Journal
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS
Volume 48, Issue 23, Pages 2468-2475Publisher
WILEY-BLACKWELL
DOI: 10.1002/polb.22145
Keywords
crystallization; crystalline form; membranes; morphology; permittivity; phase separation; polyvinylidene fluoride membrane; thermally induced phase separation
Categories
Funding
- National Basic Research Program of China [2009CB623404]
- Science and Technology Commission Foundation of Tianjin [09JCZDJC18800]
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We have studied the morphologies and crystalline forms of polyvinylidene fluoride (PVDF) membranes separately prepared in four different diluents bearing >C=O groups, namely 1,2-propylene glycol carbonate (PGC), dimethyl phthalate (DMP), diphenyl ketone (DPK), and dibutyl phthalate (DBP), by the thermally induced phase separation (TIPS) method. The permittivities of the diluents and PVDF were measured to compare the different PVDF-diluent systems. The results showed the permittivity of PGC to be much greater than that of PVDF, and those of DMP and DBP to be lower than that of PVDF. The permittivity difference between DPK and PVDF was not apparent above 120 degrees C. On cooling mixtures with a PVDF concentration of 10 wt %, PVDF crystallization was observed in the PVDF-DMP, PVDF-DBP, and PVDF-PGC systems, while liquid-liquid phase separation occurred in the PVDF-DPK system. A cross-section of the PVDF-PGC membrane presented smooth PVDF particles in the beta-phase crystalline form. Those of the PVDF-DMP and PVDF-DBP membranes presented PVDF particles consisting of a fibrillar network in the a-phase. The PVDF-DPK membrane preferentially adopted an a-phase bicontinuous channel structure. When the concentration of PVDF was 60 wt %, the cross-sections of the above four membranes revealed PVDF polyhedra, among which the PVDF-DMP, PVDF-DBP, and PVDF-DPK membranes retained the a-phase crystalline form, and the diffraction peak of the a-phase became visible in the X-ray diffraction (XRD) spectrum of the PVDF-PGC membrane. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2468-2475, 2010
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