Abstract
In this work, polyelectrolyte mixing ratio is studied as a tuning parameter to control the charge, and thus the separation properties of polyelectrolyte complex (PEC) membranes prepared via Aqueous Phase Separation (APS). In this approach, various ratios of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) are mixed at high salinity and the PEC-based membranes are then precipitated using low salinity coagulation baths. The monomeric ratio of PSS to PDADMAC is varied from 1.0 : 0.8 through to 1.0 : 1.2. Obtained membranes have an asymmetric structure and function as nanofiltration membranes with on average 1 L m−2 h−1 bar−1 pure water permeance and <400 Da molecular weight cut-off (MWCO); except for the 1.0 : 1.2 membrane, where the water permeance was much higher (>20 L m−2 h−1 bar−1) with a similarly low MWCO. For the first time, we report the formation of both negatively and positively charged PSS–PDADMAC based APS membranes, as determined by both streaming potential and salt retention measurements. We hypothesize that the salt type used in the APS process plays a key role in the observed change in membrane charge. The point where the membrane charge transitions from negative to positive is found to be between the 1.0 : 0.9 and 1.0 : 1.0 PSS : PDADMAC ratios. The polyelectrolyte ratio not only affects membrane charge, but also their mechanical properties. The 1.0 : 0.9 and 1.0 : 1.0 membranes perform the best amongst the membranes prepared in this study since they have high salt retentions (up to 90% Na2SO4 and 75% MgCl2, respectively) and better mechanical stability. The higher permeance of the more charged, and thus more swollen, 1.0 : 0.8 and 1.0 : 1.2 membranes provide a relevant new direction for the development of APS-based PEC membranes.
Highlights
The majority of polymeric membranes are produced using toxic and unsustainable organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF).[1,2] Recently, increasing attention has been given to making membrane production processes more sustainable
We prepared poly(sodium 4-styrenesulfonate) (PSS)–poly(diallyldimethylammonium chloride) (PDADMAC) membranes via a complexation induced Aqueous Phase Separation (APS) approach and the structure and performance of the membranes could be readily tuned with coagulation bath salinity, polymer molecular weight, polymer concentration, and the operation conditions.[12]
We study whether the PE mixing ratio is a relevant tuning parameter to control membrane charge and thereby membrane separation properties
Summary
The majority of polymeric membranes are produced using toxic and unsustainable organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF).[1,2] Recently, increasing attention has been given to making membrane production processes more sustainable. Either pH-responsive PEs,[10,11] or polyelectrolyte complexes (PECs)[7,12,13,14] have been utilized In the former, PEs are dissolved at a solution pH where they are charged, while after casting the polymer solution is immersed in a bath with a pH where the PEs are uncharged and insoluble in water.[10,11] This process is very similar to nonsolvent induced phase separation (NIPS), where the polymer is dissolved in an organic solvent and precipitated in a nonsolvent (typically water). Wang et al studied the phase behavior of PSS–PDADMAC complexes and they observed that prepared coacervates could have an excess of PSS.[20] Recently, Chen and coworkers studied the formation of PSS-overcompansated PECs when prepared with excess PSS powder in 0.1 M NaCl solutions and reported a change in material properties of PEC with changing PE mixing ratio.[26] In this current study, we investigate the factors affecting the charge of PEC-based membranes from PSS and PDADMAC. The work will demonstrate that for APS the PE ratio is a relevant tuning parameter to determine the membrane charge, a parameter that is not available in traditional NIPS
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
