The presence of a solvent in a dense polymeric nanofiltration membrane layer can affect the macromolecular dynamics of the polymer material and the mobility of the solvent penetrant molecules. In addition, even the affinity of the swollen material for the solvent molecules can be distinct from that of the pure polymer material. These effects can substantially affect the membrane's performance. This paper provides sorption and swelling data of 9 thin polymer films that are commonly used for organic solvent nanofiltration (P84, Matrimid, PEI, PAN, PES, PSf, PEBAX, PTMSP, PDMS) swollen by 10 common solvents (hexane, toluene, dichloromethane, ethyl acetate, methyl ethyl ketone, acetone, isopropanol, ethanol, methanol, water). The paper describes the swelling dynamics during short-term solvent exposure (0-8 h), assesses the stability upon long-term solvent exposure (up to 2 months), and provides quantitative data on the solvent volume fractions inside the swollen layers. Among the surprising findings are the glubbery behavior of PTMSP and the completely different response of PES and PSf to toluene exposure. The results of this work demonstrate three crucial findings relevant to organic solvent nanofiltration membranes and other applications: 1. For many polymers, the swelling changes over long timescales of up to 2 months and longer. Results obtained on short timescales do however not always allow for direct extrapolation to longer time scales. 2. Structural similarity of polymers does not guarantee similar swelling behavior. 3. Swelling behavior of solvents cannot be solely explained by classifying solvents into aprotic, polar aprotic and polar protic solvents. The results of this work can aid in constructing transport models and can help predicting polymer-solvent compatibility and membrane performance in OSN applications.

In the thermal imidization of an alternating inorganic− organic hybrid network, there is an inverse relationship between the length and flexibility of the organic bridges and the extent of the layer shrinkage. The hybrid material studied here consists of polyhedral oligomeric silsesquioxanes that are covalently bridged by amic acid groups. During heat treatment, shrinkage of the materials occurs due to the removal of physically bound water, imidization of the amic acid groups, and silanol condensation. For five different bridging groups with different lengths and flexibilities, comparable mass reductions are observed. For the shorter bridging groups, the dimensional changes are hindered by the limited network mobility. Longer, more flexible bridging groups allow for much greater shrinkage. The imidization step can be described by a decelerating reaction mechanism with an onset at 150°C and shows a higher activation energy than in the case of entirely organic polyimides. The differences in the imidization kinetics between hybrid and purely organic materials demonstrates the need for close study of the thermal processing of hybrid, hyper-cross-linked materials.

Sol-gel-derived thin films play an important role as the functional coatings for various applications that require crack-free films to fully function. However, the fast drying process of a standard sol-gel coating often induces mechanical stresses, which may fracture the thin films. An experimental study on the crack formation in sol-gel-derived silica and organosilica ultrathin (submicron) films is presented. The relationships among the crack density, inter-crack spacing, and film thickness were investigated by combining direct micrograph analysis with spectroscopic ellipsometry. It is found that silica thin films are more prone to fracturing than organosilica films and have a critical film thickness of 300 nm, above which the film fractures. In contrast, the organosilica films can be formed without cracks in the experimentally explored regime of film thickness up to at least 1250 nm. These results confirm that ultrathin organosilica coatings are a robust silica substitute for a wide range of applications.

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a b s t r a c tSilicon carbide (SiC) membranes have shown large potential for applications in water treatment. Being able to make these membranes in a hollow fiber geometry allows for higher surface-to-volume ratios. In this study, we present a thermal treatment procedure that is tuned to produce porous silicon carbide hollow fiber membranes with sufficient mechanical strength. Thermal treatments up to 1500 1C in either nitrogen or argon resulted in relatively strong fibers, that were still contaminated with residual carbon from the polymer binder. After treatment at a higher temperature of 1790 1C, the mechanical strength had decreased as a result of carbon removal, but after treatments at even higher temperature of 2075 1C the SiC-particles sinter together, resulting in fibers with mechanical strengths of 30-40 MPa and exceptionally high water permeabilities of 50,000 L m À 2 h À 1 bar À 1 . Combined with the unique chemical and thermal resistance of silicon carbide, these properties make the fibers suitable microfiltration membranes or as a membrane support for application under demanding conditions.