The hydrated morphology of Nafion, the short-side-chain (SSC), and 3M perfluorosulfonic acid (PFSA) fuel cell membranes have been investigated through dissipative particle dynamics (DPD) simulations as a function of ionomer equivalent weight (EW) and degree of hydration. Coarse-grained mesoscale models were constructed by dividing each hydrated ionomer into components consisting of: a common polytetrafluoroethylene backbone bead, ionomer specific backbone beads, a terminal side chain bead, and a bead consisting of a cluster of six water molecules. Flory-Huggins c-parameters describing the interactions between the various DPD particles were calculated. Equilibrated morphologies were determined for the SSC and 3M PFSA membranes both at EW's of 678 and 978, and Nafion with an EW of 1244. The hydration level was varied in each system with water contents corresponding to 5, 7, 9, 11, and 16 H 2 O/SO 3 H. The high EW ionomers exhibit significantly greater dispersion of the water regions than the low EW membranes. Water contour plots reveal that as the hydration level is increased, the isolated water clusters present at the lower water contents increase in size eventually forming continuous regions resembling channels or pores particularly at a hydration of 16 H 2 O/SO 3 H. The DPD simulations reveal differences in the hydrated morphology when only the side chain length was altered and indicate that the 3M PFSA ionomer exhibits much larger clusters of water when compared to the SSC ionomer at the same EW and water content above 9 H 2 O/SO 3 H. The average size of the clusters were estimated from the water-water particles' RDFs and vary from about 2 nm to nearly 13 nm for hydration levels from l ¼ 5 to l ¼ 16. Finally, computed Bragg spacing in each of the hydrated membranes indicate separation of the domains containing the water from 2 to 6 nm, exhibiting an approximately linear relationship with hydration.

We have carried out dissipative particle dynamics (DPD) simulations in an attempt to better understand how molecular weight (MW) affects the hydrated morphology of the short-side-chain (SSC) perfluorosulfonic acid (PFSA) fuel cell membrane. Previously, we demonstrated that such coarse-grained simulations are capable of revealing differences in the morphology of PFSA membranes when either the length of the side chain or equivalent weight (EW) of the ionomer is changed [Wu et al. Energy EnViron. Sci. 2008, 1, 284-293]. In the present investigation, the SSC ionomer was modeled using macromolecules of the ionomer with EWs of 753, 798 and 849, each at three distinct MWs. The morphological structures were then investigated as a function of EW, MW and degree of hydration (with water contents corresponding to λ ) 5, 7, 9, 11, and 16 H 2 Os/SO 3 H). Water contour plots reveal that the isolated water clusters present at lower water contents increase in size with increasing levels of hydration, and eventually form continuous water domains. The increase of MW induces aggregation of the fluorocarbon backbone in order to minimize chain bending forces while maintaining a phaseseparated structure, and results in larger, more elongated water domains, especially at high EWs. Furthermore, the Bragg spacing corresponding to periodicity of water domains, computed from radial distribution functions (RDFs), shows that the spacing between water domains increases with increasing hydration levels. This occurs especially for higher MW polymers at high hydration (16 H 2 Os/SO 3 H), whereas there is little difference at lower hydration levels between polymers with different MW.

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The coagulation behavior of aluminum salts in a eutrophic source water was investigated from the viewpoint of Al-(III) hydrolysis species transformation. Particular emphasis was paid to the coagulation effect of Al 13 species on removing particles and organic matter. The coagulation behavior of Al coagulants with different basicities was examined through jar tests and hydrolyzed Al(III) speciation distribution characterization in the coagulation process. The results showed that the coagulation efficiency of Al coagulants positively correlated with the content of Al 13 in the coagulation process rather than in the initial coagulants. Aluminum chloride (AlCl 3 ) was more effective than polyaluminum chloride (PACl) in removing turbidity and dissolved organic matter in eutrophic water because AlCl 3 could not only generate Al 13 species but also function as a pH control agent in the coagulation process. The solidstate 27 Al NMR spectra revealed that the precipitates formed from AlCl 3 and PACl were significantly different and proved that the preformed Al 13 polymer was more stable than the in situ formed one during the coagulation process. Through regulating Al speciation, pH control could improve the coagulation process especially in DOC removal, and AlCl 3 benefited most from pH control.