Surface properties of polymers treated with tetrafluoromethane plasma

Polymer films of poly(ethylene terephthalate), polypropylene, and cellophane were surface treated with tetrafluoromethane plasma under different time, power, and pressure conditions. Contact angles for water and methylene iodide and surface energy were analyzed with a dynamic contact angle analyzer. The stability of the treated surfaces was investigated by washing them with water or acetone, followed by contact angle measurements. The plasma treatments decreased the surface energies to 2–20 mJ/m² and consequently enhanced the hydrophobicity and oleophobicity of the materials. The treated surfaces were only moderately affected after washing with water and acetone, indicating stable surface treatments. The chemical composition of the material surfaces was analyzed with X-ray photoelectron spectroscopy (XPS) and revealed the incorporation of about 35–60 atomic % fluorine atoms in the surfaces after the treatments. The relative chemical composition of the C ls spectra's showed the incorporation of —CHF— groups and highly nonpolar —CF₂— and —CF₃ groups in the surfaces and also —CH₂—CF₂— groups in the surface of polypropylene. The hydrophobicity and oleophobicity improved with increased content of nonpolar —CF₂—, —CF₃, and —CH₂—CF₂— groups in the surfaces. For polyester and polypropylene, all major changes in chemical composition, advancing contact angle, and surface energy are attained after plasma treatment for one minute, while longer treatment time is required for cellophane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1591–1601, 1997     

Adhesion of copper to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces modified by vacuum UV photo-oxidation downstream from Ar microwave plasma

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces were exposed to vacuum UV (VUV) photo-oxidation downstream from Ar microwave plasma. The modified surfaces showed the following: (1) an improvement in wettability as observed by water contact angle measurements; (2) surface roughening; (3) defluorination of the surface; and (4) incorporation of oxygen as CF—O—CF₂, CF₂—O—CF₂ and CF—O—CF₃ moieties. With long treatment times, a cohesive failure of copper sputter-coated onto the modified surface occurred within the modified FEP and not at the Cu–FEP interface.     

The effect of casting solvent and water on gas permeability of poly(γ-methyl L-glutamate) membrane

Gas permeability of poly(γ-methyl L-glutamate) (PMLG) membranes prepared by using dichlorethane, trifluoroacetic acid, and formic acid as solvents was studied. The membranes prepared by casting dichloroethane and trifluoroacetic acid solutions of the polymer, designated as PMLG—DCE and PMLG—TFA, respectively, had α-helical structures according to infrared absorption spectra, while the membranes prepared by allowing the PMLG—TFA membranes to swell in formic acid, designated as PMLG—FA, had mainly a β-sheet structure. The diffusion coefficients of each gas studied for PMLG—DCE, PMLG—TFA, and PMLG—FA decreased in that order, and the apparent activation energies of diffusion increased in that order. The apparent heats of solution for Ne,O₂, N₂, and CO₂ were negative in PMLG—FA. These results were discussed in connection with the molecular conformations of PMLG in the membranes. It is suggested that the diffusion of gases in PMLG—DCE takes place in the side-chain regions between helices, while in PMLG—FA the diffusion occurs across the polymer main chain whose mobility is depressed by the intermolecular hydrogen bonds. The effect of water on oxygen permeability of PMLG—DCE was small; on the contrary that of PMLG—FA was very large. Furthermore, it is assumed that the random-coil conformation partly exists in PMLG—TFA.     

Further studies on cellulose III polymorphs. Transformations to cellulose IV lattices and subsequent reactions

Production of cellulose IV polymorphs, their characterization using X-ray diffraction and infrared spectroscopy, as well as the effect of chemical treatments on these polymorphs have been investigated. Cellulose III_I and III_II polymorphs, produced from celluloses I and II using EDA—MeOH treatments, were of particular interest as starting materials in the study. Celluloses IV_I and IV_II gave identical equatorial X-ray patterns in the absence of other crystal lattices in the samples. Crystallinity as well as conformation were indicated to influence production and further reactions of the samples. The latter included boiling in water, acid hydrolysis, and treatments with EDA—water, EDA—MeOH, and NaOH solutions. Cellulose IV_I → I, IV_I → I → II, and cellulose IV_II → II lattice conversions were demonstrated to occur with EDA—water treatments, thereby providing a new technique for observing these transformations. Conformational differences were apparent among celluloses I, II, III_I, and III_II, each produced using different experimental procedures.     

Excess enthalpy data for the ternary system methane—ethylene—carbon dioxide by flow calorimetry

Excess enthalpy data for the ternary system methane – ethylene – carbon dioxide was obtained utilizing an isothermal flow calorimeter. The measurements were made at three temperatures: 293.15, 305.15 and 313.15 K and pressures of 1.114, 1.520 and 3.445 MPa (11, 15 and 34 atm). The determination of excess enthalpies for the binary systems methane—ethylene, ethylene—carbon dioxide and methane—carbon dioxide has been reported in three preceeding articles, respectively: Gagné et al., 1985; Ba et al., 1979 and Barry et al., 1982a. The binary interaction coefficients k_ij obtained for these systems have been utilized as initial values for the optimization procedure leading to the k_ij for the ternary system. For the case of the ternary system studied in this investigation, two types of binary interaction coefficients k_ij have been determined from experimental data: k_ij independent of temperature and pressure and k_ij adjusted as function of temperature and pressure. Experimental data were compared with the predictions from Benedict—Webb—Rubin and Redlich—Kwong equations of state. In both cases, the coefficients k_ij dependent on temperature and pressure led to better prediction of excess enthalpies.     

Infrared spectroscopic study of SiOx film formation and decomposition of vinyl silane derivative by heat treatment. I. On KBr and gold surface

The free-radical copolymerization of vinyltrimethoxysilane (VTS) with vinylimidazole (VI) was carried out in benzene at 68°C. Thermooxidative degradation and the SiO_x film-formation mechanism of poly(VI-co-VTS) both on gold and KBr were studied with Fourier transform infrared (FTIR) spectroscopy. Reflection-absorption (R-A) spectra on gold were compared with transmission spectra on KBr. In the initial stage of heat treatment, the Si—O—Si bond formation was caused mainly by the residual water in the copolymer film. As heating time increased, however, both the water resulting from the thermal decomposition of the copolymer and the water vapor in air began to participate in the hydrolysis of the Si—O—CH₃ group followed by the condensation reaction. The structure of the SiO_x film became closer to the structure of SiO₂ with increasing heating temperature. In addition, the differences between the transmission spectra and R-A spectra were observed at the peaks related to Si—O—Si stretching due to the optical effect. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:775–784, 1998     

Liquefaction of aspen poplar wood

Dried and green aspen poplar wood suspended in water containing alkaline catalysts has been converted completely to an oil, water-soluble chemicals and gases if heated for one hour in the presence of carbon monoxide in a rocking batch reactor. Within the ranges of parameters studied: temperature (593—633 K), nominal reaction times (0—1 h), water-to-wood ratio (0.5:1—5:1), catalyst (Na₂CO₃, K₂CO₃, NaOH), amount of catalyst (7.0—12.5 wt %) and initial hydrogen to carbon monoxide ratios (2:1—0:1), the water-to-wood ratio was most important. Oil yields of ?50% with a carbon plus hydrogen content of ?80% and representing a carbon recovery of ?66% were obtained. The higher heats of combustion ranged from 32.2 to 36.0 MJ/kg.     

Low Temperature Selective CO Oxidation in Excess of H2 over Pt/Ce—ZrO2 Catalysts

Pt/Ce—ZrO₂ catalysts have been designed and applied to selective CO oxidation at low temperature. Both tetragonal and cubic phase Ce—ZrO₂ supports were prepared by co-precipitation method to get high surface area materials after calcination at 500 °C for 6 h in air. Selective CO oxidation was conducted using stoichiometric amounts of O₂. Cubic Ce—ZrO₂ supported Pt catalyst exhibited 78% CO conversion and 96% CO₂ selectivity even at 60 °C, while Pt/Al₂O₃ catalyst showed less than l% CO conversion at the same condition. The higher CO conversion and CO₂ selectivity (to CO₂ as opposed to H₂O) of Pt/Ce—ZrO₂ catalyst is mainly due to the high oxygen storage capacity of Ce—ZrO₂ and nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂.     

The cathodic behavior of microwave-treated manganese dioxide in lithium nonaqueous cells

The cathodic behavior of microwave-treated manganese dioxide (MnO₂) was studied in lithium nonaqueous cells. Two types of discharge tests, low rate continuous discharge at current densities of 0.1–5 mA cm^?2 and high rate pulse-discharge at current densities of 10–25 mA cm^?2 were carried out in 1 M LiClO₄—propylene carbonate—50% tetrahydrofuran—50% electrolyte, and it was found that the Li—microwave-treated MnO₂ cell exhibited good characteristics in both types of discharge tests. A stability test of microwave-treated MnO₂ in a cell was also carried out, and it was shown to have no problems with gassing and to provide long shelf life.     

Surface modification of Teflon® PFA with vacuum UV photo-oxidation

Surface modification of poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) with vacuum UV (VUV) photo-oxidation using radiation from excited Ar atoms downstream from an Ar microwave (MW) plasma shows: (1) an improvement in wettability as observed by water contactangle measurements; (2) surface roughening; (3) incorporation of oxygen as C=O, CF—O—CF₂ and CF₂—O—CF₂ moieties and (4) enhancement of the CF—O—C _n F_2n+1 concentration. Adhesion measurements of Cu sputter coated onto the photo-oxidized PFA surface results in failure within the PFA (cohesive failure) and not at the Cu–PFA interface.     

Application of wavefront analysis for kinetic investigations of watergas shif reaction

It has been demonstrated that during dynamic operation of the low temperature watergas shift reaction on the wavefront the CO₂—production is faster than the H₂—production. For a catalyst pretreated for several hours with a mixture of CO/N₂ its re-oxidation by a mixture of H₂O/CO/N₂ is a slow process, whereas on the wavefront the H₂—concentration is twofold the CO₂—concentration. The quantitative analysis of CO₂—wavefront data for a catalyst pretreated for several hours with a H₂O/N₂—Mixture has given a reaction order n_co = 0.625 and an activation energy E = 46.27 kJ/mole for the CO oxidation. It is shown that H₂O/N₂inhibits the CO oxidation. For a catalyst pretreated for a long time period with a H₂O/N₂—mixture and then reduced in a short time period by a H₂O/CO/N₂—mixture the reoxidation by a H₂O/N₂—mixture is a slow process. The wavefront analysis has also been applied to clear-up the H₂O-sorption on the low temperature catalyst, suggesting that a physisorption of Langmuir type is combined with a second mechanism saturating the H₂O—capacitance for low values of P_H2O.     

Statistical study on the batch conversion of estevan lignite into oils using carbon monoxide and hydrogen mixtures

Batch autoclave hydrogenolysis of a Saskatchewan lignite has been conducted with CO and H₂ mixtures. Conversion, oil yield and the carbon monoxide consumption patterns were measured as a function of reaction temperature (380 — 460°C), initial cold pressure (7.1 — 11.1 MPa), contact time (10 — 50 min), and initial CO/H₂ gas composition (1/3 — 3/1 vol. %). The experimental results were obtained following an unreplicated 2⁴ factorial design. Significant models were derived for conversion and the CO consumption patterns. A relationship seems to develop between carbon monoxide consumption and the amount of oil produced. The oil yield model however showed a lack-of-fit at the F_5% level. The highest conversion and oil yield experimentally obtained were 85.3 and 63.4% respectively, on the lignite m.a.f. basis. In general greater hydrogenation but less deoxygenation occurred at the lower temperature.     

Chemical Strengthening of Soda Lime Silicate Float Glass: Effect of Small Differences in the KNO3 Bath

Six slightly different KNO₃ baths were considered in this work, for the chemical strengthening of soda lime silicate glass. Five of these were commercially available pure KNO₃ salts for industrial or laboratory use and one was a salt from an unknown source that had been already used for at least 1000 h in Na–K ion exchange. Various amounts of sodium — the main impurity — calcium, and magnesium were measured in the six salts together with other more limited contaminants. Different strengthening effects associated with clearly dissimilar ion exchange efficiency were measured on glass treated in the different melts. The presence of Na — major impurity — in the salt was revealed to be not a critical aspect, at least up to concentration of about 0.5 wt%. Instead, the “blocking” effect caused by the presence of Ca and Mg in the KNO₃ bath (also in amounts of few tens of ppm) is shown to be a major issue.     

The effect of heat treatment and carbon content on the corrosion behaviour of iron—chromium steels in sulphuric acid solutions

In this study the corrosion behaviour of iron—chromium steels was investigated. The samples were subjected to heat treatment. The current density—potential curves were obtained in 1 N H₂SO₄ by electrochemical, potentiodynamic (1 mV min^?1), potentiostatic and galvanostatic methods. Corrosion rates were obtained from the extrapolation of anodic and cathodic Tafel lines and using potentiodynamic, potentiostatic and galvanostatic linear polarization techniques with the Stern—Geary equation. It was seen that the effect of chromium on the rate of corrosion varies with the heat treatment method applied and the amount of carbon content.     

Non-equilibrium thermodynamic studies of electro—kinetic effects—XI. Studies with aqueous dioxane

Experimental results for the measurements of electro—osmosis, electro—osmotic pressure difference, streaming potential for dioxane—water (DH₂O) mixtures (30%, 40%, 50% and 60% by mass of dioxane) using Pyrex sintered disc (G₃) at 25° and at voltages of 40 V to 300 V are reported. The data are analysed in the light of the theory of non-equilibrium thermodynamics. It has been found that the validity of the phenomenological relations describing electro—kinetic effects increases with the decrease in the dielectric constant of the mixture. Second-order coefficients estimated from the electro—osmosis and electro—osmotic pressure difference are reported. Onsager's reciprocity relations have been found to hold good for all the mixtures. It has been found that the concentration dependence of L₂₂ and L₂₁ do not conform to the Spiegler's frictional model. Efficiency of electro—kinetic energy conversion (η_e) for electro—osmotic flows has been calculated and it is found that for different composition of dioxane—water mixtures η_max was obtained at half the value of the electro—osmotic pressure difference.     

Synthesis of Amino Acid Conjugates and Further Derivatives of 3α‐Hydroxylup‐20(;29)ene‐23,28‐dioic acid

Triterpenes of betulinic acid type exhibit many interesting biological activities. Therefore a series of new 3α‐hydroxy‐lup‐20(29)‐ene‐23,28‐dioic acid derivatives 2a—22 with putative pharmacological activities were synthesized. As starting compounds 3α‐hydroxy‐lup‐20(29)‐ene‐23,28‐dioic acid ( 1a ), isolated from Schefflera octophylla, or its 3‐O‐acetyl derivative 1b were used. Mono‐ and diesters ( 2a—b from 1a , and 4d from 4c ) were prepared with CH₂N₂. Oxidation of the isopropenyl side chain with OsO₄ yielded the 20,29‐diols ( 4a—b from 1b , and 19 from 17 ), which were in the case of 4b further transformed to the 29‐norketones 8a/mdash;b . Oxidation of the isopropenyl side chain with m‐chloroperbenzoic acid afforded the 20,29‐epoxide 12 (from 1b ) and the 29‐aldehydes and a‐hydroxy aldehydes ( 13a—c from 2a, 14a—c from 2b , and 16a—c from 15a ). Ring A was modified by a tosylation—elimination sequence using p‐TsCl/NaOAc, which afforded diolefin 15a (from 2a ) with Δ^2,20(29) double bonds or 23‐nor‐Δ^3,20(29)diolefin 17 (from 1a ). Compounds 4b, 4c , and 8a were coupled with L ‐methionin, L ‐phenylalanin, L ‐alanin, L ‐serin, and L ‐glutaminic acid via amide bonds at positions 23 and 28 to afford the amino acid conjugates 5a—7b and 9a—11 .     

Antibacterial efficiency of alkali-free bio-glasses incorporating ZnO and/or SrO as therapeutic agents

A series of seven alkali-free silica-based bioactive glasses (SBG) with ZnO and/or SrO additives (in concentrations of 0–12?mol%) were synthesized by melt-quenching, aiming to delineate a candidate formulation possessing (i) a coefficient of thermal expansion (CTE) similar to the one of titanium (Ti) and its medical grade super-alloys (crucial for the future development of mechanically adherent implant-type SBG coatings) and (ii) antibacterial efficiency, while (iii) conserving a good cytocompatibility. The SBGs powders were multi-parametrically evaluated by X-ray diffraction, Fourier transform infrared and micro-Raman spectroscopy, dilatometry, inductively coupled plasma mass spectrometry, antibacterial (against Staphylococcus aureus and Escherichia coli strains) suspension inhibition and agar diffusion tests, and human mesenchymal stem cells cytocompatibility assays. The results showed that the coupled incorporation of zinc and strontium ions into the parent glass composition has a combinatorial and additive benefit. In particular, the “Z6S4” formulation (mol%: SiO₂—38.49, CaO—32.07, P₂O₅—5.61, MgO—13.24, CaF₂—0.59, ZnO—6.0, SrO—4.0) conferred strong antimicrobial activity against both types of strains, minimal cytotoxicity combined with good stem cells viability and proliferation, and a CTE (~?8.7?×?10^?6 ×?°C^?1) matching well those of the Ti-based implant materials.     

Adsorption of poly(dimethyl siloxanes) from solution on silica: 1

The adsorption of a broad range of poly(dimethyl siloxanes) on silica, treated and untreated, has been studied. Three solvents, n-hexane, CCl₄, and benzene were employed. Adsorption was molecular weight dependent and more polymer adsorbed from n-C₆H₁₄ than from CCl₄. Only negative adsorption from C₆H₆ solution was observed. The results are rationalized on the basis of the polymer—solvent interaction values (χ), the solvent—adsorbent and the solute—adsorbent adsorption energies. It is concluded that the loss in configurational entropy on adsorption of the macromolecules is a major factor in determining the adsorption isotherms.     

SOME RELATIONS OF COMPOSITION TO SOLUBILITY OF ENAMELS IN ACIDES1

Review of literature.—The literature on acid resisting enamels and glasses is reviewed. Acid resisting powers produced by different oxides.—When substituted one for another, in each case in equal percentage amounts, various oxides and minerals increased the resistance of various enamels to the action of boiling 20 per cent hydrochloric acid in the following order of effectiveness: Al₂O₃, cryolite, Na₂O, PbO, BaO, Li₂O, MgO, CaF₂, ZnO, SrO, CaO, B₂O₃. The first five mentioned were especially effective. The remainder are undesirable materials from the standpoint of acid resistance. Effect of the enamel base.—The relative effects of the materials were the same for various base enamel compositions. Effect of ZrO₂ and TiO₂. —ZrO₂ and TiO₂, when substituted for small amounts of SiO₂, increased the resistance of various enamels to attack by acids, ZrO₂ being most effective in this respect. The favorable action of ZrO₂, is offset by a tendency to produce excessive chipping. Rutile gives less chipping than either zirconia or silica and greater acid resistance than silica. Best compositions.—Enamels 2,17,19,26,27, and 33 of table 1 showed resistance to action of the acid equivalent to that of the original competitions based on the analysis of a French acid-resisting enamel. By use of the data developed in this investigation other highly acid-resisting compositions can readily be formulated.