Abstract
AbstractThe thermodynamics of phase inversion of polyvinylidene fluoride membrane with mixed solvents (N,N‐dimethyl formamide (DMF) and acetone) were modeled using Flory–Huggins theory. The kinetics of phase inversion were studied by measuring solvent concentration in the precipitation bath. A model was proposed to predict the time‐dependent solvent concentration profile in the precipitation bath. Depending on solvent volatility, the duration of the kinetics‐dominated regime and the evaporation‐dominated regime varies. A comparative analysis of thermodynamic and kinetic factors was used to predict membrane morphology and it was observed that the system under consideration was thermodynamics dominated. The membrane porosity exhibited decreasing porosity up to the Ac60 membrane (acetone to DMF ratio 60) and thereafter the membrane sublayer showed small pores. Addition of acetone resulted in increased crystallinity and surface hydrophilicity. The mean flow pore diameter measured using a liquid–liquid porometer decreased from 105 nm for an Ac0 membrane (acetone to DMF ratio 0) to 17 nm for an Ac60 membrane. Correspondingly, the molecular weight cut‐off of the membranes decreased from 135 kDa (for the Ac0 membrane) to 104 kDa (for the Ac60 membrane). The model proposed in this work can be used as a tool to predict the properties of intermediate compositions and prepare tailor‐made membranes with desired properties. © 2020 Society of Chemical Industry
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