Clay layers bridging polymers

Clearly, the results give strong indications that the bridging polymers are adsorbed directly onto the clay layers. This, in combination with the fact that we do not observe any well-defined polymer-clay correlation on a length scale of about... 

We end up with a picture of the interlayer structure of a bridging polymer like that illustrated in Figure 13.7. Although Figure 13.7 is only a sketch, I would like to draw your attention to several features that are consistent with all the results on the clay-PEO system described in the last three chapters. First, some PEO segments zigzag across the surface, in the layer directly adjacent to the surface oxygens of... 

Layer-silicates Recent studies have also demonstrated the potential microbial influence on clay mineral (layer silicates) formation at hydrothermal vents. Bacterial cells covered (or completely replaced) with a Fe-rich silicate mineral (putative nontronite), in some cases oriented in extracellular polymers (as revealed by TEM analysis), were found in deep-sea sediments of Iheya Basin, Okinawa Trough (Ueshima Tazaki, 2001), and in soft sediments, and on mineral surfaces in low-temperature (2-50°C) waters near vents at Southern Explorer Ridge in the northeast Pacific (Fortin etal., 1998 Fig. 8.6). The Fe-silicate is believed to form as a result of the binding and concentration of soluble Si and Fe species to reactive sites (e.g. carboxyl, phosphoryl) on EPS (Ueshima Tazaki, 2001). Formation of Fe-silicate may also involve complex binding mechanisms, whereas metal ions such as Fe possibly bridge reactive sites within cell walls to silicate anions to initiate silicate nucleation (Fortin etal., 1998). Alt (1988) also reported the presence of nontronite associated with Mn- and Fe-oxide-rich deposits from seamounts on the EPR. The presence of bacteria-like filaments within one nontronite sample was taken to indicate that bacterial activity may have been associated with nontronite formation. Although the formation of clay minerals at deep-sea hydrothermal vents has not received much attention, it seems probable that based on these studies, biomineralisation of clay minerals is ubiquitous in these environments. 

Lin and co-workers explained the superior mechanical properties of the PAN-Na-MMT-Si02 nanocomposites as follows The Na-MMT was exfoliated in the PAN nanocomposites (see Figure 11.7), and the enhancement of the storage modulus results from the delamination of the silicates in the PAN matrix and the strong interactions between the polymer chains and the Na-MMT layers. However, the reinforcement could be anisotropic because of the layer shape of the exfoliated Na-MMT layers. Cracks along the direction of the Na-MMT layers may not be resisted. However, in PAN-clay-silica nanocomposites, the well-dispersed Si02 particles could bridge the cracks that are not stopped by the Na-MMT layers. Therefore, the coexistence of the... 

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