Effects of genistein modification on miscibility and hydrogen bonding interactions in poly(amide)/poly(vinyl pyrrolidone) blends and membrane morphology development during coagulation

Miscibility characteristics of poly(amide):poly(vinyl pyrrolidone) (PA:PVP) blends containing a soybean-derived phytochemical called “genistein” have been investigated using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The occurrence of hydrogen bonding in the binary PA/genistein (PA/G) and PVP/genistein (PVP/G) pairs as well as their ternary blends has been confirmed by Fourier transformed infrared spectroscopy (FTIR). On the basis of DSC and POM data, the morphology phase diagram of PA:PVP/G blends is mapped out, which consisted of various coexistence regions such as isotropic, liquid + liquid, liquid + crystal, liquid + liquid + crystal, and solid crystal regions. Subsequently, PA:PVP membranes modified with genistein were prepared by coagulation via solvent (dimethyl sulfoxide, DMSO) and non-solvent (water) exchange. Addition of genistein reduced the miscibility gap of the PA/DMSO/water system. The actual amounts of genistein in the final membranes have been quantified as a function of the genistein in feed. Of particular interest is the development of the gradient cross-sectional porous channels, showing the progressively larger diameters from the surface to the bottom substrate with the progression of solvent/non-solvent exchange or solvent power. Scanning electron microscopy (SEM) investigation of the morphologies of the modified membranes revealed that genistein crystals were embedded on the membrane surface as well as in the cross-section even at a very low feed concentration of genistein. A schematic of a coagulation pathway was inscribed inside a prism phase diagram in order to comprehensively illustrate the formation of genistein modified PA:PVP membranes through the solvent/non-solvent exchange process followed by drying.