On a clay platelet

Figure 1. Schematic representation of Na -Ca2 exchange on a clay platelet.

The CPNC performance depends on the degree of platelets dispersion, with some properties more affected by it (e.g., mechanical, barrier) than others. The degree of dispersion is controlled by the thermodynamic miscibility between polymer and organoclay, solidification of organics on the clay platelets, and their concentration [Utracki, 2004, 2008a]. The PVT measurements and interpretation of the CPNC behavior provide a direct means of extracting information about matrix-clay... 

For elements such as silicon, alumina and sodium, there is a fairly good agreement between atomic absorption (AA) determination and EDS data for the parent Mg-rectorite. However, there are differences with respect to other elements, as shown in Table 6-1. This is not unexpected, since AA determination reports bulk analysis, whereas EDS reports the composition of the individual clay ciystal surface. The iron content measured by EDS is much higher than reported by AA analysis indicating that Fe is preferentially concentrated on the clay platelets surface, and that FejOj-containing phase impurities are negligible. The magnesium distribution is similar to that observed for Fe. 

We consider a diffusion/adsorption test of cesium (Cs), and the data provided are as follows The size of a clay platelet is 100 x 100 x 1. Based on experimental data of Baeyens and Bradbury (1997) the cross-section area of clay edges, which are adsorption sites, are assumed to be 35 m /g. Since the atomic radius of cesium is 3.34 A, and because of the monolayer adsorption, we set the layer thickness of the edge domain where cesium ions are adsorbed as 0.67 nm. The maximum amount of cesium adsorbed in this domain is 6.51 x 10 mol/g. The molecular number of interlayer water is given as n=2.5. The diffusion coefficient of cesium ions in the bulk water is 2x10 cm /s, and in the interlayer water is 2.62x 10 cm /sec, which is obtained from the MD simulation. The concentration of cesium at the upstream boundary, i.e., the l.h.s. surface of Fig. 9.2 (Dirichlet boundary condition) is given as Case (1) 10 mol/1, Case (2) 10 mol/1 and Case (3) 10 " mol/1. 

MWCNT, rather than the clay platelets. These results indicate that the FR is preferentially adsorbed onto the MWCNT surfaces, and hence no longer competes with the polymer in the formation of the in situ grafts on the clay platelet surfaces. As a result, the efficiency of the platelets in compatibilizing the blend is restored, and both blends are flame retardant with half the concentration of clay. It is interesting to note that the s-MWCNT blend satisfies the UL-94 VO requirement, whereas the blend containing the /-MWCNT only satisfies UL-94 V2, which may be because of improved FR particle dispersion. In addition, close examination of the TEM images shows that the s-MWCNT are dispersed in both the PS and PMMA phases, whereas the /-MWCNT are observed mostly in the PS phase. 

Use of the RAFT technique has evolved from the use of a free RAFT agent i.e. the RAFT agent is not attached to the clay layers) to the use of RAFT agents anchored on the clay platelets. Moad and co-workers used RAFT-mediated polar polymers that are miscible with polypropylene (PP) and then melt blended both polymers i.e. polymers and PP) in the presence of sodium montmorillonite to yield PP-CNs. Salem and Shipp showed that the use of free RAFT agents to the prepare polystyrene-, poly(methyl methacrylate)- and poly(butyl acrylate)-clay nanocomposites by in situ intercalative polymerization in bulk led to products with well-controlled molecular weights and narrow... 

Other interesting Langmuir monolayer systems include spread thermotropic liquid crystals where a foam structure forms on expansion from a collapsed state [23]. Spread monolayers of clay dispersions form a layer of overlapping clay platelets that can be subsequently deposited onto solid substrates [24]. 

Stresses caused by chemical forces, such as hydration stress, can have a considerable influence on the stability of a wellbore [364]. When the total pressure and the chemical potential of water increase, water is absorbed into the clay platelets, which results either in the platelets moving farther apart (swelling) if they are free to move or in generation of hydrational stress if swelling is constrained [1715]. Hydrational stress results in an increase in pore pressure and a subsequent reduction in effective mud support, which leads to a less stable wellbore condition. 

Fig. 1.9 (A) Exfoliation of clay platelets (white Cloisite25A and Cloisite30B after (B) two and a arrows) in a commercial polylactide matrix using half months hydrolysis and (C) after five and a a masterbatch process. (B, C) Visual aspect half months hydrolysis. (A) adapted from [144] of unfilled PLA, microcomposite based on reproduced by permission ofWiley-VCH, and CloisiteNa+, and nanocomposites based on (B, C) from [147] with permission from Elsevier.

The long-term goal of this investigation is an understanding of the effect of a particular mode of adsorption on montmorillonite which ensures that under pressure the clay platelets align parallel to a solid surface even under saline conditions. This is an important phenomenon in petroleum recovery processes. 

In this type of system, the polymer chains are constrained by a surface. They can lie between two hard surfaces such as in the galleries within two parallel clay platelets (as is illustrated in Figure 7), have one layer absorbed on to a hard surface as a coating, with the other free (as in Figure 8), they can be absorbed by the surfaces of exfoliated clay platelets (Figure 9), or by the surface of a solid reinforcing particle completely surrounded by an elastomeric phase (Figure 10). 

Additional evidence that one or both of the mechanisms are operative comes from the data obtained on Cs+-saturated clays. Now, the individual clay platelets in the aggregates are separated by at most a monolayer of water (10) The proflavine molecules adsorb preferentially in that interlamellar space to replace the water and to form a monolayer of proflavine molecules. No dimers are formed, except for a small amount on the external surface of the aggregates, and the quantum yield is almost independent of the loading. 

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