TY - JOUR
T1 - Sodium chloride diffusion in sulfonated polymers for membrane applications
AU - Geise, Geoffrey M.
AU - Freeman, Benny D.
AU - Paul, Donald R.
N1 - Funding Information:
The authors gratefully acknowledge Kraton Performance Polymers, Inc. for their support. A portion of this research is based upon work supported by the U.S. National Science Foundation under Grants DMR #0423914 and CBET #1160128 .
Copyright:
Copyright 2013 Elsevier B.V., All rights reserved.
PY - 2013/1/15
Y1 - 2013/1/15
N2 - Sodium chloride permeability and sorption measurements were used to calculate average salt diffusion coefficients for charged, sulfonated polymers of interest for membrane applications. A sulfonated polysulfone random copolymer and two phase-separated, sulfonated styrenic pentablock copolymers were considered, and data for these materials were compared with those for an uncharged cross-linked poly(ethylene glycol diacrylate) hydrogel. The average salt diffusion coefficients reported for the block copolymers are apparent salt diffusion coefficients because the values have not been adjusted for the polymer's phase separated morphology. The sodium chloride permeability of the uncharged hydrogel decreases by about 16% as upstream salt concentration increases from 0.01 to 1molL-1. This salt permeability change results from a decrease in the salt diffusion coefficient with increasing salt concentration because the polymer's water content decreases as salt concentration increases (i.e., osmotic de-swelling). This decrease in salt diffusion coefficient is consistent with free volume theory, wherein a decrease in water content leads to a decrease in free volume, thereby decreasing the salt diffusion coefficient and, in turn, salt permeability. In contrast, the sodium chloride permeability of the charged polymers increases by more than an order of magnitude as upstream salt concentration increases from 0.01 to 1molL-1. This salt permeability increase is due to increases in both mobile salt sorption and diffusion coefficients with increasing salt concentration, despite the fact that water content (and, therefore, free volume) in the polymer decreases as salt concentration increases. Thus, the increase in salt diffusion coefficient with increasing salt concentration in the charged polymers results from factors (which are currently poorly understood) other than simply water uptake or free volume.
AB - Sodium chloride permeability and sorption measurements were used to calculate average salt diffusion coefficients for charged, sulfonated polymers of interest for membrane applications. A sulfonated polysulfone random copolymer and two phase-separated, sulfonated styrenic pentablock copolymers were considered, and data for these materials were compared with those for an uncharged cross-linked poly(ethylene glycol diacrylate) hydrogel. The average salt diffusion coefficients reported for the block copolymers are apparent salt diffusion coefficients because the values have not been adjusted for the polymer's phase separated morphology. The sodium chloride permeability of the uncharged hydrogel decreases by about 16% as upstream salt concentration increases from 0.01 to 1molL-1. This salt permeability change results from a decrease in the salt diffusion coefficient with increasing salt concentration because the polymer's water content decreases as salt concentration increases (i.e., osmotic de-swelling). This decrease in salt diffusion coefficient is consistent with free volume theory, wherein a decrease in water content leads to a decrease in free volume, thereby decreasing the salt diffusion coefficient and, in turn, salt permeability. In contrast, the sodium chloride permeability of the charged polymers increases by more than an order of magnitude as upstream salt concentration increases from 0.01 to 1molL-1. This salt permeability increase is due to increases in both mobile salt sorption and diffusion coefficients with increasing salt concentration, despite the fact that water content (and, therefore, free volume) in the polymer decreases as salt concentration increases. Thus, the increase in salt diffusion coefficient with increasing salt concentration in the charged polymers results from factors (which are currently poorly understood) other than simply water uptake or free volume.
KW - Free volume
KW - Ion exchange membrane
KW - Salt diffusion
KW - Salt permeability
KW - Solution-diffusion
UR - http://www.scopus.com/inward/record.url?scp=84871738055&partnerID=8YFLogxK
U2 - 10.1016/j.memsci.2012.09.029
DO - 10.1016/j.memsci.2012.09.029
M3 - Article
AN - SCOPUS:84871738055
VL - 427
SP - 186
EP - 196
JO - Journal of Membrane Science
JF - Journal of Membrane Science
SN - 0376-7388
ER -