THE SURFACE-STRUCTURE AND MORPHOLOGY OF POLYVINYLIDENE FLUORIDE MICROFILTRATION MEMBRANES BY ATOMIC FORCE MICROSCOPY

Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to investigate the surface structure and topography of polyvinylidene fluoride (PVDF) microfiltration membranes. A structure with nodules, nodule aggregates, and supernodular aggregates consistent with the Four Tiers of Structure Model for integrally skinned phase inversion membranes advanced by Kesting is observed. AFM reveals very uniform nodule aggregates with intermediate sized pores in their interstitial regions. These nodule aggregates exist in larger assemblies of supernodular aggregates, which possess much larger pores at their boundaries. These pores are surface extensions of the openings between cells in the matrix. The smallest sized pores are detected in the nodule aggregates themselves between assemblies of nodules and are attributed to internal stresses developed as crystallization occurs after the coagulation process.