Temperature Dependency of Poly(vinylidene fluoride)Chain Dimension in Solution and Melt State

The final crystalline phase in poly(vinylidene flouride), PVDF, films mainly reflects the polymer structural arrangement or chain conformation during film formation. In this study, the intrinsic viscosity of PVDF solution or even the zero-shear-rate viscosity in polymer melt were used as indications of polymer hydrodynamic chain volume to predict the possible formation of all trans plannar zigzag conformation (β phase crystal). The studies on intrinsic viscosity of each diluted solution were carried out in Ubbelohde viscometer at temperature range of 25-100°C using two individual solvents with different polarities namely,dimethyl acetamide and cyclohexanone. In contrast to solvent polarity, the solution temperature showed negative effect in the degree of hydrodynamic chain volume.This behaviour maybe attributed to higher thermodynamic stability of gauche state rather than trans state in PVDF chains at higher crystallization temperatures. In this regard, through a temperature rise from 25°C to 100°C, the PVDF hydrodynamic chain volume experienced a reduction of about 38% and 25% in dimethyl acetamide and cyclohexanone, respectively. The further reduction of PVDF hydrodynamicchain volume in dimethyl acetamide solution may be referred to higher polymer chain mobility and reduced solvent polarity at higher temperatures. Using zero-shear rate viscosity, the increase in melt temperature showed reduction of about 87% in hydrodynamic chain volume. The temperature dependence of PVDF chain dimension in solution and melt state show a similar trend. These findings are in agreement with the previous results about the unhelpful effect of crystalization temperature in favor of β phase crystal formation in PVDF.