ABSTRACT:The existing probabilities of isolated (P.), semi-open (P,), and through pores (P,) in the micro-porous polymeric membrane were evaluated by analyzing the experimental porosity (P,.) data. Here, the following assumptions were employed: (I) the membrane consisted of the multi-thin layers, (2) the network-like structure in one layer was constituted by numerous secondary particles which grew from the primary particles generated as polymer-rich phase from the casting solution in the occurrence of the micro-phase separation, (3) the secondary particles were packed in the hexagonal closest packed model and the vacant space originating from the polymer-lean phase was composed of imaginary vacant particles having the same diameter as the secondary particle. The probability that the secondary particles surround the vacant particles perfectly corresponds to P,, and the probability of connecting with each vacant particles continuously from the· front surface to back surface equals P,. The theoretical relations between P,, P,, P,, and the structural parameters were derived. The numerical calculations were carried out for a given P,. using the equations derived. It was concluded that P, P, > P, for P,. 0.15, and P, P, > P, for 0.15 < P,. < 0.4, P,>P, and P,=0 for P,.~0.4.KEY WORDS Polymeric Membrane / Micro-Phase Separation Method / Pore Characteristics / Isolated Pore / Semi-Open Pore / Through Pore / Porosity / Secondary Particle / Layer Structure / Very recently Kamide and Manabe 1 presented a particle-growth theory for interpreting pore formation when a membrane is produced through the phase separation phenomena of polymer solution. The validity of their theory was experimentally confirmed for cellulose cuprammonium solutions and cellulose membranes regenerated from them: The pore size distribution N(r) (r, pore radius) of the regenerated cellulose membrane surface, indirectly· estimated by the theory using the two-phase volume ratio of the phase separated solution and ·the average diameter of the secondary particles constituting the membrane cast from the solution, agrees fairly well with the pore size distribution directly determined by the electron microscopic (EM) method proposed before. 2 The phase-separation proceeded from the top to bottom surface for the case of cellulose cuprammonium solution. 3 Although the overall supermolecular structure changes significantly depending on the distance Z from the top surface of the membrane, it was ascertained that within a given thin layer with constant Z the particular supermolecular structure of the layer remained almost uniform.3 Accordingly, N(r) for each portion of