The nanoscale dispersion of layered silicates or clays in
polymer matrices offers the potential for significant enhancements
in material properties,1 sparking research thrusts not only
in the characterization2,3 of these nanocomposites but also
in the understanding of the thermodynamics and kinetics4-7
governing the polymer-silicate and silicate-silicate interactions.
It is well-understood that the exfoliated state, in which
individual clay platelets are dispersed within a polymer matrix,
maximizes polymer-clay interactions and offers the most
substantial improvements in polymer properties. In the intercalated
state, competing entropic and enthalpic interactions
allow the polymer to be inserted within the spacing between
stacked clay layers, enlarging the intergallery spacing minimally.
Because the effective aspect ratio of these intercalated particle
stacks is smaller than that of an individual clay platelet, the
enhancements in the thermomechanical properties are less than
those achieved by exfoliated silicate.8 The majority of polymersilicate
nanocomposites developed to date exhibit intercalated
morphologies due to the unfavorable interactions between the
hydrophilic pristine silicate layers and the hydrophobic polymer
matrix.2 However, exfoliated morphologies have been observed
in some polymer nanocomposites containing small silicate
weight fractions or in polymers with low viscosities or containing
strong polar groups that compete with hydrogen bonding,
as in the case of nylon.9-12 Other morphologies that can be
observed in polymer-clay nanocomposites include flocculated
silicate layers, which resemble the intercalated state but include
edge-to-edge interactions due to the hydroxylated clay layers.2