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 beta and gamma crystals over the nonpolar alpha 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 alpha(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.