Poly Vinyltrimethylsilane Research Articles

The Influence of Low-Temperature Plasma on the Structure of Surface Layers and Gas-Separating Properties of Polyvinyltrimethylsilane Membranes

New results of one-sided surface modification of polymeric films and composite membranes of polyvinyltrimethylsilane (PVTMS) using low-temperature plasma are presented. The treatment was carried out by direct current discharge at the cathode and anode, air was used as the working gas, the exposure time was from 10 to 60 s, and the working pressure in the chamber was 15–20 Pa. The structure of the surface layers was analyzed by XPS, AFM and SEM, and the contact properties of the surface were also studied. The effective permeability coefficients for O2, N2, CH4, CO2, He, and H2, as well as for gas diffusion, for cathode-treated PVTMS films are experimentally obtained, and the effective gas solubility coefficients are calculated. The permeability coefficients of the studied gases for composite membranes with a selective PVTMS layer modified at the cathode and anode were determined. It has been noted that the choice of electrode significantly affects not only the chemical structure of the surface and near-surface layers of PVTMS, but also the gas transport parameters of the modified samples. At the same time, during the treatment of PVTMS films at the cathode for 30 s, it was possible to achieve an increase in the O2/N2 selectivity by more than two times relative to the initial value. It has been established that the results of modification of composite membranes differ from those obtained for homogeneous films and it was possible to achieve O2/N2 selectivity in 2.5 times higher than the initial value. The potential of using surface modification of polymer films and membranes by low-temperature plasma to improve their gas separation properties is shown.

Method of Liquid-Phase Fluorination of Polymers to Increase the Selectivity of the Air Separation

The one-sided modification of homogeneous polymer films of polyvinyltrimethylsilane (PVTMS), poly(2,6-dimethylphenyl-1,4 oxide) (PPO), and polybenzodioxane (PIM-1) was carried out by liquid-phase fluorination method using a fluorine-nitrogen mixture in perfluorodecalin. The fluorination time ranged from 10 to 60 min. For PPO films the amorphous and β-nanocrystalline phase (48%) was found by X-ray diffraction analysis of the original films. It was shown that fluorination does not significantly affect the degree of PPO crystallinity. The effect of fluorination time on the effective coefficients of permeability, diffusion, and solubility of oxygen and nitrogen has been studied. It was found that the fluorination leads to a decrease in both effective diffusion coefficients and effective gas solubility coefficients, while the resulting increase in permeability selectivity ranged from 30% for PVTMS to a 2 times increase in the case of PPO and PIM-1. It has been noted that this improvement in permeability selectivity is achieved mainly by the solubility selectivity increasing. The permeability of O2/N2 mixture for original and modified films was studied. It was found that the achieved values of the separation factors are close to the ideal selectivity. The results obtained demonstrate the possibility of effective application of the liquid-phase modification method not only for the homogeneous polymer films of the studied polymers treatment, but also for membranes with a selective non-porous layer based on them.

The gas permeability properties of poly(vinyltrimethylsilane) treated by low‐temperature plasma

AbstractThe results of one‐sided treatment of polyvinyltrimethylsilane (PVTMS) films using low‐temperature air plasma are presented. The treatment was carried out at 25°C in air at a pressure in the reaction chamber of 10–25 Pa and a processing time of 10–60 s. The surface of the plasma‐treated PVTMS films was analyzed by X‐ray photoelectron spectroscopy and atomic force microscopy and the contact angle values determined. The effect of the plasma conditions, such as the treatment time and the pressure in the reactor chamber, on the transport properties of the modified membrane for He, O2, N2, CO2, and CH4 were investigated in detail. The permeability of all plasma‐treated PVTMS films for the studied gases except for He was found to decrease depending on the modification conditions, leading to an increase in selectivity for such pairs as He/CH4, CO2/CH4, and O2/N2. The selectivity of the modified PVTMS achieved a maximum value when the films were treated with plasma for 20–40 s at a chamber pressure of 15–20 Pa. The effective diffusion coefficients of the studied gases were obtained experimentally. It was shown that the volumetric diffusion of gases, particularly O2 and N2, in PVTMS before as after plasma treatment is described by the classical diffusion equations. The theoretical approaches to the influence of boundary conditions on selective gas transfer through polymeric membrane are considered. To estimate the prospects for the long‐term use of membranes based on modified PVTMS, the stability of the parameters gas permeability and selectivity of the modified samples was investigated over 9 months. It was shown that the modification of PVTMS by the method of low‐temperature plasma in air is a promising method for expanding the spectrum of membrane processes based on existing commercial membranes.

Thin‐film hydrogel polymer layered polyvinyltrimethylsilane dual‐layer flat‐bed composite membrane for CO2 gas separation

AbstractThe gas transport property of the hydrogel chitosan (CS) and the CS‐polyethylene glycol (CS+PEG) polymer blend surface‐modified polyvinyltrimethylsilane (PVTMS) composite membranes have been evaluated for pure CO2, N2, and CH4 gases. The physic‐chemical characteristics and the surface morphological features of the prepared pure and the composite PVTMS membranes were interrogated with the Fourier transform infrared spectroscope, high‐resolution scanning electron microscope, thermogravimetric analysis, and differential scanning calorimeter. Effect of water wetting of the membrane, number of sequential coating, and the transmembrane pressure on the gas transport properties of the pure and composite PVTMS membranes was concurrently studied. The acceptable CO2 permeability of 153 barrer and the gas‐pair CO2/N2 selectivity of 33 and the CO2/CH4 selectivity of 23 were obtained for the CS+PEG‐modified PVTMS membrane under the optimum conditions, that is, transmembrane pressure of 76 cmHg and the reaction temperature of 30°C. The CO2 separation performance of the modified PVTMS composite membrane against the N2 and the CH4 gases moved close to Robeson's upper bound 2008. Enhancement in the CO2 separation efficacy of the modified PVTMS membrane than the pure PVTMS membrane has proved good efficiency of the modified membrane towards CO2 capture application.

Depth Profile Analysis of the Modified Layer of Poly(vinyltrimethylsilane) Films Treated by Direct-Current Discharge

Previously, we found that modification of the membrane surface from polyvinyltrimethylsilane (PVTMS) by treatment with low-temperature plasma induced by low pressure DC discharge leads to a significant increase in gas separation characteristics. To understand the mechanism of this phenomenon, in this article XPS combined with precision etching 10 keV beam of Ar2500+ clusters was used for depth profiling of PVTMS spin-coated films before and after DC discharge treatment. The etching craters depths were measured by stylus surface profiler. The average etching rate of the untreated PVTMS film by Ar2500+ clusters was defined (230 nm/min). It was found that the low temperature plasma treatment of PVTMS leads to a sharp increase in the oxygen concentration on a surface with a simultaneous decrease in the carbon content. The experimental data obtained indicate also that the treatment of PVTMS film by plasma leads not only to a change in the chemical structure of the surface, but also to the formation of a gradient subsurface layer with a thickness of about 50 nm.

Effect of polymer matrix on characteristics of percolation cluster composed of MWCNT

Mixed matrix membranes (MMMs) with unique transport characteristics can be prepared by the addition of the minor amounts of carbon nanotubes. The paper presents the results of study gas permeability (O2, N2, CH4) for poly(vinyltrimethylsilane (PVTMS) and Poly(methyl methacrylate) (PMMA) with embedded multiwall carbon nanotubes (MWCNT). The paper shows how the choice of a polymer matrix affects the parameters of a percolation cluster from CNTs.

Diffusion Transport of Water and Methanol Vapors in Polyvinyltrimethylsilane

The specifics of diffusion of water and methanol vapors in nonporous polymer films based on polyvinyltrimethylsilane (PVTMS) have been studied. The vapor diffusion coefficients have been determined by measuring the kinetics of unsteady flow through the membrane (differential method) and subsequent processing the results by functional scaling . The kinetic curves have been found to deviate from those described by classical Fick’s law. It has been theoretically shown that such deviations can be due to the formation of associates of penetrant molecules inside the membrane, and a modified method for calculating diffusion coefficients has been proposed for this case. The behavior of the diffusion coefficients of water and methanol vapors in PVTMS in the temperature range of 50–90°C and the vapor activity range of 0.3–0.9 has been studied. The activation energies of diffusion of water and methanol vapors in PVTMS have been determined to be 23 and 44 kJ/mol, respectively, and the effective kinetic diameters of the molecules have been calculated to be 0.29 and 0.37 nm, respectively. The proposed approach opens the possibility for systematic studies of the diffusion kinetics of vapors of different organic compounds with an assessment of their kinetic contribution to the membrane permselectivity.

Composite Membranes with a Polyvinyltrimethylsilane Skin Layer for Separation of Water–Alcohol Mixtures

The paper presents the characteristics of a laboratory-made water-selective composite membrane with a selective layer of hydrophobic polyvinyltrimethylsilane (PVTMS) for use in the processes of vapor-phase membrane recovery of alcohols from dilute aqueous alcohol mixtures of biogenic origin. The support is a polyacrylonitrile ultrafiltration membrane, and the PVTMS skin layer of the resulting composite membrane has a thickness of 3 to 4 microns. The vapor transport and separation characteristics of the membrane for water–ethanol and water–butanol mixtures in the temperature range of 60–80°C have been studied. It has been shown that the membrane selectivity varies in the range of 23–39 for the water/ethanol pair or 100–140 for the water/butanol pair. A specific feature of the hydrophobic water-selective membrane as applied to the vapor-phase process is the stability of its characteristics due to the absence of swelling, in contrast to hydrophilic water-selective membranes whose characteristics substantially depend on the activity of water vapor. The process of vapor-phase membrane recovery of ethanol and butanol from dilute aqueous alcohol mixtures of biogenic origin with their initial concentrations of 10 and 1 wt %, respectively, has been mathematically modeled on the basis of the experimental data. The calculation results show that the composite membrane obtained makes it possible to concentrate ethanol and butanol to 95 and 98 wt % with degrees of recovery of more than 0.8 and more than 0.9, respectively.

Carbon Dioxide Desorption from Amine Solution in a Nonporous Membrane Contactor

Long-term testing of a membrane contactor based on a blend of the nonporous polymers polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) has been carried out. The flat-sheet membrane contactor has been tested for CO2 desorption from an aqueous methyldiethanolamine solution at 100°C. It has been found that the mass transfer parameters (CO2 flux and stripping efficiency) of the 95%PTMSP/5%PVTMS membrane stabilize after the 7th day of testing. The CO2 mass transfer coefficient in the membrane contactor has been evaluated, and optimal desorption parameters have been determined.

Kinetics of carbon dioxide removal from water in flat membrane contactor

The problem of regeneration of a carbon dioxide physical absorbent in gas-liquid membrane contactor has been addressed using water as the absorbent. An analytical solution for the mass transfer equation has been obtained with taking into account not only axial, but also radial diffusion of the solute in the liquid flow and thereby significantly extending the area of applicability of the solution. The kinetics of carbon dioxide desorption from aqueous solutions has been described for the membrane contactor based on asymmetric gas separation membrane made of polyvinyltrimethylsilane (PVTMS). It has been shown that the model agrees well with experimental data for different pressures of water saturation with carbon dioxide and desorption temperatures.

Investigation of volatile aliphatic and aromatic amine detection using a fluorescent pH indicator ethyl eosin in polymer matrices

Changes in the fluorescence spectra (F) of ethyl eosin (EE) embedded into polymer matrices of different compositions, gas permeability, and polarity under the action of gaseous aliphatic and aromatic amines (dimethylamine (DMA), trimethylamine (TMA), and pyridine (Pyr)), depending on the pH and the structure of polymer matrix, were investigated. Organic methanesulfonic acid was used to adjust pH in a polymer matrix. Cellulose acetate-propionate (CAP), polyvinyl trimethylsilane (PVTMS), polyethylene oxide (PEO), and polyvinylpyrrolidone (PVP), as well as mesoporous silica gel microspheres, were used as polymer matrices. Absorption and fluorescence maxima of EE in solution and in most polymers are in the region of 505 nm and 550 nm, respectively. The maximum of EE fluorescence intensity increases in all polymer matrices except for PVP in the presence of amines, while the F decreases in the PVP matrix and silica gel microspheres. The fluorescence response to DMA is higher than to TMA and Pyr for all the polymers; the F response is two-phase in the case of Pyr: an increase in F followed by a decrease. Characteristic response times for different matrices change in a sequence: CAP < PVP < PEO < MS < PVTMS. These differences are probably due to the different contributions to the process of the analyte diffusion, its affinity to the polymer, and the internal polarity of the polymer matrix for different polymers.

Membrane systems for the recovery of energy carriers from products of organic waste recycling

One of the most promising technologies for separating energy carriers from renewable feedstocks is the biological recycling of organic waste to derive gas (biogas, biohydrogen) or liquid mixtures that contain methane and hydrogen or lower alcohols, respectively. This technology has many advantages: low power consumption, high ecological safety, high level of organic waste recycling, affordability, and ease of implementation and control. The main practical problem of the microbiologic recycling of biomass is the low calorific value of resulting gas and liquid mixtures for their use as energy carriers, because products of bioconversion are diluted aqueous organic mixtures and/or gas mixtures containing a significant amount of ballast CO2. In the capacity of promising systems for separating energy carriers from gas mixtures, we discuss conventional membrane systems and propose original gas-liquid membrane contactors (MCs), which do not require the precompression (additional energy consumption) of the initial gas mixture. After the stage of separation, for example, of biogas, resulting commercial-purity methane (>95%) can be injected into the pipeline network or supplied to a receiver. Our low energy consumption membrane system was designed on the basis of developments of the Topchiev Institute of Petrochemical Synthesis of the Russian Academy of Sciences in cooperation with microbiologists and experts in bioengineering. MCs were prepared of nonporous highly permeable asymmetric membranes based on polyvinyltrimethylsilane (PVTMS) with a CO2 permeance of more than 15 l/(m2 h kPa), which completely meets the requirements on a highly permeable and, at the same time, sterile barrier. Composite membranes based on a glassy polymer with high internal free volume, i.e., polytrimethylsilylpropyne (PTMSP), which are now being produced on a laboratory scale, are regarded as promising for MCs. The use of membrane methods, i.e., pervaporation and membrane separation of the organic component of the vapor phase, is also promising for separating liquid energy carriers (bioalcohols) from dilute aqueous organic solutions (the range of concentrations of organic substances is 1–7%) that are derived by biofermentation. It is shown that organophilic membranes based on PTMSP can be advantageously employed for the continuous extraction of liquid energy carriers from products of biomass conversion.

Molecular mobility of nitroxide spin probes in glassy polymers. Quasi‐libration model

AbstractESR spectra of three spin probes with different molecular volumes: 2,2,6,6‐tetramethyl‐4‐oxopiperidine‐1‐oxyl, di‐p‐anisylnitroxide, and nitroxide derivative of fullerene in glassy polystyrene, polyvinyl trimethylsilane, and Teflon AF‐2400 were calculated numerically within the model of quasi‐libration motions. Temperature ranges, where the model is capable to reproduce spectra within experimental errors, were defined. It was found that simulation of X‐band ESR spectra allows to determine quasi‐libration amplitudes around molecular axes X and Y with accuracy ∼ 3° and around Z axis with accuracy ∼ 15–20°. A shape of distribution of quasi‐libration amplitudes was also determined qualitatively by ESR spectra simulations. It was established that the average amplitude of quasi‐libration motion depends on the free volume of each polymer and geometrical molecular volume of a spin probe. Quasi‐libration amplitudes increase as the temperature increases, and reach the value of 40 degrees. We found that upon further temperature increase, quasi‐libration model becomes inapplicable for quantitative numerical spectra simulation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 107–120, 2009

Membrane contactor air conditioning system: Experience and prospects

This paper presents theoretical and experimental study of humidity control and independently carbon dioxide removal from indoors conditions by means of the pilot recycle membrane contactor air conditioning system (MCACS). The system can be successfully used for indoor air purifying for clean room facilities, industrial processes improvement, food and agricultural products storages and others. Advantages of membrane-absorptive separation method realized in membrane contactors are relative construction simplicity, reliability, high parameters of separation, lower energy consumption and absence of high-pressure drop. Developed air conditioning system represents combination of recycle membrane contactors (RMC) in single block designed to operate with atmosphere restricted air exchange for indoor air purification. Triethylene glycol (TEG) was used as effective hygroscopic liquid carrier for air dehumidification system. Carbon dioxide control system was tested on pure water. Polydimethylsiloxane (PDMS) and polyvinyltrimethylsilane (PVTMS) based nonporous membranes were used in spiral wound and flat frame membrane modules. The experiments with membrane contactor systems demonstrated effective air-drying ( T dew point = −30 °C) under high gas flow to liquid carrier flow ratio ( G/ L = 10 3) with membrane absorber and desorber temperature difference about Δ T = 30 °C. Carbon dioxide removal system showed possibility of CO 2 concentration reduction 10 times.

Structure and gas separation properties of composite films based on polyaniline

AbstractComposite films based on the polyvinyltrimethylsilane (PVTMS) with polyaniline (PANI) coating were obtained by borderline polymerization of aniline. The obtained coating was shown to differ from the polymer forming in the reaction mixture bulk both in chemical structure and morphology. Ratio and concentration of the reagents, mixing rate, reaction time, and condition of support surface were among the investigated factors affecting the growth and quality of PANI coating. The gas separation characteristics of composite membranes, as affected by the process conditions and the type of PANI, were investigated. It is shown that the proposed method provides a means for obtaining composite membranes that combine high selectivity, especially in O2/N2, He/CH4, and CO2/CH4 separation, with permeability higher than that of known composite materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1379–1384, 2003

Experimental and theoretical investigation of optical properties of poly-(1-trimethylsilyl-1 propyne) molecules in solution

The optical anisotropy of poly-(1-trimethylsilyl-1 propyne) (PTMSP) molecules has been studied by flow birefringence. High positive birefringence was detected which is one order of magnitude higher than that of a polymer with a similar structure, poly-vinyltrimethylsilane (PVTMS). Semiempirical quantum-chemical calculation of the optical anisotropy of the polymer molecules under investigation was carried out. It was established that high optical anisotropy of molecules (with a low anisotropy of the monomer unit) indicates that these macromolecules exhibit high intramolecular orientational order. This is also confirmed by the correct choice of the ordered helical model in the quantum-chemical calculation of the optical anisotropy of PTMSP molecules. This model gave good quantitative agreement between the theoretical and experimental optical and geometric parameters of the macromolecules being investigated.

Modification of poly(vinyltrimethylsilane) by radiation-induced graft polymerization

The modification of polyvinyltrimethylsilane (PVTMS) has been carried out using the radiation-induced graft polymerization. PVTMS is applied as a basis for gas-separating membranes. Acrylonitrile, acrolein, ethyl acrylate, acrylic acid and acrylamide were used as monomers. The grafting was performed both from vapour and liquid phase of monomers and their solutions by the direct radiation method. Some kinetic regularities of radiation graft polymerization of monomers and the character of distribution of grafted polymers along the thickness of PVTMS films were studied. It was shown that grafting improves the chemical resistance, the selective permeability of gases and some mechanical properties of PVTMS films.

Plasma fluorination of organosilicon polymeric films for gas separation applications

SF 6 plasma treatment using an RF discharge was carried out for the surface fluorination of polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) films. Gas permeation of the fluorinated and untreated films for O 2, N 2, He, H 2, CH 4 and CO 2 gases has been measured. Plasma fluorination increases the ideal selectivities of the PTMSP films decreasing their permeances for all the gases measured, and does not affect the permeances and selectivities of the PVTMS films. The composition and chemical structure of the fluorinated polymer surface were investigated using X-ray photoelectron spectroscopy (XPS) and 19F nuclear magnetic resonance (NMR) spectroscopy. Within the range of the treatment parameters studied, permselectivity and surface composition of the fluorinated PTMSP films depend slightly on the treatment time and the density of the fluorine atom flux on the modified surface. The trimethylsilyl substituents are detached and carbon atoms are partially fluorinated during modification. The structure of the fluorinated layer contains crosslinks and unsaturated bonds.

Modification of gas separation membranes on a nanometric scale

Fast atom bombardment (FAB) of asymmetric polyvinyltrimethylsilane (PVTMS) membranes by 1 keV Ar, or 1 keV He, or 0.8 keV H beams, with fluences of about 10 15 particles cm −2, resulted in a decrease in the transmembrane flux of various test gases (He, H 2, O 2, N 2, CH 4) and in a significant increase in the component selectivity. The pristine and the FAB-treated samples were studied by XPS and SIMS. According to XPS results, the FAB-treatment of the membranes led to an enrichment of carbon, while SIMS showed a simultaneous decrease in the hydrogen content in the surface layer, modified primarily on a nanometric scale.

High-energy ion implantation in polymer films

Results of experimental and theoretical studies on gas selective properties of polyvinyltrimethylsilane (PVTMS) under bombardment with 50–150 keV C + and Ar + ions with doses of 5×10 14−10 16 cm −2 are presented. It was found that permeability and selectivity for various gases change essentially under high-energy irradiation. This effect depends on ion type and energy, implantation dose, and is conditioned by peculiarities of the interaction of the ion-polymer system and processes of defect formation and excitation of the electronic subsystem.