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The article aims to pay respects to the excellent scientist and good friend Yuri Pavlovich Yampolskii. This article describes several scientific areas that Yampolskii was actively engaged in, and is divided accordingly into three chapters. The first chapter contains information about the main group of polymers (polyvinyl-trimethyl silane, polynorbornenes, PIM-family polymers, perfluorinated polymers, etc) that Yampolskii investigated in the framework of membrane gas separation. The second chapter considers the application of the inverse gas chromatography technique for the characterization of penetrant sorption in polymeric membrane materials (highly permeable glassy polymers) that was mainly developed by Yampolskii's group. The third chapter describes the work of Yampolskii's group on computational chemistry, compiling gas transport data into the TIPS RAS Database, its capabilities in correlation analysis, and "structure-property" predictions. We will miss our beloved teacher and colleague and hope this article will, to some extent, tell a story of his eventful and energetic life in the scientific world.
This paper is not a usual review and is written to illustrate the scientific activity of the outstanding researcher Yuri Pavlovich Yampolskii in one of the fields of interest: the creation and investigation of the new amorphous polymeric materials with chosen characteristics of gas separation and permeation. In this review, the specific property of the free volume number densities and the effective size of polymers determined using positron annihilation will be described. The exciting results will be highlighted, touching on several points of the research, such as the relations between permeation properties and elementary free volume characteristics, the multimodality of the distribution of ortho-positronium lifetimes, the dependence of the size of elementary free volumes on the conformation rigidity of the polymer chain, the relation between local rigidity and multimodality and the experiments with thermostimulated luminescence, and the low-temperature gas sorption connected to the free volume elements. These studies' importance for solving chemistry and ecology problems is obvious.
In the search for more efficient gas separation membranes, blends offer a compromise between costly high-performance polymers and low-cost commercial polymers. Here, blends of the polymer of intrinsic microporosity, AO-PIM-1, and commercial Matrimid® 5218 polyimide are used to prepare dense films by solution casting. The morphology of the pure polymers and their blends with 20, 40, 60 and 80 wt% of AO-PIM-1 in Matrimid® are studied by scanning electron microscopy (SEM), and their pure gas permeability is studied as a function of the blend composition with H2, He, O2, N2, CH4 and CO2. The polymers were found only partially miscible and a two-phase structure was formed with large domains of each polymer. When necessary, the films were coated with a thin silicone layer to heal possible pinhole defects. Even small amounts of Matrimid® in AO-PIM-1 resulted in an unexpectedly strong decrease in the permeability of the PIM, whereas a small amount of the PIM led to a modest increase in permeability of Matrimid®. Due to the two-hase structure, the Maxwell model was more suitable to describe the gas permeability as a function of the blend composition than the model for miscible blends. At low Matrimid® concentrations in AO-PIM-1, all models fail to describe the experimental data due to an unexpectedly strong depression of the permeability of the PIM by Matrimid®. Time lag measurements reveal that the changes in permeability as a function of the blend composition are mostly due to changes in the diffusion coefficient.
Global warming is a public alarming issue caused by extreme CO2 emissions. Thus, CO2 removing using thin film nanocomposite (TFN) membranes is an efficient procedure to enhance the CO2 gas separation efficiency. TFN membranes composed of Pebax 1657 embedded by porous organic polymers over the porous polysulfone support used to separate CO2 from CH4 and N2 gases. Porous organic polymers (POPs) were synthesized via Friedel-Crafts one-step reaction. The obtained results from TGA and FESEM revealed that the modified TFN membranes declared a superior compatibility between Pebax and fillers. Permeation properties of membrane samples were tested over various feed pressure with the range of 2-10 bar. Pure gases permeability, CO2/N2 and CO2/CH4 selectivities improved via adding porous organic polymers into the Pebax. At porous organic polymers loading of 5wt% and applied feed pressure of 2 bar, the CO2, CH4 and N2 permeability enhanced to 310.6, 27.6 and 4.5 Barrer, respectively; which exhibited a significant improvement compared to neat membrane. Moreover, the CO2/N2 and CO2/CH4 selectivities also enhanced to 11.25 and 70.04; respectively. Obtained results revealed that the membranes performance was enhanced as the feed gas pressure increased. TFN containing 5wt% porous organic polymers imply a CO2 gas permeability of 348.4 Barrer at feed pressure of 10 bar.
Hyperbranched polybenzoxazole (HBPBO) – silica hybrids were treated at different thermal protocols and their gas permselectivity were studied. Inter-chain distance and free volume of pristine HBPBO were enlarged with increasing treated temperature. Gas permeability and diffusivity of the HBPBO were considerably increased with increasing treated temperature, which was resulted from increased fractional free volume due to enlarged inter-chain distance. Gas permeability of the HBPBO was further increased by the hybridization with silica, mainly owing to the increased gas diffusivity. This fact indicated additional free volume holes were formed at the HBPBO matrix – silica interfaces. It was worth noting the HBPBO – silica hybrids had a prominent CO2/CH4 permselectivity which exceeded the upper bound, and the CO2/CH4 permselectivity was enhanced with increasing treated temperature. The notable CO2/CH4 permselectivity of the HBPBO – silica hybrids would be achieved by the synergistic effect of characteristic hyperbranched molecular structure, thermal treatment, and hybridization with silica.
We report dielectric and calorimetric studies on metathesis and addition-type polytricyclononenes, both based on the same monomer bearing three pendant -OSiMe3 groups. For the addition-type polymer, dielectric spectroscopy reveals a ß*-process related to the microporosity, whereas for its metathesis counterpart, the segmental dynamics (α-process) manifests. Besides active dielectric processes, a significant conductivity contribution is detected for both samples which for the microporous addition-type polymer is three orders of magnitude greater than for the metathesis polymer. The broadband dielectric spectroscopy is complemented by detailed calorimetric investigations, comprising DSC, FSC, and TMDSC. The calorimetric methods detected the glass transition for the metathesis polymer in agreement with the observed dielectric α-process. We then compare the already reported gas transport properties for both polymers, setting them in correlation with the observed molecular mobility and conductivity behavior. The discussed results reflect significant differences in molecular mobility of the two polymers affecting the appearance of microporosity which strongly determines the gas transport properties.
Typically, gas separation with membranes concentrates on mixtures profusely studied, such as CO2/N2, CO2/CH4, H2/CO2, O2/N2, H2/N2, He/CH4, H2/CH4, and certain hydrocarbon mixtures, not addressing some non-common, rare but technologically interesting mixtures. However, membrane technology has the potential to address the efficient separation of such rare mixtures, not reported in the current upper bounds basically due to the lack of experimental studies. This review devotes to the membrane application to mixtures including the following: H2/He, H2/D2, 3He/4He, He/Ne, Kr/Xe, CO2/He, and traces from the air. In most cases, the membrane performance has only been studied from a theoretical point of view suggesting that a lot of work is still needed to eventually think of an industrial operation. In any event, there is no doubt about the fact that the advantages that the membrane technology presents for the most studied and better-established gas separations will contribute to solving the future gas separation of these rare mixtures.
Thermally rearranged (TR) polymers have shown outstanding gas transport properties due to their rigid polymer structure. Additionally, bulky fluorinated substituents, such as hexafluoroisopropylidene, have enhanced the gas permeability of TR polymers. Herein, the role of the fluorinated content in TR polymers in terms of their microporous structure and gas separation performance was investigated by controlling fluorine content via either a copolymerization or a polymer blending approach. A series of TR copolymers and TR polyblends were successfully prepared via post-fabrication of their precursors of copolyimides or polyimide blends, respectively. All of the precursor polyimides exhibited an imide-to-benzoxazole thermal cyclization reaction around 400 °C, regardless of the fluorinated unit contents and polymer preparation methods. The microporosity and gas permeability of the polymers were enhanced by TR conversion and the presence of hexafluoroisopropylidene moieties due to the rigid polymer backbone and the bulky units. Furthermore, the TR polymer blends exhibited distinctive thermomechanical properties with two distinct glass transition temperatures and improved gas transport properties compared to the corresponding TR copolymers synthesized from the same starting monomers. In this study, the TR polymer blend containing 90% fluorinated diamine, TR-Blend-AH91, showed the highest gas permeability (P(CO2) = 603 Barrer) among the TR polymers in this work.
Loose nanofiltration (LNF) membrane separation is the fastest-growing textile wastewater treatment technology, due to its tremendous progress in related material and engineering science. Although LNF membranes outperform traditional treatment in the treatment of textile wastewater, the demand for improved selectivity and specificity in membranes separations is growing as we move our focus to the low-energy recovery of valuable compounds from textile wastewater. In this review, we discuss the separation mechanisms for the treatment of textile wastewater, fabrication of LNF membranes, membrane fouling, and control strategies, as well as recent research on LNF membranes. LNF membranes that can achieve high selectivity for dye/salt mixtures, high water permeance, and excellent antifouling performance—as well as the construction mechanisms involved—are highlighted. We further identify practical needs, knowledge gaps, and technological barriers in both material development and structure design for the high selectivity LNF membrane process. Finally, we discuss research priorities in the context of constructing high-performance LNF membranes.
Two-dimensional covalent organic framework (COFs) membranes have shown promise for organic solvent nanofiltration applications. However, the ability to modulate the chemical properties of the membranes and their effects on the molecular transport process has not yet been explored. Here, we demonstrate the synthesis of two COF membranes (TFP-MPOHF and TFP-MPF) with the same scaffold structures but different internal chemical properties. The presence of hydroxyl groups in the TFP-MPOHF membranes resulted in a significant improvement in polar solvent permeability. In contrast, the hydrophobic TFP-MPF membranes offered excellent permeability to nonpolar solvents, which was 130 – 235% higher than the TFP-MPOHF and commercial polymeric membranes. In addition, both COF membranes exhibited precise molecular sieving capacity with an apparent molecular weight cut-off (MWCO) of 800 g mol-1 and excellent stability. A deviation from the pore-flow model was observed for the TFP-MPOHF membranes, which was due to the specific interactions between solvent molecules and polar channel walls.