Molecularly Mixed Composite Membranes: Challenges and Opportunities

Abstract

The fabrication of porous molecules, such as metal–organic polyhedra (MOPs), porous organic cages (POCs) and others, has given rise to the potential for creating “solid solutions” of molecular fillers and polymers. Such solid solutions circumvent longstanding interface issues associated with mixed matrix membranes (MMMs), and are referred to as molecularly mixed composite membranes (MMCMs) to distinguish them from traditional two‐phase MMMs. Early investigations of MMCMs highlight the advantages of solid solutions over MMMs, including dispersion of the filler, anti‐plasticization of the polymer network, and removal of deleterious interfacial issues. However, the exact microscopic structure as well as the transport modality in this new class of membrane are not well understood. Moreover, there are clear engineering challenges that need to be addressed for MMCMs to transition into the field. In this Minireview, the authors outline several scientific and technological challenges associated with the aforementioned questions and their suggestions to tackle them.

The Chemistry of Porous Organic Molecular Materials

“…[337,338] Amorphous POCs have also been coated onto microbalances for sensing applications, [35] and can be processed into amorphous thin films which have shown promise for molecular-sieving applications. [34,339] Composites are possible, too: mixed-matrix membrane materials, prepared using in situ crystallization of POCs within a polymer of intrinsic microporosity, [340] or by processing amorphous scrambled POCs [197] into polymer membranes, [341,342] thus improving gas permeability and selectivity. Perhaps one of the most exciting developments in porous organic molecular materials discovery is the application of computational methods to predict their structure and function.…”

“…For example, crystalline POCs have been coated onto microporous beads,336 and chiral crystalline POCs have been used as stationary phases in gas chromatography columns for molecular separations 337,338. Amorphous POCs have also been coated onto microbalances for sensing applications,35 and can be processed into amorphous thin films which have shown promise for molecular‐sieving applications 34,339. Composites are possible, too: mixed‐matrix membrane materials, prepared using in situ crystallization of POCs within a polymer of intrinsic microporosity,340 or by processing amorphous scrambled POCs197 into polymer membranes,341,342 thus improving gas permeability and selectivity.…”

Polyphenylsulfone (PPSU)-Based Copolymeric Membranes: Effects of Chemical Structure and Content on Gas Permeation and Separation

“…To overcome this challenge, several strategies have been proposed and studied. For example, synthesis of new polymeric materials [ 6 , 7 , 10 , 11 , 12 , 13 , 16 , 22 , 23 , 24 ], cross-linking [ 7 , 24 , 25 , 26 ], development of mixed matrix membranes [ 3 , 11 , 27 , 28 , 29 , 30 , 31 , 32 ], and polymer blends [ 9 , 33 , 34 ].…”

Designing organic solvent separation membranes: polymers, porous structures, 2D materials, and their combinations

“…To this end, materials with advanced separation properties have been reviewed, including polymers, 8,14 crosslinked polymers, 15,16 porous polymeric and carbonaceous materials, 17 metal-organic frameworks (MOFs), 18,19 covalent organic frameworks (COFs), 18,20 two-dimensional (2D) materials, 21 thin-film composite (TFC) membranes, 22 surfacemodified membranes, 23 and mixed-matrix membranes (MMMs). 24,25 Modeling of liquid transport in membranes has also been described, [26][27][28][29] and important membrane materials were highlighted. 10,14 The rapid growth of this field can benefit from a timely review of materials designs for OSN and OSRO applications, integrating high-performance material structures from various material platforms and their fabrication into industrial TFC membranes.…”