Mixed matrix membrane materials with glassy polymers. Part 1

Abstract

Mixed matrix materials comprising molecular sieve entities embedded in a polymer matrix can economically increase membrane permselectivity, thereby addressing a key challenge hindering the widespread use of membrane‐based gas separations. Prior work has clarified the importance of proper selection of the dispersed sieve phase and the continuous matrix phase based on their intrinsic transport properties. Proper material selection for the two components, while necessary, is not sufficient since the interfacial contact zone appears to be equally important to achieve optimum transport properties. Specifically, it was found that chemical coupling of the sieve to the polymer can lead to better macroscopic adhesion but to even poorer transport properties than in the absence of the adhesion promoter. This counterintuitive behavior may be attributed to a nanometric region of disturbed packing at the polymer sieve interphase. The poor properties are believed to result from “leakage” of gas molecules along this nanometric interface. The Maxwell model was modified to take into account these complexities and to provide a first order quantification of the nanometric interphase. The analysis indicates that optimization of the transport properties of the interfacial region is key to the formation of ideal mixed matrix materials. This approach is used in the second part of this paper to form successful mixed matrix membrane materials.

Ultem®/ZIF-8 Mixed Matrix Membranes for Gas Separation: Transport and Physical Properties

“…Although the model describes ideal transport properties of mixed matrix membranes, it has limitations when non-ideal effects exist like sieve-in-cage, matrix rigidification and stress dilated matrices 7,10 . To account for non-ideal effects one can apply a "nested" version of the Maxwell model.…”

“…For glassy polymers the formation of defect-free membranes can be achieved by the compatibilization of the two phases with silanes as reported in the literature 3,5 . Unfortunately, high performance membranes are more complex to obtain, due to difficulties in avoiding the formation of interfacial defects between the dispersed and continuous matrix phases [6][7][8][9][10] . Zeolitic imidazolate frameworks (ZIFs) [11][12][13] created a new possibility for mixed matrix membranes formation.…”

Nanomembrane Materials Based on Polymer Blends

“…Investigations have shown that the interfacial region, which is a transition phase between the continuous polymer and dispersed sieve phases, is of particular importance in successful MMM formation [29,34,35].…”

“…Therefore, it is highly desirable to provide an alternate cost-effective nanomembrane in a position above the trade-off curves between permeability and selectivity [19]. Mixed-matrix membranes (MMMs) are considered as hybrid membranes containing liquid, solid, or both liquid and solid fillers embedded in a polymer matrix [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. They are densely packed polymer membranes with organic or inorganic nanoparticles introduced into their structure.…”

Mixed Matrix Membranes for Gas Separation Applications

“…One of these widely used approaches is to perform the casting at temperature above the polymer glass transition or either use a polymer with low glass transition temperature and perform the membrane fabrication close to the polymer glass transition temperature. 26,47,49,54,55 To maximize stress relaxation in this method, the matrix flexibility is maintained during the membrane formation. Thus, a low volatile solvent is the choice, however, such a solvent is difficult to find since the typical solvents used for film casting boil below this temperature.…”