Solubility parameter estimation and phase inversion modeling of bentonite‐doped polymeric membrane systems

Abstract

Effects of bentonite concentration on morphology and permeation characteristics of bentonite-doped polysulfone membranes were investigated. Solubility sphere for bentonite was constructed to estimate its solubility parameter. Thermodynamic modeling of phase inversion of this system was carried out using Flory-Huggins theory. The trade-off between thermodynamic and kinetic parameters was used to predict the membrane morphology for bentonite concentration varying from 0 to 5 wt %. The porosity of bentonitedoped membranes decreased up to 3 wt % that increased thereafter. Morphological analysis showed dense cross section with finger-like macrovoids at 3 wt % beyond which it changed to honeycomb structure with large circular voids. Permeability of 3 wt % membrane was the lowest (5.6 × 10 −12 m/Pa s) with 95% bovine serum albumin rejection. Contact angle of the membranes decreased from 83 to 66 with bentonite addition making the membrane more hydrophilic.

Effect of mixed solvents on phase inversion of polymeric membranes

“…In the studies previously reported with various additives, thermodynamic and kinetic factors were opposing, i.e. thermodynamic enhancement was accompanied by kinetic hindrance or vice versa 27,28,30,31,41 . Sadrzadeh and Bhattacharjee have reported thermodynamic enhancement and kinetic hindrance due to the addition of polyethylene glycol and polyvinylpyrrolidone in polyethersulfone 41 .…”

“…The effect of acetone on the thermodynamic parameter was quantified by calculating the thermodynamic parameter 31,41 . An increase in thermodynamic instability results in a shift of the binodal curve towards the polymer–solvent axis leading to a porous membrane morphology, whereas a shift away from the polymer–solvent axis signifies increased stability and a dense morphology 41,44 .…”

“…Thermodynamic hindrance The effect of acetone on the thermodynamic parameter was quantified by calculating the thermodynamic parameter. 31,41 An increase in thermodynamic instability results in a shift of the binodal curve towards the polymer-solvent axis leading to a porous membrane morphology, whereas a shift away from the polymer-solvent axis signifies increased stability and a dense morphology. 41,44 The distance between the polymer-solvent axis and the binodal curve is termed the miscibility gap (MG) and is used to calculate the thermodynamic hindrance parameter (Γ) defined as…”

“…Modeling of the thermodynamic phase diagram for a ternary system has been studied extensively for various membrane‐forming polymers, such as polysulfone, polyethersulfone, cellulose acetate, polyvinylidene fluoride (PVDF), polyacrylonitrile etc 3,11,22,25,26 . A few authors have attempted to model the thermodynamics for a quaternary system of polymer blends, organic and inorganic additives and complex materials 27–31 . However, the study of the solution thermodynamics and phase inversion kinetics for a mixture of solvents has still not been attempted.…”

“…3,11,22,25,26 A few authors have attempted to model the thermodynamics for a quaternary system of polymer blends, organic and inorganic additives and complex materials. [27][28][29][30][31] However, the study of the solution thermodynamics and phase inversion kinetics for a mixture of solvents has still not been attempted.…”