Most PNC fabrication techniques offer only partial control over the filler dispersion morphology within the polymer matrix.
As Table 1 showed, while improvements in oxygen and moisture vapor barriers can be achieved in virtually any polymer by clay nanoparticle dispersion, with only a few exceptions these improvements are generally modest.
The complicating factor here is attaining complete exfoliation of dispersed clays, which limits the achievable diffusion path tortuosity.
While advances have been made toward understanding the factors which influence the degree of clay platelet exfoliation in PNC films, these relationships are complex and difficult to control in practice.
Therefore top-down approaches to PNC fabrication are limited in their ability to provide consistently impressive improvements in oxygen and moisture vapor permeabilities.