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

The  fnal  crystalline  phase  in  poly(vinylidene  fouride),  PVDF,  flms mainly
refects  the  polymer  structural  arrangement  or  chain  conformation  during
flm  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  hydrodynamic chain  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 fndings are in agreement with the previous results about the unhelpful effect of crystalization temperature in favor of β phase crystal formation in PVDF.