Conductometric and computational study of cationic polymer membranes in H+ and Na+-forms at various hydration levels

• Published in: Journal of membrane science 2013-10, Vol.444, p.127-138
• Main Authors: Karpenko-Jereb, Larisa V., Kelterer, Anne-Marie, Berezina, Ninel P., Pimenov, Alexander V.
• Format: Article
• Language: English
• Subjects: aqueous solutions; artificial membranes; Binding energy; Cationic; Correlation; Diffusion coefficient; diffusivity; dissociation; electrolytes; gels; Hydration; Hydrocarbons; hydrochloric acid; ion exchange; Ion-exchange membrane; Mathematical models; Membranes; Microheterogeneous two-phase model; Molar conductivity; polymers; protons; Quantum chemical calculation; sodium; sodium chloride; Transport properties
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2013.05.012

Knowledge of the correlation between the molecular polyelectrolyte structure of membranes and their transport properties helps to develop new ion-exchange polymers with improved characteristics. This research paper studies the transport properties of two counter-ions, H+ and Na+, inside four commercial cationic membranes with experimental methods: three aromatic hydrocarbon polymer membranes CM-1, CMX, MK-40, and one tetrafluoroethylene polymer Nafion analog membrane MF-4SK. Ab initio calculations of the membrane structures with various hydration levels were applied in order to interpret the difference in the transport parameters of counter-ions between aromatic hydrocarbon MK-40 and non-aromatic perfluorinated MF-4SK polymer membranes. The membrane physico-chemical characteristics and the conductivity were experimentally investigated as a function of NaCl and HCl aqueous solution concentration. The conductivity and diffusion coefficients of the counter-ions, as well as volume fractions of ‘gel’ and ‘inter-gel’ phases were determined based on the microheterogeneous two-phase model. For the first time, ab initio calculations on membrane models were correlated with experimental findings in order to explain the difference in the mobility of the two counter-ions. The static ab initio study indicates the dissociation of the functional groups and a stronger water connectivity in perfluorinated membrane, providing an explanation for the measured highest diffusion coefficient and molar conductivity of the counter-ions H+ and Na+ in MF-4SK membrane in comparison to MK-40 membrane. Influence of the polymer nature on the water connectivity, dissociation of −SO3H group and proton transport characteristics (λ¯, D¯) in membrane ‘gel’ phase. [Display omitted] •The correlation between membrane structure and counter-ion transport characteristics is studied.•Experimental conductivity of ion-exchange membranes is explained within the two-phase model.•The counter ions in MF-4SK have the highest diffusion coefficient and molar conductivity.•Ab initio quantum chemical models interpret macroscopic transport parameters of Na+ and H+.•Sulfo group dissociation and dense water network promote the counter-ion mobility.