In this work, membranes based on polyetherimide (PEI), a ZIF-8 metal–organic framework and 1-ethyl-methylimidazolium tetrafluoroborate ionic liquid (IL) were prepared. IL and ZIF-8 contents amounting ...to 7 wt% and 25 wt%, respectively, were investigated. CO2, He and H2 transport properties of PEI/IL/ZIF-8 membranes were compared to those obtained for the respective PEI/ZIF-8 and PEI/IL systems. Membranes’ gas permeability and selectivity are discussed as a function of the membrane composition and morphology, and they were assessed in relation to existing experimental and theoretical data from the literature. Promising gas transport properties were obtained using the appropriate combination of ZIF-8 and IL amounts in the PEI matrix. Indeed, an increase in the CO2 permeability coefficient by a factor of around 7.5 and the He and H2 permeability coefficients by a factor of around 4 was achieved by adding 7 wt% IL and 10 wt% ZIF-8 to the PEI matrix. Moreover, diffusion was evidenced as a governing factor in the studied membrane series.
The toughness of a high-performance thermosetting epoxy network can be greatly improved by generating polyether sulfone-based macro- to nano-scale morphologies. Two polyethersulfones (PES) which only ...differ by their chain-end nature have been successively investigated as potential tougheners of a high-T
thermoset matrix based on a mixture of trifunctional and difunctional aromatic epoxies and an aromatic diamine. For a given PES content, morphologies and toughness of the resulting matrices have been tuned by changing curing conditions and put into perspective with PES chain-end nature.
We designed and characterized chitosan-caseinate fibers processed through wet spinning for biomedical applications such as drug delivery from knitted medical devices. Sodium caseinate was either ...incorporated directly into the chitosan dope or allowed to diffuse into the chitosan hydrogel from a coagulation bath containing sodium caseinate and sodium hydroxide (NaOH). The latter route, where caseinate was incorporated in the neutralization bath, produced fibers with better mechanical properties for textile applications than those formed by the chitosan-caseinate mixed collodion route. The latter processing method consists of enriching a pre-formed chitosan hydrogel with caseinate, preserving the structure of the semicrystalline hydrogel without drastically affecting interactions involved in the chitosan self-assembly. Thus, dried fibers, after coagulation in a NaOH/sodium caseinate aqueous bath, exhibited preserved ultimate mechanical properties. The crystallinity ratio of chitosan was not significantly impacted by the presence of caseinate. However, when caseinate was incorporated into the chitosan dope, chitosan-caseinate fibers exhibited lower ultimate mechanical properties, possibly due to a lower entanglement density in the amorphous phase of the chitosan matrix. A standpoint is to optimize the chitosan-caseinate composition ratio and processing route to find a good compromise between the preservation of fiber mechanical properties and appropriate fiber composition for potential application in drug release.
The synthesis by aqueous RAFT polymerization of hydrophilic narrowly dispersed imidazolium-based poly(ionic liquid)s ( Đ typically below 1.20) is reported. Full monomer conversion is achieved ...within hours and high end-group fidelity of the living end groups affords the preparation of well-defined block copolymers. The resulting poly(ionic liquid) macroRAFT agents are finally exploited to polymerize 2-vinylpyridine in water and generate PIL-based nanoparticles of various morphologies (spheres, vesicles, or worms) in a one-pot surfactant-free process.
Abstract The colossal development of modern electronic devices has inevitably led to an increase in electromagnetic interference (EMI), which has gradually become the fourth most prevalent type of ...pollution in the world. It is therefore necessary to seek more effective EMI‐shielding materials to overcome the shortcomings of conventional metal‐based materials, which include high density, a lack of mechanical flexibility, low corrosion resistance and costly processing. Conductive polymer composites (CPCs) have attracted more and more attention due to their superiority in many aspects. However, their performances should be further enhanced for future applications. One polymer with only one type of filler often cannot meet this kind of requirement. In this paper, filled polymer materials for EMI shielding are reviewed in terms of their processing, rheological properties, conductivity, and shielding effectiveness. Moreover, the combination of different ingredients and fillers when fabricating multicomponent composites for EMI shielding is also highlighted. The coordination of various components in composites with different structures, including solid, segregated, layered/sandwiched, and foamed/porous structures, is then discussed.
Here we report a nanofluidics approach that allows one to discriminate, for the first time, between static and kinetic effects on the crystallization of polymers in 2-dimensional nanoconfinement. ...Nanofluidics cells designed to monitor in real time, via permittivity measurements, the flow process of polymers into cylindrical nanopores were employed to investigate the crystallization of poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) under static and under kinetic confinement conditions. A significant separation between static confinement effects and flow effects in confinement is reported. A characteristic time is deduced, to quantify the impact of flow on the crystallization process of polymers taking place under conditions of 2D geometrical nanoconfinement.
Supramolecular miktoarm stars (AB2 type) composed of poly (methyl methacrylate)-polystyrene2 (PMMA-PS2), poly(isoprene)-polystyrene2 (PI-PS2), and poly(vinyl acetate)-polystyrene2 (PVAc-PS2) were ...successfully synthesized by assembling reversible addition−fragmentation chain transfer (RAFT)-polymerized chains bearing hydrogen-bonding heterocomplementary associating units. To this end, thymine and diaminopyridine-functionalized chain transfer agents were designed to efficiently mediate the polymerization of vinyl acetate, methyl methacrylate, isoprene, and styrene. The selective associations of the resulting hydrogen-bonding macromolecular building blocks PVAc/PS, PI/PS, and PMMA/PS were demonstrated by 1H NMR in CDCl3 solutions. Miktoarm stars formation in the bulk was also confirmed by transmission electronic microscopy.
Physical chitosan hydrogels are potential biomaterials for several biomedical applications, such as wound healing, tissue repair, and drug delivery. Controlling the microstructural organization of ...chitosan gels is one of the keys for monitoring the physical, mechanical, and biological properties. As a result, the main objective of the present work was to explore the microstructural organization of chitosan hydrogels in relation with the processing conditions of gelation. For this purpose, different gelation routes were studied, that is, chitosan solution neutralization of an aqueous or hydroalcoholic solution and neutralization of an alco-gel. Overall, the resulting morphology after processing was determined by the medium viscosity during neutralization and the nature and concentration of the base. The effect of these processing parameters on the morphology was evaluated mainly through small angle light scattering (SALS) measurements including in situ measurements during chitosan neutralization. As a result, we reported different bulk microstructures consisting in 200−400 nm aggregates (primary particles) agglomerated into micrometer range clusters or arranged into more organized structures, that is, forming microchannels (4−6 μm). We thus established a qualitative and quantitative relation between supramolecular morphology and gelation conditions of chitosan hydrogels.
Using dewetting as a characterization tool, we demonstrate that physical properties of thin polymer films can be regulated and tuned by employing variable processing conditions. For different ...molecular weights, the variable behavior of polystyrene films of identical thickness, prepared along systematically altered pathways, became predictable through a single parameter P, defined as the ratio of time required over time available for the equilibration of polymers. In particular, preparation-induced residual stresses, the corresponding relaxation times as well as the rupture probability of such films (of identical thickness) varied by orders of magnitude following scaling relations with P. Our experimental findings suggest that we can predictably enhance properties and hence maximize the performance of thin polymer films via appropriately chosen processing conditions.
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