| Summary: | 碩士 === 淡江大學 === 化學工程學系 === 86 === The mechanism of poly(vinylidene fluoride) (PVDF) membrane formation
by isothermal immersion-precipitation method was studied. During the
process, phase separation might either be initiated by liquid-liquid
demixing or crystallization. Depending upon the preparation conditions
(e.g., the dope and bath concentrations and the system temperature),
dominance of these phase separation processes differed; thereby affected
the structure of the formed membranes.
Both the thermodynamic and the kinetic aspects were considered for
the membrane formation systems : water/dimethyl formamide/PVDF and
1- octanol/DMF/PVDF. The phase diagrams of these systems in different
temperatures provided the information of the effects of temperature on
the membrane structure, whereas diffusion trajectory and concentration
profile computations yielded the effects of the dope and bath conditions.
For PVDF precipitation from 1-octanol/DMF solutions, because mass
transfer was slow, rather than exhibiting an asymmetric structure, the
membrane was uniform composed of interfused spherulites. For the
water/DMF/PVDF system, various structures characterizing different
degrees of dominance of liquid-liquid demixing and crystallization in the
precipitation process could be prepared by adjusting the solvent content in
the bath. Based upon experimental results and theoretical analysis, we
have a better insight into the formation mechanism of the PVDF
membranes in this research.
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