Free-standing, polysilsesquioxane-based inorganic/organic hybrid membranes for gas separations

Pervaporation and Gas Separation Properties of High-Molecular Ladder-like Polyphenylsilsesquioxanes

This paper presents the results of studies on the pervaporation properties (for benzene/hexane mixtures) and gas permeability (for He, H2, N2, O2, CO2, CH4, C2H6, and C4H10) of ladder-like polyphenylsesquioxanes (L-PPSQ) with improved physical and chemical properties. These polymers were obtained by condensation of cis-tetraphenylcyclotetrasiloxanetetraol in ammonia medium. The structure of L-PPSQ was fully confirmed by a combination of physicochemical analysis methods: 1H, 29Si NMR, IR spectroscopy, HPLC, powder XRD, and viscometry in solution. For the first time, a high molecular weight of the polymer (Mn = 238 kDa, Mw = 540 kDa) was achieved, which determines its improved mechanical properties and high potential for use in membrane separation. Using TGA and mechanical analysis methods, it was found that this polymer has high thermal (Td5% = 537 °C) and thermal-oxidative stability (Td5% = 587 °C) and good mechanical properties (Young's module (E) = 1700 MPa, ultimate tensile stress (σ) = 44 MPa, elongation at break (ε) = 6%), which is important for making membranes workable under various conditions. The polymer showed a high separation factor for a mixture of 10% wt. benzene in n-hexane (126) at a benzene flow of 33 g/(m2h).

Free-Standing Metal-Organic Framework Membranes Made by Solvent-Free Space-Confined Conversion for Efficient H2/CO2 Separation

Metal-organic frameworks (MOFs) are promising candidates for the advanced membrane materials based on their diverse structures, modifiable pore environment, precise pore sizes, etc. Nevertheless, the use of supports and large amounts of solvents in traditional solvothermal synthesis of MOF membranes is considered inefficient, costly, and environmentally problematic, coupled with challenges in their scalable manufacturing. In this work, we report a solvent-free space-confined conversion (SFSC) approach for the fabrication of a series of free-standing MOF (ZIF-8, Zn(EtIm)₂, and Zn₂(BIm)₄) membranes. This approach excludes the employment of solvents and supports that require tedious pretreatment and, thus, makes the process more environment-friendly and highly efficient. The free-standing membranes feature a robust and unique architecture, which comprise dense surface layers and highly porous interlayer with large amounts of irregular-shaped micron-scale pore cavities, inducing satisfactory H₂/CO₂ selectivities and exceptional H₂ permeances. The ZIF-8 membrane affords a considerable H₂ permeance of 2653.7 GPU with a competitive H₂/CO₂ selectivity of 17.1, and the Zn(EtIm)₂ membrane exhibits a high H₂/CO₂ selectivity of 22.1 with an excellent H₂ permeance (6268.7 GPU). The SFSC approach potentially provides a new pathway for preparing free-standing MOF membranes under solvent-free conditions, rendering it feasible for scale-up production of membrane materials for gas separation.

Spectroscopic studies on phosphate-modified silicon oxycarbide-based amorphous materials

Vibrational spectroscopy is the most effective, efficient and informative method of structural analysis of amorphous materials with silica matrix and, therefore, an indispensable tool for examining silicon oxycarbide-based amorphous materials (SiOC). The subject of this work is a description of the modification process of SiOC glasses with phosphate ions based on the structural examination including mainly Infrared and Raman Spectroscopy. They were obtained as polymer-derived ceramics based on ladder-like silsesquioxanes synthesised via the sol-gel method. With the high phosphate's volatility, it was decided to introduce the co-doping ions to create [AlPO₄] and [BPO₄] stable structural units. As a result, several samples from the SiPOC, SiPAlOC and SiPBOC systems were obtained with various quantities of the modifiers. All samples underwent a detailed structural evaluation of both polymer precursors and ceramics after high-temperature treatment with Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS-NMR). Obtained results proved the efficient preparation of desired materials that exhibit structural parameters similar to the unmodified one. They were X-ray-amorphous with no phase separation and crystallisation. Spectroscopic measurements confirmed the presence of the crucial Si-C bond and how modifying ions are incorporated into the SiOC network. It was also possible to characterise the turbostratic free carbon phase. The modification was aimed to improve the bioperformance of the materials in the context of their future application as bioactive coatings on metallic implants.

Amphiphilic Poly(dimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate Cross-Linked Block Copolymers in a Membrane Gas Separation

Amphiphilic poly(dimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate cross-linked block copolymers based on triblock copolymers of propylene and ethylene oxides with terminal potassium-alcoholate groups (PPEG), octamethylcyclotetrasiloxane (D4) and 2,4-toluene diisocyanate (TDI) were synthesized and investigated. In the first stage of the polymerization process, a multiblock copolymer (MBC) was previously synthesized by polyaddition of D4 to PPEG. The usage of the amphiphilic branched silica derivatives associated with oligomeric medium (ASiP) leads to the structuring of block copolymers via the transetherification reaction of the terminal silanol groups of MBC with ASiP. The molar ratio of PPEG, D4, and TDI, where the polymer chains are packed in the "core-shell" supramolecular structure with microphase separation of the polyoxyethylene, polyoxypropylene and polydimethylsiloxane segments as the shell, was established. Polyisocyanurates build the "core" of the described macromolecular structure. The obtained polymers were studied as membrane materials for the separation of gas mixtures CO2/CH4 and CO2/N2. It was found that obtained polymers are promising as highly selective and productive membrane materials for the separation of gas mixtures containing CO2, CH4 and N2.

Tunable Crystalline Phases in UV-Curable PEG-Grafted Ladder-Structured Silsesquioxane/Polyimide Composites

A series of UV-curable hybrid composite blends containing a carboxylic acid functionalized polyimidewith varying amounts of high molecular weight (~1 K) PEG-grafted ladder-structured polysilsesquioxanes copolymerized with methacryl groups were fabricated and their structural, thermal, mechanical, and surface properties characterized. At a composite weight ratio of polyimide above 50 wt.%, a stark shift from amorphous to crystalline polyethylene glycol (PEG) phases were observed, accompanied by a drastic increase in both surface moduli and brittleness index. Moreover, fabricated composites were shown to have a wide range water contact angle, 9.8°-73.8°, attesting to the tunable surface properties of these amphiphilic hybrid polymer composites. The enhanced mechanical properties, combined with the utility of tunable surface hydrophilicity allows for the possible use of these hybrid polymer composites to be utilized as photosensitive polyimide negative photoresists for a myriad of semiconductor patterning processes.

Near-Infrared Light-Stimulus-Responsive Film as a Sacrificial Layer for the Preparation of Free-Standing Films

It remains a challenge to fabricate sacrificial films that are stable in most of solvents and can be readily decomposed on demand. Here we report the fabrication of a near-infrared (NIR) light decomposable sacrificial film by layer-by-layer (LbL) assembly of UV-light-decomposable poly((4-(2-bromoethoxy)-5-methoxy-2-nitrobenzyl acrylate) triethylammonium bromide) (PNBA-TEA), poly(sodium 4-styrene-sulfonate) (PSS), branched polyethyleimine (bPEI), and lanthanide-doped upconversion nanoparticles (UCNPs). The [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films are stable in deposition solutions of various materials and decompose upon NIR light irradiation. In the [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films, UCNPs can convert NIR light into UV light, which can decompose PNBA-TEA. After immersing the NIR light-irradiated [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films in 0.1 M aqueous NaHCO3 solution, the disintegration of the entire films occurs because of the repulsive force between the negatively charged photoproduct of PNBA-TEA and PSS. LbL-assembled (PAH/PAA)*50 films deposited on top of the NIR-light-decomposable [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films can be conveniently released to produce large-area and defect-free (PAH/PAA)*50 free-standing films after NIR light irradiation and subsequent immersion in 0.1 M aqueous NaHCO3 solution. Because of the satisfactory stability and on-demand decomposable property, the [(PNBA-TEA/PSS)*2/(bPEI/UCNPs)*3]*2 films are promising as sacrificial layers for the fabrication of various free-standing films.

Rational molecular design of PEOlated ladder-structured polysilsesquioxane membranes for high performance CO2 removal

By selectively introducing PEO groups into the ladder-structured polysilsesquioxane, PEO crystallization was suppressed, allowing for the exceptional CO₂ separation performance.