Thermally-induced phase separation mechanism study for membrane formation

The thermally-induced phase separation mechanism was investigated for the system isotactic polypropylene and diphenyl ether. Droplet growth was monitored by using a thermo-optical microscope. The degree of supercooling for liquid-liquid phase separation affected the size and growth rate of the droplets. Increasing the polymer content affected the solution viscosity and interaction parameter which resulted in a decrease of the size and growth rate of the droplets. Crystallization interfered with the droplet growth at lower quench temperatures from the onset of crystallization. The droplet growth rate followed the equation proposed by Furukawa, and the droplet growth was well described by the theories for coarsening and coalescence. Equilibrium droplet size was estimated by the Laplace equation and was in good agreement with the experimental data. The cell size of the membrane was about half of the droplet size of the melt sample due to shrinkage of the sample during extraction of the diluent and the drying process.