Water dynamics within a highly rigid sulfonated polyphenylene

• Water environments within an ionomer are dependent upon structure, and composition.
• Increasing ionomer sulfonation led to more water states and sites.
• Confined water relaxation time T1 in sulfonated domains is less than bulk water.
• FTIR reveals that bound water evaporates slower than unbound during drying.
• Water diffusivity increases at hydrophilic bundle interfaces.

Complex water molecule interactions within the confined environments of a sulfonated polyphenylene (sPP) ionomer were studied using 1H nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. Multiple water environments were observed due to variations in hydrophilicity created by its structure, and chemical composition. Confined water properties are strongly dependent upon water content, degree of ionization, and temperature. Increasing the degree of sulfonation (DS) results in the creation of more water states and sites. The chemical shifts of water depend upon its environment with a smaller dependence on temperature. Confined water relaxation time T1 is than significantly lower bulk water and increases with temperature. Pulse field gradient (PFG) NMR studies reveals that water self-diffusion coefficients increase with. Water molecules diffuse faster in sPP than Nafion™, which implies that diffusion is facilitated by bundled hydrophilic pathways. Time-dependent FTIR reveals that bound water evaporates slower than unbound water during drying, which illustrates the difference of bulk and confined water within sPP ionomers. Hindered water evaporation is due to a reduction in the degrees of freedom for ion containing domains and mass transfer limitations at interfacial boundaries between hydrophobic and hydrophilic domains.

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