$1$: Permeation in Heterogeneous Blends

Two polymers, A and B$,$ form phase$-$separated blends whose permeation properties obey the Maxwell model. Polymer A has an oxygen permeability of $1$ Barrer and an O$2/$N$2$ selectivity of $10.$ Polymer B has an oxygen permeability of $100$ Barrers and an O$2/$N$2$ selectivity of $4.$ In blends containing less than $50$ volume percent A$,$ polymer B is the continuous phase. Otherwise, B is the continuous phase.