But in the present work, the aspect ratio of TRG platelets was
found to be around 225 according to the Neilson model. It is evident
that the TRG sheets are having a high aspect ratio as compared
to clay platelets. For this reason a very low amount of TRG leads to
significant reduction in gas permeability as compared to clay. In
general, most of the polymeric nanocomposite systems obey the
tortuous path model, however, there are several cases where the
theoretical equation does not match with the experimental data.
The tortous path model was found to deviate from the experimental
results reported by Lape et al. (2004). The deviation is mainly
due to constrained polymer region, low diffusion coefficient and
the orientation factor. In order to overcome this deviation and tortuosity
factor, the Nielsen equation was modified by Bharadwaj
(2001) by including the orientation order of the filler. According to
Bharadwaj model the relative permeability is given by: