§ Technical

Process path analysis — from ternary diagram to membrane microstructure.

Mapping the composition trajectory of a casting film during nonsolvent-induced phase separation (NIPS) onto the resulting polysulfone membrane cross-section.

Fig. 01

Process path analysis (sketch) mapped onto SEM cross-section

Cross-section of a polysulfone membrane with skin and substructure layers, mapped to a ternary phase diagram showing the composition path during nonsolvent-induced phase separation

ζ = z / L(t) ∈ [0, 1] · dimensionless depth across the casting film during nonsolvent-induced phase separation. Local composition at each depth traces a path through the polymer / solvent / nonsolvent ternary diagram, crossing the binodal and spinodal envelopes at different times — producing the dense skin, fine-pored intermediate zone, and open-celled porous substructure observed in the SEM.