An attempt was made (1) to establish a theory on particle growth during the membrane formation by the phase separation method with an aid of computer simulation technique, and (2) to compare results of the computer simulation with those of actual experiments. In the particle simulation, primary particles consisting of polymer-rich phase are generated at random position in a hypothetical space, and moving velocity v1 was given to them, assuming Brownian movement in a solution of polymer-lean phase. If a distance between the centers of gravity of two arbitrary chosen particles is less than the summation of their radii, they are considered to have collided, yielding a new larger particle. The simulation reveals that the growth rate of particles is theoretically expected to be larger when the phase separation occurs under the conditions of lower concentration (i.e., lower viscosity) of polymer-lean phase and of smaller two phase volume ratio R(= V(1)/V(2); V(1) and V(2) are the volumes of polymer-lean and -rich phases, respectively). The lower viscosity yields lager velocity and the smaller R gives larger collision frequency. Particle size distribution N(S) and the number-average radius of growing particles SBAR were evaluated by dynamic light scattering measurement on systems of polymer solution/coagulating solution, i.e., cellulose cuprammonium solution/acetone-ammonia-water solution and cellulose cuprammonium solution/sodium hydroxide-water solution and it is experimentally confirmed that the primary particles grow by amalgamation and under some conditions, their radii approach an asymptotic value, which is the radius of the secondary particle S2.
