SBS) polymers were prepared via two steps. In the first step, dimethylchlorosilane HSi(CH₃)₂Cl and SBS (Korea Kumho Petrochem. Co.; 35% vinyl content; M_o = 48,000, M_o/M_n = 1.05) were reacted in toluene using H₂PtCl₆ catalyst to produce a hydrosilylated polymer. In the second step, chloride in the silyl group was replaced with alkyl by reaction with RLi (R = Me, n-Bu). Under severe conditions, silylation occurs on all the double bonds of the polymer so that their elastomeric nature disappears. However, under mild conditions, selective hydrosilylation of the pendant vinyl groups of SBS could be accomplished so that the polymer retained its elastomeric properties with two low T_g values. These modified SBS polymers were easily dissolved in THF, and thus could be formed into film-type membranes by solvent casting on teflon plates. From the measurements of their gas permeability for O₂ and N₂, they showed higher selectivity for O₂ compared with the unmodified SBS. The permeability for oxygen was dependent on the size of the alkylsilyl group. Methylsilane and butylsilane-modified SBS membranes showed the higher permeability values of 31.2 and 37.5 barrer (1 barrer = 1 × 10⁻¹⁰ cm³ (STP) cm cm⁻² s⁻¹ cmHg⁻¹) at 30°C, respectively, compared with 2.39 barrer of the unmodified SBS. Furthermore, their selectivities for O₂ over N₂ were increased to 3.0 and 3.2, respectively, from 2.5 of the unmodified SBS case. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1117–1122, 1997     

Characterization of novel thermoplastic polymers with phenolphthalein in their backbone chains

Different molecular weight phenolphthalein poly(ether ketone) (PEK-C) and phenolphthalein poly(ether sulfone) (PES-C) fractions in chloroform (CHCl₃) were studied by static and dynamic laser light scattering (LLS). The dynamic LLS revealed that both the PEK-C and PES-C samples contain some large polymer clusters formed in the process of polymerization. These large clusters can be removed by filtering the solution with a 0.1-μm filter. The positive second virial coefficient (A₂) shows that CHCl₃ is a good solvent for these polymers at room temperature. The persistence length and the Flory characteristic ratio of these polymers in CHCl₃ at 25°C are ～2 nm and ～3, respectively, which indicate that these polymer chains are flexible. A combination of static and dynamic LLS results, namely the weight-average molecular weight from static LLS and the line-width distribution from dynamic LLS, lead to two calibrations between the translational diffusion coefficient (D) and molecular weight (M): D = 2.20 × 10^?4 M^?0.56 for PEK-C and D = 2.45 × 10^?4 M^?0.55 for PES-C in CHCl₃. Using these calibrations, we are able to estimate not only the molecular weight distributions of these fractionated polymers, but also unfractionated PEK-C and PES-C samples.     

Thermal desorption spectra of the oxidized surfaces of diamond powders

Thermal desorption mass spectrometry was carried out in the range from room temperature to 960°C for the diamond powders oxidized in 10^?2Torr O₂ at temperatures from 25 to 554°C. The spectra show two desorption peaks (α, β) and the major peak α seems to consist of at least four types of adsorption states (α₁?α₄). The first state α₁, may arise from “labile” carbon atoms created during degassing, and disappears with high temperature oxidation changing into the more stable states (α₂-α₄). IR absorption spectroscopy shows that α₂?α₄ states include carbonyl and ether structures. The minor peak β shows little change with oxidation temperature. The amount of oxygen chemisorbed at 420°C (1.22 × 10¹⁵ atom/cm²) is in good agreement with the estimated value of full coverage.     

New membranes for reverse osmosis I. Characteristics of the base polymer: sulphonated polysulphones

Within the scope of our research programme on new materials for the preparation of reverse osmosis membranes, we have studied the specific characteristics and performance of a new polymer which is a sulphonated aromatic polysulphone.Film properties were determined in reverse osmosis, permeability constants were calculated from measurements carried out at 52 bars and 20°C on a 35 g/l NaCl solution:Water permeability D₁C₁ = 2.8 × 10^-7 g/cm/sSalt permeability D₂K = 1.9×10^-10 cm²/sThere the ratio (D₁C₁/D₂K) = 1.470 g/cm³Under the same conditions, a cellulose acetate film allows a ratio D₁C₁:D₂K of 1,200 g/cm³ which is in agreement with results in the literature.     

The Stretching Frequencies of Isotopic Arsenate and Permanganate Ions in Aqueous Solutions

The infrared absorption of crystalline powders and D₂O solutions of normal and 84.5 atom % ¹⁸O-labelled sodium arsenate as well as normal and 83.3 atom % ¹⁸O-labelled sodium permanganate was measured in the 780–980 cm^?1 region. The ν₁ and ν₃ fundamentals of the aqueous As¹⁸O₄^3? ion appear at 834(sh) and 866(s) cm^?1 while the respective As¹⁸O₄^3? values are 808 and 822 cm^?1 These as well as other data are shown to indicate that the water molecules which hydrate this ion are attached to its As atom. The ν₃ frequency of the aqueous Mn¹⁸O₄^? ion is observed at 917 cm^?1 and that of hydrated Mn¹⁸O₄^? at 878 cm^?1.     

Ablation resistance of HfC(Si,O)-HfB2(Si,O) composites fabricated by one-step reactive spark plasma sintering

A dense HfC(Si, O)-HfB₂(Si, O) composite was fabricated by reactive spark plasma sintering using HfC and SiB₆ as starting reactants. The best ablation resistance was obtained with the composite fabricated with the addition of 15 vol.% SiB₆. After ablation under an oxyacetylene flame for 60 s, the mass and linear ablation rates of this composite were ?0.007 mg cm^?2 s^?1 and ?0.233 μm s^?1, respectively. The negative ablation rates are the result of a slight mass gain/thickness increase, which indicate that the oxidation process was stable and mechanical scouring was limited during ablation. This enhanced ablation resistance was attributed to a unique double-layered oxide formation, which possessed lower oxygen permeability and better mechanical strength. The solid solution nature of the composite and its appropriate phase composition were responsible for the stable oxide structure formation.