3.1. Solution Casting

One of the most common methods to synthesize flat-sheet membranes is solution casting, which applies in various situations. The polymer and potential additives such as inorganic fillers are initially dissolved in a solvent to form a solution and then the mixtures are casted onto a flat surface such as petri dish or stainless steel plate. The solvent can be removed through evaporation and/or phase inversion processes. Through the casting method with or without the participation of porous support, the multilayer film can be successfully prepared. By removing the solvent slowly and completely through evaporation, a high-density cell membrane can be prepared. In contrast, when the solvent removal process involves a phase inversion process, an asymmetric membrane with interconnected cell structures can be obtained by immersing in a non-solvent bath. In order to achieve the purpose of preparing the top dense layer, an effective way is to add a highly volatile solvent to the casting solution and perform phase inversion after evaporation. For the instance of mixed matrix membranes (MMMs), to prevent the agglomeration phenomenon of fillers, the mixtures are commonly treated by thorough stirring and sonication before casting. Subsequently, MMMs are synthesized by the similar procedures as aforementioned. For example, poly (vinyl alcohol) with acrylamide to form a polymeric membrane is prepared in this way.