Thermal properties and structure of electrospun blends of PVDF with a fluorinated copolymer

We report the structure and thermal properties of blends comprising poly(vinylidene fluoride) (PVDF) and a random fluorinated copolymer (FCP) of poly(methyl methacrylate)‐random‐1H,1H,2H,2H‐perfluorodecyl methacrylate, promising membrane materials for oil–water separation. The roles of processing method and copolymer content on structure and properties were studied for fibrous membranes and films with varying compositions. Bead‐free, nonwoven fibrous membranes were obtained by electrospinning. Fiber diameters ranged from 0.4 to 1.9 μm, and thinner fibers were obtained for PVDF content >80%. As copolymer content increased, degree of crystallinity and onset of degradation for each blend decreased. Processing conditions have a greater impact on the crystallographic phase of PVDF than copolymer content. Fibers have polar beta phase; solution‐cast films contain gamma and beta phase; and melt crystallized films form alpha phase. Kwei's model was used to model the glass transition temperatures of the blends. Addition of FCP increases hydrophobicity of the electrospun membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 312–322     

Relaxation dynamics of blends of PVDF and zwitterionic copolymer by dielectric relaxation spectroscopy

Relaxation dynamics of PVDF blended with a random zwitterionic copolymer (r-ZCP) of methyl methacrylate and zwitterionic sulfobetaine-2-vinylpyridine (PMMA-r-SB2VP) were investigated using dielectric relaxation spectroscopy. FTIR spectroscopy was used to determine the PVDF crystal phase of compression molded blends. Adding 25 wt% of r-ZCP promoted the formation of the polar β and γ crystals over the nonpolar α phase. A structural model is proposed where the r-ZCP biases the PVDF to form polar crystal phases. Boyd's model was used to calculate the room temperature dielectric constants and led to good agreement with our measurements. Dielectric spectra of neat r-ZCP showed two relaxation peaks attributed to PMMA units, with no additional relaxations present from the zwitterions. Blends of PVDF with r-ZCP were dominated by the α_c relaxation associated with the crystalline phase of PVDF, which showed an Arrhenius temperature dependence. Analysis of the conductivity spectra shows a larger DC conductivity in the blends than in either r-ZCP or homopolymer PVDF. Blends show an additional peak in the loss tangent, absent in the copolymer or PVDF attributed to space-charge polarization. Higher DC conductivity and space-charge polarization indicate that the combination of zwitterions and unique microstructure affects charge transport properties.