In order for nanocomposites to be useful, they must be thermodynamically stable. It is therefore critical to ensure that clay nanoparticles have surfaces that interact with polymer in a way that yields exfoliated structures that do not spontaneously phase separate. Although some intercalated–exfoliated systems may yield useful improvements in properties, the exfoliated state is still the ultimate goal in producing a nanocomposite with the ultimate property enhancements.
The rate at which intercalation/exfoliation occurs is also of some importance in ensuring that a nanocomposite can be made on a timescale that is commercially viable. Since the level of exfoliation is critical in order that the maximum change in properties in nanocomposites is reached, the ability to measure the level of exfoliation is of paramount importance.
In this chapter, the thermodynamics of intercalation/exfoliation will be discussed in detail, including surface modification of clays, processing strategies, and the enthalpic and entropic components of the intercalation/exfoliation process. In addition, the kinetics related to intercalation/exfoliation will be presented. Finally, a critical evaluation of the analytical methods utilized commonly to determine the level of intercalation/exfoliation will be given.
Clay surface compatibility with polymers
Smectite clay structure
The discussion of clay surface compatibility with polymers in this section will focus primarily on montmorillonite as the example clay. The characteristics discussed will only vary by degree for other smectic clays.