Issue 9, 2011

Conductivity and water uptake in block copolymers containing protonated polystyrene sulfonate and their imidazolium salts

Abstract

There is considerable interest in the properties of polymer electrolyte membranes due to their presence in fuel cells. In this paper, we report on the ionic conductivity and degree of hydration, λ, of model membranes composed of polystyrene sulfonate-b-polymethylbutylene (PSS–PMB) copolymers and their imidazolium salts (PSI–PMB). The membranes were in intimate contact with humid air, and their properties were studied as a function of temperature and relative humidity of the air (RH = 50 and 98%). All of the samples have a lamellar structure in the dry state, and λ = 14 ± 2 for PSS–PMB and PSI–PMB at RH = 98%. However, the conductivity behaviors of PSS–PMB and PSI–PMB are very different. The normalized conductivity, σn (the normalization accounts for small differences in the ion concentrations in the different samples), of PSS–PMB is highly history-dependent and equilibrated behavior is only seen when the samples are annealed at high temperature (80 °C) for long times (about 24 h). In contrast, the equilibrated behavior is obtained rapidly in PSI–PMB samples over the entire temperature window (25–90 °C). At RH = 98%, the equilibrated conductivities of the PSI–PMB samples at RH = 98% were independent of sample molecular weight and within the experimental error of that obtained from the high molecular weight PSS–PMB sample. The low molecular weight PSS–PMB sample exhibited higher conductivity than the three samples described above. At RH = 50% both PSS–PMB and PSI–PMB samples were relatively dry with λ < 5 over the accessible temperature window. In the dry state (1) PSS–PMB samples exhibited slow kinetics while PSI–PMB samples equilibrated rapidly, (2) molecular weight had no effect on conductivity in both PSS–PMB and PSI–PMB samples, and (3) the conductivities of PSI–PMB were significantly lower than those of PSS–PMB.

Graphical abstract: Conductivity and water uptake in block copolymers containing protonated polystyrene sulfonate and their imidazolium salts

Article information

Article type
Paper
Submitted
20 Dec 2010
Accepted
17 Feb 2011
First published
17 Mar 2011

Soft Matter, 2011,7, 4446-4452

Conductivity and water uptake in block copolymers containing protonated polystyrene sulfonate and their imidazolium salts

X. Wang, K. M. Beers, J. B. Kerr and N. P. Balsara, Soft Matter, 2011, 7, 4446 DOI: 10.1039/C0SM01520B

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