*Condensation heat was evaluated
at 40°C
Form the previously reported data 57, it was noticed
that the ln(D 0) is proportional to the activation
entropy change. Thus, the decreased diffusional activation energy in
15% Ni-ZIF-8 MMM confirms that the activation entropy change is less in
the 15% Ni-ZIF-8 MMM relative to the pure PDMS, and 15% ZIF-8 MMM.
Besides, Barrer’s “zone” theory of diffusion also states that a
penetrant molecule executes a diffusion jump in an activated zone
comprising segments of polymer molecules near the diffusing penetrant
molecule. So, the size of the activated zone is also associated with
both E D and activation entropy (lnD 0). Consequently, the larger the size of the
activated zone required for diffusion, the higher is the diffusional
activation energy and the entropy change, which is associated with the
creation of the activated zone58. Therefore, it was
concluded that the addition of Ni-ZIF-8 in PDMS reduced the size of
activated zones for BD molecule jumps for diffusion, and also reduced
the entropy change. Moreover, the permeation activation energy of BD
reduced 66% in 15% Ni-ZIF-8 MMM from PDMS, and 27% less than 15%
ZIF-8 MMM. Contrary, the permeation activation energy of
N2 in 15% Ni-ZIF-8 MMM showed a 43% increased from
PDMS and 19% higher than 15% ZIF-8 MMM.