Solubility and diffusivity of sodium chloride in phase-separated block copolymers of poly(2-dimethylaminoethyl methacrylate), poly(1,1′-dihydroperfluorooctyl methacrylate) and poly(1,1,2,2-tetrahydroperfluorooctyl acrylate)

Abstract

Solubility and diffusivity of sodium chloride were determined in a series of dense films of phase-separated diblock and triblock copolymers composed of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and either poly(1,1′-dihydroperfluorooctyl methacrylate (PFOMA) or poly(1,1,2,2-tetrahydroperfluorooctyl acrylate) (PTAN). As the content of hydrophilic PDMAEMA increases in PDMAEMA- b-PFOMA films, total water uptake increases. The salt partition coefficient of these films increases with increasing PDMAEMA content and weight fraction of water in the PDMAEMA domains. In contrast, salt diffusivity is not monotonically correlated with PDMAEMA content and effective hydration. Triblock copolymers exhibit different values of total water uptake, total hydration, salt partition, and diffusion coefficients than those of diblock copolymers (PDMAEMA- b-PFOMA) at the same PDMAEMA concentration. The total water uptake of PFOMA- b-PDMAEMA- b-PFOMA copolymers is lower than that of PDMAEMA- b-PFOMA, while water uptake of PTAN- b-PDMAEMA- b-PTAN films is higher than that of PDMAEMA- b-PFOMA. Salt partition and diffusion coefficients increase monotonically with the amount of freezing water in the hydrophilic domains, suggesting that the state of water in the phase-separated block copolymers is an important factor influencing their salt uptake and transport properties.