Morphologies and crystalline forms of polyvinylidene fluoride membranes prepared in different diluents by thermally induced phase separation

Abstract

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 °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 β‐phase crystalline form. Those of the PVDF–DMP and PVDF–DBP membranes presented PVDF particles consisting of a fibrillar network in the α‐phase. The PVDF–DPK membrane preferentially adopted an α‐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 α‐phase crystalline form, and the diffraction peak of the α‐phase became visible in the X‐ray diffraction (XRD) spectrum of the PVDF–PGC membrane. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Crystalline polymorphism in poly(vinylidenefluoride) membranes

“…To investigate the effects of the relationship between diluent and polymer on the final polymorph, the permittivity was used as a parameter to characterize the difference between the diluents and PVDF, which affects the phase of the resulting membrane. It is believed that there are positive correlations between permittivity and the polarity, cohesive energy density, and solubility parameter of a polymer [89]. The content of the coagulation bath also influences the final polymorphs of the PVDF membranes.…”

Preparation and characterization of nano-chitin whisker reinforced PVDF membrane with excellent antifouling property

“…Į phase, ȕ phase and Ȗ phase, with different properties under different forming conditions [33][34][35]. Į phase is more easily obtained, which is always resulted from melt crystallization at high temperature.…”

Membrane Materials

“…In addition, coloumbic forces stimulated by electrospinning may promote the formation of β-phase, which is beneficial for use in ionic membranes. 13 Applicable solvents for NIPS 14 are N,N-dimethyl acetamide (DMAc), N,Ndimethyl formamide (DMF), dimethyl sulfoxide (DMSO), hexamethyl phosphoramide (HMPA), N-methyl-2-pyrrolidone(NMP), tetramethylurea (TMU), triethyl phosphate (TEP), trimethyl phosphate (TMP), acetone (Ac), and tetrahydrofuran (THF); applicable diluents for TIPS 15 are dimethyl phthalate (DMP), diethyl phthalate (DEP), dibuthyl phthalate (DBP), dihexyl phthalate (DHP), glycerin triacetate (GTA), ethyl acetoacetate (EAA), propylene glycol carbonate (PGC), diphenyl ketone (DPK), diphenyl carbonate (DPC), cyclohexanone, camphor, and butyrolactone.…”