Intercalation of water-soluble polymers

PVP is dissolved in water prior to mixing it with the clay. The intercalation can be measured easily using X-ray diffraction by following the change in basal d-spacing. 

It appears that the first step corresponds to a monolayer of PVP trapped between the plates of clay. The second step would be a mono-layer covering both faces of the plates and which results in a bilayer complex in the gallery between the plates, and the third appears to form a trilayer structure in the gallery. If PVP is added to higher and higher concentrations, the intercalation peak continues to grow and broaden with the eventual complete exfohation of the clay into the PVP polymer. 

The ability to form a stepwise intercalation that leads to exfoliation is unique to PVP. The other water-soluble polymers behave in a different way than PVP that is illustrative of the forees important in producing an exfohated nanocomposite. 

It was hypothesized that if the number of cations available for ion-dipole bonding was reduced on the clay surface, the bilayer intercalate could be formed. The clay was exchanged with ammonium ions to replace half of the sodium cations. When the intercalation experiments were repeated, the PVOH now formed the bilayer structure, but the PEG still formed only the monolayer. This behavior for PEG has also been 

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The intercalation of water-soluble polymers is a clear case where the edge effect does not present any barrier to intercalation. An example would be the intercalation of PVP into sodium montmorillonite [1]. In this case, hydrated sodium montmorillonite as a powder can be mixed with powdered PVP in a bowl mixer and the intercalation occiurs in seconds. 

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