V.S. Khotimsky

Effect of yeast fermentation by-products on poly[1-(trimethylsilyl)-1-propyne] pervaporative performance

The pervaporation recovery of ethanol from yeast fermentation broth was investigated using poly[1-(trimethylsilyl)-1-propyne]. The deterioration of membrane performance in the presence of fermentation broth was observed. The fouled membrane was characterized by gas permeation and density measurements, and sorption of pure components of the fermentation broth in PTMSP was studied to clarify the fouling mechanism. It was concluded that properties of the membrane deteriorate due to internal contamination of the PTMSP free volume with non-volatile by-products of the fermentation. The PTMSP film did not show appreciable deterioration of membrane properties in the pervaporation of aqueous solution of organic compounds with high volatility.

Plasma fluorination of organosilicon polymeric films for gas separation applications

SF6 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 O2, N2, He, H2, CH4 and CO2 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.

Investigations on the peculiar permeation properties of volatile organic compounds and permanent gases through PTMSP

Abstract In contrast to common glassy polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free volume glassy polymer, shows a preferable permeation of large condensable organic vapors in comparison to permanent gases. In order to investigate this phenomenon, a systematic permeability study over a large activity range has been performed on PTMSP with three types of volatile organic compounds (VOCs) as diffusing probes: toluene, dimethylketone and dichloromethane. PTMSP was synthesized with different catalytic systems (Nb or Ta based) able to induce controlled sub-molecular cis–trans structures. Whereas dimethylketone and dichloromethane permeability can be correctly described by a classical dual-mode equation, a peculiar bell shaped pattern was obtained for toluene, with a minimum permeability located at an activity value around a=0.3–0.4. In that case, only a dual-mode expression taking into account a concentration dependent diffusion coefficient can account for the results. On the other hand some apparent conflicting data recorded from PTMSP brand new films were related to the microstructure of the polymer main chain thanks to 13 C NMR spectroscopy analysis showing importance of cis- and trans-forms of the main chain of PTMSP. cis-Structure is more flexible and can be responsible for the creation of a higher density physical network (HDN) in polymeric matrix; conversely, trans-structure is more rigid and can provide lower density physical network (LDN). The higher permeability recorded for several probes through PTMSP synthesized with TaCl5/Al(i-Bu)3 catalytic system compared to those of NbCl5 based polymer can be explained by the geometric difference of the macromolecule networks.

Particle-beam treatment of organosilicon gas separation membranes: A novel way of controlling their mass transport properties

Fast atom bombardment applied in the low keV energy range to organosilicon gas separation membranes was found to modify their mass transport properties in a controllable manner. In particular, asymmetric polyvinyltrimethylsilane membranes and polydimethylsiloxane-based composite ones were treated by particle beams obtained from various gases like Ar, He, H2, and NH3, with particle energies of about 1 keV and does of about 1015 particles cm−2. In each case, improvements in the component selectivities for various gas mixtures coupled with decreases in the component permeances were obtained. The extent of mod-ification of the mass transport properties increased with increase of the calculated average depth of penetration of the bombarding particles. The modification of the mass transport properties was considered to take place as a result of compaction of the surface layer due to reaction like crosslinking and loss of pendant groups.

Surface modification of PTMSP membranes by plasma treatment: Asymmetry of transport in organic solvent nanofiltration.

For the first time, the effect of asymmetry of the membrane transport was studied for organic solvents and solutes upon their nanofiltration through the plasma-modified membranes based on poly(1-trimethylsilyl-1-propyne) (PTMSP). Plasma treatment is shown to provide a marked hydrophilization of the hydrophobic PTMSP surface (the contact angle of water decreases from 88 down to 20°) and leads to the development of a negative charge of -5.2 nC/cm(2). The XPS measurements prove the formation of the oxygen-containing groups (Si-O and C-O) due to the surface modification. The AFM images show that the small-scale surface roughness of the plasma-treated PTMSP sample is reduced but the large-scale surface heterogeneities become more pronounced. The modified membranes retain their hydrophilic surface properties even after the nanofiltration tests and 30-day storage under ambient conditions. The results of the filtration tests show that when the membrane is oriented so that its modified layer contacts the feed solution, the membrane permeability for linear alcohols (methanol-propanol) and acetone decreases nearly two times. When the modified membrane surface faces the permeate, the membrane is seen to regain its transport characteristics: the flux becomes equal to that of the unmodified PTMSP. The well-pronounced effect of the transport asymmetry is observed for the solution of the neutral dye Solvent Blue 35 in methanol, ethanol, and acetone. For example, the initial membrane shows the negative retention for the Solvent Blue 35 dye (-16%) upon its filtration from the ethanol solution whereas, for the modified PTMSP membrane, the retention increases up to 17%. Various effects contributing to the asymmetry of the membrane transport characteristics are discussed.

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 gas separation membranes on a nanometric scale

Abstract 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 1015 particles cm−2, resulted in a decrease in the transmembrane flux of various test gases (He, H2, O2, N2, CH4) 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.

VOC's removal from water with a hybrid system coupling a PTMSP membrane module with a stripper☆

Abstract The treatment of waste water streams containing low amounts of VOCs is still quite difficult to handle. In particular, for small or medium flow rates this problem remains most often unsolved by conventional techniques orcannot be treated directly at the source to authorize water recycling in the process. This study is concerned with thisaspect and has investigated theoretically and experimentally a hybrid system which should allow recovery of VOCs and recycling of purified waste water. This system is based on an initial VOCs stripping step followed by the removal of VOCs by membrane permeation. The simulation of the system was first carried out with experimental resultsconcerning only the membrane permeation step. Then a lab scale membrane module was constructed and combinedin a closed loop with a stripper to recycle, on one hand, the stripping gas and, on the other hand, the purified water. As typical cases, the removal of toluene and dichloromethane from water was simulated under the following conditions:waste water flux of ≈ 1 m 3 /h with a VOC concentration of 0.1–0.6 wt%, stripping column of 2 m height, inert gas flux of 400–1000 NL/h, module of 0.8 m 2 . The experimental results obtained were compared to the simulation ones and discussed in the light of original polymer properties (PTMSP).

Effect of solvent nature on the optical anisotropy of poly(1-trimethylsilyl-1-propyne) molecules

The optical properties of poly(1-trimethylsilyl-1-propyne) solutions in solvents possessing optical anisotropy have been studied with dynamic birefringence measurements. In solvents characterized by refractive indexes different from the refractive index of a dry polymer, the optical form effect has been discovered. This effect is determined by the shape asymmetry of a macromolecular segment and its rigidity. Estimates showed that the length of the statistical segment, which characterizes the thermodynamic rigidity of the macromolecular chains under study, is 82 × 10−8 cm. The shear optical coefficient for solutions of the test polymer in an anisotropic solvent is markedly higher than the corresponding value in an isotropic solvent. This difference is related to the orientation of anisotropic solvent molecules along the main chain of a macromolecule by their highest polarizability axis. Under the assumption that the orientational order of solvent molecules relative to chain macromolecules is independent of the thermodynamic rigidity of chain molecules, the size of the statistical segment of the macromolecules in question has been independently estimated as 98 × 10−8 cm.

Synthesis and properties of poly(acrylonitrile‐co‐p‐trimethylsilylstyrene) and poly(acrylonitrile‐co‐p‐trimethylsilylstyrene‐co‐styrene)

Copolymerization of acrylonitrile (AN) with p-trimethylsilylstyrene (TMSS) was carried out at 60°C in bulk and in solution in the presence of 2,2′-azobisisobutyronitrile (AIBN). The reactivity ratios of AN (M1) and TMSS (M2) were determined to be r1 = 0.068 and r2 = 0.309. The effects of the AIBN concentration and that of the chain transfer agent CCl4 on the molecular weights (MWs) of the copolymers were investigated. An increase in the concentrations of AIBN or CCl4 in solution led to a decrease in MW. Poly(AN-co-TMSS-co-St) was synthesized in solution using AIBN as the initiator. The molar fraction of AN was 0.415, while the molar ratio of TMSS/St varied from 1 : 1 to 1 : 9. The transition temperatures and thermal and thermooxidative stabilities of poly(AN-co-TMSS) and poly(AN-co-TMSS-co-St) were investigated. The differential scanning calorimeter technique was used to determine the compatibility of the poly(AN-co-TMSS) and poly(AN-co-TMSS-co-St) with commercial poly(AN-co-St). All the blends show a single glass transition temperature, which indicates the compatibility of the blend components. The surface film morphology of the blends mentioned above was examined by X-ray photoelectron spectroscopy. The data obtained indicate that the silicon-containing copolymer is concentrated in the surface layer.