Dense polymer film and membrane formation via the dry-cast process part II. Model validation and morphological studies

In order to validate the dry-cast model developed by us, a multifaceted experimental approach was undertaken whereby three process variables can be followed independently in real time. Since it is extremely difficult to determine experimentally the concentration and temperature profiles within the cast polymer solution, experiments were designed so as to provide information on the coupled mass- and heat-transfer processes by measuring other process variables. The experimental data-acquisition technique combined gravimetric, inframetric, and light-reflection analyses which provided information on the overall mass change, surface temperature, and the onset and duration of phase separation, respectively. Structural studies were conducted using scanning electron microscopy. These studies revealed that macrovoids or “fingers” can be fomred in dry-cast membranes. A hypothesis for the formation of fingers based on the model predictions and experimental observations is proposed.