The contribution of surface roughness of nonporous polymeric membranes to their gas separation and mechanical properties was studied in terms of surface free energy. The membranes samples were prepared based on glassy polymers with different chain rigidity, namely polysulfone (PSU), cellulose triacetate (CTA), and poly(vinyl alcohol) (PVA). The results were obtained by atomic force and scanning electron microscopy (AFM and SEM) with individual gas permeation, wettability, and mechanical testing. The specific surface free energy (as well as its polar and dispersive components) for the polymers was calculated by the Owens−Wendt method. It was proven that the surface roughness of the polymer membranes affects both energy components; however, the degree of this influence depends on the chemical nature of the corresponding polymer. Moreover, it was assumed that the dispersive energy component is inversely correlated with any gases' total permeability. In contrast, the polar one is inversely correlated with the permeability by gases with the ability for site-specific interactions. The gas separation results confirmed this assumption. It was also shown that the mechanical properties of the polymer membranes are also influenced by the surface energy, namely, its dispersive component.
The effect of the morphology and content of zinc oxide nanoparticles (ZnO-NPs) on the physicochemical, mechanical, and gas transport properties of the polyurethane (PU) mixed matrix membranes (MMMs) with respect to CO2 recovery from CH4, O2, and N2 was studied. The MMMs based on PU with spherical and rod-shaped ZnO-NPs at various loadings, namely, 0.05, 0.1, 0.5, 1, and 2 wt. %, were prepared with membrane density control and studied using AFM, wettability measurements, surface free energy calculation, gas separation and mechanical testing. To evaluate the resistance of the ZnO-NPs to agglomeration in the polymer solutions, zeta potential was determined. The ZnO-NPs with average cross sectional size of 30 nm were obtained by plasma-enhanced chemical vapor deposition (PECVD) from elemental high-purity zinc in a zinc-oxygen-hydrogen plasma-forming gas mixture. It was established that the spherical ZnO-NPs are promising to improve the gas performance of PU-based MMMs for CO2 recovery from natural gas, while the rod-shaped NPs better demonstrate their potential in capturing CO2 in flue gases.
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