A,B	material constants in Paul’s equation	q	flux of heat
Aij	coefficients in current coupling model	R	thermodynamic potential
C	mass concentration	S	solubility
f	flux of gas	s	entropy densities of the mass mixture
G	Gibbs free energy	T	temperature
h	enthalpy	u	internal energy density
k	Boltzmann’s constant	vf	fractional free volume
L	membrane thickness	x	thermodynamic force vectors
Lij	phenomenological coefficients	$\gamma$	material constant
m0	mass of a single molecular	$\mu$	chemical potential
Nc	flux of penetrant mass	$\rho$	mass density
P	permeability	$\tau$	relaxation time
p	pressure	$\Psi$	flux of free volume