Drying Kinetics And Phase Separation Of Polymer Blend Membrane

The quality of membrane is connected with drying process and the defects of membrane may be caused by improper drying conditions. So it is significant to study the effect of drying parameter on the solidifying process of polymer membrane. In this paper, The drying process of polystyrene(PS)/polycarbonate(PC) blend within dichloromethane solution has been investigated by using the quartz crystal microbalance(QCM) and self-made forced air convection drying device. By varying the blending ratio, hot airflow velocityand temperature, novel results were found and correlated by a creep transport model.The results show that the drying rate is great affected by the blending ratio of PS/PC. Due to the hydrogen bonds between PC chains, the microphase of PC might come into being crystal, which blocks the diffusion of solvent molecules in PC microphase. So the infinitely dilute diffusion coefficient decreases with the increasing of PC in polymer blend.The microstructures of polymer membrane is greatly influenced by drying condition, Appropriate structure facilitates the transfer of solvent molecule in membrane. In this paper, the nanoscale phase separation structure of polystyrene (PS)/polycarbonate(PC) blend within dichloromethane solution, as well as polystyrene(PS)/poly(methyl methacrylate)(PMMA) blend within tetrahydrofuran, under different blending ratio, hot airflow velocityand temperature has been investigated by atomic force microscope(AFM). The results show that the strip channels in phase separation caused by solvent evaporation facilitate the transfer of solvent molecule in the membrane. The size of microphase enlarges with the increase of drying temperature, which is obviously weakened under that there is a great difference in the compositions of polymer blend. The microstructures of immiscible polymer with poor compatibility blend are greatly influenced by airflow speed. The polymer-rich phase with higher solubility is more quickly depleted from a homogeneous fluid to the surface of membrane, whereas the second polymer-rich phase deposited as an inner layer onto the substrate. When the content proportion of upper layer phase is small, both the distribution and array of upper layer are affected by the direction of airflow. Whereas, the "skinning" phenomena might emerge in the membrane surface, which is not favor of the transfer of solvent molecules.