The methods and mechanisms of nonsolvent induced phase separation have been studied for more than fifty years. Today, phase inversion membranes are widely used in numerous chemical industries, biotechnology, and environmental separation processes. The body of knowledge has grown exponentially in the past fifty years, which suggests the need for a critical review of the literature. Here we present a review of nonsolvent induced phase separation membrane preparation and characterization for many commonly used membrane polymers. The key factors in membrane preparation discussed include the solvent type, polymer type and concentration, nonsolvent system type and composition, additives to the polymer solution, and film casting conditions. A brief introduction to membrane characterization is also given, which includes membrane porosity and pore size distribution characterization, membrane physical and chemical properties characterization, and thermodynamic and kinetic evaluation of the phase inversion process. One aim of this review is to lay out the basics for selecting polymer-solvent-nonsolvent systems with appropriate film casting conditions to produce membranes with the desired performance, morphology, and stability, and to choose the proper way to characterize these properties of nonsolvent induced phase inversion membranes.

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A highly processable form of polyaniline was synthesized and used to form pure polyaniline and polyaniline-polysulfone ultrafiltration membranes by nonsolvent induced phase inversion. Blends containing up to 75% polyaniline were 10-20% more permeable than pure polysulfone membranes, while pure polyaniline membranes were 10 times more permeable and extremely hydrophilic. A novel scanning electron microscope imaging technique was combined with characterization data and the Hagen-Poiseuille pore-flow model to elucidate that increasing polyaniline content increased the apparent membrane pore size and hydrophilicity, while decreasing skin layer thickness and porosity. Pure polyaniline membranes exhibited relatively larger, shorter pores that combined with the increased hydrophilicity to produce the observed separation performance enhancements.