Formation of anisotropic flat sheet membranes via evaporative TIPS

This dissertation deals with the formation of microporous membranes from binary polymer-diluent systems via thermally-induced phase separation (TIPS). Specifically, the formation of anisotropic membrane structures through the addition of an evaporative step prior to phase separation is studied. This research looks at anisotropic structures formed in a flat sheet geometry. This is the first comprehensive study combining model with experiment on the use of evaporation to produce anisotropic membranes via the TIPS process.; Evaporation induces a concentration gradient within the nascent membrane, which upon cooling results in an anisotropic structure due to the effect of polymer concentration on droplet growth kinetics. The evaporation step is modeled, examining the simultaneous mass and heat transfer that results from diluent loss to the atmosphere.; Evaporation experiments were conducted by setting the sample cell upon a hot stage, which controls both the sample temperature and cooling rate. Samples were examined experimentally by measuring weight loss, and by examination of the cross section using scanning electron micrography (SEM). Other experimental techniques used in this research include optical light microscopy, differential scanning calorimetry, and digital image analysis.; The variables studied that affect the evaporation process were: the initial sample temperature, the atmospheric temperature, the applied cooling rate, the rate of atmospheric convection, the polymer molecular weight, and the choice of diluent. It was found that use and control of atmospheric convection was the most significant factor in producing anisotropic structures. Sensitivity studies were run under model conditions to observe the effect of parameters not studied through experiment. The primary polymer-diluent system of interest in this research was isotactic polypropylene (iPP) and diphenyl ether (DPE); p-tertbutylphenol (pTBP) was also studied as a diluent with iPP.; In addition to studying the formation of anisotropic membranes via evaporative TIPS, an initial study was made of nonisothermal droplet growth kinetics. The effects of cooling rate, polymer concentration, and polymer molecular weight were examined. A linear relationship between log (r_d) and log (time) was found for all nonisothermal conditions, which is the same relationship observed in isothermal experiments.