Hydrocarbon and fluorocarbon solubility and dilation in poly(dimethylsiloxane): Comparison of experimental data with predictions of the Sanchez–Lacombe equation of state

Sorption and dilation isotherms are reported for a series of gases (N₂, O₂, CO₂), hydrocarbon vapors (CH₄, C₂H₆, C₃H₈), and their fluorocarbon analogs (CF₄, C₂F₆, C₃F₈) in poly(dimethylsiloxane) (PDMS) at 35°C and pressures up to 27 atmospheres. The hydrocarbons are significantly more soluble in hydrocarbon-based PDMS than their fluorocarbon analogs. Infinite dilution partial molar volumes of both hydrocarbons and fluorocarbons in PDMS were similar to their partial molar volumes in other hydrocarbon polymers and in organic liquids. Except for C₂H₆ and C₃H₈, partial molar volume was independent of penetrant concentration. For these penetrants, partial molar volume increased with increasing concentration. The Sanchez–Lacombe equation of state is used to predict gas solubility and polymer dilation. If the Sanchez–Lacombe model is used with no adjustable parameters, solubility is always overpredicted. The extent of overprediction is more substantial for fluorocarbon penetrants than for hydrocarbons. Very good fits of the model to the experimental sorption and dilation data are obtained when the mixture interaction parameter is treated as an adjustable parameter. For the hydrocarbons, the interaction parameter is approximately 0.96, and for the fluorocarbons, it is approximately 0.87. These values suggest less favorable interactions between the hydrocarbon-based PDMS matrix and the fluorocarbon penetrants than between PDMS and hydrocarbons. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3011–3026, 1999     

Sorption and transport of hydrocarbon and perfluorocarbon gases in poly(1‐trimethylsilyl‐1‐propyne)

Pure gas solubility and permeability of H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, CF₄, C₂F₆, and C₃F₈ in poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) were determined as a function of pressure at 35°C. Permeability coefficients of the perfluorinated penetrants are approximately an order of magnitude lower than those of their hydrocarbon analogs, and lower even than those of the permanent gases. In striking contrast to hydrocarbon penetrants, PTMSP permeability to fluorocarbon penetrants decreases with increasing penetrant size. This unusual size‐sieving behavior in PTMSP is attributed to low perfluorocarbon solubilities in PTMSP coupled with low diffusion coefficients relative to those of their hydrocarbon analogs. In general, perfluorocarbon penetrants are less soluble than their hydrocarbon analogs in PTMSP. The difference in hydrocarbon and perfluorocarbon solubilities in high free volume, hydrocarbon‐rich PTMSP is much smaller than in hydrocarbon liquids and liquidlike polydimethylsiloxane. The low solubility of perfluorocarbon penetrants is ascribed to the large size of the fluorocarbons, which inhibits their dissolution into the densified regions of the polymer matrix and reduces the number of penetrant molecules that can be accommodated in Langmuir sites. From the permeability and sorption data, diffusion coefficients were calculated as a function of penetrant concentration. With the exception of H₂ and the C₃ analogs, all of the penetrants exhibit a maximum in their concentration‐dependent diffusion coefficients. Resolution of diffusion coefficients into a mobility factor and a thermodynamic factor reveals that it is the interplay between these two terms that causes the maxima. The mobility of the smaller penetrants (H₂, O₂, N₂, CH₄, and CO₂) decreases monotonically with increasing penetrant concentration, suggesting that the net free volume of the polymer–penetrant mixture decreases as additional penetrant is added to PTMSP. For larger penetrants mobility either: (1) remains constant at low concentrations and then decreases at higher penetrant concentrations (C₂H₆, CF₄, and C₂F₆); (2) remains constant for all concentrations examined (C₃H₈); or (3) increases monotonically with increasing penetrant concentration (C₃F₈). Presumably these results reflect the varying effects of these penetrants on the net free volume of the polymer–penetrant system. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 273–296, 2000     

Preparation and characterization of a composite PDMS membrane on CA support

Polydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C₃H₈, CO₂, CH₄, and H₂ in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C₃H₈, compared to the lighter ones, such as CO₂, CH₄, and H₂. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C₃H₈/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C₃H₈ over CO₂, CH₄, and H₂, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of NaOH on the solubility of fluorocarbon in alcohol–NaOH systems

We propose a dechlorination process that allows safe and environmental conversion of chlorinated fluorocarbons. Starting with dissolving a fluorocarbon in an alcohol–NaOH solution, the fluorocarbons are reacted with alcohol–NaOH solvents at room temperature and pressure. In this work, the effect of the NaOH concentration on the solubility of CCl₂F₂ (CFC-12), CH₂F₂ (HFC-32), C₂HF₅ (HFC-125), C₂H₂F₄ (HFC-134a) and C₂H₄F₂ (HFC-152a) in methanol–NaOH, ethanol–NaOH and 1-propanol–NaOH solutions was measured. The experimental salting-out effects can be explained by solvation of a few alcohol molecules on sodium ion. Setchenov coefficients were determined and found to be independent of temperature.     

Fundamental aspect and behavior of saturated fluorocarbons in glow discharge in absence of potential source of hydrogen

The glow discharge of a series of saturated fluorocarbons, C_nF_2n+2 (n = 1, 2, 4, 6, and 8), was studied with glass substrates which do not contain any hydrogen. It was found that the deposition rate was a function of the F/C ratio of the starting fluorocarbons. That is, fluorocarbons with higher F/C ratio, such as CF₄ and C₂F₆, hardly polymerized, while fluorocarbons with lower F/C ratio, such as C₈F₁₈, polymerized as well as C₂F₄. After plasma exposure, the surface of glass substrate was characterized by measurements of water contact angle, water droplet rolling-off angle, and ESCA. Although all saturated fluorocarbon plasmas could alter the surface more hydrophobic than before, the deposited materials from fluorocarbons with higher F/C were not stable. Also, in plasmas with high F/C fluorocarbons, i.e., CF₄ and C₂F₆, sputtering of the electrode material was observed. © 1992 John Wiley & Sons, Inc.     

The diffusion of CO2, CH4, C2H4, and C3H8 in polyethylene at elevated pressures

Diffusion and solubility coefficients have been determined for the CO₂^?, CH₄^?, C₂H₄^?, and C₃H₈-polyethylene systems at temperatures of 5, 20, and 35°C and at gas pressures up to 40 atm. Diffusion coefficients were obtained from rates of gas absorption in polyethylene rods under isothermal-isobaric conditions by means of a new diffusivity apparatus. The concentration dependence of the diffusion coefficients was represented satisfactorily by Fujita's free-volume model, modified for semicrystalline polymers, while the solubility of all the penetrants in polyethylene was within the limit of Henry's law. Semiempirical correlations were found for the free-volume parameters in terms of physicochemical properties of the penetrant gases and the penetrant-polymer systems. These correlations, if confirmed, should permit the prediction of diffusion and permeability coefficients of other gases and of gas mixtures in polyethylene as functions of pressure and temperature.     

Gas sorption and characterization of poly(ether‐b‐amide) segmented block copolymers

The solubilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n‐C₄H₁₀ were determined at 35°C and pressures up to 27 atmospheres in a systematic series of phase separated polyether–polyamide segmented block copolymers containing either poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and nylon 6 [PA6] or nylon 12 [PA12] as the hard polyamide phase. Sorption isotherms are linear for the least soluble gases (He, H₂, N₂, O₂, and CH₄), convex to the pressure axis for more soluble penetrants (CO₂, C₃H₈, and n‐C₄H₁₀) and slightly concave to the pressure axis for ethane. These polymers exhibit high CO₂/N₂ and CO₂/H₂ solubility selectivity. This property appears to derive mainly from high carbon dioxide solubility, which is ascribed to the strong affinity of the polar ether linkages for CO₂. As the amount of the polyether phase in the copolymers increases, gas solubility increases. The solubility of all gases is higher in polymers with less polar constituents, PTMEO and PA12, than in polymers with more polar PEO and PA6 units. CO₂/N₂ and CO₂/H₂ solubility selectivity, however, are higher in polymers with higher concentrations of polar repeat units. The sorption data are complemented with physical characterization (differential scanning calorimetry, elemental analysis, and wide angle X‐ray diffraction) of the various block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2463–2475, 1999     

Interaction of 1,3,2,4‐Benzodithiadiazines with Aromatic Phosphines and Phosphites

Although an interaction between hydrocarbon and fluorocarbon 1,3,2,4‐benzodithiadiazines ( 1 ) and P(C₆H₅)₃ continuously produces chiral 1,2,3‐benzodithiadiazol‐2‐yl iminophosporanes ( 2 ; in this work, 5,7‐difluoro derivative 2a ) via 1:1 condensation, an interaction between 1 and other PR₃ reagents gives different products. With R  OC₆H₅ and both hydrocarbon and fluorocarbon 1 , only X=P(OC₆H₅)₃ (X = S, O) were identified in the complex reaction mixtures by ¹³С and ³¹Р NMR and GC‐MS. With R = C₆F₅, no interaction with the archetypal 1 was observed but catalytic addition of atmospheric water to the heterocycle afforded 2‐amino‐N‐sulfinylbenzenesulfenamide ( 4 ). With electrophilic B(C₆F₅)₃ instead of nucleophilic P(C₆F₅)₃, only adduct H₃N→B(C₆F₅)₃ and a new polymorph of C₆F₅B(OH)₂ were isolated and identified by X‐ray diffraction (XRD). A molecular structure of 2a was confirmed by XRD, and the π‐stacked orientation of one of phenyl groups and heterocyclic moiety was observed. This structure is in general agreement with that calculated at the RI‐MP2 level of theory, as well as at three different levels of DFT theory with the PBE and B3LYP functionals. Mild thermolysis of 2a in a dilute decane solution gave persistent 5,7‐difluoro‐1,2,3‐benzodithiazolyl ( 3a ) identified by EPR in combination with DFT calculations.     

Improvement in gas separation properties of a polymeric membrane through the incorporation of inorganic nano‐particles

The present work tries to introduce a high‐performance nano‐composite membrane by using polydimethylsiloxane (PDMS) as its main polymer matrix to meet some specific requirements in industrial gas separations. Different nano‐composite membranes were synthesized by incorporating various amounts of nano‐sized silica particles into the PDMS matrix. A uniform dispersion of nano‐particles in the host membranes was obtained. The nano‐composite membranes were characterized morphologically by scanning electron microscopy and atomic force microscopy. Separation properties, permeability, and ideal selectivity of C₃H₈, CH₄, and H₂ through the synthesized nano‐composite membranes with different nano‐particle contents (0.5, 1, 1.5, 2, 2.5, and 3 wt%) were investigated at different pressures (2, 3, 4, 5, 6, and 7 atm) and constant temperature (35°C). It was found out that a 2 wt% loading of nano‐particles into the PDMS matrix is optimal to obtain the best separation performance. Afterwards, sorption experiments for the synthesized nano‐composite membranes were carried out, and diffusion coefficients of the gases were calculated based on solution‐diffusion mechanism. Gas permeation and sorption experiments showed an increase in sorption and a decrease in diffusion coefficients of the gases through the nano‐composite membranes by adding nano‐particles into the host polymer matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Pure and mixed gas permeation through a composite polydimethylsiloxane membrane

A thin polydimethylsiloxane (PDMS) layer on polyethersulfone (PES) support was synthesized and pure and mixed gas permeation of C₃H₈, CH₄, and H₂ through it was measured. At first, a macroporous PES support was prepared by using the phase inversion method and characterized. Then, a thin layer of PDMS was coated over the support. Finally, permeation behavior of the synthesized composite membrane was investigated by pure and mixed gas experiments under various operating conditions. The synthesized PDMS/PES membrane showed much better gas permeation performance than others reported in the literature. Pure gas experiments showed that increase in the transmembrane pressure increases the permeability coefficient of heavier gases, C₃H₈, while decreases those of lighter ones, CH₄ and H₂. Exactly opposite behavior was observed in mixed gas experiments due to the competitive sorption and diffusion in the plasticized polymer matrix. Temperature was realized to induce similar effects on the permeability of pure and mixed gases. As expected, in rubbery membranes such as PDMS, permeability values of more condensable gases decrease with increasing temperature, whereas those of permanent gases increase. In the case of mixed gas experiments, increase in the C₃H₈ concentration in feed led to increase in the permeabilities of all the components due to the C₃H₈‐induced swelling of the PDMS film. High C₃H₈/H₂ and C₃H₈/CH₄ ideal selectivities of 22.1 and 14.7, respectively, at a transmembrane pressure of 7 atm as well as reasonable C₃H₈ separation factor (SF) values for all mixed gas experiments (in the range of 8.1–16.8) demonstrated the ability of the synthesized PDMS/PES membrane for the separation of organic vapors from permanent gases. Copyright © 2009 John Wiley & Sons, Ltd.     

A study of the deposition of polymeric material onto surfaces from fluorocarbon RF plasmas

A series of fluorocarbon gases, viz., CF₄, C₂F₆, C₃F₈, and CHF₃, have been compared for their relative tendencies to deposit polymeric material onto various surfaces, including Si and SiO₂, under RF plasma conditions. The plasmas were examined by optical emission spectroscopy. C₃F₈ and CHF₃ were found to produce the highest yields of polymers, although these exhibited significant differences in structure (as shown by XPS and IR) and differences in thermal stability, both of which could be minimized by replacing the C₃F₈ gas with a C₃F₈/H₂ mixture. The polymers produced from CHF₃ under the conditions of the present study were found to accumulate preferentially onto Si rather than SiO₂, as verified by the technique of Rutherford backscattering spectrometry.     

Gas sorption-induced dilation of poly(4-methyl-1-pentene)

Sorption and volume dilation isotherms of semicrystalline poly(4-methyl-1-pentene) (PMP) were measured using CO₂ and C₃H₈ as penetrants, which have sieving diameters of 3.3 and 4.3 Å, respectively. On the other hand, the PMP crystal has a void width of approximately 4 Å as estimated by X-ray diffraction, so it was anticipated that CO₂ would be able to sorb into the PMP crystal while C₃H₈ would not. The data show that C₃H₈ has a constant partial molar volume of approximately 87 cc/mol, just above the value reported in other rubbery polymers, and are consistent with the hypothesis that the C₃H₈ molecules are too large to sorb into the PMP crystals. The partial molar volume of CO₂ was found to be 39 cc/mol for CO₂ weight fractions of up to 0.03. Since the typical partial molar volume of CO₂ in rubbery materials is 46 cc/mol, the lower values in this study were attributed to CO₂ sorption into crystalline regions of the polymer, which provided no dilation. Application of a two-phase model using the assumption of Henry's law sorption showed that apparently all C₃H₈ sorption was occurring in the amorphous region but approximately 16% of CO₂ sorption occurred in the crystalline regions. © 1996 John Wiley & Sons, Inc.     

Investigation of the low-pressure plasma-chemical conversion of fluorocarbon waste gases

The kinetics of the plasma-chemical conversion of a number of saturated, as well as of unsaturated, fluorocarbon compounds is studied in an oxygen-based rf discharge by FTIR spectroscopy. Unsaturated fluorocarbons are rapidly converted into CF₄ and C₂F₆, which, in the presence of silica walls, are finally converted quantitatively into SiF₄ (etch reaction). The results of this investigation are used to design a plasma-chemical reactor for the conversion of fluorocarbon exhaust gases into SiF₄ in the vacuum line of a technological low-pressure plasma reactor. Furthermore, it is shown that the primary conversion product SiF₄ can be effectively converted into CaF₂ in a heterogeneous reaction with a CaO/Ca(OH)₂ absorber, also in the low-pressure line of the pumping system.     

Thermodynamics of some perfluorocarbon gases in water

The solubilities of CF₄ and C₂F₆ gases in H₂O and D₂O in the temperature range of 5 to 30°C at 5° intervals and C₃F₈ and c-C₄F₈ gases in H₂O over the temperature ranges of 5 to 15°C and 5 to 30°C, respectively, have been determined. From the solubility data various thermodynamic quantities for the process of dissolution have been derived. These data were compared with our results of applying the scaled-particle theory to gain an insight into the various thermodynamic processes accompanying the gas dissolution. One of our conclusions is that the hydrophobicity of the perfluorocarbons is greater than that of the corresponding alkanes.     

Tests of a “free-volume” model of gas permeation through polymer membranes. II. Pure Ar,SF6, CF4, and C2H2F2 in polyethylene

Permeability coefficients for Ar, SF₆, CF₄, and C₂H₂F₂ (1,1-difluoroethylene) in polyethylene membranes were determined from steady-state permeation rates at temperatures from 5 to 50°C, and at applied gas pressures of up to 15 atm. The temperature and pressure dependence of the permeability coefficients was represented satisfactorily by an extension of Fujita's free volume model of diffusion of small molecules in polymers. The parameters required by this model were determined from independent absorption (diffusivity) measurements with the above gases in polyethylene rods. The present work confirms the results of previous studies with CO₂, CH₄ C₂H₄ and C₃H₈ in polyethylene.     

Synthesis, characterization, and coordination chemistry of several novel electroneutral phosphane ligands

The reaction of fluorocarbon (R_f) reagents C₂F₅Li or C₂F₃Li with diaminochlorophosphanes (R₂N)₂PCl produced four new phosphane ligands of the type (R₂N)₂P(R_f). Addition of (Et₂N)₂PCl to ethereal solutions of C₂F₅Li or C₂F₃Li produced (Et₂N)₂PC₂F₅1 and (Et₂N)₂PC₂F₃2; treatment of (C₄H₄N)₂PCl and (C₄H₈N)₂PCl with C₂F₅Li afforded (C₄H₄N)₂PC₂F₅3 and (C₄H₈N)₂PC₂F₅4. All ligands were isolated as colorless, high-boiling liquids. Substitution reactions of 1-4 with Mo(CO)₆ in a refluxing alkane solvent yielded complexes of the type (L)Mo(CO)₅ (L = (Et₂N)₂PC₂F₅, 5; (Et₂N)₂PC₂F₃6; (C₄H₄N)₂PC₂F₅7 and (C₄H₈N)₂PC₂F₅8) as colorless solids in low to moderate (25-62%) yields. Complexes 5, 7 and 8 were structurally characterized by single crystal X-ray diffraction. A comparison of IR stretching frequencies and X-ray bond length data suggests these ligands approximate the electronic influence of phosphites.     

A radiofrequency plasma in a polydimethylsiloxane (PDMS) microchip

This is the first report of an analytical plasma in a polymer (polydimethylsiloxane, PDMS) microchip. The plasma channel has dimensions 2 mm diameter × 50 mm long, is operated at atmospheric pressure in Ar, 27.12 MHz and 70 W, and is viewed axially through a purged fiber optic cable. CF₄ gas at 0.1% in argon yields mainly C₂ emission bands. This PDMS microchip is manufactured easily, inexpensive, and more tolerant to fluorocarbons than microchip plasmas in silica. Based on these initial results, this PDMS microchip plasma could become useful as a sensor for the fluorocarbon gases emitted in semiconductor process or as a gas chromatography (GC) detector for potential application.     

Permeability and thermal properties of PDMS/LDPE multilayer composite membranes

This work reports on the preparation and properties of polydimethylsiloxane (PDMS)/low‐density polyethylene (LDPE) multilayer composite polymer membranes (MCPM) for gas separation applications. The membranes were produced by combining sequential coating with melt‐extrusion/salt leaching techniques. In particular, the gas sorption and permeation properties at different pressure (40–90 psig) and temperature (27–55 °C) are reported with morphology and thermogravimetric properties. The results show that a 20 μm PDMS layer was able to penetrate the microporous LDPE surface layer substrate leading to improved interfacial adhesion. Based on the different gases (CO₂, CH₄, and C₃H₈) solubility, permeability, and diffusivity obtained, these membranes are seen as good candidates for industrial gas separations. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1045–1052     

Tests of a free-volume model for the permeation of gas mixtures through polymer membranes. CO2-C2H4, CO2-C3H8, and C2H4-C3H8 mixtures in polyethylene

Steady-state permeability coefficients have been measured for equimolar mixtures of CO₂-C₂H₄, CO₂-C₃H₈, and C₂H₄-C₃H₈, as well as for a mixture of 74.9 mol % CO₂ and 25.1 mol % C₂H₄ in polyethylene membranes. The measurements were made at 20, 35, and 50°C and at pressures of up to 28 atm. Each component of the permeating mixtures studied had the effect of increasing the permeability coefficient for the other component. Furthermore, at equal partial pressures and at the same temperature, the component exhibiting the highest solubility in the polymer had the largest effect in increasing the permeability coefficient of the other component. This behavior is in agreement with the predictions of a free-volume model for the permeation of gas mixtures proposed by Fang, Stern, and Frisch. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the predicted values. The theoretical permeability coefficients can be estimated from the model by using parameters determined with the pure components only.     

Aryl(pentafluorphenyl)iodoniumtetrafluoroborate: allgemeine Synthesemethode,typische Eigenschaften und strukturelle Gemeinsamkeiten

Pentafluorophenyliodine(III) Compounds. 4 [1] Aryl(pentafluorophenyl)iodoniumtetrafluoroborates: General Method of Synthesis, Typical Properties, and Structural Features Aryl(pentafluorophenyl)iodoniumtetrafluoroborates [Ar′Ar″I][BF₄] (Ar′ = C₆F₅, Ar″ = C₆H₅, o‐C₆H₄F, m‐C₆H₄F, p‐C₆H₄F, 2,6‐C₆H₃F₂, 3,5‐C₆H₃F₂, 2,4,6‐C₆H₂F₃, 3,4,5‐C₆H₂F₃, C₆F₅) are prepared in good yields and high purity by the reaction of C₆F₅IF₂ with Ar″BF₂ in CH₂Cl₂. This convenient method can be applied generally to many iodonium compounds. Thermal and spectroscopic properties (¹H, ¹³C, ¹⁹F NMR, IR, Raman) are reported and discussed. The solid state structures of six iodonium compounds show significant cation‐anion interactions which result in two different arrangements: a dimer with a 8‐membered ring or polymers with infinite zigzag chains. Ab initio calculations on prototypes of aryliodonium cations show relations between the kind of the aryl group (C₆H₅ vs. C₆F₅) and structural parameters as well as charges. By means of ¹⁹F NMR the σ_I‐ and σ_R‐constants of the [C₆F₅I]⁺‐substituent are determined.