Water molecules, random network

The reduction of the long-range diffusivity, Di by a factor of four with respect to bulk water can be attributed to the random morphology of the nanoporous network (i.e., effects of connectivity and tortuosity of nanopores). For comparison, the water self-diffusion coefficient in Nafion measured by PFG-NMR is = 0.58 x 10 cm s at T = 15. Notice that PFG-NMR probes mobilities over length scales > 0.1 /rm. Comparison of QENS and PFG-NMR studies thus reveals that the local mobility of water in Nafion is almost bulk-like within the confined domains at the nanometer scale and that the effective water diffusivity decreases due to the channeling of water molecules through the network of randomly interconnected and tortuous water-filled domains. ... 

A series of polyamine-graft copolymers (See Sect. 4.3) were found to form microdomain structure and to exhibit unique biomedical behavior at the interface with living cells, e.g. blood platelets or lymphocytes. Although a number of postulates were proposed to explain the unique behavior of microdomain-structured surface, mechanisms for the mode of interaction of living cells with any of the domain-structured materials have not been adequately explained. In Sect. 4, the author will review results on the biomedical behavior of SPUs, HEMA-STY, and polyamine-graft copolymers, and discuss their interfacial properties in terms of the random network concept of water molecules on the material s surface. 

The mobility concept for surrounding water molecules is closely related to the random-network concept, as will be discussed in Sect. 4.4. 

The Random Network Concept of Water Molecules on Materials Surface... 

Stuart s studies of the structure of the liquid-vapor interfaces of metals and alloys can also be related to his previous research. He developed the first theory of transport in dense simple fluids that explicitly recognizes, and accounts for, the different dynamics associated with short-range repulsion and longer-ranged attraction. He has contributed to the theory of the three-molecule distribution function in a liquid and the theory of melting, and he developed the Random Network Model of water and the first consistent... 

Recently, this behavioral difference of nonpolar and polar solutes could be reproduced by heat capacity calculations using a combination of Monte Carlo simulations and the random network model (RNM) of water." "" It was found that the hydrogen bonds between the water molecules in the first hydration shell of a nonpolar solute are shorter and less bent (i.e., are more ice-like) compared to those in pure water. The opposite effect occurs around... 

The dynamics of protons and water molecules in the bulk of pores are very similar to those in free bulk water. Percolation models and random network simulations can be used to study the impact of pore swelling and changes in pore connectivity upon water uptake on proton conductivity. Existing pore network models provide a good agreement with conductivity data. Updates of these models are needed to account for advances in understanding of the membrane morphology. 

The stmcture of Pmssian Blue and its analogues consists of a three-dimensional polymeric network of Fe —CN—Fe linkages. Single-crystal x-ray and neutron diffraction studies of insoluble Pmssian Blue estabUsh that the stmcture is based on a rock salt-like face-centered cubic (fee) arrangement with Fe centers occupying one type of site and [Fe(CN)3] units randomly occupying three-quarters of the complementary sites (5). The cyanides bridge the two types of sites. The vacant [Fe(CN)3] sites are occupied by some of the water molecules. Other waters are zeoHtic, ie, interstitial, and occupy the centers of octants of the unit cell. The stmcture contains three different iron coordination environments, Fe C, Fe N, and Fe N4(H20), in a 3 1 3 ratio. 

In summary, pure liquid water consists of HgO molecules held in a random, three-dimensional network that has a local preference for tetrahedral geometry but contains a large number of strained or broken hydrogen bonds. The presence of strain creates a kinetic situation in which HgO molecules can switch H-bond allegiances fluidity ensues. 

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