Abstract
AbstractNonsolvent induced phase separation (NIPS) is the most common approach to produce polymeric membranes. Unfortunately, NIPS relies heavily on aprotic organic solvents like N‐methyl‐pyrrolidone. These solvents are unsustainable, repro‐toxic for humans and are therefore becoming increasingly restricted within the European Union. A new and sustainable method, aqueous phase separation (APS), is reported that eliminates the use of organic solvents. A homogeneous solution of two polyelectrolytes, the strong polyanion poly(sodium 4‐styrenesulfonate) (PSS) and the weak polycation poly(allylamine hydrochloride) (PAH), is prepared at high pH, where PAH is uncharged. Immersing a film of this solution in a low pH bath charges the PAH and results in a controlled precipitation, forming a porous water‐insoluble polyelectrolyte complex, a membrane. Pore sizes can be tuned from micrometers to just a few nanometers, and even to dense films, simply by tuning the polyelectrolyte concentrations, molecular weights, and by changing the salinity of the bath. This leads to excellent examples of microfiltration, ultrafiltration, and nanofiltration membranes. Polyelectrolyte complexation induced APS is a viable and sustainable approach to membrane production that provides excellent control over membrane properties and even allows new types of separations.
Highlights
Nonsolvent induced phase separation (NIPS) is the most common approach with NIPS it became possible to prepare defect-free asymmetric membranes in a to produce polymeric membranes
poly(allylamine hydrochloride) (PAH) is uncharged at high pH and this prevents it from forming a complex with Poly(sodium 4-styrenesulfonate) (PSS)
The phase separation that occurs when immersing a film of the high pH homogeneous polyelectrolyte solution in a low pH bath leads to the formation of membranes with desired structures and excellent properties
Summary
A new APS approach is proposed that uses water as a solvent and nonsolvent for the polyelectrolytes. Such a drastic increase in the solution viscosity causes a delay in demixing during the phase inversion process, resulting in a sponge-like structure with a dense top layer This can be seen in the SEM cross-section images of the membranes in Figure 4a where the morphology gradually shifts from finger-like macrovoids (8 and 10 wt%) to a sponge-like structure with a denser top layer (12 wt%). It is known from the literature that the addition of salt increases the mobility of PE chains in polyelectrolyte complexes.[13,31] Figure 5a shows the cross-section and top surface SEM images of the membranes prepared at different concentrations of NaCl in the coagulation bath. Full cross-section images of two different membranes are shown in Figure S4 (Supporting Information) This shows that the membranes become denser with the addition of NaCl in the coagulation bath due to the increased PE chain mobility. The polyelectrolyte complex membranes are stable and resistant to plasticization by NaCl and KBr at least up to concentrations of 1 m
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
