Phase Segregated Membranes

In spite of many computational advantages, DPD and SCMF methods are not able accurately to predict physical properties that rely upon time correlation functions (e.g., diffusion), making them less applicable to extract structure-related transport properties of phase-segregated membranes. 

Self-Organization of Phase-Segregated Membrane Morphology... 

Figure 6.4 shows that long-range diff usivities of water in Nafion membranes measured by QENS, Di are equal to self-diff usivities determined by PFG-NMR, Dg, at A > 10. In well-hydrated membranes, the major geometric constraints for water mobility due to the phase-segregated, random network morphology of... 

In this section, we describe the role of fhe specific membrane environment on proton transport. As we have already seen in previous sections, it is insufficient to consider the membrane as an inert container for water pathways. The membrane conductivity depends on the distribution of water and the coupled dynamics of wafer molecules and protons af multiple scales. In order to rationalize structural effects on proton conductivity, one needs to take into account explicit polymer-water interactions at molecular scale and phenomena at polymer-water interfaces and in wafer-filled pores at mesoscopic scale, as well as the statistical geometry and percolation effects of the phase-segregated random domains of polymer and wafer at the macroscopic scale. 

In the case of the horizontal cathode facing upward (gy), the plume along the flow direction vanishes and gas accumulates just below the rigid membrane, where the simulation predicts a phase segregation (a2 — 1). Convergence... 

These electron spin resonance studies directly show the existence of phase segregation in these ion exchange membranes. The ionic phase is made of the ions, water molecules, and part of the side chains. 

The general structure of Nafion in particular, and ionomers in general, as a function of water content has been the source of many studies as recently reviewed by Mauritz and Moore [21] and Kreuer et al. [10] For the most part, the experimental data have shown that a hydrated membrane phase separates into ionic and matrix or nonionic phases. The ionic phase is associated with the hydrated sulfonic acid groups and the matrix phase with the polymer backbone. Thus, water is associated with the hydrophilic ionic phase and not the hydrophobic matrix phase. The actual way in which the phases segregate within the polymer depends on the water content. 

The basic conclusions of the Gierke model were supported by the results of the DuPont [34], Kyoto [35] and Grenoble [36] groups and by many further studies (see e.g. [37]. Claims of cylindrical micelles [38] or flat lamellar structures [39-41] have also been made, but the occurrence of such structures is more typical for E-membranes. For N-membranes the concept of spherical or quasi-spherical micelles continues to be the most common conjecture about the phase segregation in the membrane, particularly in view of reports on the absence of elongated objects in the patterns of reconstruction of SAXS data [42]. 

Figure 33 Advancing the control to generate substructure compartments (a) as well as to position functional groups (b), multifunctional peptide segments (c), or catalytically active proteins (enzymes) (d) within self-assembled colloidal structures, (a) Cation-induced generation of membrane compartments by lateral phase segregation of charged and a neutral, fluorescently labeled diblock copolymers (pH 4,0.1 mM calcium at 50% AB1). Reprinted with permission from Christian, D. A. flan, A. W. Ellenbroek, W. G. etal. Nat. Mater. 2009, 8,843. Copyright 2009, Nature Materials .

In the area of membranes, DOE research strategies include studies of hydrophilic additives, non-aqueous proton conductors, and phase segregation control - both in polymers and two-polymer composites. The DOE s catalysts strategies include lowering platinum group metals (PGM) content, developing affordable platinum-based alloys, and developing non-platinum catalysts. 

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